Theoretical Response of a ZnS (Ag) Scintillation Detector to Alpha-emitting Sources and Suggested Applications

Abstract

The classic problem of alpha absorption is discussed in terms of the quantitative determination of the activity of "weightless" alpha sources and the specific alpha activity of extended sources accounting for absorption in the source medium and the window of a large area ZnS(Ag) scintillation detector. The relationship for the expected counting rate gamma of a monoenergetic source of active area A, specific alpha activity C, and thickness H that exceeds the effective mass density range Rs of the alpha particle in the source medium can be expressed by a quadratic equation in the window thickness x when this source is placed in direct contact with the window of the ZnS(Ag) detector. This expression also gives the expected counting rate of a finite detector of sensitive area A exposed to an infinite homogeneous source medium. Counting rates y obtained for a source separated from a ZnS(Ag) detector by different thicknesses x of window material can be used to estimate parameter values in the quadratic equation, y = a + bx + cx2. The experimental value determined for the coefficient b provides a direct estimation of the specific activity C. This coefficient, which depends on the ratio of the ranges in the source medium and detector window and not the ranges themselves, is essentially independent of the energy of the alpha particle. Although certain experimental precautions must be taken, this method for estimating the specific activity C is essentially an absolute method that does not require the use of standards, special calibrations, or complicated radiochemical procedures. Applications include the quantitative determination of Rn and progeny in air, water, and charcoal, and the measurement of the alpha activity in soil and on air filter samples.

A new statistical method for transfer coefficient calculations in the framework of the general multiple-compartment model of transport for radionuclides in biological systems

“…The need for mathematical models to quantify the penetration of a trace substance in animals, and their products, has often been stressed in the literature (Lassey 1980, Assimakopoulos et al 1989, Skrable et al 1974, Simmonds et al 1979, Johnson and Carver 1981, Birchall 1986, Birchall and James 1989, Ward and Kirchnert 1987. A biokinetics model (as applied in metabolic, retention and pharmacokinetics studies) is a mathematical description of the time-dependent distribution, and excretion, of a substance in the body after its absorption or injection into blood.…”

Determination of the specific alpha activity of thick sources with a large area ZnS(Ag) scintillation detector

“…The thick source alpha counting (TSAC) technique is used for gross alpha activity measurements (Turner et al, 1958;Somana et al, 1997). In this technique the sample is in contact with a ZnS scintillation screen.…”

“…The relationship between detector response, count rate, y, and window mass density thickness, x, for sources emitting monoenergetic alpha particles is (Skrable et al, 1991):…”

“…(1) is correctly applicable if, besides the adequate source thickness, the surface of the source is smaller than the detector surface, and if the source is in contact with the detector window. Also, thick sources should be well homogenized (Skrable et al, 1991). The previous expression could be written as a quadratic equation: y ¼ a þ bx þ cx 2 .…”

Direct measurement of alpha emitters in liquids using passivated ion implanted planar silicon (PIPS) diode detectors

“…The linear function E air (x)=ax+b was used to describe the reduction of the count rate response as a function of absorber (air) thickness. In the case of infinitely thick alpha sources, the count rate as function of the absorber thickness can be approximated either by linear (absorber thicknesso alpha particle range) or quadratic (absorber thickness p alpha particle range) functions [22,23]. We determined that for the air layer thicknesses used in this study (0-2.5 cm), linear approximation enabled better fit of the experimental data relative to the quadratic function.…”