Isotopes: Sulfur 35

Physical Characteristics:
  • Half-life: 87.6 days
  • Emissions: Beta particles with a maximum energy of 167 keV and an average energy of 49 keV.
  • Maximum Range in Air: 24 cm in air; 0.030 cm in tissue.
  • Fraction transmitted through the dead layer of the skin: 0.12
Dose and Shielding:
  • Dose rate to the skin at 10 cm: 625 mrad/hour/mCi
  • (for an unshielded point source)
  • Dose rate to epidermal basal cells from skin contamination of 1 mCi/cm2:1460 mrad/hour
  • Shielding: None needed, when used in millicurie quantities under normal laboratory conditions
  • Annual Limit on Intake (ALI): 10 millicuries via ingestion for most compounds of sulfur. The intake of one ALI will produce a dose of 5 rem.

Liquid scintillation counting is the preferred method for detecting S-35. Most G-M detectors are not likely to detect the presence of S-35 in amounts less than about 100,000 dpm (0.05 μCi).


35S-labeled methionine/cysteine compounds can volatilize. Stock solutions and thawed materials should be opened within a fume hood. Activated charcoal can be used to trap contamination within equipment such as incubators. Contact EHS for further information. Low-level S-35 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: through the Off-Site Radioactive Waste Disposal Program