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DOE Standard Guide of Good Practices for Occupational Radiological Protection In Plutonium Facilities
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Calculated Neutron Dose Equivalent Rates - doe-std-1128-98_ch10165


DOE-STD-1128-98
fi
= the weight fraction of the ith isotope of plutonium
t
= the time since chemical separation of the plutonium, days.
This equation is only valid for a year or so after chemical separation,
when the ingrowth of 241Am can be represented linearly.
A similar equation has been derived for lead-loaded rubber gloves using
the calculations from the computer code PUSHLD. The 80-mil lead-
loaded glove is nominally 1.9-mm (0.076-in.) thick in the palm and
forearm and contains the equivalent of about 1 mm of lead. The surface
dose rate, DPbGl, is given by the following equation:
DPbGl(t) = 2.83 f238 e-0.00789t + 0.104 f239 + 0.0315 f240
(6.3)
+ 6.35 x 10-5 f242 + f241 (158.5 e-0.0016t - 152.5 e-0.0457t)
where DpbGl(t) = surface dose rate as a function of time, rad/h
fi
= weight fraction of the ith plutonium isotope
t
= time since chemical separation of the plutonium, years.
This equation includes the radiations from plutonium, as well as the 237U
and 241Am progeny from the decay of 241Pu. The expression is valid for
times between 50 days and 100 years after the chemical separation of the
plutonium. The formula predicts dose rates from 0% to +20% of those
calculated by the computer code PUSHLD.
6.2.3
Neutron Dose Equivalents
Neutron dose equivalents are significant in any process or decommissioning
efforts involving kilogram quantities of plutonium or gram quantities of 238Pu.
Neutrons originate from three sources:
-- Spontaneous fission of even isotopes of plutonium
-- alpha-neutron reactions with low-atomic-number elements, including oxygen
and fluorine in plutonium compounds and impurities in metals
-- neutron-induced fissions.
6-12


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