New answers tagged

3

In fact it turns out to be very useful to generate cold, or slow, neutrons. A neutron which has gotten close to thermal equilibrium with some material at room temperature (kinetic energy $E=kT=p^2/2m\approx\frac1{40}\rm\,eV$) has a de Broglie wavelength $\lambda = h/p \approx 2\,\text{Å}$ which is comparable to the interatomic spacing in most materials. ...


10

So there's this funny rule whose provenance I can't recall, but whose essence is: everything that is not forbidden, eventually happens. This rule is particularly fecund in quantum mechanics. If the process you describe is allowed, then every neutron already is a superposition of neutron and antineutron, and the question is just whether the oscillations ...


3

Fast neutrons are produced as a product of most nuclear reactions. In fission reactions, the mean energy of the released neutrons is approximately 2 MeV. Since the mass of the neutron is 939 Mev/c2, their velocity is 0.065 c. In fusion reactions, like the deuterium-tritium reaction, the neutron gets 14 MeV, and thus its velocity is 0.17 c. Larger ...


2

It's possible to imagine living in a different universe where most nuclei of the element with charge 1 were deuterium, and the lighter protium was the rare outlier. However, we don't live in that universe. Most of the ordinary matter in the universe is hydrogen (75% by mass) and helium (25% by mass) which has been unprocessed since the Big Bang. Deuterium ...


1

A neutron has baryon number = 1, while the anti-neutron has baryon number = -1. Physics Guy has much the same here with quarks, that works as well. In the language of CPT the charge operator reverses the charge of the quarks, so the two up quarks with charge $-1/3$ is flipped to $1/3$ and the down quark from $2/3$ to $-2/3$. I gave this question a 1-vote, ...


4

Every particle has (or can have) an antiparticle. Sometimes, it is even his own antiparticle. An antiparticle $D'$ is (easily said) defined as a particle $D$ after a CPT-transformation. CPT-Symmetry is believed to be a fundamental concept of physical nature. A CPT-transformation is a complete changing of observables of a particle. The C stands for ...



Top 50 recent answers are included