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Industrial sterilisation

High dose cobalt-60 irradiations

Accurate irradiation of samples

NPL's three 60Co self-shielded irradiators are available for the irradiation of dosimeters or investigations, and tests of materials. The irradiators provide 60Co gamma-ray fields covering dose rates from 0.4 Gy min-1 to 225 Gy min-1 (as of July 2011).

For the irradiation of samples where the most accurate dose possible is required, for example as part of a dosimeter calibration exercise, small thermostatically controlled holders are available. These holders enable precise dosing to small volumes at a customer-selected temperature. Depending on the specific holder used overall dose uncertainties of better than 2.5%* can be achieved.

The most precise holder has a usable volume of 3 cm by 3 cm by 3 cm and the irradiation temperature can be controlled (±2 °C) over the range 20 °C to 55 °C. The minimum dose deliverable is 100 Gy. This holder is most frequently used for the irradiation of dosimeters such as dyed PMMA, alanine pellets and dye films. As an example a typical standard load involves the irradiation of twenty-four Red PMMA dosimeters (the maximum capacity for a single load) to a series of six doses in the range 10 kGy to 40 kGy.

Special holders are available in the industrial-level dose rate irradiators, which enable irradiations at other controlled temperatures from cryogenic to 70 °C. Use of these holders requires advance notice.

For doses below 100 Gy, precise irradiations are possible using our lowest dose rate irradiator in a usable volume of 1.2 cm by 1.2 cm base by 1.5 cm high and the irradiation temperature can be controlled (±2 °C) over the range 15 °C to 30  °C.

It may be possible to accommodate slightly larger samples in the low dose irradiator. Please contact us for details.

*[dose to water, coverage factor k=2, providing a level of confidence of approximately 95%]

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