Plant Materials
DOE-HDBK-1017/2-93
EFFECT DUE TO NEUTRON CAPTURE
EFFECT DUE TO NEUTRON CAPTURE
Neutron radiation affects material because of neutrons being captured. This chapter
discusses the effects that the neutrons being captured have on the material.
EO 1.20
DESCRIBE how the emission of radiation can cause dislocation
of the atom emitting the radiation.
EO 1.21
STATE the two effects on a crystalline structure resulting from
the capture of a neutron.
EO 1.22
STATE
how
thermal
neutrons
can
produce
atomic
displacements.
Effect Due to Neutron Capture
The effects of neutrons on materials arise largely from the transfer of kinetic energy to atomic
nuclei in one way or another. Thus, highly energetic recoil nuclei may be indirectly produced
by the absorption of a neutron and the subsequent emission of a g. As previously discussed, if
the energy of the recoil nucleus is sufficient to permit it to be displaced from its normal (or
equilibrium) position in the crystal lattice of a solid, physical changes of an essentially permanent
nature will be observed. The effects of fast neutrons in disrupting (or damaging) the crystal
lattice by displacement of atoms are discussed in the two previous chapters, "Atomic
Displacement Due to Irradiation" and "Thermal and Displacement Spikes Due to Irradiation."
This damage is commonly referred to as radiation damage. The absorption or capture of lower
energy thermal neutrons can produce two effects.
a.
introduction of an impurity atom (this is used in the electronics industry to
uniformly dope semiconductors) due to the transmutation of the absorbing nucleus
b.
atomic displacement caused by recoil atoms or knock-ons
As noted, the introduction of an impurity atom was discussed previously, and atomic
displacement is the result of (n,p) and (n,a) reactions and (n,g) reactions followed by radioactive
decay. Thermal neutrons cannot produce atomic displacements directly, but they can do so
indirectly as the result of radioactive capture (n,g) and other neutron reactions or elastic
scattering.
Rev. 0
Page 37
MS-05
