# Tag Info

## New answers tagged nuclear-physics

### How can photons interact with nuclei?

German researchers recently excited 229 Th nucleus using a tabletop laser of wavelength 148 nm. They had specially create the laser since normal laser does not operate at that wavelength. The 229Th ...
1 vote
Accepted

### I don't understand how energy is conserved when an electron-positron pair decay into a muon-antimuon pair

The electron and positron each with mass m and momentum p may collide to produce a muon of mass M and an antimuon both at rest, no? Nondimensionalizing c=1, $$E_{TOT}^2/4=m^2+p^2=M^2.$$ You might ...
• 64.1k
1 vote
Accepted

### Extracting electron wave functions from experiments

Is it possible to do something similar for the electromagnetic form factors of the electron shell in atoms? That means to calculate something like "electron-hydrogen scattering minus electron-...
• 21.8k

### Extracting electron wave functions from experiments

I like this question, as former SLAC DISer (and TJNAF, MIT-Bates, DESY), where elastic-scattering was used to calibrate the instrument, I've thought about it (long ago). Also, if you want to tackle ...
• 35.3k
Accepted

### Why is the mass-energy graph for atomic mass $A=98$ not quadratic?

Who told you this would be a quadratic? The famous binding energy expression from the semi-empirical mass formula includes five terms. The volume and surface terms are constant in $Z$. The Coulomb and ...
• 1,220

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

The centre of a neutron star is at densities of $\sim 10^{18}$ kg/m$^3$, temperatures of $10^8$K-$10^{10}$K. The pressures are $\sim 10^{34}$ Pa and the nucleons are separated by $\sim 10^{-15}$ m. ...
• 133k

### Is there any formula for calculating the temperature required for nuclear fusion for a specific pressure?

I would be really thankful if someone could derive/lead me to the formula. There is none, at least no general solution. First off though, we need to know what you mean by "temperature required ...
• 8,373
1 vote

### Is there any formula for calculating the temperature required for nuclear fusion for a specific pressure?

Key to getting the answer you wish is first knowing what the equation of state is for the fusion reactants. This lets you relate pressure, temperature, and density. Please note that all equations of ...
• 95.4k

### How is the RMS energy of a nucleon in a nucleus of mass number A in its ground state depend on mass number of the nucleus?

We can solve this by using the uncertainty principle: $$\Delta x \Delta p = \frac{h}{2\pi}.$$ According to variation of radius of nucleus with atomic mass, $R= R_0 A^{1/3}$ so \Delta p = \frac{h}{2\...

### What would happen if the sun became the size of the earth?

The ideal gas law gives a first hint of trouble: if you compress gas by a factor of $(r_{sun}/r_{earth})^3\approx 100^3=10^6$, you should expect the temperature to go up by a factor of a million if ...
• 32.9k

### How is an $\alpha$-particle formed inside a nucleus and with what probability?

There are also models that compute the alpha pre-formation probability using only nucleon-nucleon interaction. This is typically done in the framework of energy density functional theory, in which the ...
1 vote

### What will happen if we keep bringing two protons closer and closer to each other, starting from a large distance?

Proton-proton collision induces parton (constituents of proton) scattering. From here1: Protons consist of three valence quarks, two up-quarks and one down-quark, held together by gluons and a sea of ...
• 1,273
1 vote

### What will happen if we keep bringing two protons closer and closer to each other, starting from a large distance?

The protons distract each other by the coulomb force. As you coerce them more and more close, you invest energy into the system. At a point, beta decay of one of the protons becomes energetically ...
• 8,247

### What will happen if we keep bringing two protons closer and closer to each other, starting from a large distance?

If you did it slowly enough, you could create a very short-lived particle called a diproton, the 2He nucleus (Helium without any neutrons). Wikipedia says its half time is 10-9 seconds because the ...
Accepted

### Why does the mass-energy equivalence apply to binding energy when it is derived purely through kinematic means?

I understand that by defining the four velocity, multiplying it by the rest mass and taking the entire thing's norm we get E2=m2+p2 This is not always an accurate description of the process. For some ...
• 103k

### What will happen if we keep bringing two protons closer and closer to each other, starting from a large distance?

This really depends on the energy scale at which you bring them together. At CERN they do proton-proton collisions, where the protons move at speeds close to the speed of light. At those energy scales,...
• 291

### Why does fission of large nuclei always result in energy released?

Yes. There are cases where nuclear fission reaction is endothermic rather than exothermic. These occur on fissioning of small nuclei. An example would be Lithium-7 absorbing a high energy neutron (>...
• 69
Accepted

### Y90 and Sr90 beta emissions have the same ranges but different average energies?

90Sr decays to 90Y which decays to 90Zr, which is stable. I notice in your datasheet for 90Sr that it lists two "major betas," one for the 90Sr decay, and one for the subsequent 90Y decay. I ...
• 7,434

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

The almost-instant of the big bang can be modeled because it is a simpler system than the interior of a supermassive star or a neutron star. In fact the universe as a whole will never again be as ...
• 95.4k

### How can photons interact with nuclei?

There are three main types of interactions a photon can have with an atom: elastic scattering inelastic scattering absorption and re-emission I am only going to talk about the first one, as the ...
1 vote
Accepted

### Neutron Dose Rate to Activity Calculation

It is simply impossible to give the activity of a radioactive source (unit: Bq, becquerel) by determining the radiation level emitted. In your case, the emission of a neutron does not necessarily mean ...
• 706

### How can photons interact with nuclei?

This is the same question as: "How can visible light interact with atoms?" And it has the same answer: Quantum mechanics. Your nucleons/electrons are charged particles bound in some field. ...
Accepted

### How is an $\alpha$-particle formed inside a nucleus and with what probability?

I was searching for models describing this and found two: The alpha particle model of nuclei, which circumvents the issue, more or less like you already said in your question, by just assuming that ...
• 88
1 vote

### What stops us from creating a nuclear fusion reactor as we already have the hydrogen bomb working on the same principle of fusion?

The physics or engineering is not stopping us from building such a reactor, but rather international treaties. There is the design of a plant that works on the principle of using a hydrogen bomb to ...
Accepted

### What is the standard reference medium in which positron ranges data are obtained in property tables, specifically for isotopes used in PET?

Not sure if this will fully answer your question, but the following reference describes positron ranges (for the table in the article) as being in water. Please see this reference for more details: ...

Top 50 recent answers are included