Isotopes: Phosphorus 33

Physical Characteristics:
  • Half-life: 25.3 days
  • Emissions: Beta particles with a maximum energy of 249 keV and an average energy of 76 keV.
  • Maximum Range in Air: 45 cm in air; 0.06 cm in tissue
  • Fraction transmitted through the dead layer of the skin: 0.35
Dose and Shielding:
  • Dose rate to the skin at 10 cm: 2000 mrad/hour/mCi
  • (for an unshielded point source)
  • Dose rate to epidermal basal cells from skin contamination of 1 mCi/cm2:4500 mrad/hour
  • Shielding:None needed, when used in millicurie quantities or less, under normal laboratory conditions
  • Annual Limit on Intake (ALI): 6 millicuries via ingestion. The intake of one ALI will produce a dose of 5 rem.

Liquid scintillation counting is the preferred method for detecting P-33. Most G-M detectors are not likely to detect the presence of P-33 in amounts less than about 100,000 dpm (0.05 μCi).


Low-level P-33 contamination cannot be easily detected with a G-M meter, and special precautions are needed to keep the work environment clean. The regular use of wipe testing, using a liquid scintillation counter, is the only way to insure that the work space does not contain low-level removable contamination.

Waste Disposal:
  • Solid Wastes/Liquid Scintillation Wastes: through the Off-Site Radioactive Waste Disposal Program