Zinc-65

Physical Characteristics

  • Half-life: 243.9 days
  • Emissions: Beta (positron) particles with a maximum energy of 0.33 MeV (2%) and an average energy of 0.099 MeV. Gamma rays: 1.116 MeV (51%) and 0.511 MeV (2%).
  • Beta Maximum Range: 76.2 cm in air; 0.10 cm in tissue; 0.08 cm in plexiglas
  • Fraction transmitted through the dead layer of the skin: 0.95
  • Half-Value Layer: 14 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

  • Beta Dose rate to the skin at 30 cm: 1.93 mrem/hour/mCi (for an unshielded point source)
  • Gamma Dose rate (deep tissue dose) at 30 cm: 3.44 mrem/hour/mCi (for an unshielded point source)
  • Dose rate to epidermal basal cells from skin contamination of 1 µCi/cm2: 281 mrem/hour
  • Shielding: Shield stock vials with lead. Generally, lead is the preferred shielding material for Zn-65 for lower activity operations. However, since significant bremsstrahlung may be produced with higher activities, it may be desirable to use a combination of plexiglas and lead/steel as shielding when working with multi-millicurie amounts. In such a case, plexiglas should be placed closest to the source as primary shielding, and lead should be used outside the plexiglas as secondary shielding.
  • Annual Limit on Intake (ALI): 400 microcuries via ingestion and 300 microcuries via inhalation. The intake of one ALI will produce a dose of 5 rem.

Detection

A G-M detector will readily detect low-level Zn-65 contamination, although liquid scintillation counting is also an acceptable method for detecting removable contamination.

Precautions

High localized doses are possible while handling millicurie amounts of Zn-65 and as a result of skin contamination. Reduce doses by wearing safety glasses (for shielding the eyes), 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 Zn-65 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 & Liquid Scintillation Wastes: through the Off-Site Radioactive Waste Disposal Program
  • Liquid Wastes: through the Sewer Disposal Program. The laboratory disposal limit for Zn-65 is 0.3 mCi per month.