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Table 6.7.1 Spontaneous Fission Nuetron Yields - doe-std-1128-98_ch10167
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DOE Standard Guide of Good Practices for Occupational Radiological Protection In Plutonium Facilities
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Table 6.8. Nuetron Yields from Alpha-Neutron Reactions for Oxides and Fluorides


DOE-STD-1128-98
Table 6.9 contains the neutron yields for trace amounts of elemental
impurities in plutonium metal or oxide. These data are also from
NUREG/CR-5550 (Reilly et al., 1991) and are derived from thick target
yields from accelerator data. The data in Table 6.9 differ from previous
values in BNWL-2086 (Faust et al., 1977), and the authors have not
experimentally checked the accuracy of these values. Two sets of data
are included: one for alphas emitted from enriched uranium and the other
for alphas emitted from 239Pu. To determine the neutron yield from trace
impurities, it is first necessary to determine the specific alpha activity
from Table 6.8, and the neutron yield per parts per million per 106 alphas
from Table 6.9 for either enriched uranium or plutonium. The specific
neutron yield from impurities can be estimated from the following
formula:
n
Y imp = 10 - 12 A  ∑ P j  I j
(6.8)
α
j
where A α =
alpha activity of the plutonium nuclides
Pj =
specific neutron yield from the jth element
(neutrons/alpha part per million) from Table 6.8
Ij =
elemental impurity concentration in plutonium (parts per
million).
Note that this formula is valid only if the impurities are uniformly
distributed with the plutonium so that the alpha particles directly interact
with the impurities. Dust layers of plutonium oxide can also produce
high neutron yields. For example, plutonium oxide dust layers on HEPA
filters with borosilicate glass can produce neutron emission rates 10
times higher than those for pure oxide because of alpha-neutron reactions
with boron in the glass fibers and aluminum spacer plates.
The total neutron yield per gram of plutonium can be found by summing
the contributions from:
-- Spontaneous fission (from Table 6.7)
-- alpha-neutron reactions in oxides or fluorides (from Table 6.8)
-- neutrons from low-atomic-number impurities (from Table 6.9).
6-16


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