The PTM-1812 Handheld Tritium Monitor

The femto-TECH Model PTM-1812 Hand Held Tritium Monitor is a precision airborne beta radiation detection instrument that serves as two instruments in one. The user can select between a perforated ion chamber shell for passive sampling or a solid ion chamber shell for active sampling. Both ion chamber shells are supplied with the instrument and are easily exchangeable in the field. In the passive configuration the PTM-1812 serves as a continuous real-time area monitor. In the active configuration, it uses an internal pump to pull samples from tritium containers, glove boxes, etc.

The intrinsic calibration of the ion chamber used in a PTM-1812 system is established by the physical size and geometry of the ion chamber and the value of the feedback resistor (high-meg). The National Institute of Standards and Technology (NIST) traceable tritium gas standards have been used to verify the electronic calibration factor for this type of ion chamber. Production ion chambers maintain the same parameters as those that have been calibrated with the tritium gas standard, therefore, the production ion chambers have the same intrinsic calibration. The feedback resistor of each production unit is measured once by the supplier of the resistors and a second time at femto-TECH. NIST traceable resistor standards and voltmeters are used to perform this measurement. A built-in electronic calibration adjustment provides field adjustment and calibration verification of all electronic components back to the feedback resistor. Field calibration checks can also be performed using a fixed geometry gamma source to provide a known amount of ionization in the ion chamber.