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DOE-STD-1128-98
Guide of Good Practices for Occupational Radiological Protection in Plutonium Facilities
of LIS will have reduced concentration of these isotopes, resulting in lower intrinsic neutron
exposures. The LIS process can also result in significant reductions in gamma-ray
exposures for the product enriched in 239Pu. Much of the whole-body and most of the
extremity exposure is a result of surface contamination on the gloves and the interior of the
glovebox. The 241Am decay product, which results from the beta decay of 241Pu, is a major
contributor. Thus, the reduction of 241Pu can significantly reduce exposures to hands and
arms, as well as reduce the radiation streaming through glove ports in shielded gloveboxes.
2.2
NUCLEAR PROPERTIES
Of the 15 plutonium isotopes, the two that have proven most useful are masses 239 and 238.
Plutonium-239 is fissile, i.e., atoms of plutonium split upon exposure to thermal or fast neutrons.
Chemical reactions can release a few electron volts of energy per atom; however, when a plutonium
nucleus splits, it releases about 200 MeV of energy and two or three neutrons. This release of
energy makes 239Pu useful for nuclear weapons and reactor fuel. In fact, in light water reactors
(LWRs) much of the power originates from the fission of 239Pu, which is produced by neutron
capture in 238U. Because of its higher specific activity, 238Pu is used as long-lived heat sources for
powering planetary space missions where adequate solar energy is not available.
As mentioned before, all plutonium isotopes are radioactive. Isotopes with even mass numbers
(except mass number 246) are primarily alpha emitters. Isotopes of mass numbers 232, 233, 234,
235, and 237 also decay by electron capture; isotopes of mass numbers 241, 243, 245, and 246
decay by beta emission. Many of the alpha-emitting isotopes, such as 238Pu and 240Pu, also fission
spontaneously and emit neutrons. All of the particle emissions are accompanied by X-ray and
gamma-ray emissions over a wide range of energies.
A review of the nuclear properties of plutonium (e.g., cross-sections, nuclear levels, half-lives, and
fission yields) can be found in Volume 1 of the Plutonium Handbook: A Guide to the Technology
(Wick, 1967) and in American National Standards Institute (ANSI) Standard N317, Performance
Criteria for Instrumentation Used for In-Plant Plutonium Monitoring (ANSI, 1980a). Plutonium
decay schemes, neutron yields, and neutron energy spectra are described in the following sections.
2.2.1 Decay Schemes
The decay modes of some important plutonium and other isotopes and decay products are
shown in Table 2.3. For brevity, only the most abundant radiations have been included in
the table; more detailed information can be found in papers by Gunnink and Morrow (1967)
and Klein (1971), in ICRP Publication 38 (ICRP, 1983), and from the National Nuclear Data
Center. Most of the isotopes are strong alpha-emitters, making alpha heating a problem for
the storage and handling of large amounts of plutonium. The specific activities
2-5


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