Dose detective

New portable radiation sensor technology will allow emergency teams to measure the level and source of radioactivity more accurately, its UK developers claim.

Called the isotopic personal dosimeter (IPD), the unit is designed to replace conventional Geiger counter radiation detection devices. It is more sensitive and offers a greater dynamic range, according to engineers working on the project.

The IPD is being developed by Cambridge Design Partnership (CDP) for Isle of Wight-based radiological monitoring specialist Radiation Watch. CDP said the first version of the IPD will be used as a personal dose meter.

A local fire department in the US, with whom the developers are at an advanced stage of discussions, is likely to be the first user. There has also been interest from potential users in the UK and Japan.

The first version of the IPD, which has been designed to be wearable and rugged enough to withstand use in emergency situations, contains a cadmium telluride pixelated sensor, which sits on a bed of silicon. When photons hit the cadmium telluride, electrons are released. These are collected by the silicon, which behaves in a similar fashion to a camera. But instead of capturing light, the device measures photons.

The IPD can detect the type of radiation being emitted, not just its intensity, said CDP’s Mike Beadman, who is leading the project. Beadman said incorporating the sensor technology posed complex engineering issues.

Cadmium telluride is extremely expensive, which means the IPD must make highly efficient use of the material to avoid prohibitive product cost. The material is also unstable beyond temperatures of 120ºC, presenting welding complications where temperatures reach 200ºC.

‘The sensor is a world first in this field,’ claimed Beadman, who said the underlying technology had been considerably adapted to allow it to ‘get right through the gamma spectrum.’

It also has extremely good signal-to-noise characteristics. Currently the device has been tested down to 50eV. Beadman said the eventual aim is to reach the X-ray end of the spectrum (20eV), which is problematic due to noise experienced in that region.

Such is its sensitivity the portable device can measure across a wide range of absorbed radiation, from below one microsievert (sV) to several sVs. Anything over 1sV is regarded as life threatening while exposure to 5sVs or more is fatal.