# What would the Sun be like if nuclear reactions could not proceed via quantum tunneling?

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Without quantum tunneling our Sun wouldn't be hot or massive enough to produce the energy it does at the moment. So what would have been the temperature or mass of our Sun without quantum tunneling of protons to maintain the same energy we receive from our Sun?

Short answer: Without tunnelling, stars like the Sun would never reach nuclear fusion temperatures; stars less massive than around $5M_{odot}$ would become "hydrogen white dwarfs" supported by electron degeneracy pressure. More massive objects would contract to around a tenth of a solar radius and commence nuclear fusion. They would be hotter than "normal" stars of a similar mass, but my best estimate is that they have similar luminosities. Thus it would not be possible to get a stable nuclear burning star with 1 solar luminosity. Stars of 1 solar luminosity could exist, but they would be on cooling tracks, much like brown dwarfs are in the real universe.

A very interesting hypothetical question. What would happen to a star if you "turned off" tunnelling. I think the answer to this is that the pre-main-sequence stage would become significantly longer. The star would continue to contract, releasing gravitational potential energy in the form of radiation and by heating the core of the star. The virial theorem tells us that the central temperature is roughly proportional to $M/R$ (mass/radius). So for a fixed mass, as the star contracts, its core gets hotter.

There are then (at least) two possibilities.

The core becomes hot enough for protons to overcome the Coulomb barrier and begin nuclear fusion. For this to happen, the protons need to get within about a nuclear radius of each other, let's say $10^{-15}$ m. The potential energy is $e^2/(4pi epsilon_0 r) = 1.44$ MeV or $2.3 imes 10^{-13}$ J.

The protons in the core will have a mean kinetic energy of $3kT/2$, but some small fraction will have energies much higher than this according to a Maxwell-Boltzmann distribution. Let's say (and this is a weak point in my calculation that I may need to revisit when I have more time) that fusion will take place when protons with energies of $10 kT$ exceed the Coulomb potential energy barrier. There will be a small numerical uncertainty on this, but because the reaction rate would be highly temperature sensitive it will not be an order of magnitude out. This means that fusion would not begin until the core temperature reached about $1.5 imes 10^{9}$ K.

In the Sun, fusion happens at around $1.5 imes 10^7$ K, so the virial theorem result tells us that stars would need to contract by about a factor of 100 for this to happen.

Because the gravity and density of such a star would be much higher than the Sun, hydrostatic equlibrium would demand a very high pressure gradient, but the temperature gradient would be limited by convection, so there would need to be an extremely centrally concentrated core with a fluffy envelope. Working through some simple proportionalities I think that the luminosity would be almost unchanged (see luminosity-mass relation but consider how luminosity depends on radius at a fixed mass), but that means the temperature would have to be hotter by a factor of the square root of the radius contraction factor. However, this could be academic, since we need to consider the second possibility.

(2) As the star shrinks, the electrons become degenerate and contribute degeneracy pressure. This becomes important when the phase space occupied by each electron approaches $h^3$. There is a standard bit of bookwork, which I am not going to repeat here - you can find it something like "The Physics of Stars" by Phillips - which shows that degeneracy sets in when $$frac{ 4pi mu_e}{3h^3}left(frac{6G Rmu m_e}{5} ight)^{3/2} m_u^{5/2} M^{1/2} = 1,$$ where $mu_e$ is the number of mass units per electron, $mu$ is the number of mass units per particle, $m_e$ is the electron mass and $m_u$ is an atomic mass unit. If I've done my sums right this means for a hydrogen gas (let's assume) with $mu_e=1$ and $mu = 0.5$ that degeneracy sets in when $$left(frac{R}{R_{odot}} ight) simeq 0.18 left(frac{M}{M_{odot}} ight)^{-1/3}$$

In other words, when the star shrinks to the size of $sim$ Jupiter, its interior will be governed by electron degeneracy pressure, not by perfect gas pressure. The significance of this is that electron degeneracy pressure is only weakly dependent (or independent for a completely degenerate gas) on temperature. This means that the star can cool whilst only decreasing its radius very slightly. The central temperature would never reach the high temperatures required for nuclear burning and the "star" would become a hydrogen white dwarf with a final radius of a few hundredths of a solar radius (or a bit smaller for more massive stars).

The second possibility must be the fate of something the mass of the Sun. However, there is a cross-over point in mass where the first possibility becomes viable. To see this, we note that the radius at which degeneracy sets in depends on $M^{-1/3}$, but the radius the star needs to shrink to in order to begin nuclear burning is proportional to $M$. The cross-over takes place somewhere in the range 5-10 $M_{odot}$. So stars more massive than this could commence nuclear burning at radii of about a tenth of a solar radius, without their cores being degenerate. An interesting possibility is that at a few solar masses there should be a class of object that contracts sufficiently that nuclear ignition is reached when the core is substantially degenerate. This might lead to a runaway "hydrogen flash", depending on whether the temperature dependence of the reaction rate is extreme enough.

Best question of the year so far. I do hope that someone has run some simulations to test these ideas.

Edit: As a postscript it is of course anomalous to neglect a quantum effect like tunnelling, whilst at the same time relying on degeneracy pressure to support the star! If one were to neglect quantum effects entirely and allow a star like the Sun to collapse, then the end result would surely be a classical black hole.

A further point that would need further consideration is to what extent radiation pressure would offer support in stars that were smaller, but much hotter.

## How the Sun *really* shines

“Mr. Burns: Smithers, hand me that ice-cream scoop.
Smithers: Ice-cream scoop?
Mr. Burns: Damn it, Smithers! This isn’t rocket science, it’s brain surgery!”

-The Simpsons

The Sun is the one object that’s out-of-this-world that everyone on Earth is familiar with. With a mass that’s some 300,000 times our entire planet’s worth, it’s the most powerful source of heat, light, and radiation in the Solar System by far.

The amount of energy it emits is literally astronomical. Here are some fun facts about the Sun:

• It emits 4 × 10^26 Watts of power, or as much energy as tenquadrillion high-powered power plants would emit running full-bore at once.
• It’s been shining for 4.5 billion years, emitting energy at a nearly constant rate the entire time. (Changing under 20% over that entire time frame.)
• The energy emitted comes from Einstein’s famous E=mc^2, as matter gets turned into energy in the Sun’s core.
• And finally, that core energy needs to propagate to the Sun’s surface, a journey that requires it to pass through 700,000 kilometers of plasma.

That last step is a lot of fun! Because photons collide with ionized, charged particles very easily, it takes somewhere around 170,000 years for a photon created in the Sun’s core to make it to the surface.

Only then can it leave the Sun and light up the Solar System, our planets, and the Universe beyond. We’ve talked about why the Sun shines (and how we know it works) before, but we never talked about how that all-important step — how its mass gets converted into energy — in detail before.

At a macro level, it’s pretty simple, at least as far as nuclear physics goes.

The way nuclear fusion works in the Sun — and in all except the absolute most massive stars — is by fusing humble protons (hydrogen nuclei) into helium-4 (nuclei with two protons and two neutrons), releasing energy in the process.

This might puzzle you slightly, as you may remember that neutrons are ever so slightly heavier than protons.

Nuclear fusion only releases energy when the mass of the products — of the helium-4 nucleus, in this case — is less than the mass of the reactants. Well, even though helium-4 is made up of two protons and two neutrons, these nuclei are bound together, which means that their combined mass of the whole is lighter than the individual parts.

In fact, not only is helium-4 lighter than two protons and two neutrons individually, it’s lighter than four individual protons! It isn’t by all that much — just 0.7% — but with enough reactions, it adds up quickly. In our Sun, for example, somewhere around a whopping 4 × 10^38 protons fuse into helium-4 every second in our Sun that’s how many it takes to account for the Sun’s energy output.

But it’s not like you can just turn four protons into helium-4 in point of fact, you never get more than two particles colliding at the same time. So how, then, do you build up to helium-4? It might not proceed how you expect!

Most of the time, when two protons collide together, they simply do just that: collide, and bounce off one another. But under just the right conditions, with high enough temperatures and densities, they can fuse together to form a state of helium you’ve probably never heard of: a diproton, made up of two protons and no neutrons.

The overwhelming majority of the time, the diproton — an incredibly unstable configuration — simply decays back into two protons.

But every rare once-in-a-while, less than 0.01% of the time, this diproton will undergo beta-plus decay, where it emits a positron (the electron’s antiparticle), a neutrino, and where the proton transmutes into a neutron.

To someone who was only viewing the initial reactants and the final products, the diproton lifetime is so small that they’d only see something like the diagram below.

So you wind up with deuterium — a heavy isotope of hydrogen — a positron, which will immediately annihilate with an electron, producing gamma-ray energy, and a neutrino, which will escape at a speed indistinguishable from the speed of light.

And making deuterium is hard! In fact, it’s so difficult that even at a temperature of 15,000,000 K — which is what we achieve in our Sun’s core — those protons have a mean kinetic energy of 1.3 keV apiece. The distribution of these energies is Poisson, meaning that there is a small probability of having protons with extremely high energies, and speeds rivaling the speed of light. With 10^57 protons (of which maybe a few times 10^55 are in the core), I get the highest kinetic energy a proton is likely to have is about 170 MeV. This is almost (but not quite) enough energy to overcome the Coulomb barrier between protons.

But we don’t need to overcome the Coulomb barrier completely, because the Universe has another way out of this mess: quantum mechanics!

So these protons can quantum tunnel into a diproton state, a small (but important) fraction of which will decay into deuterium, and once you make deuterium, it’s smooth sailing to the next step. While deuterium is only a slightly energetically favorable state compared to two protons, it’s far easier to take the next step: to helium-3!

Combining two protons to make deuterium releases a total energy of about 2 MeV, or about 0.1% of the mass of the initial protons. But if you add a proton to deuterium, you can make helium-3 — a much more stable nucleus, with two protons and one neutron — and that’s a reaction that releases 5.5 MeV of energy, and one that proceeds far more quickly and spontaneously.

While it takes billions of years for two protons in the core to fuse together into deuterium, it takes only about a second for deuterium — once it’s created — to fuse with a proton and become helium-3!

Sure, it’s possible to have two deuterium nuclei fuse together, but that’s so rare (and protons are so common in the core) that it’s safe to say 100% of the deuterium that forms fuses with a proton to become helium-3.

This is interesting because we normally think of fusion in the Sun as “hydrogen fusing into helium,” but in reality, this step in the reaction is the only lasting one that involves multiple hydrogen atoms going in and a helium atom coming out! After that — after helium-3 is made — there are four possible ways to get to helium-4, which is the most energetically favorable state at the energies achieved in the Sun’s core.

The first and most common way is to have two helium-3 nuclei fuse together, producing a helium-4 nucleus and spitting out two protons. Of all the helium-4 nuclei made in the Sun, some 86% of them are made by this path. This is the reaction that dominates at temperature below 14 million Kelvin, by the way, and the Sun is a hotter, more massive star than 95% of stars in the Universe.

In other words, this is by far the most common path to helium-4 in stars in the Universe: two protons quantum mechanically make a diproton that occasionally decays into deuterium, deuterium fuses with a proton to make helium-3, and then after about a million years, two helium-3 nuclei fuse together to make helium-4, spitting two protons back out in the process.

But at higher energies and temperatures — including in the innermost 1% of the Sun’s core — another reaction dominates.

Instead of two helium-3 nuclei merging together, helium-3 can merge with a pre-existing helium-4, producing beryllium-7. Now, eventually, that beryllium-7 will find a proton because it’s unstable, however, it might decay into lithium-7 first. In our Sun, typically the decay to lithium happens first, and then adding a proton creates beryllium-8, which immediately decays to two helium-4 nuclei: this is responsible for about 14% of the Sun’s helium-4.

But in even more massive stars, proton fusion with beryllium-7 happens before that decay to lithium, creating boron-8, which decays first to beryllium-8 and then into two helium-4 nuclei. This isn’t important in Sun-like stars — accounting for just 0.1% of our helium-4 — but in the massive O-and-B-class stars, this may be the most important fusion reaction for producing helium-4 of all.

And — as a footnote — helium-3 can in theory fuse directly with a proton, producing helium-4 and a positron (and a neutrino) straightaway. Although it’s so rare in our Sun that less than one-in-a-million helium-4 nuclei are produced this way, it may yet dominate** in the most massive O-stars!

So, to recap, the vast majority of nuclear reactions in the Sun, listing only the heaviest final product in each reaction are:

• two protons fusing together to produce deuterium (about 40%),
• deuterium and a proton fusing, producing helium-3 (about 40%),
• two helium-3 nuclei fusing to produce helium-4 (about 17%),
• helium-3 and helium-4 fusing to produce beryllium-7, which then fuses with a proton to produce two helium-4 nuclei (about 3%).

So it might surprise you to learn that hydrogen-fusing-into-helium makes up less than half of all nuclear reactions in our Sun, and that at no point do free neutrons come into the mix!

There are strange, unearthly phenomena along the way: the diproton that usually just decays back to the original protons that made it, positrons spontaneously emitted from unstable nuclei, and in a small (but important) percentage of these reactions, a rare mass-8 nucleus, something you’ll never find naturally occurring here on Earth!

But that’s the nuclear physics of where the Sun gets its energy from, and what reactions make it happen along the way!

** — And that’s just considering the proton-proton chain in more massive stars, the CNO-cycle comes into play, a way of making helium-4 with the aid of pre-existing carbon, nitrogen and oxygen, something that happens in all but the very first generation of massive stars!

## Observation of quantum tunneling of the magnetization vector in small particles with or without domain walls

### 1 INTRODUCTION

It is well known that quantum phenomena can take place at the macroscopic scale in those systems with negligible dissipation e.g. superconductors, quantum fluids (1) or eventually one-dimensional metals (2) . Magnetic systems also seem to show such effects (3) , but to smaller extent, the effect of dissipation being not always negligible there. This is the reason why the interpretation of relaxation experiments in terms of Macroscopic Quantum Tunneling must be carefully tested by considering at least some of the most relevant possible spurious effects.

We first discuss, in the framework of the results obtained in part 1, the conditions required for a safe analysis of the magnetic viscosity at low temperature ( section 2 ). Then we show that it is possible to determine experimentally a characteristic energy berrier (Most Probable Energy Barrier) describing the macroscopic relaxation of the magnetization of a given sample. This MPEB does not depend on the distribution of energy barriers (contrarily to the case of the magnetic viscosity) and therefore it allows save evaluations of the temperature dependence of intrinsic relaxation mechanisms ( section 3 ). In the same section we also give the results obtained in multilayers of Cu/SmFe/Cu and in small particles of FeC and (TbCe)Fe2. All there systems show a MPEB proportional to the reciprocal applied field 1/H. They also show a cross-over temperature Tc below which a departure from thermal activation is observed. In the small particles Tc, of the order of 1 K, correspond to a passage to a quantum tunneling regime In the multilayer system Tc is close to 3K. However in this system the relaxation becomes slightly faster below this temperature, instead of staying constant, as this should be the case in a quantum regime. This puzzling behaviour seems to be due to sample self-heating resulting from important phonons and/or spin-waves assisted MQT. A discussion of this phenomenon in terms of sample self-dissipation will be given.

## Quantum Tunneling Allows “Impossible” Chemical Reactions to Occur in Space

A team of scientists from the University of Leeds has discovered that chemical reactions once thought to be ‘impossible’ in the coldness of space can actually occur thanks to a phenomenon called ‘quantum tunneling.’

New research has revealed that chemical reactions previously thought to be ‘impossible’ in space actually occur ‘with vigor,’ a discovery that could ultimately change our understanding of how alcohols are formed and destroyed in space – and which could also mean that places like Saturn’s moon Titan, once considered too cold for life to form, may have a shortcut for biochemical reactions.

A team at the University of Leeds, UK recreated the cold environment of space in the laboratory and observed a reaction of the alcohol methanol and an oxidizing chemical called the ‘hydroxyl radical’ at minus 210 degrees Celsius. They found that not only do these gases react to create methoxy radicals at such an incredibly cold temperature, but that the rate of reaction is 50 times faster than at room temperature.

They also found that this faster than expected reaction can only occur in the gas phase in space, that a product is formed (CH3O) – and that it can only form via a phenomenon they call ‘quantum tunneling.’

As research leader Dwayne Heard, Professor of Atmospheric Chemistry at the School of Chemistry, University of Leeds explains, quantum tunneling is a ‘non-classical phenomenon,’ which means that the wave function for the interaction of OH with methanol has ‘a non-zero probability of extending beyond the barrier to reaction.’ This means that the system can emerge on the ‘product side’ of the reaction without having to go ‘over the top of the reaction barrier.’

In other words, the tunneling phenomenon is based on the quirky rules of quantum mechanics, which contend that particles do not tend to have defined states, positions and speeds, but instead exist in a haze of probability. This means that although a given particle might have a strong probability of being on one side of a barrier, there is still a very small chance of it actually being found on the other side of it – in effect allowing it to occasionally ‘tunnel’ through a wall that would otherwise be impenetrable.

An artist’s impression of Ganesa Macula, a mountain on Saturn’s moon Titan believed to be an “ice volcano” that periodically belches “lava” containing liquid water. This water may react with organic compounds in Titan’s atmosphere to create complex molecules similar to those on the early Earth. Credit: Michael Carroll

“Chemical reactions get slower as temperatures decrease, as there is less energy to get over the ‘reaction barrier.’ But quantum mechanics tells us that it is possible to cheat and dig through this barrier instead of going over it. This is called ‘quantum tunneling,’” says Heard.

Put simply, Heard says that the research shows that organic chemistry can occur in space, here converting an alcohol into an alkoxy radical – which can then go on to form a carbonyl group such as formaldehyde.

“So we are showing that one functional group can be converted to another despite the cold conditions of space. Reactions that were discounted in space because it was too cold may now occur – owing to the tunneling,” he adds.

The research, summarized in the recent Nature Chemistry paper ‘Accelerated chemistry in the reaction between the hydroxyl radical and methanol at interstellar temperatures facilitated by tunneling,’ also demonstrates that such quantum tunneling reactions can occur in a wide range of environments, including cold planetary atmospheres, star forming regions, stellar outflows and circumstellar envelopes.

‘Key Interstellar Molecule’

Commenting on the findings, Dr. Robin T. Garrod, Senior Research Associate at the Center for Radiophysics & Space Research, Cornell University, says that methanol (CH3OH) is a ‘key interstellar molecule’ that is ‘crucial to complex organic chemistry in interstellar and star-forming environments.’ “It acts as the feed-stock for various more complex organic molecules during the star-formation process, providing a molecular building-block from which more complex structures may form. Understanding how it is destroyed – and thus whether and how its vestigial molecular structure is passed on to its destruction products – is therefore important to our understanding of the evolution of chemical complexity from interstellar clouds to star and planet formation,” he explains.

Methanol is also interesting to scientists because it appears to have no gas-phase formation mechanism of its own, in spite of its ubiquity in interstellar space. He points out that recent chemical kinetics models rely on its formation from carbon monoxide (CO) on interstellar dust-grain surfaces – where he says it has been ‘detected in abundance’ through Infrared (IR) absorption studies of interstellar clouds. These models assume that a small portion of the surface-formed methanol is sublimated into the gas phase, where it is detected through mm/sub-mm emission spectroscopy to have an abundance around a thousand times lower than on the grains in cold regions of around 10K.

“The very existence of methanol in space underscores the delicate interplay between different chemical phases – gas phase and surface chemistry – in the interstellar medium,” says Garrod.

In Garrod’s view, the University of Leeds work has several implications. Most directly, he says it provides a ‘neat explanation’ for the recent detection of abundant CH3O toward object B1-b (a recently detected low-mass protostar). Moreover, he says the new work shows a ‘strong bias’ toward the production of CH3O over CH2OH at the low temperatures prevalent in interstellar clouds, through the hitherto ‘little-considered’ OH+CH3OH reaction.

“In general, little is known of gas-phase reactions at very low temperature, although it is becoming increasingly clear that quantum effects can be critical to low-temperature reaction rates for many processes that are relevant to interstellar chemistry,” he says.

“Some key low-temperature reactions don’t appear to obey the expectations based on room-temperature behavior. They no longer display the classical Arrhenius-type behavior that one might expect. Low temperatures mean that slow, non-thermal processes (i.e. quantum tunneling) can dominate the reaction process,” he adds.

For Garrod, the new work also indicates that reactive radicals such as CH3O may be important in gas-phase chemistry, as well as dust-grain surface chemistry – to ‘perhaps produce more complex species.’ “Recent detections of molecules such as methyl formate (HCOOCH3) and dimethyl ether (CH3OCH3) in interstellar clouds at very low temperatures – meaning not associated with relatively high temperatures caused by star-formation – have still not been adequately explained. Gas-phase reactions such as the one investigated here may play a role in this process,” he says.

The nearby Milky Way galaxy in cold dust. This remarkable dust tapestry was resolved in detail in a wide region of the sky imaged in far-infrared light — the image is a digital fusion of three infrared colors. Red corresponds to temperatures as cold as 10 degrees Kelvin, while white corresponds to gas as warm at 40 Kelvins. The pink band across the lower part of the image is warm gas confined to the plane of our galaxy. The bright regions typically hold dense molecular clouds that are slowly collapsing to form stars, whereas the dimmer regions are most usually diffuse interstellar gas and dust. Why these regions have intricate filamentary shapes shared on both large and small scales remains a topic of research. Future study of the origin and evolution of dust may help in the understanding the recent history of our galaxy as well as how planetary systems such as our solar system came to be born. Credit: ESA, Planck HFI Consortium, IRAS

“This investigation also points to the possibility that other, similar reactions may be affected by the consideration of hydrogen-bonding at low temperatures, allowing a sufficiently stable intermediate to form for quantum tunneling processes to shape the formation of products,” he adds. However, Garrod argues that there is still ‘a great deal of work’ to be done in this field – and stresses that our understanding of low-temperature gas-phase chemistry is ‘far from complete.’ He also highlights the fact that there is potential for a range of other gas-phase processes to be ‘influential in the formation of complex chemical structures in interstellar space and during the star-formation process.’ For him, the work may also have implications for the chemistry that occurs on dust-grain surfaces in the interstellar medium (ISM). Current astronomical observations suggest a tendency toward organics with a C-O-C structure that may result from the ‘preferential’ formation of CH3O radicals over the isomeric CH2OH form, in line with these results – and Garrod points out that an ‘enormous and growing’ number of complex organic molecules appear to be formed on dust grain surfaces at moderate (

30 – 100 K) temperatures during the star-formation process.

“Both OH and CH3OH are likely to be abundant in the ice mantles that form on interstellar dust grains, and in which organic chemistry is expected to occur. The new findings may suggest a similar bias toward CH3O-related chemistry on dust grains as the investigated reaction may produce in the gas phase,” says Garrod.

“However, it is unclear to what degree the reaction kinetics of the gas-phase processes investigated here may be applied to the same or similar reactions taking place on surfaces or within an ice matrix,” he adds.

Although more research is needed, the revelation that such cold chemistry reactions can occur in cold planetary atmospheres, as well as star forming regions, stellar outflows and circumstellar envelopes, is likely to excite a good deal of interest in the astrobiology community – and help to boost the chances that such complex reactions occur with frequency in places like Titan.

Publication: Robin J. Shannon, et al., “Accelerated chemistry in the reaction between the hydroxyl radical and methanol at interstellar temperatures facilitated by tunnelling,” Nature Chemistry 5, 745–749, 2013 doi:10.1038/nchem.1692

Images: T. A. Rector & B. A. Wolpa, NOAO, AURA Michael Carroll ESA, Planck HFI Consortium, IRAS

## Using Quantum Mechanics to Trigger Atomic Fusion

Nuclear physics usually involves high energies, as illustrated by experiments to master controlled nuclear fusion. One of the problems is how to overcome the strong electrical repulsion between atomic nuclei which requires high energies to make them fuse. But fusion could be initiated at lower energies with electromagnetic fields that are generated, for example, by state-of-the-art free electron lasers emitting X-ray light. Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) describe how this could be done in the journal Physical Review C.

During nuclear fusion two atomic nuclei fuse into one new nucleus. In the lab this can be done by particle accelerators, when researchers use fusion reactions to create fast free neutrons for other experiments. On a much larger scale, the idea is to implement controlled fusion of light nuclei to generate power – with the sun acting as the model: its energy is the product of a series of fusion reactions that take place in its interior.

For many years, scientists have been working on strategies for generating power from fusion energy. “On the one hand we are looking at a practically limitless source of power. On the other hand, there are all the many technological hurdles that we want to help surmount through our work,” says Professor Ralf Schützhold, Director of the Department of Theoretical Physics at HZDR, describing the motivation for his research.

#### Tunneling at a high level, to be accessible soon

In order to trigger nuclear fusion, you first have to overcome the strong electrical repulsion between the identically charged atomic nuclei. This usually requires high energies. But there is a different way, explains the co-author of the study, Dr. Friedemann Queißer: “If there isn’t enough energy available, fusion can be achieved by tunneling. That’s a quantum mechanical process. It means that you can pass (i.e., tunnel) through the energy barrier caused by nuclear repulsion at lower energies.”

This is not some theoretical construct it really happens: The temperature and pressure conditions in the sun’s core do not suffice to overcome the energy barrier directly and enable hydrogen nuclei to fuse. But fusion happens nonetheless because the prevailing conditions allow the fusion reaction to be sustained thanks to a sufficiently high number of tunneling processes.

In their current work, the HZDR scientists are investigating whether controlled fusion could be facilitated with the assistance of tunneling processes using radiation. But that is also a question of energy: the lower it is, the lesser the likelihood of tunneling. Up to now, conventional laser radiation intensity was too low to trigger the processes.

#### XFEL and electron beams to assist fusion reactions

This could all change in the near future: With X-ray free electron lasers (XFEL) it is already possible to achieve power densities of 10 20 watts per square centimeter. This is the equivalent of approximately a thousand times the energy of the sun hitting the earth, concentrated on the surface of a one-cent coin. “We are now advancing into areas that suggest the possibility of assisting these tunneling processes with strong X-ray lasers,” says Schützhold.

The idea is that the strong electric field causing the nuclei repulsion is superimposed with a weaker, but rapidly changing, electromagnetic field that can be produced with the aid of an XFEL. The Dresden researchers investigated the process theoretically for the fusion of the hydrogen isotopes deuterium and tritium. This reaction is currently considered to be one of the most promising candidates for future fusion power plants. The results show that it should be possible to increase the tunneling rate in this way a sufficiently high number of tunneling processes could eventually facilitate a successful, controlled fusion reaction.

Today, just a handful of laser systems around the world with the requisite potential are the flagships of large-scale research facilities, like those in Japan and the United States – and in Germany where the world’s strongest laser of its type, the European XFEL, is to be found in the Hamburg area. At the Helmholtz International Beamline for Extreme Fields (HIBEF) located there, experiments with unique ultra-short and extremely bright X-ray flashes are planned. HZDR is currently in the process of constructing HIBEF.

The Dresden strong field physicists’ next step is to dive even deeper into the theory in order to understand other fusion reactions better and be able to assess their potential for assisting tunneling processes with radiation. Analogous processes have already been observed in laboratory systems, such as quantum dots in solid-state physics or Bose-Einstein condensates, but in nuclear fusion experimental proof is still pending. Thinking yet further ahead, the authors of the study believe other radiation sources could possibly assist tunneling processes. The first theoretical results on electron beams have already been obtained.

Reference: “Dynamically assisted nuclear fusion” by Friedemann Queisser and Ralf Schützhold, 21 October 2019, Physical Review C.
DOI: 10.1103/PhysRevC.100.041601

## Fusion by strong lasers

Nuclear physics usually involves high energies, as illustrated by experiments to master controlled nuclear fusion. One of the problems is how to overcome the strong electrical repulsion between atomic nuclei which requires high energies to make them fuse. But fusion could be initiated at lower energies with electromagnetic fields that are generated, for example, by state-of-the-art free electron lasers emitting X-ray light. Researchers at the Helmholtz-Zentrum Dresden-Rossendorf (HZDR) describe how this could be done in the journal Physical Review C.

During nuclear fusion two atomic nuclei fuse into one new nucleus. In the lab this can be done by particle accelerators, when researchers use fusion reactions to create fast free neutrons for other experiments. On a much larger scale, the idea is to implement controlled fusion of light nuclei to generate power -- with the sun acting as the model: its energy is the product of a series of fusion reactions that take place in its interior.

For many years, scientists have been working on strategies for generating power from fusion energy. "On the one hand we are looking at a practically limitless source of power. On the other hand, there are all the many technological hurdles that we want to help surmount through our work," says Professor Ralf Schützhold, Director of the Department of Theoretical Physics at HZDR, describing the motivation for his research.

Tunneling at a high level, to be accessible soon

In order to trigger nuclear fusion, you first have to overcome the strong electrical repulsion between the identically charged atomic nuclei. This usually requires high energies. But there is a different way, explains the co-author of the study, Dr. Friedemann Queißer: "If there isn't enough energy available, fusion can be achieved by tunneling. That's a quantum mechanical process. It means that you can pass (i.e., tunnel) through the energy barrier caused by nuclear repulsion at lower energies."

This is not some theoretical construct it really happens: The temperature and pressure conditions in the sun's core do not suffice to overcome the energy barrier directly and enable hydrogen nuclei to fuse. But fusion happens nonetheless because the prevailing conditions allow the fusion reaction to be sustained thanks to a sufficiently high number of tunneling processes.

In their current work, the HZDR scientists are investigating whether controlled fusion could be facilitated with the assistance of tunneling processes using radiation. But that is also a question of energy: the lower it is, the lesser the likelihood of tunneling. Up to now, conventional laser radiation intensity was too low to trigger the processes.

XFEL and electron beams to assist fusion reactions

This could all change in the near future: With X-ray free electron lasers (XFEL) it is already possible to achieve power densities of 10^20 watts per square centimeter. This is the equivalent of approximately a thousand times the energy of the sun hitting the earth, concentrated on the surface of a one-cent coin. "We are now advancing into areas that suggest the possibility of assisting these tunneling processes with strong X-ray lasers," says Schützhold.

The idea is that the strong electric field causing the nuclei repulsion is superimposed with a weaker, but rapidly changing, electromagnetic field that can be produced with the aid of an XFEL. The Dresden researchers investigated the process theoretically for the fusion of the hydrogen isotopes deuterium and tritium. This reaction is currently considered to be one of the most promising candidates for future fusion power plants. The results show that it should be possible to increase the tunneling rate in this way a sufficiently high number of tunneling processes could eventually facilitate a successful, controlled fusion reaction.

Today, just a handful of laser systems around the world with the requisite potential are the flagships of large-scale research facilities, like those in Japan and the United States -- and in Germany where the world's strongest laser of its type, the European XFEL, is to be found in the Hamburg area. At the Helmholtz International Beamline for Extreme Fields (HIBEF) located there, experiments with unique ultra-short and extremely bright X-ray flashes are planned. HZDR is currently in the process of constructing HIBEF.

The Dresden strong field physicists' next step is to dive even deeper into the theory in order to understand other fusion reactions better and be able to assess their potential for assisting tunneling processes with radiation. Analogous processes have already been observed in laboratory systems, such as quantum dots in solid-state physics or Bose-Einstein condensates, but in nuclear fusion experimental proof is still pending. Thinking yet further ahead, the authors of the study believe other radiation sources could possibly assist tunneling processes. The first theoretical results on electron beams have already been obtained.

## Research opportunities with compact accelerator-driven neutron sources

I.S. Anderson , . R. Senesi , in Physics Reports , 2016

### 3.2.5 Photonuclear reactions

Neutron production based on the photonuclear reaction from electron bremsstrahlung has played an important role in the development of accelerator-driven sources (see Fig. 3.7 ). Energetic electrons striking high-mass targets slow down to emit bremsstrahlung (e, γ ) photons. Photons proceed to interact with target nuclei to produce ( γ , n) photoneutrons. Fig. 3.7 shows the global neutron yields, the number of neutrons of all energies in all directions per unit of electron beam energy, as functions of electron energy for a range of materials [18] . Heavy elements are clearly best as bremsstrahlung photoneutron sources and yield plateaus at high electron energies.

Fig. 3.7 . Global yield of bremsstrahlung photoneutrons as a function of electron energy for different targets [18] .

Most of the neutrons are emitted in an evaporation spectrum according to

with T ≈ 1–2 MeV . Most of the electron energy dissipates as heat, which must be removed from the target consequently the process is rather inefficient. The yield saturates for electron energies above ∼100 MeV,

for tungsten (W). This amounts to 2800 MeV of heat per useful neutron.

In practice, target heat transfer limitations constrain power on targets a few cm in diameter to about 50 kW. More power would melt even refractory metals like tungsten, as in electron-beam welding.

Recently being recognized as a prospective neutron source is photonuclear neutron production based on gamma rays arising from inverse Compton scattering (ICS). ICS is the process in which a relativistic electron collides more or less head-on with a laser photon, whereby the photon gains a significant fraction of the electron kinetic energy. The process can produce photons in the gamma-ray range for electrons of ∼ GeV energy. For example, a 0.06-J, 1-μm-wavelength laser pulse colliding with a 2×10 9 bunch of 875 MeV electrons could produce 3×10 7 photons of 14-MeV energy [19] . Such energetic γ rays, exciting heavy nuclei through the giant dipole reaction, lead to substantial production of evaporation (∼1-MeV) neutrons. The process is about ten times more efficient than bremsstrahlung photoneutron production because it avoids the intermediate, inefficient step of bremsstrahlung radiation and consequent target heating. A 1-kW beam of 15-MeV photons incident on a small tantalum target would produce about 10 13 neutrons [20] .

Table 3.3 lists the key characteristics of nuclear reactions driven by low-energy charged particles. Here, we include neutron production driven by very high-power (>10 18 W cm −2 ) tabletop lasers. This research began in the 1990s with studies of the motions of electrons subjected to a very high electric field of the order of GV/m sustained by relativistic plasma waves driven by lasers. The conditions in terms of the laser power and pulse length, target setup, and so on were subsequently formulated to achieve acceleration of intense, quasi-monoenergetic “hot” electrons that are capable of triggering photonuclear reactions in a solid target for neutron production. These conditions were further extended to apply for the generation and acceleration of other charged particles, such as p and d , hence the prospect for inducing low-energy neutron-producing nuclear reactions. A number of experiments have been reported to successfully demonstrate these capabilities. The obvious merits of these tabletop laser-driven neutron sources are the achievable compact size, the very short neutron pulses, and the concentrated neutron intensity in the forward direction. However, the practice of harvesting the useful neutrons within the complex emission background and the conditioning of the target for sustained operation has yet to be worked out [22,23] .

Table 3.3 . Neutron production from low-energy nuclear reactions. Typical values are tabulated though exact values depends on the incident particle energies and targets.

The Sun obviously produces far more energy per second than is required to fuse an iron nucleus with some other nucleus. The problem is concentrating all that energy on the iron nucleus. It's not enough to know that it takes the energy from $n$ hydrogen fusions to fuse one iron nucleus, it's getting the energetic products from those $n$ hydrogen fusion events to all collide with the iron nucleus at the same time. Under normal conditions the probability of this is negligible.

However, under extreme conditions it can occur. For example in supernovae the pressures and temperatures are so high that iron and heavier nuclei undergo fusion reactions to produce the elements heavier than iron.

Iron fusion can take place in stars - what you need is lots of iron and very high temperatures to overcome the ever-increasing Coulomb repulsion between alpha particles and heavier nuclei. These conditions exist in the cores of massive stars near the ends of their lives.

For example alpha particles can fuse with an iron-56 nucleus to produce nickel-60 and then zinc-64 these reactions are almost energetically neutral because the binding energy per nucleon curve is almost flat over this atomic mass range. The problem is that there are competing decay and fission processes (particularly photodisintegration at high temperatures) that act to break up nuclei at these temperatures which disfavour the significant production of heavier nuclei in any kind of equilibrium.

Heavier elements can be produced by neutron capture. This can be an exothermic process, but requires less energetic conditions since the neutrons are neutral and it can occur even near the centres of intermediate mass stars (see Origin of elements heavier than Iron (Fe) ). Heavier nuclei such as Sr, Ba and even Pb can be produced by a chain of slow neutron captures followed by rapid decay events, which are then stable, and the interior conditions at the centres of intermediate mass AGB stars are not hot enough to cause photodisintegration. Neutron capture can also occur more rapidly during a supernova explosion - a highly "non-equilibrium event" where a tiny fraction of the supernova energy goes into endothermically producing the heavier elements and all of those beyond lead.

## Nuclear Fusion in the Sun’s Core

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Before we delve deeper into the heart of the Sun, the most sophisticated thermonuclear reactor we know, some basics must be clarified.

### The Atomic Nucleus

This small introduction is for those, who are not familiar with atomic physics. Everything is made up of atoms. They are the smallest indivisible units of any object. The central core of an atom is the nucleus, which is quite dense and packed with most of the atom’s mass, with electrons revolving around it.

### What is Nucleus?

The nucleus consists of two types of particles – protons and neutrons. A proton has a unit positive electric charge (1.6 x 10 -19 Coulomb), while the neutron is neutral. A type of an atom is decided by the number of protons in it.

There are 92 different types of naturally occurring atoms. Hydrogen is the simplest type of atom that you could think of. Its nucleus is just a proton. Every atom is denoted by an abbreviation of its chemical name. When I want to denote Hydrogen, I use the symbol ‘H’.

### Atomic Weight

Atomic weight is the total number of protons and neutrons in the nucleus, while atomic number is the number of protons or electrons that make the atom. Hydrogen is denoted as 1 1H, where the number in the superscript is the atomic weight and the number in subscript is the atomic number. Since the thermonuclear reactions occur at the level of a million Kelvins, all atoms are stripped of their electrons in the solar core.

### What is Nuclear Fusion?

Sun is a star and all stars are big balls of gas, primarily made up of gargantuan amounts of Hydrogen and Helium. About 75% of the Sun is made up of Hydrogen, while the rest is mostly all Helium.

### What Makes Sun, Stable?

Solar interior witnesses a constant tussle between the crushing gravitational force and thermal pressure, generated by nuclear fusion in the core. The Sun is stable due to the hydrostatic equilibrium achieved between the self-gravity of the Sun and the thermal pressure generated by fusion in the core.

### How Does Fusion Take Place?

Fusion is a process by which rapidly-colliding nuclei, like those of Hydrogen, fuse together at very high temperatures, to form nuclei of higher atomic weight. In this process some mass is lost and converted into energy. That is the secret of Sun’s energy production. To put it simply, Sun generates its energy, primarily through the fusion of four Hydrogen nuclei to form a Helium nucleus.

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The amount of energy obtained from conversion of 1 gm of matter into energy (by Albert Einstein’s celebrated equation, E = mc 2 ) would be roughly 9 X 10 13 Joules. So matter is just a form of energy. They are two manifestations of the same thing. All matter that makes up the Earth, along with the stuff that we are made of – Carbon, Nitrogen, Oxygen, was forged in the cores of high mass stars that burned and died long before the Sun.

For the past 4.57 billion years, since its birth, the Sun has been steadily fusing Hydrogen into Helium (a stage known as the Main Sequence in stellar physics parlance) and it will continue to do so for the next 5.43 billion years. In this entire time, the Sun has burnt Hydrogen, equivalent to about 100-Earth masses.

### Where Does Nuclear Fusion Occur in the Sun

Nuclear fusion occurs in the Sun’s core, which, not coincidentally, is also the hottest part of its whole constitution. The heart of the Sun has a temperature close to 15.7 million Kelvin. The total radius of the Sun is 6.955×10 5 km (about 109 times radius of Earth). Its core extends from the center to about 1.391 X 10 5 Km.

Let me explain why fusion occurs only near the center. It can be easily understood, if you try to understand how the Sun formed.

Stars like the Sun are thermonuclear fusion reactors. Fusion is a merger of smaller nuclei into heavier ones, releasing a tremendous amount of energy in the process. However, Hydrogen nuclei, which are protons, do not fuse easily. The reason for that is a fundamental fact of nature, which is, ‘Like charges repel each other‘.

The phenomena of a positively charged proton repelling from another one of its kind, because of the same charge is called Coulomb repulsion. Ergo, nuclear fusion can only occur at a high temperature, at the central core of the Sun. Sun’s core is hottest due to its phenomenally high density (150 gm/cm 3 ), a result of its compression under self-gravity.

Nuclear fusion is only possible when the repulsion between protons (Hydrogen nuclei) is overcome. For that to happen, energy and temperature at the Sun’s core has to be substantially high. However, nature has arranged it such, that the fusion in Sun’s core can occur at a much lower temperature, than that required to overcome Coulomb repulsion. How does nature pull off this trick? The answer lies in quantum mechanics.

### Nuclear Fusion is Possible Due to Barrier Penetration

The reason why protons with energy lesser than that required to overcome Coulomb Repulsion fuse, is barrier penetration. It is a quantum physics concept. Consider the following analogy. Imagine an adamant old man, trying to scale a wall. He doesn’t have the energy or the tools to climb it. Even so, he is of the opinion that if he keeps banging and ramming into the wall, one day it will give in and he will be on the other side by tunneling through.

The chances of that happening in the Classical (Non-Quantum Mechanical) world is zero. However, if our old man was the size of a proton (< 10 -15 m), and the wall represented the Coulomb energy required to overcome repulsion, then if he keeps hitting the wall, there is a chance (small finite probability) that he will tunnel through.

In the weird, sub-microsopic world of quantum mechanics, there is always a finite probability that the protons will fuse together at an energy that will be, lower than required energy to climb the Coulomb repulsion hill.

Since the probability of tunneling through Coulomb barriers is very low, fusion processes in low mass, relatively cooler stars like Sun, occur very slowly. A crucial step in the nuclear fusion process, which is the fusing of Hydrogen ( 1 1H) into Deuterium ( 2 1D) also has a very low probability of occurrence. That’s why, stars like the Sun burn or rather fuse their Hydrogen fuel into Helium at a very low rate and have long lifespans. Long-lived G-type main-sequence stars like the Sun can, therefore, have a high probability of harboring life around them on some revolving planet, as they last long enough for life to evolve.

### What Happens During Fusion inside the Sun?

The type of nuclear fusion reactions that occur inside a star, are entirely dependent on the core temperature. In the Sun, with a core temperature close to 15.6 million Kelvin, the predominant pathway, by which more than 99% of solar energy is produced (through conversion of hydrogen into helium nuclei), is the Proton-proton (p-p) chain reaction. The other primary pathway which produces about 0.8% of Solar energy is the CNO cycle.

### Solar Nuclear Fusion Process #1: The Proton-Proton (p-p) Chain Reaction

This is the dominant fusion process in the Sun. This phenomenon is possible due to tunneling or barrier penetration. There are many alternative ways in which the proton-proton chain reaction itself can occur. Besides the prime p-p pathway, other associated pathways are h-e-p and p-e-p, explained.

### Step 1a

The process begins with the fusion of two hydrogen nuclei (protons) to form Helium-2 or a diproton ( 2 2He).

### Step 1b

Further, the diproton undergoes beta decay (proton gets converted into a neutron, along with the release of an electron neutrino and a positron, which is the antiparticle of the electron) to get converted into deuterium, along with the release of a positron and an electron neutrino. Beta decay of the diproton being an extremely rare event, this is the step that causes maximum delay in the fusion process, extending the lifespan of the Sun.

2 2He → 2 1D + e + + νe
Summing up, this is what happens in the first step, in totality –

(*Electron volt is a measure of energy. One electron volt (eV) is the energy gained by an electron as it passes through a potential difference of 1 Volt.)

When matter and antimatter, come together, they get annihilated to create pure energy. The positron created in the beta decay gets annihilated, when it comes in contact with an electron, to release two high-energy gamma ray photons.

### PEP Reaction

Very rarely, the production of Deuterium (D) might also occur through another process, known as the proton-electron-proton (p-e-p) reaction. It involves electron capture and works as follows:

Although it is 400 times more likely that Deuterium will be created by the p-p pathway, the p-e-p reaction does occur rarely, creating high-energy neutrinos.

### Step 2

The fusion of Deuterium with a Hydrogen nucleus (proton) leads to the production of a light Helium isotope ( 3 He), besides releasing a gamma ray (an electromagnetic wave, with a frequency greater than 10 19 Hz).

### Step 3

After the previous stage, there are more than one ways in which the reaction may proceed. There are four prime paths: pp1, pp2, pp3, and pp4. Let us look at each path in detail.

### PpI Pathway: Light Helium Fusion

This is the dominant pathway among the four possible alternative paths that the reaction can take after creation of 3 He when the temperature of the core ranges between 10 million to 14 million Kelvin. It involves the fusion of two light helium nuclei to produce two protons (Hydrogen nuclei), along with the release of 12.86 Kelvin of pure energy. The frequency of pp1 pathway is around 86%.

In totality, the energy released by the pp1 reaction is 26.22 MeV.

### PpII Pathway: Lithium Burning

At temperatures between 14 million to 23 million Kelvin, the ppII branch is dominant. Here are the prime reactions that constitute it.

Since the Sun’s core temperature has a maximum around 15 million Kelvin, the ppII pathway only occurs with a frequency of 14%.

### PpIII Pathway: Beryllium Boron Transmutation

Since this type of reaction requires a temperature in excess of 23 million Kelvin, its frequency is only 0.11%. The pathway involves transmutation between Beryllium (Be) and Boron (B) isotopes. Here are the steps:

### PpIV Pathway: Hep Reaction

Theorized, but not yet observed, this Helium-Proton fusion pathway is extremely rare. The pathway consist of just one reaction. It consists of a direct fusion of a Helium-3 nucleus with a proton.

The difference between the ‘fusing masses’ (the four protons) and ‘fused mass’ (Helium-4) is 0.7% of the total mass of 4 protons, which is converted into energy. The total energy produced by the fusion of 4 protons through these processes is 26.73 MeV.

### Solar Nuclear Fusion Process #2: Carbon-Nitrogen-Oxygen (CNO) Cycle

This nuclear fusion process occurs very marginally in the Sun, but is the dominant fusion pathway in stars 1.5 times more massive, than our Sun. This process also fuses four protons into a Helium nucleus, by using Carbon (C), Nitrogen (N) and Oxygen (O) nuclei as catalysts. There are several alternative CNO pathways that can lead to Helium-4 production. This process produces only 0.8% of the Sun’s total energy output. Like p-p chain reaction, the CNO cycle has several alternative paths, but the dominant one, occurring in the Sun, is primarily CNO-I. The reactions constituting the cycle are as follows:

Step 1: 12 6C + 1 1H → 13 7N + γ + 1.95 MeV

Step 2: 13 7N → 13 C6 + e + + νe + 1.2 MeV (Half-life: 9.965 min)

Step 3: 13 6C + 1 1H → 14 7N + γ + 7.54 MeV

Step 4: 14 7N + 1 1H → 15 8O + γ + 7.35 MeV

Step 5: 15 8O → 15 7N + e + + νe + 1.73 MeV (Half-life: 122.24s)Step 6: 15 7N + 1 1H → 12 6C + 4 2He + 4.96 MeV

The end products of both the processes are same. However, CNO cycle is dominant in stars with stellar cores much hotter than that of Sun (in the range of 13 Million Kelvin). However, despite occurring at higher temperature, overall energy released through the whole reaction is again 26.73 MeV, which is round about the same as p-p cycle.

The energy released through gamma rays and the kinetic energy of the particles contributes to generation of thermal pressure in the solar interior, effectively balancing it with the gravitational pressure to maintain an overall steady state. It takes 10,000 to 170,000 years for a photon to travel from the Sun’s core, to its surface. On its way, the gamma ray photons emitted in the fusion reactions are converted into visible light, infrared and ultraviolet photons, as they reach the photosphere.

The multiple processes involved in fusing Hydrogen into Helium are testimony to the way nature always has many alternative ways to achieve the same result. Redundancy seems to be built into the fabric of the cosmos, for some reason. Stars are the furnaces that cook the stuff we are made of. Next time you see a sunrise, you will be able to appreciate the beauty of the glowing hot ball of fire, even more, as you now know what goes on in its very heart.

## New Research Reveals That Quantum Physics Causes Mutations in Our DNA

Quantum biology is an emerging field of science, established in the 1920s, which looks at whether the subatomic world of quantum mechanics plays a role in living cells. Quantum mechanics is an interdisciplinary field by nature, bringing together nuclear physicists, biochemists and molecular biologists.

In a research paper published by the journal Physical Chemistry Chemical Physics, a team from Surrey’s Leverhulme Quantum Biology Doctoral Training Centre used state-of-the-art computer simulations and quantum mechanical methods to determine the role proton tunneling, a purely quantum phenomenon, plays in spontaneous mutations inside DNA.

Proton tunneling involves the spontaneous disappearance of a proton from one location and the same proton’s re-appearance nearby.

The research team found that atoms of hydrogen, which are very light, provide the bonds that hold the two strands of the DNA’s double helix together and can, under certain conditions, behave like spread-out waves that can exist in multiple locations at once, thanks to proton tunneling. This leads to these atoms occasionally being found on the wrong strand of DNA, leading to mutations.

Although these mutations’ lifetime is short, the team from Surrey has revealed that they can still survive the DNA replication mechanism inside cells and could potentially have health consequences.

Dr. Marco Sacchi, the project lead and Royal Society University Research Fellow at the University of Surrey, said: “Many have long suspected that the quantum world – which is weird, counter-intuitive and wonderful – plays a role in life as we know it. While the idea that something can be present in two places at the same time might be absurd to many of us, this happens all the time in the quantum world, and our study confirms that quantum tunneling also happens in DNA at room temperature.”

Louie Slocombe, a PhD student at the Leverhulme Quantum Biology Doctoral Training Centre and co-author of the study, said: “There is still a long and exciting road ahead of us to understand how biological processes work on the subatomic level, but our study – and countless others over the recent years – have confirmed quantum mechanics are at play. In the future, we are hoping to investigate how tautomers produced by quantum tunneling can propagate and generate genetic mutations.”

Jim Al-Khalili, a co-author of the study and Co-Director of the Leverhulme Quantum Biology Doctoral Training Centre at the University of Surrey, said: “It has been thrilling to work with this group of young, diverse and talented thinkers – made up of a broad coalition of the scientific world. This work cements quantum biology as the most exciting field of scientific research in the 21st century.”

Reference: ” Quantum and classical effects in DNA point mutations: Watson–Crick tautomerism in AT and GC base pairs” by L. Slocombe, J. S. Al-Khalilib and M. Sacchi, 29 January 2021, Physical Chemistry Chemical Physics.
DOI: 10.1039/D0CP05781A