Study of the scattering correction for thick uranium-oxide and other α-particle sources—II: Experimental

NIST measurement services :

“…The baffle is designed such that the detection efficiency is insensitive to positional changes in the source with respect to the detector. As shown in [7], a 10 mm vertical or horizontal displacement of the source results in a count rate change on the order of 0.1 percent. This detector should not be used with sources with diameters greater than 1.6 cm.…”

“…Figure 11 also shows the angles subtended by several of the defined-geometry counters for the standardization of alpha-particle sources. Several defined-geometry counters have been described in the literature [7,9,10,11]. One problem that arises in the use of such counters, especially those with large solid angles, is that the geometry is very dependent upon the position of the source in the counter.…”

“…The 0.8πα SC, the so-called Robinson counter [7], after the designer of the instrument, is a CsI(Tl) scintillation counter, with defined solid angle, and a three dimensional central baffle (Figs. 8 and 9).…”

“…As a result most [9,10], but not all [7,11], counters of this type are operated with the chamber under vacuum and with a solid scintillator as the alpha-particle detector. A question that always arises is, "What is the intrinsic detection efficiency of the solid scintillator?"…”

“…As explained by Robinson [9], the three dimensional central baffle is so designed that changes in the geometrical factor defined by the outside baffle due to changes in source position, are offset by equal and opposite changes in the screening of the alpha-particle beam by the central baffle. Hutchinson et al [7] have shown that for a vertical displacement of 0.4 cm or a horizontal displacement of 1 cm of the source from the central position, the change in the count rate varies by less than 0.3 percent.…”