New answers tagged

2

The chemical properties of an element are always determined by the atomic number, that is, the number of protons in the nucleus. All carbon atoms have six protons, all iron atoms have 26, etc. It's the atomic number which is featured prominently in the periodic table, for example. Until the neutron was discovered in 1932, this was fine. After the neutron ...


4

The most common isotope of hydrogen has no neutrons. Other isotopes are deuterium with 1 neutron and tritium, with 2 neutrons. Since virtually all (99.98% according to wiki) naturally occurring hydrogen comes in the no neutron isotope, it seems reasonable that books show a schematic of that one when illustrating hydrogen. As a secondary motivation, the one ...


2

In a degenerate gas of fermions, the fermions fully occupy momentum states from zero up to a momentum corresponding to the Fermi energy. It is the momentum of the fermions that leads to degeneracy pressure. As long as the kinetic energy of particles at the Fermi energy is much less than $kT$, then the fermions can be considered completely degenerate, so ...


2

Free neutrons cannot be targets because of their limited lifetime. An enormous number of neutron-nucleus crossections and data exist. By using isotopic spin the neutron neutron crossections can be extracted from neutron-nucleus crossections. This presentation explores possibilities of neutron on neutron experiments.


1

Assuming the water can't cool, then after about 30 minutes, all the neutrons have decayed to protons and electrons, the resultant antineutrinos escape, but an average of around 0.5 MeV per decay will get thermalised in the water (the range of the electrons will be of order 1cm). As Floris points out, it takes 15.8kJ to heat a gallon of water by 1K, so this ...


2

One really, really energetic one might do it. But it would need to be very close to the speed of light, and I'm not sure you could capture its energy to boil the water. Assuming you want to convert the mass of a non-relativistic neutron to energy, it's about 940 MeV per neutron. Boiling a gallon of water (starting at room temperature, 20°C) requires raising ...



Top 50 recent answers are included