(See Section 6.3.3 for more information.) Also, 241Am can contribute to neutron
dose. Americium-241 contributes to increased alpha emission which affects the
neutron dose as well as radiolysis and helium retention and release. Because of
its importance to radiation exposure, the fractional amount of 241Am produced
by beta decay from 241Pu is given as a function of time since chemical
separation (see Figure 2.2).
2.2.2 Neutron Yields and Spectra
Plutonium and plutonium compounds also emit neutrons from spontaneous
fission and from alpha-neutron reactions with light elements. The spontaneous
fission half-life and the neutron yields from spontaneous fission and alpha-
neutron reactions for plutonium metal and plutonium compounds are provided
in Section 6.0 of this TS. The approximate neutron yield from a substance with
a known isotopic composition can be determined by adding the contributions
from each component. This procedure and its limitations are described in detail
in Section 6.0, which also discusses neutron dose equivalent rates.
Energy spectra from Pu-Be and Pu-B neutron sources are shown in Figure 2.3
Because of licensing restrictions on plutonium, these sources have been
replaced with source fabricated from americium. Metallic plutonium emits
neutrons having a Maxwellian energy distribution, with an average energy of
about 1.9 MeV. Plutonium compounds and alloys also emit neutrons from
alpha-neutron reactions, and these neutrons have significantly different
-- PuF4, about 1.3 MeV
-- 10% plutonium-aluminum alloys, 1.6 MeV
-- PuO2, slightly more than 2 MeV
-- PuBe, 4.3 MeV.
Plutonium compounds or alloys containing sodium, magnesium, silicon,
chlorine, carbon, or oxygen have significant alpha-neutron yields, but little
information is available about their neutron energy spectra.