Carbon-14

Physical Characteristics

  • Half-life: 5,730 years
  • Emissions: Beta particles with a maximum energy of 156 keV and an average energy of 49 keV.
  • Maximum Range: 22 cm in air; 0.027 cm in tissue
  • Fraction transmitted through the dead layer of the skin: 0.11

Dose Rate and Shielding

  • Dose rate to the skin at 10 cm: 600 mrad/hour/mCi (for an unshielded point source)
  • Dose rate to epidermal basal cells from skin contamination of 1 mCi/cm2: 1400 mrad/hour
  • Shielding: None needed, when used in millicurie quantities under normal laboratory conditions.
  • Annual Limit on Intake (ALI): 2 millicuries via ingestion. The ingestion of one ALI will produce a dose of 5 rem.

Detection

Wipe surveys using liquid scintillation counting is the preferred method for detecting C-14. Most G-M detectors are not likely to detect the presence of C-14 in amounts less than about 100,000 dpm (0.05 µCi).

Precautions

Low-level C-14 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 your work space does not contain low-level removable contamination.

Waste Disposal

  • Solid Wastes/Liquid Scintillation Wastes: through the Off-Site Radioactive Waste Disposal Program
  • Liquid Wastes: through the Sewer Disposal Program. The laboratory disposal limit for C-14 is 3 mCi per month.