<P> A thermal neutron is a free neutron that is Boltzmann distributed with kT = 6979405350651211000 ♠ 0.0253 eV (6979399999999999999 ♠ 4.0 × 10 J) at room temperature . This gives characteristic (not average, or median) speed of 2.2 km / s . The name' thermal' comes from their energy being that of the room temperature gas or material they are permeating . (see kinetic theory for energies and speeds of molecules). After a number of collisions (often in the range of 10--20) with nuclei, neutrons arrive at this energy level, provided that they are not absorbed . </P> <P> In many substances, thermal neutron reactions show a much larger effective cross-section than reactions involving faster neutrons, and thermal neutrons can therefore be absorbed more readily (i.e., with higher probability) by any atomic nuclei that they collide with, creating a heavier--and often unstable--isotope of the chemical element as a result . </P> <P> Most fission reactors use a neutron moderator to slow down, or thermalize the neutrons that are emitted by nuclear fission so that they are more easily captured, causing further fission . Others, called fast breeder reactors, use fission energy neutrons directly . </P> <P> Cold neutrons are thermal neutrons that have been equilibrated in a very cold substance such as liquid deuterium . Such a cold source is placed in the moderator of a research reactor or spallation source . Cold neutrons are particularly valuable for neutron scattering experiments . </P>

What is the charge and location of a neutron