Agent Name

Protactinium

CAS Number

7440-13-3

Formula

Pa

Major Category

Physical/Radiation

Synonyms

Brevium; Uranium X2; UX2; [Merck Index # 7883]

Category

Radionuclides

Description

Shiny, silvery, malleable metal; All isotopes are radioactive; Pa-231 decays by alpha emission to Actinium-227; [Merck Index # 7883]

Sources/Uses

Used in scientific research with no commercial uses; It is present in uranium ores at a concentration of 1 part proactinium per 3 million parts uranium. Of the 20 known isotopes, 3 are naturally occurring: Pa-231, Pa-234, and Pa-234m with half lives of 33,000 years, 6.7 hours, and 1.2 minutes, respectively. [Argonne]

Comments

Pa-231 decays to Actinium-227 by emitting an alpha particle. Actinium-227 and its decay products account for more than 80% of the inhalation hazard associated with exposure to Pa-231. [Argonne] Most Important Radionuclide: Pa-231 Source: Uranium ores; Half-Life: 33,000 years Specific Activity: 0.048 Ci/g Decay Mode: Alpha GI Absorption: 0.05% Lung Clearance Half-Time: Years for oxides and hydroxides; Weeks for all other compounds; Internal Toxicity: Very High Annual Limit on Intake: 0.000002 mCi Average Radiation Energy (MeV): Alpha 5.0; Beta 0.065; Gamma 0.048 [Argonne] [See Glossary for references.] See "Radiation, ionizing."

Exposure Assessment
Half Life

Biological half life: 50 years (skeleton); 10 days (liver); 10 days to 60 days (kidneys); [ANL Radiological Fact Sheets]

Links to Other NLM Databases
Health Studies

Human Health Effects from Hazardous Substances Data Bank:

Toxicity Information

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Chemical Information

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Other Information

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