ABSTRACT
The conditioning and preparation of samples for radiation counting have also been treated to an extent in other parts of this book.
Samples for
α
counting must be thin enough that range straggling does not prevent
α
particles from
entering the sensitive area of the detector or degrade the peak structure of the spectrum. This is accomplished by purifying
α
- emitting chemical fractions from all inert contaminants. In the case of longlived
α
emitters, such as isotopes of U and Th, care must be taken to balance the decay rate of the source against the quantity of analyte mass that accompanies it. Spreading an
α
-emitting sample over a larger area helps alleviate this problem until the dimensions of the source became comparable to the area subtended by the counter, at which point counting geometry causes a loss of counting efficiency. Final samples for
α
counting are usually limited to lateral dimensions of 2.5 cm. Alpha samples for absolute emission measurements must be mounted on the same substrate as the calibration standard (usually Pt), so that the degree of backscatter (
α
particles emitted into the sample backing that are subsequently reflected backward into the detector volume) is the same.
