Purchasing
Cr51 Reference Sheet
Handling Precautions: Chromium-51
Long Lived Radionuclide
- Half-life: 27.7 days
- Type of Emitter: Gamma
- Beta Energy: 0.320 MeV
- Travel Distance in Air: 337m: 1,105 ft (approx. for 99% reduction)
- Travel Distance in Lead: 1.27cm : 0.5 inch (approx for 99% reduction)
Annual Intake Limits
- Inhalation: 20,000 µCi
- Ingestion: 40,000 µCi
Concerns
Concerns
The major concern with using 51Cr is radiation exposure from an unshielded vial. The dose rate at the opening of an unshielded vial containing 1 millicurie of 51Cr can be 180 millirem per hour. 51Cr gives off many x-rays and gammas and requires more lead shielding in comparison to typical biomedical radionuclides.
Shielding
None required for quantities under 1 mCi.
For mCi quantities use lead shielding. Store material in an isolated area away from work areas and places where people could be exposed. A 1.7 mm (0.067 inch) thick lead sheet will reduce exposure by 50%. Add enough lead shielding until the measured exposure rate is almost 2-3 times background. This also applies to waste containers.
Detection
Use a survey meter equipped with a pancake probe to detect 51Cr. Use the pancake probe with the screen side facing up toward the ceiling when surveying. Alternatively, use a survey meter equipped with a NaI scintillation probe to detect 51Cr.
Wipe samples counted in a Liquid Scintillation Counter provide detection of removable 51Cr surface contamination.
Specific Equipment/Supplies
In addition to general equipment, the following is required for specific use of 51Cr:
- Survey meter with a sodium iodide probe or pancake probe.
- Thin lead (½ inch) for shielding.
- TLD ring (for quantities greater than 1 mCi).
Safety Rules for 51Cr
Follow General Safety Precautions for all isotopes.
Specific Recommendations: While Working
- Do not work directly over an open container of 51Cr. Place all vials and test tubes containing 51Cr behind a lead shield. Place the Lead shielding near a wall (not toward another work area on the other side of the bench) away from the main flow of traffic in the lab. This applies to both work conditions and waste storage.
- Check the radiation level in front of the shield to determine if additional lead should be added.
Specific Recommendations: Post Use
- 51Cr waste must be segregated and kept separate from other radioactive waste. The waste should be stored and shielded in an isolated spot away from work areas (for more efficient shielding).
- Dispose of 51Cr waste according to the waste disposal guidelines. If by sink disposal, ensure that it is soluble in water and does not exceed the posted limit ( 1000 µCi daily, if only one radionuclide is being disposed of). Do not exceed this limit , unless otherwise authorized by the Radiation Safety Committee in the permit.
Email radiation_protection at harvard dot edu to send comments and suggestions to the Radiation Protection Office
