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DOE-STD-1128-98
Figure 6.1.
Absorbed Surface Dose Rate from Plutonium Dioxide as Measured with
an Extrapolation Chamber
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 reduce 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


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