. ▪ . N OTABLE R ADIOISOTOPES OF S ECURITY C ONCERN ▪ . RADIOISOTOPE Abbreviation Half-Life Activity Level Specific Activity Route of Health High-Energy High-Energy High-Energy Applications Hazard Alpha? Beta? Gamma Rays? CBq/G (Ci/G) Inhalation Well-logging Am-241 433 years low 125.8 (3.4) No Low americium-241 and/or ingestion Yes High- and medium-dose brachytherapy Inhalation Well-logging 19,832 (536) No Low californium-252 Cf-252 2.7 years medium and/or ingestion Yes Well-logging 30 years Single-beam teletherapy Cs-137 medium 3,256 [19,980 million] Internal and Low Research and blood irradiators cesium-137 N/A Yes (88 [540 million]) External High- and medium-dose barium 137m (Ba-137m) ( 2.6 minutes ) brachytherapy Level and conveyor gauges Single-beam teletherapy Research and blood irradiators Internal and Co-60 5.3 years medium 40,700 (1,100) N/A Low Yes High- and medium-dose brachytherapy cobalt-60 External Level and conveyor gauges Multi-beam teletherapy (gamma knife, e.g.): Internal and 4.8 million (130,000) N/A Yes Yes iodine-131 I-131 8 days high External >16,650 (>450) std Internal and Industrial radiography Ir-192 74 days medium N/A Yes Yes iridium-192 >37,000 (<1,000) high External 166,500 Inhalation Po-210 140 days medium Low Low polonium-210 (4,500) and/or ingestion Yes Inhalation Radioisotope thermoelectric generator (RTG): 636.4 (17.2) No Low plutonium-238 Pu-238 88 years low and/or ingestion Yes Inhalation 2.33 (0.063) Low Low plutonium-239 Pu-239 24,000 years low and/or ingestion Yes Inhalation 37 (1) No Low radium-226 Ra-226 1,600 years low and/or ingestion Yes Radioisotope thermoelectric generator (RTG): 5,180 [20.35 million] Internal and Yes N/A 29 years strontium-90 Sr-90 high N/A (140 [550,000]) External [Yes] [Low] ( yttrium-90 ) ( Y-90 ) ( 64 days ) α. .β. γ Federation of ALPHA EMISSIONS BETA EMISSIONS GAMMA EMISSIONS American Scientists (Alpha emissions can be “blocked” with a piece of paper; their danger to (Beta emissions can be “blocked” with thick lead; the danger with beta emissions (Gamma emissions are difficult to block; they are Charles P. Blair humans lies with inhalation) primarily lie with low level penetration and, to a greater degree, via inhalation) very penetrating) June 2013 .