Products

Health Physics Standards

Airborne Particulate and Wipe-Test Determinations

Analytics supplies custom-geometry filter-paper standards that provide accurate calibrations for air particulate and contamination (wipe test) measurements. Analytics' custom-made alpha and beta filter-paper standards are Mylar™ covered and calibrated in total activity contained in the standard. As shown in the published study (Reference 1), Mylar™ covered activity calibrated standards are vastly superior to electrodeposited, emission-rate calibrated standards for alpha/beta air filter and wipe-test determinations. Measurements performed using instruments calibrated with emission-rate sources or electrodeposited standards may under report the activity by as much as 100% for alpha emitters, 40% for low-energy beta emitters, and 25% for high-energy beta emitters. The Mylar™ covering gives realistic attenuation characteristics and the custom mounting using the customer's filter and planchet gives realistic backscattering characteristics. The Mylar™ covering can be 0.5, 0.85 or 1.7 mg/cm2 depending on the application. Other coverings are available upon request.

Analytics' filter standards are prepared gravimetrically from calibrated solutions. A wide variety of alpha, beta or gamma-ray emitting radionuclides can be used. The preparation is performed using a computer- controlled applicator that applies a large number of microliter-sized drops in the specified active area on a Mylar™ covering for alpha/beta counting or on a more rugged polyester tape for gamma-ray counting. The advantages of this preparation technique are discussed in Reference 2. After the drops are evaporated the Mylar™/tape covering is fixed to the customer specified filter substrate with the activity between the covering and the filter. The covering and filter composite is then mounted in the customers' planchet or specified backing for counting. The calibration of the standard comes from the gravimetric preparation and is given in total activity contained in the standard. After preparation the standard is QC tested as described at the beginning of this section.

Analytics' filter standards can be prepared with a wide variety of active areas to accurately reproduce the actual counting geometry: circular, semi-circular, a quarter circle to simulate a folded filter, square, rectangular and many others. For special applications the activity can be made to vary across the active area.

References

1 McFarland, R.C., "Comparison of Alpha and Beta Calibration Standards for Air-filter and Wipe-Test Analyses: Does Your Analysis Seriously Under-Report the Activity?" Radioact. Radiochem., 9(3), 8, (1998).

2 McFarland, R.C., "Geometric Considerations in the Calibration of Germanium Detectors for Filter-Paper Counting." Radioact Radiochem., 2(1), 4, (1991).