The photographic film dosemeter is designed to measure doses from X, beta and gamma radiations in terms of the radiation quantities specified by the Health and Safety Executive (HSE). The film badge service is approved by the HSE under Regulation 35 of the Ionising Radiations Regulations 1999. The dosemeter consists of a photographic film (manufactured by Kodak) contained in light tight wrapper. To cover the required dose range the film incorporates two emulsions, of different sensitivities. It is uniquely identified by means of a number which is stamped onto the film and wrapper. The dosemeter also bears the wearer's name or a serial number, the establishment code number, the expiry date and an optional personal identifier for each employee, e.g. department name or a works number. We also provide 'wear and care' cards for each member of staff. These are designed to help users understand more about how and why they should wear the dosemeter. The wearer places the wrapped film in a plastic holder, which is supplied by the NRPB on permanent loan. The holder contains a number of metallic and plastic filters which are necessary to ensure that the dosemeters provide an adequate measurement over a suitably wide radiation energy range. When developed the film darkens in proportion to the amount of radiation energy received. From the differing amounts of filtration we can gain information on the energy of radiation causing the dose. Radioactive contamination of the film can be readily identified.

Film dosemeter technical specification

Special features of the film dosemeter

Energy discriminating dosemeter

Through the use of several filters, the dosemeter is able to provide information on the type and energy of the incident radiation.

Contamination

Radioactive contamination of the film can be readily identified.

Physical record

The film forms a physical record of the dose received by the wearer. The processed film is stored by the NRPB for at least five years and may be accessed by the customer.

The film badge's multi-filter system is designed so that radiation will reach one quadrant of the exposed film after penetrating three different filter areas (plastic, cadmium and copper) and passing
through an open window. A cadmium (Cd) filter absorbs particles with energies less than 2 MeV and photons with energies less than 150 keV. Exposure to photons with energies more than 150 keV is determined by comparing film response in the cadmium filter area with the equivalent response on a calibration curve developed with a Cesium-137 source. The film area under the copper (Cu) and plastic filters are used to determine radiation exposures from photons of energy levels less than 150keV. Exposure to beta particles is determined from the film response in the open window area (after correcting for response from other radiations, as measured under the Cd, Cu, and plastic filters) using the appropriate calibration curves.

Image 2 Diagram of a Film Badge Holder and Film

All calculations are performed on the dosimetry service's state-of-the-art computer systems using data from calibration curves and related film response measurements for each
film processed. Uniformity is important in film irradiation. Since all calibration measurements for the film are made in the designated filter areas, film packets must be exposed inside the film holder. The dosimetry service will not report results for film exposed outside the holder.

The film holder is constructed of impact resistant plastic and features a snap-tight hinged door that allows for easy replacement of film packets. Whole body or area badges come
equipped with a sturdy metal clip.

Film
Kodak Type 2 Personal Monitoring Film packets. Type 2 film consists of a single film base with a
fast (sensitive) emulsion on one side and a slow (insensitive) emulsion on the other side. Therefore, a single film in a convenient-to-use packet is capable of monitoring exposures from a vast array of radiation hazards.