Instruments & Calibration
All new radiation instruments must be source checked, approved and tracked by RSO.
All new and existing radiation instruments must be calibrated in accordance with the OHSU Radiation Safety Regulations Section 13: Instrument Calibrations and the Calibration Procedure(RSOP 1301.pdf).
For OHSU Research this must be performed biennially (every two years), and for OHSU Healthcare this must be performed annually.
RSO provides this service on a fee per service basis to include:
Initial response check from manufacturer (no charge)
Radiation Instrument Information
Geiger Mueller (GM) Detector
- Used for the detection of beta particles.
- Pressurized gas filled detector with grid-like screen to protect it from being damaged. Beta particles enter the thin mica window and ionize the gas inside the detector.
- Typical background is 20-50 counts per minute (cpm).
- Covering the probe with parafilm or plastic wrap will lower the efficiency for detecting low energy beta emitters (14C and 35S).
Scintillation Detector (NaI)
- Used for the detection of photon radiation (gamma, x-ray & Bremmstrahlung).
- Crystalline solid detector protective with thin, opaque, plastic covering to protect the crystal.
- Typical background is 150-300 counts per minute (cpm).
- Can be used to detect 32P because of the high energy beta particle which gives off bremmstrahlung when it interacts with the detector.
Liquid Scintillation Counter (LSC)
To count using an LSC, you must use Liquid Scintillation Cocktail. This cocktail contains a chemical that absorbs the decay energy of the radionuclide that is in it and re-emits the energy as light. The exception to this is Cerenkov counting with 32P (no cocktail used). This method results in a much lower efficiency.
The LSC has the greatest counting efficiency for all radionuclides. Any radionuclide that decays by beta or electron emission may be counted.
This is the only instrument capable of detecting 3H.
Have LSC's serviced annually. Most departments have outside contracts for this, as the RSO does not provide this service.
What types of cocktail to use:
Biodegradable: (ecolume, ecolite, biosafe, ecoscint,) Easy to dispose of through the RSO or down a "hot sink".
Hazardous: (organic compounds such as tolune or xylene) More expensive to dispose of through the RSO and CANNOT dispose of down the drain.
Use 10mL of cocktail in 20mL vials and 5mL cocktail in 7mL vials to ensure maximum efficiency.
Static discharge can produce false counts when loading plastic vials with latex gloves. Wipe down with damp paper towel or "static guard" or simply recount.