Neutron Absorbers (Poisons) - doe-hdbk-1113-98_reaffirm_2005

DOE-HDBK-1113-98

Module 105 Criticality Safety

Lesson Plan

Instructor's Notes

5. Neutron Absorbers (Poisons)

If neutron absorbers are present (i.e., atoms and

molecules with relatively high neutron absorption

coefficients), these materials will remove neutrons

from being available to begin or sustain criticality.

Boron is an example of a frequently used neutron

absorber, or "poison".

6. Concentration or Density of Fissile Material

As the concentration or density of fissile material

increases, the opportunity for criticality increases

because of an increased likelihood of neutron

interaction with the fissile material.

7. Enrichment

Enrichment is the separation of isotopes. With

uranium, enrichment is typically referred to as

increasing the percentage (by weight) of the 235U

isotope in material to greater than that found in natural

uranium.