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Questions tagged [nucleosynthesis]

Nucleosynthesis is the process by which stars create heavier elements from hydrogen and helium

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How can we model the primordial Universe while the interior of a neutron star and comparable states of matter are still mostly unknown?

There is something I never quite understood about the physics of the primordial Universe. There are states of matter at high temperature/high pressure that are still, today, poorly understood. The ...
Vincent's user avatar
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Explain what happens in the alpha rich freeze out phase of a core collapse supernova(ccSNe) and which reactions takes place

In a core collapse supernova many nuclear reactions takes place and one of them is phase known as alpha rich freeze out phase, it is said to be very important in the production of alpha rich heavy ...
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Artificial Nucleosynthesis

Is it possible to artificially turn hydrogen into helium, let's say, and then go from helium to lithium and so on? I know that fusion reactors do that by fusing deuterium and tritium. Could this be a ...
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When a proton and neutron fuse in Big Bang Nucleosynthesis, do they emit a virtual neutral pion that emits two photons?

In Big Bang Nucleosynthesis, when a proton and neutron fuse to form a deuteron, how does the binding energy get shed? The binding is remanent strong nuclear force so does it emit a virtual neutral ...
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Power from CNO Cycle Fusion

There are all sorts of projects trying to get power from fusion reactions. The best known and funded are the Tokamaks, big expensive crush Deuterium and Tritium (He3 sometimes) plasmas and spew ...
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Confusion about energy conservation for fusion and fission (binding energy and $Q$-value)

In a nuclear reaction, a system consisting of a nucleus or nuclei lose mass, and this mass gets turned into energy, which is quantified by $E=mc^{2}$. But I'm conceptually confused. According to ...
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Why can we make those approximations regarding the Big Bang Nucleosynthesis (BBN)?

(About neutron decoupling) Consider $$p+e^{-}\rightarrow n+\nu_{e}.$$ In particular if we consider temperatures about $\simeq1\mbox{MeV}$ both neutrons and protons are non relativistic and we can find ...
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How do nuclear physicists know for certain if a very short-lived nucleus has been formed (a new isotope)?

Some very short-lived nuclides (sometimes called 'resonances') are nevertheless considered to have actually existed, if only very very briefly.... How do nuclear physicists know the isotope actually ...
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Why is the deuterium bottleneck temperature 0.1 MeV?

During big bang nucleosynthesis (BBN), deuterium has a lower binding energy per nucleon (~1.1 MeV) than the other similar nuclei, and so prevents heavy elements from forming until the temperature ...
arow257's user avatar
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Solving this first-order differential equation for neutron abundance using given data

The time rate of change of neutron abundance $X_n$ is given by $$\frac{dX_n}{dt} = \lambda - (\lambda + \hat\lambda)X_n$$ where $\lambda$ is neutron production rate per proton and $\hat\lambda$ is ...
Gurbir Singh's user avatar
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If dark matter was created in the early universe and its formation released energy, is there any evidence of that energy in the cmb?

When atomic nuclei fuse, energy is released. Is there anything about the CMB energy distribution that suggests that dark matter could have formed from other particles that released energy?
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LCDM epoch or point where it fails

Nobody denies the currently success of the LCDM of cosmology. Recently, I wondered myself if there is a point or epoch (beyond the space-time singularity) where it breaks down. Does it fail at phase ...
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Why can't high-level nuclear waste be disposed of by bombarding troublesome isotopes with neutrons, protons and gamma rays (photodisintegration)?

Why can't isotopes with long half-lives be radiated with free protons, neutron radiation and gamma rays (photodisintegration) in order to transmutate those isotopes into something either stable (or ...
Kurt Hikes's user avatar
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Why is lithium burned at lower temperatures than hydrogen inside stars?

The destruction of lithium inside stars through the reaction $$ ^{7}_{3}{\rm Li} + {\rm p} \rightarrow 2\ ^{4}_{2}{\rm He}$$ takes place at just $\sim 3\times 10^6$ K. This is much lower than the ...
ProfRob's user avatar
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How does absorbing a free thermal neutron convert nitrogen-14 into carbon-14? (Radiocarbon dating, etc.)

Why doesn't a nuclide of N-14 simply absorb the neutron created by cosmic rays or solar wind interacting with the atmosphere and become N-15, which is stable? How or why does the resulting Nitrogen-15 ...
Kurt Hikes's user avatar
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Why is $^{58}\rm Ni$ the most common isotope or nuclide of nickel if $^{62}\rm Ni$ has the most binding energy (per nucleon) of ANY known nucleus?

Nickel-58 and nickel-62 are four neutrons apart, not even just two, so this fact is especially confusing to me... I have read about how nickel is synthesized in stars from silicon, so this is perhaps ...
Kurt Hikes's user avatar
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Why is the baryon to photon ratio assumed to be constant?

For standard BBN calculations, we use the baryon to photon ratio $$ \eta=\frac{n_b}{n_\gamma} $$ that we get from CMB. Now, this clearly assumes that $$ \eta_{BBN}=\eta_{CMB}. $$ There are around ...
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Can particles (atoms, protons, neutrons and quarks) combine together in empty space? [closed]

Can particles (atoms, protons, neutrons and quarks) combine together in empty space without the use of energy to form macroscopic objects? Can elements form with an atomic number that is greater than ...
Zeruel017's user avatar
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Can someone clarify this quote about weak interactions causing neutron-to-proton ratio to go to zero if equilibrium were possible?

I'm self-studying Modern Cosmology by Dodelson and Schmidt 2nd edition, and I've found a certain passage in Section 4.2.1 particularly interesting. It says, Therefore, at high temperatures, there ...
Maximal Ideal's user avatar
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Conceptual problem understanding chemical equilibrium in the context of cosmology

In the context of describing the departures from equilibrium in the early universe (i.e. Big Bang Nucleosynthesis, recombination), one uses Boltzmann equations. Let's suppose we have a binary ...
Guillermo Franco Abellán's user avatar
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Would a head-on collision between two stars create heavier elements?

I was thinking about Przybylski's Star, and I was wondering how it was possible that so many heavy elements ended up in the star, such as einsteinium, californium, berkelium, etc. But there is ...
Curious Layman's user avatar
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How is formation of elements from particle accelerators different from the fusion process in a star?

I have a query assigned with the formation of elements in particle accelerators. We know that two hydrogen atoms for example fuse under extreme conditions to give a helium atom to release a lot of ...
Siddharth Nair's user avatar
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Does pressure alter nuclear reaction rates?

I'm studying the nuclear reactions involved in nucleosynthesis. As I understand it, the primary variables are the density of the particles, the cross section of the particle, and the average ...
Quark Soup's user avatar
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What are the number densities of neutrinos and positrons during BBN?

I'm attempting to work through the third chapter of Dodelson's Modern Cosmology. He gives an approximation for the neutron-proton conversion rate, $\lambda_{\rm np}$ that he lifted from Bernstein, but ...
Quark Soup's user avatar
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Why are lithium-$7$ and boron-$11$ respectively more abundant than lithium-$6$ and boron-$10$?

Lithium, beryllium and boron are unusually low in abundance for low-$Z$ elements, because their stable isotopes aren't the ones stellar nucleosynthesis makes without consuming them. What little ...
J.G.'s user avatar
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If for heavier atoms to form, you need a lot of pressure, then why do we say that the early universe was too hot for atoms to form?

I have read this question: Over the next 380,000 years, the universe gradually cooled down enough for the sub-atomic particles to condense and form the first Hydrogen atoms After the big bang As far ...
Árpád Szendrei's user avatar
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Photon temperature at nucleosynthesis

I've been asked about photon temperature at nucleosynthesis (3 minutes from Big Bang). So I guessed this is the moment when Matter and Radiation where in equilibrium: $$ \rho_M(T) = \rho_R(T)$$ Taking ...
Milamaranth's user avatar
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In Big Bang Nucleosynthesis (BBN), why aren't anti-protons created and destroyed?

I'm working through BBN theory with Dodelson and other papers. I have a question about the reactions between particles in the $1\space MeV$ range. We have reactions that produce and annihilate ...
Quark Soup's user avatar
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Why is Big Bang Nucleosynthesis favored over Stellar Nucleosynthesis?

We know that a hot soup of plasma as it cools (as space expands) can produce light elements if the baryon-photon ratio is just right and the space expands quickly enough so that the neutrons and ...
Quark Soup's user avatar
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Can someone please explain how Dodelson derives his formula for the neutron to proton ratio during BBN?

On page 66 of Modern Cosmology by Dodelson, we have the formula for the change in neutron to proton ratio as a function of time:$$\frac{dXn}{dt}=\lambda_{np}\left\{(1-X_n)e^{-\frac{Q}{T}}-X_n\right\}$$...
Quark Soup's user avatar
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How does Dodelson calculate the number density of a particle species?

In chapter three of Modern Cosmology, Dodelson models the evolution of a particle plasma as the universe expands. On page 61, the author gives the formula for the species-dependent equilibrium ...
Quark Soup's user avatar
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Why is aluminum more common in the solar system, etc. than sodium and fluorine?

I know that odd-numbered elements are less common than even-numbered ones, but why is aluminum more commonly created in the galaxy, apparently, than lighter odd-numbered elements? Sure, sodium and ...
Kurt Hikes's user avatar
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Why is nitrogen (with 7 protons and 7 neutrons) so much more abundant than any other odd-odd isotope?

Having an even number of neutrons and/or an even number of protons tends to make a nucleus more stable against radioactive decay. There are only 5 stable nuclei with both an odd number of neutrons and ...
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What are the major difficulties to the production of elements?

Searching online about this topic only gives results about nucleosynthesis (making elements by nature) and the 24 radioactive artificial elements. Why isn't there any information about methods to make ...
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Is the beta-plus decay that converts two colliding protons into deuterium more likely (energetically favorable) than beta-plus in a larger nucleus?

In the Sun, two nearby protons have to get extremely lucky and have one (or both?) of the protons convert to a neutron in a positron-emission, or beta-plus decay... I would think that there is less ...
Kurt Hikes's user avatar
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Why is the isotope Nitrogen-14 formed preferentially to Nitrogen-15 in the CNO-cycle in stars?

Most of the universe's nitrogen is formed in larger, main sequence stars using the CNO Cycle, right? But I cannot find a good, specific explanation as to why $^{14}$N, with both an odd number of ...
Kurt Hikes's user avatar
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Nuclear synthesis and neutron star collisions

When I look up the wikipedia article on nuclear synthesis, this https://en.wikipedia.org/wiki/File:Nucleosynthesis_periodic_table.svg picture tells me that quite a lot of chemical elements would have ...
Gyro Gearloose's user avatar
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Can Uranium-235 absorb neutrons and become U-238 instead of splitting?

Does that happen, on occasion? Does anyone know? I suppose it is quite rare, ... To absorb three neutrons without once fissioning... Could U-235 absorb three neutrons at once? Or just one, becoming ...
Kurt Hikes's user avatar
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What is the reheating temperature of neutrinos during the BBN?

I want to integrate a differential distribution function of sterile neutrinos and the boundaries are the decoupling and the reheating temperature of neutrinos, but I don't know what is an acceptable ...
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Why is the density of atoms in space so much higher than the baryon density from BBN and CMB?

If you ask the question: "how many atoms per cubic meter in space", you can get a consensus of around $5$ atoms per cubic cm or about $5\times 10^6\space \text{atoms}\space m^{-3}$. If we ...
Quark Soup's user avatar
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What is the proton to neutron ratio at freeze-out?

I'm reading through Dodelson chapter on BBN. I'm trying to follow the examples, but having trouble with the basics. First, the proton to neutron ratio is quoted as: $$\frac{n_p}{n_n}=e^{\frac{Q}{T}}$...
Quark Soup's user avatar
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1 answer
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Could one, with enough electricity to spare, use particle accelerators to mass produce heavy elements

If electrical, and economic limitations are ignored, would it be possible for a civilization to mass produce many millions of tonnes of useful heavy elements using particle accelerators? Could they ...
David Ricci's user avatar
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1 answer
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Weak interactions in nucleosynthesis

During the Bing Bang nucleosynthesis the particles present in the universe are, photons ($\gamma$), neutrinos ($\nu$), antineutrinos ($\overline{\nu}$), electrons($e^{+}$), positrons ($e^{+}$), ...
Nothing's user avatar
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Why do main sequence stars get bigger and more luminous as they age?

As stars age, the concentration of hydrogen in the core decreases, which lowers the power output, causing an imbalance between outward radiation pressure and inward gravitational pressure. This causes ...
never took courses but why's user avatar
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1 answer
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Why did the Big Bang produce hydrogen?

I know that first generation stars' main fuel was Hydrogen. I know the Big Bang happened at some point in time. Now if the strong force exists, then why aren't different, higher mass, number elements ...
baponkar's user avatar
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What means $h$ which appears following cosmological measured parameters?

For example, Big Bang Nucleossynthesis says that baryonic content in the Universe is around $0.018 \leq \Omega_{b}h^{2} \leq 0.024$. I know it is something related to measurement error but I do not ...
Jacinto Paulo's user avatar
1 vote
1 answer
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How the dark matter density parameter appears in Big Bang Nucleosynthesis (BBN)?

I know that it is possible to obtain the light element abundances ($^{4}\mathrm{He}, \mathrm D, ^{7}\mathrm{Li}$ etc.) and to determine the baryon-to-photon ratio $\eta$ from the total baryon ...
Jacinto Paulo's user avatar
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1 answer
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Thermal fission of gold? [closed]

Here's a slightly silly idea that arose from this question "What elements would be created in a star composed entirely of gold?": If we accumulate a lot of gold (really a lot) fast enough, it will ...
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Why does the formation of iron in stars not produce any energy?

Why does the formation of iron in stars not produce any energy. I have a hunch that it might have something to do with the fact that iron has the highest binding energy per nucleon and hence (...
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Intermediate product of CNO cycle

CNO cycle of stellar nucleosynthesis involves several steps in which different isotopes of Carbon, Nitrogen, and Oxygen are transmuted into each other when hit by a ...
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