The LB 110 is a special measuring system for monitoring the tritium activity concentration in room and exhaust air.
Tritium (3H) in air is mostly available in the form of water vapor (H1H3O) or gaseous hydrogen (H1H3). Since the Beta particles emitted by Tritium have a very short range (only a few millimeters in air), windowless counter tubes must be used, i.e. the air to be measured has to be added to the counting gas. For a continuous measurement, the counter tube must therefore operate in the flow-through mode.
The air to be measured is mixed with a suitable counting gas and passed through a 1.3 liter volume proportional counter tube. Methane (mixing ratio air/gas 1:3) or Argon-Methane (P10, mixing ratio air/gas 1:4) are used as counting gas.
The distinction of Tritium pulses from those of other nuclides or from Gamma radiation – and hence the Tritium-specific measurement – is carried out using Berthold's patented pulse rise discrimination method, which offers major benefits as compared to the earlier used range discrimination (F. Berthold, Tritium-in-Air Measurements by Pulse Shape Discrimination Methods, in: Radiation-Risk-Protection Vol. III, Pages 1091 - 1094, FS-84-35 T, Verlag TÜV Rheinland, Köln 1984). This method yields better response sensitivity data, relative to the same gas consumption.
Rise time discrimination is based on the fact that the rise time in proportional counter tubes is dependent on differences in the drift time that electrons occurring in the primary ionization track need to get in the vicinity of counting wires. These drift time differences are dependent on the length and the course of the primary ionization track. In the case of Tritium, this track – due to the low particle energy – has to be regarded as point-shaped in contrast to the long ionization tracks caused by high-energy Beta or Gamma sources.
Counting gas control
The accuracy of the measurement is dependent on the constancy of the mixing ratio of air and counting gas. Due to that the LB 110 ensures a good and reliable gas-air control. Measuring air and counting gas flow are measured separately and kept at a constant level via a control circuit. The current gas and air flow rate is measured using an electronically controlled flow-through meter which operates according to the principle of thermal mass measurement.
An essential benefit of this principle is that the measurement is largely independent of pressure and temperature. Compared to volumetric principles, neither pressure nor temperature has to be measured in addition. The electronics integrated into the air and gas module is used to control and evaluate the signals modified by the flow-through controller. Gas and air supply are measured separately and kept on a constant level by one control circuit each.
There are two evaluation units for the LB 110 Tritium-Monitor: The data loggers LB 5340 or LB 9000.
(90% Ar, 10% CH4)
(90% Ar, 10% CH4)
BERTHOLD TECHNOLOGIESGmbH & Co. KG
Calmbacher Str. 2275323 Bad WildbadGermany
+49 7081 177-0+49 7081 177-100info@Berthold.com