New dosimetry technology coming your way

Beginning with the September 1998, shipment, those of you assigned dosimeters will receive new dosimeters that differ significantly in appearance and performance. The new technology—proprietary to our dosimetry vendor, Landauer, Inc.—is optically stimulated luminescence (OSL). Both film badges and TLD rings eventually will be replaced, however the rings will not be replaced for another year or so. Landauer literature states that OSL measures radiation through a thin layer of aluminum oxide. The dosimeter is analyzed by shining a laser light on the aluminum oxide, causing it to luminesce in proportion to the amount of radiation exposure. The dosimeter contains built-in filters that provide qualitative information about the exposure. One significant change is that the lowest recordable dose will be 1 mrem versus the current 10 mrem.

The new dosimeter consists of a hexagonal plastic holder with a swivel clip. The sensitive element and filters are enclosed in a clear, sealed, snap-in packet. The dosimeter graphics may include the radiation worker’s name and series code, and they will be color-coded each month to aid in program administration. We will provide more detailed information about the new dosimeters in the coming months.

Are you getting the most out of your scintillation counter?

ORS staff has noticed an increased tendency for radiation workers to write on the walls of scintillation vials. This practice can affect the analysis, and it provides us with an opportunity to give you some tips on maximizing scintillation counter performance.

Scintillation counting is an optical process, and anything that interferes with transmission of light to the detectors will degrade performance. Writing on the vials can decrease light transmission by several percent through optical quenching. Color quenching occurs when photons emitted by the fluors are attenuated as they pass through a colored sample. This can be especially significant if the sample is in the yellow to red spectrum. In chemical quenching, various chemical species absorb beta particle energy before it can be converted to photons. Newer scintillation counters can automatically correct for color and chemical quenching, but not for ink on the side of a vial. Write on the caps only!

Plastic vials are permeable to scintillation fluids. They are economical and great for one-time counting, however over time the sample volume will decrease. Scintillation cocktail diffusing through plastic vials can cause increased chemical exposure to the worker. It also can cause the vial to swell, which potentially could cause it to become hung up in the transport mechanism. So, use plastic vials for one-time counts and use glass vials for counting and recounting over long periods of time. Make sure the caps are securely tightened.