Contamination Monitors

1. Introduction
When working with radiation it is vitally important that some form of monitoring
is undertaken to determine and check upon the risk from the radiation or
radioactivity being used. The appropriate form of monitoring depends upon
the radiation application. There are in addition many different types of
radiation detectors, and it is important that the appropriate detection method is
used for the form of monitoring required and the type of radiation being
measured.
This Code of Practice outlines the appropriate procedures for both surface
contamination monitoring and personal contamination monitoring when using
relatively small activities of unsealed radioactive material in laboratories for
research purposes.
It does not include measurement of airborne contamination, bulk
contamination or contamination within the body.
2. Method of Measurement
2.1 Direct Measurement
The most common method of measurement of surface contamination is to use
direct-reading portable contamination meters. The method is often referred to
as direct measurement, and is the most expedient.
Readings from contamination meters are normally given in “counts per second
(c.p.s.)” or “disintegrations per second (d.p.s.)”1
. This is because the response
of the instrument to surface radioactivity varies with the radionuclide being
measured. However some contamination meters have standard conversion
factors programmed into the instrument’s signal processing circuits, thus
giving the user the option of reading in surface contamination units of
becquerels per square centimetre of surface (Bq cm-2
), having selected the
particular isotope. Some typical contamination meters are shown below: