Rocky Flats: Building 774
Rocky Flats-Building 774, Prototype Technology Deployment of Xenon Detector System
March 2002
As tested, the Xenon counter appears to be capable of monitoring levels down to 50 dpm per 100 square centimeters of contamination (TRU, 32 years of decay) when averaged over an area of one square meter, and with counting periods of less than one hour per measurement. This criterion is met when assessed using the standard a priori formula with standard assumptions. This was a primary requirement for the system.
There is negligible attenuation due to paint. No correction need be applied unless extremely heavy coatings of lead-based paint are present. Simple field estimation of heavy paint thickness would be sufficient for correction, as desired. This is another primary result sought from this development effort.
As tested, the Xenon counter appears to be capable of detecting an isolated area of 300 dpm per 100 square centimeters with similar counting periods as those for the area average (less than one hour), if the contamination is due to Am-241 alone. The count times required to detect 300 dpm for mixed TRU depend on age, reaching a counting period about 63 hours for 32 year decayed material. This result was based on detection of a 3,000-dpm source of Am-241 within a five-minute count time. This was a requirement identified for this system after the field tests performed at RFETS were completed.
Finally, as tested, the Xenon counter intrinsic peak efficiency is an order of magnitude lower than the theoretical limit. Simple modification of the counter (different gas pressure and composition) and re-testing will likely identify more suitable operating conditions that could reduce the (as tested) count times required to meet the regulatory limits sought for this measurement. Other modifications, including varying the counter diameter, could also offer improvements.
There is a range of missions for which the detector could provide useful information beyond replacement of the sampling method currently in use. These include measurements to assist in decontamination and other health and safety purposes.
