Radiations In Plutonium Facilities - doe-std-1128-98

DOE-STD-1128-98

In reality, most instruments and personnel dosimeters used at DOE facilities are

still calibrated in terms of dose equivalent. For example, consider the case in

which personnel neutron dosimeters are calibrated on acrylic plastic phantoms at

a specified distance from a calibrated neutron source. For DOELAP testing, the

dose equivalent at this point has been calculated in accordance with NBS Special

Publication 633, Procedures for Calibration of Neutron Personnel Dosimeters

(Schwartz and Eisenhauer, 1982). These calculations are based on the Grundl-

Eisenhauer energy spectrum and the conversion coefficients from NCRP Report

38 (NCRP, 1971), which are for the "old" values of dose equivalent from the

cylindrical phantom calculations.

In most instances, the present methods based on dose equivalent over-estimate

effective dose equivalent. In cases where personnel are approaching dose limits,

it may be prudent to more accurately evaluate effective dose equivalent using

special calibrations. Depending on the irradiation geometry and energy, effective

dose equivalent may be as much as a factor of two less than dose equivalent.

6.2

RADIATIONS IN PLUTONIUM FACILITIES

As outlined in Section 2.0 of this report, plutonium emits a wide variety of radiations,

including alpha and beta particles, as well as more penetrating X-rays and gamma rays.

Because of the short half-life of 241Pu, the radioactive decay progeny are also important

sources of radiation. This section outlines methods to calculate the dose equivalents from

radiations emitted by plutonium and its progeny. Examples of measured dose rates are also

included.

6.2.1

Alpha and Beta Doses

Plutonium is primarily an alpha-emitter and is of great concern if inhaled,

ingested or injected into the body. However, the skin is an effective barrier to

alpha particles, and external contamination is only a problem if there is a wound

or break in the skin.

Plutonium-241 is a beta-emitter that produces low-energy beta particles with a

maximum energy of 0.022 MeV. Both alpha and beta particles are completely

shielded by thin rubber gloves or other protective devices. The dose rate through

a rubber glove originates primarily from the X-rays and low-energy photons

generated from plutonium and 241Am, the decay progeny of 241Pu.

6-5