Neutron absorption is the process wherein an atomic nucleus will absorb a neutron. Many different atomic nuclei will do this, and different nuclei will present a larger of smaller target for the neutron, as you might have guessed. This is the neutron absorption cross section for the material, and it varies as the material does and as the kinetic energy of the neutron does, as well. You may have figured out that there are many different resulting products or outcomes that can be seen from neutron absorption. It is neutron absorption that powers up a chain reaction, so let's look at that aspect of this phenomenon.
In a nuclear reactor, some spontaneous fissions will release neutrons, and these neutrons will, if the control rods are pulled out sufficiently, begin a chain reaction. The nuclear fuel, usually either uranium or plutonium, will absorb a neutron (after some slowing down of that neutron), and they'll fission as a result. These fissions will release more neutrons, which will be absorbed and will create more fissions, which will release more neutrons, etc. A neutron released from a fission event will have a high kinetic energy; it will be moving very quickly. It might be absorbed, but will have a higher probability of being absorbed if it is slowed down, or thermalized. The moderator in a reactor, usually water, does this slowing down of the neutrons. The slower neutrons have a much higher probability of being absorbed and continuing the chain. Fission by neutron absorption is the mechanism by which a nuclear chain reaction is maintained in a nuclear reactor.
Absorption of neutrons by an element depends on neutron cross-section data for that element at the energy of interest. The absorption cross-section gives the probability of a neutron being absorbed by an atom of the element. Measuring the absorptions at a certain neutron energy can help in determining the propensity of an element to absorb neutrons at that energy level.
you already partly answered your own question. Neutrons.
Yes, graphite can slow down neutrons through a process called moderation. Graphite has a lower neutron absorption cross-section compared to other materials, allowing neutrons to penetrate and interact with the carbon atoms, effectively slowing down the neutrons.
Jimmy Neutron's parents are Hugh Neutron (his father) and Judy Neutron (his mother).
The neutral or no charge particle in an atom is called a neutron. Neutrons are located in the nucleus, along with protons. Neutrons have the same mass as protons.
Absorption of neutrons by an element depends on neutron cross-section data for that element at the energy of interest. The absorption cross-section gives the probability of a neutron being absorbed by an atom of the element. Measuring the absorptions at a certain neutron energy can help in determining the propensity of an element to absorb neutrons at that energy level.
Lead is a metal in gunshot residue that can be detected by atomic absorption but not neutron activation. This is because atomic absorption spectroscopy relies on the absorption of light by ground-state atoms, which lead exhibits. Neutron activation analysis, on the other hand, requires the irradiation of samples with neutrons to induce radioactivity, which is not applicable to lead.
The absorption of a free moving neutron by the atom's nucleus
neutron moderation
neutron moderation
Aluminum is not very effective at stopping neutron radiation penetration compared to other materials like lead or concrete. Neutrons can easily pass through aluminum due to its relatively low neutron absorption and scattering properties. For effective shielding against neutron radiation, materials with high neutron absorption cross-sections such as boron or water are more suitable.
Neutron moderation
When it is mixed or alloyed with beryllium, polonium can be a neutron source: beryllium releases a neutron upon absorption of an alpha particle that is supplied by 210Po. It has been used in this capacity as a neutron trigger or initiator for nuclear weapons
Ram K. Tripathi has written: 'Universal parameterization of absorption cross sections' -- subject(s): Mathematical models, Ions, Cross sections (Nuclear physics), Absorption cross sections, Heavy ion collisions, Absorption, Neutron cross sections 'Can Bose condensation of alpha particles be observed in heavy ion collisions' -- subject(s): Collisions (Nuclear physics), Bose-Einstein condensation, Heavy ions, Alpha rays 'New parameterization of neutron absorption cross sections' -- subject(s): Absorption cross sections, Neutron cross sections, Parameterization
Neutron absorption is the key to the operation of a nuclear reactor as this is what perpetuates the chain reaction. Neutrons can be absorbed by a number of things within the core of an operating reactor, but when a fuel atom absorbs a neutron, it becomes unstable and fissions. The fission event releases fission fragments, energy, and more neutrons, which will, when absorbed, continue the chain reaction.
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.
The 2 most common materials are cadmium or boron, due to their large neutron absorption crosssection.