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Gamma Radiation Source Facility


The Gamma Radiation Facility known as GRSF houses a cesium-137 gamma ray source which can provide gamma rays at a variety of dose rates. The gamma source is an industry standard

J.L. Shepherd Mark I Model 68A 137Cs γ Irradiator.

The photon energy from the source is 662 keV, with a Lineal Energy Transfer (LET) in water of approximately 0.8 keV/μm.

The source chamber has been enhanced with the ability to provide constant air exchange and interior lighting during exposures, if desired. The facility also boasts a ThermoFisher Scientific Forma Series II 3110 water-jacketed CO2 incubator, and a Sorvall RT7 refrigerated centrifuge.

The dose delivered to a sample is controlled by selecting the length of time the sample is exposed to the source. Dose rates are controlled by mounting the samples at one of three different distances from the source within the irradiation chamber, and by varying the thickness of the lead attenuation sheets between the source and the sample. A minimum dose of 0.5 cGray or 0.5 Rads can be achieved in 25 seconds using the thickest attenuator (x100). Doses of 1200 cGy can be delivered in 1.82 minutes with no attenuation. Tables showing the length of time in minutes required for a given exposure are shown below for each of the three different sample locations. These tables are updated three times annually.

Technical Capabilities

The figures at the bottom of this page show images of the room containing the 137Cs gamma source. The source is lowered into the vault to shield users from it when not in use, and raised pneumatically to give the exposures. The dose rate is controlled by locating the samples at one of three calibrated locations within the source chamber, at one of three different distances from the source. Doses are controlled by exposing samples for shorter or longer exposure times. Attenuators are added to lower the dose rate if needed.

View the GRSF Dose Information Table (.xlsx) for up to date dose rate calibrations for the GRSF. By changing the Todays calibration date field, calibrations can be adjusted for your experiments exact exposure date.

The J.L. Shepherd Mark I Model 68A has a sample region that can accommodate sample sizes up to 12" diameter x 14" high, with a total volume of 26 liters and there are a variety of sample holders available for your exposures.

The J.L. Shepherd company made a map of the uniformity of the radiation field for different attenuation settings. The accompanying plots show how the intensity of the radiation field varies relative to the center. The central point is normalized to 100%, and contours in intensity are plotted in 5% increments. The distance scale is 0.5 inches per box.

Radiation Field Uniformity Distribution

Cables may be run in or out of the vault through 4 openings; 2 are 1” in diameter, and 2 are 0.5” in diameter.
The through-holes can be seen here.

Facility Images

image 1

J.L.Shepherd Irradiator closed and locked.

image 2

Vault open awaiting samples.

image 3

Filled T-75 flasks being prepared for irradiation.

image 4

Cell samples installed in the irradiator.