Questions tagged [nuclear-physics]

Nuclear physics is the study of the composition, behavior and interaction of atomic nuclei and their constituent parts.

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37
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3answers
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Why is the (free) neutron lifetime so long?

A neutron outside the nucleus lives for about 15 minutes and decays mainly through weak decays (beta decay). Many other weakly decaying particles decay with lifetimes between $10^{-10}$ and $10^{-12}$ ...
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Origin of elements heavier than Iron (Fe)

In all the discussions about how the heavy elements in the universe are forged in the guts of stars and especially during a stars death, I usually hear that once the star begins fusing lighter atoms ...
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Can Jupiter be ignited?

Our solar system itself contains two candidate "Earths" One is Jupiter's moon Europa and another is Saturn's moon Titan. Both of them have the problem of having at low temperature as Sun's heat ...
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How does rest mass become energy?

I know that there's a difference between relativistic and rest mass. Relativistic mass is "acquired" when an object is moving at speeds comparable to the speed of light. Rest mass is the inherent mass ...
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Conversion of mass to energy in chemical/nuclear reactions

Is mass converted into energy in exothermic chemical/nuclear reactions? My (A Level) knowledge of chemistry suggests that this isn't the case. In a simple burning reaction, e.g. $$\mathrm{C + O_2 \...
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What are good examples to demonstrate Einstein's mass-energy relation [duplicate]

According to Einstein's mass-energy relation mass and energy are interchangeable. Can you provide some examples where: Mass gets converted into energy. Energy gets converted into mass.
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What stabilizes neutrons against beta decay in a neutron star?

Free neutrons are known to undergo beta decay with a half-life of slightly above 10 minutes. Binding with other nucleons stabilizes the neutrons in an atomic nucleus, but only if the fraction of ...
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Protons' repulsion within a nucleus

Do the protons inside the nucleus repel each other by the electrostatic force? If they do, why doesn't the repulsion drive the protons apart so that the nuclei get disintegrated?
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What makes the number of neutrons the number of proton similar?

In basic chemistry, we are taught that an atom has roughly the same number of neutrons and number of protons, this doesn't seems to hold for larger atoms, but it is always roughly proportional (i.e. ...
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References on the non-compositeness of the known elementary particles

What paper(s) or theory(s) describe or prove that the elementary particles that we have determined today cannot be made up of smaller more fundamental particles?
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Age of the Earth and the star that preceded the Sun

One of the great unheralded advances made in the history of science was the ability to determine the age of Earth based on the decay of isotopic uranium. Based on the apparent abundance of uranium in ...
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What is an intuitive picture of the motion of nucleons?

I understand the "motion" of electrons within an ordinary atom (say argon at room temperature and pressure). They are moving in "orbits" defined by quantum mechanical wavefunctions where the "orbits" ...
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How can the nucleus of an atom be in an excited state?

An example of the nucleus of an atom being in an excited state is the Hoyle State, which was a theory devised by the Astronomer Fred Hoyle to help describe the vast quantities of carbon-12 present in ...
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1answer
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Binding energy and mass

I’ve been told that a greater binding energy means the nucleus is more tightly bound, and therefore that decreases the mass of the nucleus with respect to its nucleons when separated. But why does a ...
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How do we know that some radioactive materials have a half life of millions or even billions of years?

If a radioactive material takes a very long time to decay, how is its half life measured or calculated? Do we have to actually observe the radioactive material for a very long time to extrapolate its ...
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Adding many more neutrons to a nucleus decreases stability?

If you take any large nucleus and add protons to it, the electrostatic repulsion between them will make the nucleus more unstable, because the electrostatic force between them is more repulsive at a ...
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Why doesn't the deuterium nucleus have spin 0?

A deuterium nucleus is composed of a proton and a neutron. Both have spin 1/2 so I would expect the deuterium to have two possible spins: 1 for the triplet and 0 for the singlet. But apparently ...
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Why are alpha particles such a prominent form of radiation and not other types of nucleon arrangement?

It is said in many textbooks that alpha decay involves emitting alpha particles, which are very stable. Indeed, the binding energy (~28.3 MeV) is higher than for $Z$-neighboring stable isotopes. But ...
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Why does the Sun's (or other stars') nuclear reaction not use up all its “fuel” immediately?

The temperature and pressure everywhere inside the Sun reach the critical point to start nuclear reactions - there is no reason for it to take such a long time to complete the reaction process. Just ...
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Why is the nucleus of an Iron atom so stable?

Lighter nuclei liberate energy when undergoing fusion, heavier nuclei when undergoing fission. What is it about the nucleus of an Iron atom that makes it so stable? Alternatively: Iron has the ...
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How to explain $E=mc^2$ mass defect in fission/fusion?

What is the nature of nuclear energy? This is closely related to the correct explanation of mass defect. I did some research of that topic and cannot come to a single comprehensive and consistent ...
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1answer
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Why are pear-shaped nuclei possible?

In a recent question, Ben Crowell raised an observation which really puzzled me. I obtained a partial answer by looking in the literature, but I would like to know if it's on the right track, and a ...
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Why are the dineutron and diproton unbound?

It is known that there is no diproton and dineutron nuclei. Does this mean that two protons or neutrons are not actually attracted to each other? Even if the attraction was weak, wouldn't it cause ...
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What prevents an atom's electrons from “collapsing” onto its protons? [duplicate]

Forgive me if the answer to this is obvious. I have no formal physics training, and I remember that when I asked my physics teacher this, she just frowned and said "Good question." An electron is ...
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What is the the Ehrenfest-Oppenheimer rule on the statistics of composite systems?

Ehrenfest 1931 gives an argument to the effect that the application of the spin-statistics theorem to composite systems is valid, but only as an approximation and under certain conditions. ...
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“Dear radioactive ladies and gentlemen” - Letter by Wolfgang Pauli

In 1930, Wolfgang Pauli wrote a letter to Lise Meitner for a convention in Tübingen, considering the problem of beta decay. Does anybody know, where to find the original letter online ?
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Why is nuclear force spin dependent?

Why nucleons with parallel spins have greater nuclear force than the ones with anti-parallel spins? I just want a clear and easy explanation. Thank you!
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Why can't electrons fall into the nucleus? [duplicate]

I read a book on pop sci book on quantum mechanics and the author said that electrons do not fall into the nucleus due to quantum mechanics- which principles suggest this (I think it was Heisenberg's ...
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How can a proton be converted to a neutron via positron emission and yet gain mass?

The mass of a neutron is greater than mass of a proton so how is it possible in positron emission for a proton to form a neutron and a positron?
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Are the protons and neutrons in the nucleus arranged in any particular way?

I was wondering this: suppose you have two oxygen atoms. They will both have 8 protons and 8 neutrons in the nucleus (at least if they are the most common isotope). Now, will all those particles be ...
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With what probability does nuclear fusion occur at energies far below the Coulomb barrier?

Even at the core of the sun, the temperature of $\sim 10^7$ K only results in $kT\sim1$ keV, which is about a thousand times less than the electrical potential energy of $\sim1$ MeV needed in order to ...
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Is there any thing other than time that “triggers” a radioactive atom to decay?

Say you have a vial of tritium and monitor their atomic decay with a geiger counter. How does an atom "know" when it's time to decay? It seems odd that all the tritium atoms are identical except with ...
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binding energy of a nucleus is positive?

I have found from this link http://hyperphysics.phy-astr.gsu.edu/hbase/nucene/nucbin.html that: Nuclei are made up of protons and neutron, but the mass of a nucleus is always less than the sum of the ...
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How large would the steam explosion at Chernobyl have been?

So the second episode of the HBO series began to cover the risk of a steam explosion that led to them sending three divers into the water below the reactor to drain the tanks. This occurred after the ...
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Mass defect- From where mass is being lost?

As a school student, I have wondered while studying mass defect the following mysterious problem My assumption Just like a car's mass is constituted by each part of it(i.e total mass of car will be ...
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What Happens to electrons after Alpha Decay and Nuclear Fission?

Where do the electrons go? In alpha decay do 2 electrons follow the alpha particle and make stable Helium or does the larger daughter nucleus become an anion? Also what do the electrons do in the ...
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What happens if we put together a proton and an antineutron?

A hydrogen nucleus consists of a single proton. A 2-hydrogen (deuterium) nucleus consists of a proton and a neutron. A tritium nucleus consists of a proton and two neutrons. This makes me wonder how ...
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Why is the spectrum of the $\beta$-decay continuous?

the spectrum of the Gamma and Alpha decays are both discrete, i.e. the $\alpha$-particles and the $\gamma$-rays take on only discrete values when emitted from a decaying nucleus. Why is it then, that ...
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Is radioactive decay spontaneous or random?

When it comes to radioactive decay, what is the difference between random and spontaneous? For example, when the count rate of a radioactive isotope is measured, the readings fluctuate. Is this a ...
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How much iron would I have to shoot into the Sun to blow it up?

My understanding--though it's from a Science Channel show so I'm not sure if it is correct--is that there is a fusion reaction happening in the center of the sun. Atomic nuclei are being created and ...
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Do pear-shaped nuclei really have anything to do with time travel?

Recently (in the last week or two), various articles about pear shaped nuclei have appeared, such as this one from Science Alert and this from the BBC The Science Alert article includes the quote ...
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Long time deviations from exponential decay in radioactivity

Are there any examples of common substances whose decay is not exponential? We're used to thinking about radioactivity in terms of half-lives. This is a concept that makes sense only for a decay that ...
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1answer
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What are the average matter, antimatter, and binding energy composition of protons and neutrons?

For a free baryon at rest at room temperature, how much of its ~1Gev (rest) mass can (on average) be considered as matter, as antimatter, and as binding energy? For a baryon in a nucleus, I assume ...
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What would be the characteristics of Jupiter if it shrank?

So, I've heard from various works of science fiction about the prospect of turning Jupiter into a star. From what I know about the physics of such a task, it would require somehow condensing Jupiter ...
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Construction of interaction Lagrangian invariant under isospin $SU(2)$ transformations

The problem considered here is, as the title says, to construct a Lagrangian that is invariant with respect to $SU(2)$ transformations. I will present first the context and the reason of my ...
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How many times has the matter in our solar system been recycled from previous stars?

I've got a basic understanding of these facts: The Universe is a little over 13 billion years old. Our galaxy is almost that old. Our solar system is roughly 4.6 billion years old. The heavier ...
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How do we know that the nucleus isn't a quark-gluon plasma?

The standard picture of the nucleus of atom is that is several distinct nucleons, which themselves are composed of quarks. However, it seems to me like a much simpler picture is that the nucleus is ...
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Proton - neutron fusion?

In reviewing some problems in an elementary book, I ran across a reference to the reaction $p+n\rightarrow d$ + "energy". Is that possible? I don't see any reason why not, but I don't find any ...
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What is the percentage of useful energy do we get from matter-antimatter annihilation?

This is a theoretical question since we haven't made enough antimatter to try it in reality of course. But I am asking about the physics part in this. Also, by "useful energy" I mean the energy we ...
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Evidence that nuclei contain neutrons and protons (other than nucleons appearing if a nucleus is smashed)?

This may seem like a silly question, but I believe this to be very fundamental because the Standard Model of particle physics seems based on the axiom or assumption that neutrons and protons exist “as-...