Answer to Question #6998 Submitted to "Ask the Experts"

Is there equipment that measures nuclear radiation in terms of Bq cm^-2? Where can I buy it in Singapore? What is the difference between mR/hr and Bq cm^-2?

When measuring radioactivity in the form of surface-distributed activity, we commonly wish for the results to be expressed in units indicative of activity per unit area, Bq cm^-2 being one such dimension. Such dimensions can be used to make estimations of the potential dose impacts of occupancy in contaminated areas and can be compared against values that might be specified as release limits for areas that contain contaminated surfaces.

The dimension of mR hr^-1 is dose-related, intended to provide an indication of the gamma and/or x-ray intensity in air, which approximates the dose equivalent rate in soft tissue over a fairly wide range of photon energies. The surface-contamination units of Bq cm^-2 describe the amount of radioactivity per unit area. In order to transform count rate (e.g., cpm) into activity per unit area, certain assumptions must be made about the characteristics of the radionuclide and its spatial distribution over the surface of interest. While most surface-contamination measuring instruments read out in count rate (cpm or cps), since the incorporation of microprocessors and/or computers into a number of instruments, there are a number of instruments on the market that allow readout in activity per unit area, such as Bq cm^-2. The user may have to input required information about the radionuclide(s) and the source geometry, etc. Some of these instruments are intended for measuring primarily beta and/or alpha radiation from contaminated surfaces. Here are links to a few companies and instruments that are in this category:

Elimpex (Victoreen instrument)
Berthold
synOdys
Canberra

I would expect that you could get more information and/or purchase detectors through the above or other international companies. Good luck.

George Chabot, PhD, CHP