# Tag Info

31

Neutrons (and protons) being spin 1/2 fermions, must fit antisymmetric wavefunctions. This "wavefunction" doesn't always involve waves, though. For nucleons - the generic term for neutron or proton - this wavefunction for the pair is a produce of (1) a spatial part, (2) a spin part, and (3) an isospin part. The isospin part is a clever way to describe ...

27

Basically, the answer is no, it's not possible. When we produce neutrons for research purposes, we have to produce them using nuclear reactions. They come out of the nuclear reactions with energies that are determined by the reaction, are not otherwise under our control, and that are on the MeV energy scale of nuclear physics. Examples of a neutron source ...

21

A neutron is not a proton and an electron lumped together (as your question seems to suggest you think) A hydrogen atom is a bound state of an electron and a proton (bound by the electromagnetic force) whereas a neutron is a bound state of three quarks (bound by the strong force). You might be tempted to think that a neutron is also a bound state of an ...

20

The neutron is in no way "composed" of a proton and an electron. It can decay to a proton, electron, and an antineutrino. But that doesn't mean that these three particles literally co-exist inside the neutron at the beginning. Instead, the decay involves some real transmutation of elementary particles. The only thing that one can say because of the decay is ...

19

Neutrons have spin 1/2 and therefore obey the pauli exclusion principle, meaning two neutrons cannot occupy the same space at the same time. When two neutrons' wavefunctions overlap, they feel a strong repulsive force. See http://en.wikipedia.org/wiki/Exchange_interaction .

15

Isotones are nuclides having the same number of neutrons. Magic proton or neutron numbers give the nucleus greater stability. Magic 82-isotone nuclides for instance: Isobars are nuclides having the same mass number (i.e. sum of protons plus neutrons). The number of protons in beta-plus (beta-minus) decay decreases (increases) by a unit and the number of ...

15

Spontaneous processes such as neutron decay require that the final state is lower in energy than the initial state. In (stable) nuclei, this is not the case, because the energy you gain from the neutron decay is lower than the energy it costs you to have an additional proton in the core. For neutron decay in the nuclei to be energetically favorable, the ...

14

Conservation of energy and the electron-degenerate pressure. For the neutron to decay you must have $$n \to p + e^- + \bar{\nu}$$ or $$n + \nu \to p + e^- \quad.$$ In either case that electron is going to stay around, but in addition to the neutrons being in a degenerate gas, the few remaining electrons are also degenerate, which means that adding a ...

13

Although a neutron is electrically neutral, it has a non-zero magnetic dipole moment. It interacts with a magnetic field to give a potential $$U = \vec{\mu} \cdot \vec{B}$$ A gradient of magnetic field strength will give a force $$\vec{F} = \nabla|\vec{\mu} \cdot \vec{B} |$$ It's not possible to produce large, sustained field gradients, nor is it ...

11

The anti-particle corresponding to a neutron is an anti neutron! The neutron is made up of one up quark and two down quarks. The anti-neutron is made up of an anti-up quark and two anti-down quarks. Both have zero charge because the charges of the quarks within them balance out. You are correct that elementary particles with no charge are often their own ...

11

Masses and coupling between quarks are free parameters in the standard model, so there is not real explanation to that fact. About the measurment: you can have a look at this wikipedia article about Penning traps which are devices used for precision measurements for nucleus. Through the cyclotron frequency (Larmor factor) we can obtain the mass of the ...

10

Detectors at particle colliders are layered like onions around the collision vertex. The CMS detector at CERN First there are charged particle sensitive detectors where charged particles leave tracks because of ionisation, but mass density is low so strong interactions do not happen often; their momentum can be measured by the curvature in the ...

9

You didn't understand any of these questions right. Antiquarks and their bound states, including the antineutrons, are produced and observed as easily as bread and butter. Lots of details experiments with e.g. antineutrons have been performed, e.g. Scattering of antineutrons with hydrogen ...

9

A neutron is a fermion, a hydrogen atom is a boson. This is related to the fact that a neutron decays into three fermions rather than two which is what you seem to think. A neutron is composed of three valence quarks, $u,d,d$, while a hydrogen atom is made out of $u,u,d,e^-$. The internal size of a neutron is about $10^{-14}$ meters while the internal size ...

8

The neutron is made of two down quarks and an up quark; the proton of two up quarks and a down quark. This leads to two effects that differentiate their masses. One is that the up and down quark themselves have different masses. The other is that the proton is charged, and so quantum corrections involving virtual photons affect its mass. The details are ...

8

Neutron sources You can buy a commercial off-the shelf "neutron generator", or you can use a radioactive source. Neutron generators are accelerator-based fusion reactors1 and have the advantage of being able to simply turn the neutron supply on and off. The most common source is AmBe (Americium-241/Beryllium), though Californium-252 and tritium both have ...

8

Neutron decay is not a electromagnetic phenomena at all. It is governed by the weak nuclear force. This is well supported by fact that the lifetime of the neutron fits neatly into weak universality. Secondly the neutron is not it's own antiparticle. The anti-neutron is a distnct particle.

8

It can't be solo neutrons, because they are unstable and decay into protons. So far as we know, there's not a stable configuration of mostly-neutrons that occurs in nature intermediate between heavy nuclei (uranium is roughly 3-to-2 parts neutrons) and neutron stars of 1-3 solar masses (which are about 90% neutrons). What you're describing would be the kind ...

8

The mass of a free neutron is 939.566 MeV/c$^2$ (almost 1 GeV/c$^2$, so that's probably where your instructor got the "1" value), and the mass of a free proton is 938.272 MeV/c$^2$. A free neutron will decay into a free proton, free electron ($\beta^-$), and an anti-neutrino, $\bar{\nu}$. The mass of the electron is 0.511 MeV/c$^2$, and of the ...

7

A proton is made of two up quarks and a down quark, whereas a neutron is made of two down quarks and an up quark. The quark masses contribute very little of the actual mass of the proton and neutron, which mostly arises from energy associated with the strong interactions among the quarks. Still, they do contribute a small fraction, and the down quark is ...

7

OK, here is something concrete and quantitative, "Guidelines for predicting single-event upsets in neutron environments": Neutrons in the atmosphere result from cosmic-ray spallation interactions with nitrogen and oxygen nuclei. A typical reaction is a 1 GeV proton fragmenting a nitrogen necleus into lighter charged particles and simultaneoously emitting ...

7

Thermal neutrons capture on hydrogen and carbon with reasonable (i.e. not large, but significant) cross-sections (this is the delayed event detection methods of most organic liquid scintillator anti-neutrino detectors--i.e the one that don't dope their scintillator with Gadolinium). So though a "cloud"--meaning a localized diffuse gas--of neutrons can ...

6

Two nuclides (a type of a nucleus with some values of $Z$ and $N$) that have the same number of neutrons $N$ have the same number of neutrons. The previous sentence is a tautology but I wrote it to show that the equality doesn't mean anything special, aside from the things that are obviously implied by it. Two nuclides that have the same total number of ...

6

The neutron decays into a proton, an electron and an antineutrino. So even the end components are different from Hydrogen which is just a proton with an electron orbiting around it. The binding forces are also different. The proton and the electron are bound by the electromagnetic force. The neutron by the strong to the rest of the nucleons in a nucleus. ...

6

The Pauli Exclusion Principle states that no two identical fermions (neutrons and protons are fermions - they have half-integer spins and obey Fermi-Dirac statistics) can occupy the same quantum state at the same time. If the neutron were to $\beta$-decay as: $$n \longrightarrow p + e^- + \bar{\nu_e}$$ then this freshly minted ...

6

In spite of the name, neutron stars also contain protons and electrons. This is required for equilibrium with respect to weak-interaction processes which can convert neutrons into protons and electrons. Since neutron stars also contain protons and electrons, they can contain electric currents which generate magnetic fields. It is thought that the protons ...

6

The neutron has no net charge, but it does have a net magnetic moment. As an aside, this simple fact provides strong evidence that the neutron is a composite particle (made of smaller things like quarks and gluons), because if it were a neutral elementary particle we would not expect it to have any magnetic moment. But we know that the neutron is composite, ...

6

Yes, heavy shielding is needed primarily for gamma radiation. Neutron radiation (with energies seen in fission reactors) is easily stopped with boron-10 (isotopically enriched boric acid in water). While alpha and beta radiation is easier to shield, it is even more dangerous if alpha and beta active particles (dust) is consumed by human, because they will ...

6

The magnetic moment generates a magnetic field on it's own, even if the neutron is not moving. This field will Lorentz transform just like any other Electromagnetic field. More interestingly, you'll find that a moving neutron will generate an electric field in addition to its magnetic field.

6

An early bit of evidence for the neutron as an uncharged constituent of the nucleus, with approximately the mass of the proton, actually comes from the exclusion principle, and the low-temperature heat capacities and excitation spectra of atomic gases. The argument is a little bit subtle, so you'll have to bear with me. First, we have the exclusion ...

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