What is the neutron absorption cross section of an atom?

Answer 1

The neutron absorption cross section of an atom is the size of the target presented by that atom to an incoming neutron. Let's look at a couple of things and we'll get to it. Ready? Let's go.

There is a funny group of rules associated with the way an atomic nucleus reacts to an incoming neutron. It isn't necessarily like breaking a rack of billiard balls like in so many science shows. It's more like the neutron manages to press up against the nucleus and the nucleus captures it. Then what happens, happens.

One of the concepts to be considered is the energy of the incoming neutron. How fast is it going? Faster isn't necessarily better for increasing the probability of capture. It usually isn't. Another factor is the size of the target that a given nucleus presents to that neutron. We call that a neutron absorption cross section, and it's measured in barns. (Yes, like the broad side of a barn, as in hitting the broad side of a barn. And who said physicists weren't funny and couldn't make jokes!) There are tables to look this stuff up on because each given isotope of each given element has a given neutron capture cross section. That makes things challenging. And the actual cross section is different for different energies of neutrons. That ups the challenge for investigators even more.

Answer 2

The neutron absorption cross section of an atom is a measure of how likely an atom is to absorb a neutron when it collides with one. It provides information on the probability of a neutron being absorbed by the nucleus of an atom. The units for neutron absorption cross section are typically in barns (1 barn = 10^-24 cm^2).