1
0
n
238
92
U
239
92
U
239
92
U
0
0
1
0
n
10
5
B
11
5
B
7
3
Li
4
2
NEUTRON INTERACTIONS
DOE-HDBK-1019/1-93
Atomic and Nuclear Physics
NP-01
Page 46
Rev. 0
Absorption Reactions
Most absorption reactions result in the loss of a neutron coupled with the production of a
charged particle or gamma ray. When the product nucleus is radioactive, additional radiation
is emitted at some later time. Radiative capture, particle ejection, and fission are all categorized
as absorption reactions and are briefly described below.
Radiative Capture
In radiative capture the incident neutron enters the target nucleus forming a compound nucleus.
The compound nucleus then decays to its ground state by gamma emission. An example of a
radiative capture reaction is shown below.
Particle Ejection
In a particle ejection reaction the incident particle enters the target nucleus forming a compound
nucleus. The newly formed compound nucleus has been excited to a high enough energy level
to cause it to eject a new particle while the incident neutron remains in the nucleus. After the
new particle is ejected, the remaining nucleus may or may not exist in an excited state depending
upon the mass-energy balance of the reaction. An example of a particle ejection reaction is
shown below.
Fission
One of the most important interactions that neutrons can cause is fission, in which the nucleus
that absorbs the neutron actually splits into two similarly sized parts. Fission will be discussed
in detail in the next chapter.
