The nuclide-specific clearance levels of the total activity and specific activity which have been defined new in Directive 96/29/ Euratom apply to all radionuclides that are typically used in nuclear medicine.
The Clearance Monitor LB 2050 is based on BERTHOLD’S proportional counter tube technique which has been tried and tested for several decades and which is ideally suited for the measurement of these isotopes.
In nuclear medicine, waste is very often collected and stored in plastic containers holding 30 to 60 liters. A 4-Pi arrangement of the detectors is required to be able to carry out representative measurements of these waste containers. The standard version of the Clearance Monitor LB 2050 is therefore using six large-area proportional counter tubes with a total of 10 measuring channels, covering a volume of about 150 liters in 4-Pi. The large-area proportional counter tubes on the side walls are split up into two measuring channels each, so that different waste distributions, especially for radioactive liquids, can be taken into account.
Waste containers can be placed ergonomically and easily into the metering box by means of a door and a base plate mounted on two sliders. The built-in detectors are protected by a grid against mechanical damage. A load cell scale is integrated in the bottom of the container slider; this does not have any adverse effect on the sensitivity
of the bottom detector. Thus, any radioactive liquid may be measured optimally. The integrated loading display shows the container weight in the metering box and sends the data to the PC for further processing.
The measuring station is delivered with a 5 mm thick all-round lead shielding (optionally 7 mm). If strongly varying background radiation is likely to occur at the Clearance Monitor’s setup location, the measuring station may also be provided with
up to two background compensation detectors.
The Monitor is operated by means of a standard PC. Clearance measurements can be carried out by untrained personnel in a semi-automated operation in the Routine measuring mode using pre-defined factors (container type, nuclide, calibration
factors, etc.).
The Automatic mode supports measurements which do not require operation via PC: loading and unloading of the metering box and operation of the Start/Stop button on the metering box control the measurement procedure.
For radionuclides like 11C, 18F, 57Co, 90Sr, 99mTc, 111In, 125I or 131I in typical waste containers filled with low density waste detection limits below 0.2 Bq/g can be achieved within a few minutes. The monitor also measures simultaneously the surface contamination of the container on all sides.
In addition to the Monitor’s operating functions, the software program offers administrative tools for a radioactive waste depot in accordance with the radiation protection guidelines.
