National Physical Laboratory

High dose cobalt-60 irradiations

High-Dose Sample Compartment
60Co high dose irradiator sample compartment

NPL's three 60Co self-shielded irradiators for high dose irradiations

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.

For more general irradiations the full cylindrical irradiation volume of the three irradiators may be used. The volumes are approximately 500 cm3 (6.5 cm diameter by 15 cm high), 1700 cm3 (12 cm diameter by 15 cm high) and 3300 cm3 (15 cm diameter by 19 cm high). The 1700 cm3 and 3300 cm3 volumes have access points for cables. If required, dose distribution studies can be undertaken to determine exact doses and uncertainties at the time of irradiation.

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

Contact

Customer Services tel: +44 20 8943 8695
E-mail: chemdos@npl.co.uk

Last Updated: 9 Aug 2016
Created: 17 Apr 2007

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