Density and Thickness Measurement
with Narrow-Beam Geometries.
Measurements that are designed to measure the ATTENUATION of the ORIGINAL INTENSITY of a beam of photons
(measured in photons * cm-2 * sec-1), are frequently referred to as measurements with "Narrow Beam Geometries". To perform such measurements, the source must be monoenergetic and collimated, and the detector must be collimated and sensitive ONLY to the full energy of the photon source. The radiation read by the detector MUST NOT include secondary or scattered radiation components. When these conditions are met, then (see "Calculation of Transmission of Photons")
(Equation 1)
i = I e-
(a) d,
where
i = the intensity of the transmitted beam,
I = the intensity of the incident beam,
(a)
= the total attenuation coefficient of
the absorber, and
d = the thickness of the absorber.
When I is known and i is measured, then Eq. 1 determines the quantity
(a) d, which means that, when the density of the absorber and its attenuation coefficient
(a) are known, Eq. 1 can be used for the determination of the thickness d of the absorber, as illustrated in Figure 1.
When the thickness d and the chemical composition of the absorber are known, then Eq. 1 can be used for the determination of the density of the absorber, as illustrated in Figure 2.
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Edited on 14 September 2001 - E-mail to the
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