Physical Characteristics

  • Half-life: 119.8 days
  • Emissions: Principal emissions are 136 keV and 265 keV x-rays.
  • Half-Value Layer: 0.02 mm lead; 2 cm in tissue (The half-value layer is the amount of material required to reduce the radiation intensity by 50%.)

Dose Rate and Shielding

  • Gamma Dose rate (deep tissue dose) at 30 cm: 2.74 mrem/hour/mCi (for an unshielded point source)
  • Dose rate to epidermal basal cells from skin contamination of 1 µCi/cm2: 519 mrem/hour
  • Shielding: Lead foil or sheets, when used in hundreds of microcuries or in millicurie quantities. None needed when used in low microcurie amounts.
  • Annual Limit on Intake (ALI): 700 microcuries via inhalation, and 500 microcuries via ingestion. The intake of one ALI will produce a dose of 5 rem.


A sodium iodide crystal scintillation detector is the preferred method for detecting Se-75. Additionally a G-M detector will readily detect Se-75 contamination, although liquid scintillation counting is also an acceptable method for detecting removable contamination.


High localized doses are possible while handling millicurie amounts of Se-75 and as a result of skin contamination. Reduce doses by using remote handling tools such as tongs, using shielding extensively to shield storage and experimental containers and work areas, and performing thorough and frequent surveys of the work area, clothing and the body.

Radiation Monitoring Requirements: Radiation monitoring badges must be worn by any person who uses open sources of Se-75 in amounts of 0.5 mCi or more for extended operations (applies to most operations other than simple aliquoting from a stock vial).

Waste Disposal

  • Solid Wastes: through the Onsite Decay-in-Storage Program
  • Liquid Scintillation Wastes:  through the Off-Site Radioactive Waste Disposal Program
  • Liquid Wastes: through the Sewer Disposal Program. The laboratory disposal limit for Se-75 is 3 mCi per month.