National Physical Laboratory

Hire of protection level Gamma-ray facility

Protection-Level Gamma

The protection level gamma-ray facility at NPL has a multi-source exposure unit situated in a large electrically screened, temperature-controlled exposure room. Its main use is in the provision and development of the NPL calibration services for protection level secondary standard instruments and environmental radiation monitors.

The main gamma-ray exposure unit contains four 137Cs and four 60Co sources of different activity. The air kerma rates in the beams produced by the highest activity 137Cs and 60Co sources are approximately 0.2 Gy h-1 at 2 m from the source. In addition, an 241Am source with optional collimator is housed on the outer face of the exposure unit, producing an air kerma rate of about 0.3 mGy h-1.

A motorised carriage runs on rails in the exposure room to allow precise remote positioning of the detectors or samples in the beam. A telescope and two lasers mounted in the exposure room assist in aligning objects with the beam axis. The facility also includes a freestanding collimator and radionuclide system for the calibration of environmental level radiation monitors using a series of 137Cs sources.

There are about 30 centres in the UK in industry, power generation and the health service that are required by law to regularly calibrate their secondary standards. These centres use their calibrated secondary standards to calibrate field instruments. In the UK alone, tens of thousands of field instruments are calibrated annually. This facility therefore plays an important role in ensuring safe working and living environments for thousands of employees and the general public.

The protection level gamma-ray facility is available for hire, along with dosimetry expertise, if required.


Customer Services tel: +44 20 8943 8695

Last Updated: 9 Aug 2016
Created: 17 Apr 2007


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