Co60 Gamma Ray Irradiation

The Radiation Science and Engineering Center has two gamma-ray irradiation facilities, which provide flexibility for research and industry projects. The Center has a pool irradiator with movable sources that can be configured to suit the researcher. Discrete neutron sources can be inserted in the pool to provide a mixed field. There is also a dry cell gamma irradiator that has a much higher dose rate for samples that require it. Using these two facilities, doses of kiloRads to GigaRads can be provided to the researcher.

Pool Irradiator

The sources are made of solid radioactive cobalt-60 pellets encased in aluminum or stainless steel. They are used and stored in a large pool filled with demineralized water. The water is easy to work through, allows change of dose rates by moving the sources, and shields users from the radiation coming from the cobalt-60.

There are two dry vertical irradiation tubes that are frequently used to irradiate materials. Samples are lowered down through one of these tubes (6-inches or 3-inches in diameter), which are surrounded by the radioactive cobalt-60 sources close to the bottom of the pool. Since there is no water in the tube, a nearly three foot long lead plug is used to shield the radiation at the top of the tube. Gamma-rays from the sources pass through the tube and expose the material inside. Samples are irradiated in this way for research and testing in many different fields. These tubes are fixed in location; however varying the number of sources around the tube can change the dose-rate.

There is also a large tube and rectangular channel available for irradiations. These tubes can be positioned at distances away from a planar source, which then provides different dose rates. This facility has the most flexibility for users.

Dry Irradiation Facilities

The Dry Cell irradiator has the highest dose rate and is used for sterilization, cross-linking, polymerization, cryogenic reduction, and electronic material testing. The irradiation chamber is a cylinder approximately 6-inches in diameter and 7 inches high. A one-inch diameter access tube allows for electronic monitoring of devices during irradiation. The dose rate in this facility was measured and certified under NIST’s National Voluntary Laboratory Accreditation Program (NVLAP) using the Fricke dosimetry system – the overall uncertainty of the absorbed dose rate is +/- 2.4% at the 95% confidence level.