As a result of the Comprehensive Nuclear-Test-Ban Treaty, the International Monitoring System's network of stations has been established to detect nuclear detonations. Some stations continuously monitor the air for radioactive isotopes of xenon, the presence of which confirms nuclear fission. To ensure accuracy, these monitors must be calibrated and verified regularly; however, the current verification method using radioxenon gas lacks the accuracy desired. The imprecise calibration standards do not typically match the specific characteristics of the radioactive gas being monitored.

Pacific Northwest National Laboratory's new radioactive gas assay system is a dramatic improvement over current methods for several reasons. First, the approach can determine the absolute activity of a radioactive gas. Second, because this new system is both the sample container and the nuclear detector to make the absolute activity measurement, the system is more efficient, more accurate, and more versatile than conventional systems. The approach allows the entire sample to be accounted for in standards preparation.

The system comprises four parts:

1. Scintillation cell production assembly
2. Detector assembly
3. Computer assembly
4. Scintillation cell destruction assembly.

The scintillation cell production assembly is configured to produce a substantially non-porous glass scintillation shell containing a volume of radioactive gas. The detector assembly receives the scintillation cell, uses a light sensor to detect photons emitted by the cell, and transmits data to the computer assembly. The computer assembly automatically calculates an absolute activity of the volume of radioactive gas of the scintillation cell and radiation detection efficiencies of the detector assembly. The scintillation cell destruction assembly ruptures the glass scintillator shell to release the radioactive gas, which can then be recovered and reused, if needed. Using this system, technicians can quickly calibrate detectors to a more precise level, ensuring accuracy of results.

APPLICABILITY

The assay system can be used to calibrate all types of radioactive gas detectors, including those for radioxenon. It could be used not only for Comprehensive Nuclear-Test-Ban Treaty monitoring but monitoring inside industrial facilities where radioactive gas is created or used as well as the surrounding environment.