Neutron Yields and Spectra - doe-std-1128-98

DOE-STD-1128-98

(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

energies:

-- 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.

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