Gamma Doses - STD-1128-98master0170

DOE-STD-1128-98

Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities

Figure 6.1.

Absorbed Surface Dose Rate from Plutonium Dioxide as Measured with an

Figure 6.1 shows the dose rate as a function of tissue equivalent plastic absorber thickness,

as measured by an extrapolation chamber in contact with a 3-in.-diameter plutonium dioxide

source coated with a very thin layer of beryllium for contamination control. The plutonium

was compressed to about 80% of its theoretical density and vitrified by a Dynapack process

in which powder was compressed into a glassy solid by extreme pressure and heat evolved

during the compression process. The plutonium oxide disk is mechanically stable and

produces little smearable contamination. Even minute layers of tissue equivalent plastic

reduces the dose rate significantly, as shown in Figure 6.1.

6.2.2 Gamma Doses

There can be substantial gamma doses involved in the processing and handling of

plutonium, particularly in glove-box operations involving plutonium dioxide powders.

Plutonium emits very few highly penetrating gamma rays; most of the radiations are L X-

rays, which are very easily shielded. Because most of the photons emitted by plutonium are

of low energy, plutonium sources are "infinitely thick" relative to their photon radiations,

i.e., an additional thickness of plutonium does not appreciably increase the photon dose rate.

A plutonium metal source of about 1-mm thickness or a plutonium oxide source about

6-mm-thick is "infinitely thick" due to self-shielding.

6-6