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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 shows 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. The most recent set of dose rate calibrations for the GRSF were made on 3 April 2017. Those calibrations have been adjusted to account for the source lifetime.

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. The dose rate with the 2,200 Curie 137Cs source is ~ 150 cGy/minute. Dose rates for 100 mm diameter samples is ~ 800 cGy/minute.

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.