Neutron Dose Equivalents - doe-std-1128-98

DOE-STD-1128-98

= the weight fraction of the ith isotope of plutonium

= 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

= weight fraction of the ith plutonium isotope

= 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.

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