permanent injury of individuals who may be in close proximity to the radioactive source for a longer period of time than for Category 1 sources. Based on direction and authority in the Energy Policy Act of 2005 (P.L. 109-58), the U.S. NRC limited the radiation sources within the study scope to Category 1 and 2 sources.

Data from the U.S. NRC show that out of the thousands of manufactured and natural radionuclides, americium-241, cesium-137, cobalt-60, and iridium-192 account for nearly all (over 99 percent) of the Category 1 and 2 sources. The features of these and some other key radionuclide radiation sources are summarized in Table S-1.

TABLE S-1 Summary of Radionuclides in Category 1 and 2 Radiation Sources in the United Statesa

Radionuclide

Half-life

Radioactive Emissions and Energies

Typical Specific Activity (TBq/g) [Ci/g]

Total Activity in U.S. Inventory (TBq) [Ci]

Major Applications

Typical Activity (TBq) [Ci]

Physical or Chemical Form

Americium-241

432.2 yr

α–5.64 MeV, γ-60 keV, principal

0.13 [3.5]

240 [6,482]

Well logging

0.50.8 [13–22]

Pressed powder (americium oxide)

Californium-252

2.645 yr

α–6.22 MeV, fission fragments, neutrons, and gamma rays

20 [540]

0.26 [7]

Well logging

0.0004 [0.011]

Metal oxide

Cesium-137 (Ba-137m)

30.17 yr

β-518 keV max with γ-662 keV (94.4% of decays) or β-1.18 MeV max

0.75 [20]

104,100 [2.8 million]

Self-contained irradiators

75 [2,000]

Pressed powder (cesium chloride)

Teletherapy

50 [1,400]

Calibrators

15 [400]

Cobalt-60

5.27 yr

γ-1.173 and 1.333 MeV

3.7 [100]

7.32 million [198 million]

Panoramic irradiators

150,000 [4 million]

Metal slugs

Self-contained irradiators

900 [24,000]

11 [300]

Teletherapy

500 [14,000]

Metal pellets

Industrial radiography

4 [100]

Iridium-192

74 d

β-1.46 MeV max with 2.3 γ-380 keV avg, 1.378 MeV max (0.04% of decays)

18.5 [500]

5,436 [146,922]

Industrial radiography

4 [100]

Metal

Plutonium-238

87.7 yr

α–5.59 MeV, and γ-43 keV (30% of decays)

2.6 [70]

34.7 [937]

RTG

10 [270]

Metal oxide

Pacemakers (obsolete)

0.1 [3]

Fixed gauges

0.75 [20]

Selenium-75

119.8 d

γ-280 keV average, 800 keV max

20–45 [530–1200]

9.7 [261]

Industrial radiography

3 [75]

Elemental or metal compound

Strontium-90 (Yttrium-90)

28.9 yr

β-546 keV

5.2 [140]

64,000 [1.73 million]

RTG

750 [20,000]

Metal oxide

aNuclear decay data for this table and throughout the report are from Firestone and Shirley (1996).



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