Co-60 Underwater Irradiator
The Cobalt-60 Underwater Irradiator is used for research and development and for educational activities, including:
- Observation of radiation effects on materials and devices.
- Inducement of radiation effects in materials and devices, with subsequent investigation and/or utilization of the effects.
- Demonstration of operation of radiation detectors, and their behavior in high-dose gamma radiation fields.
No irradiation of explosive, flammable, or corrosive materials, or of food destined for human consumption is allowed.
The irradiation chamber is a dry, air-filled, 6-in I.D. tube that is open to atmosphere. For irradiations, a shielded elevator assembly moves within the dry tube to lower experiments or samples into the irradiation position. The shielding in the elevator allows cables to be run out of the irradiator to enable in-situ measurements during the irradiation. The available space for experiments or samples to be irradiated is ~3.5-in diameter by the usable height seen in the flux profile below. (The usable height for irradiations is limited by the falloff of radiation. For experimenters wanting to keep the dose rate across the height of the experiment within 10%, the maximum experiment height is 6 in. For experimenters wanting to keep the dose rate across the height of the experiment within 20%, the maximum experiment height is ~11 in.) A cross-section of the experiment elevator is also shown below.
Note - the hoist that raises and lowers the shielded elevator has a 10% duty cycle, which limits its use to three up/down cycles per hour.
Per nucleide.org, the decay of Co-60 results in the emission of 1173 keV and 1332 keV gammas 99.9% of the time. (Co-60 decays by beta minus emission to excited levels of Ni-60, which emits the gammas.)
The approximate dose rate in silicon (unfiltered) at the peak location is:
Because a common use for the irradiator has been irradiation of electronics parts for radiation damage testing, a filter box has been designed and built using the guidance in ASTM E1249-10, 'Standard Practice for Minimizing Dosimetry Errors in Radiation Hardness Testing of Silicon Electronic Devices Using Co-60 Sources', in order to minimize low energy photon absorbed-dose enhancement effects.