Opinion on a recent paper by Takeshi Morita

This paper, Morita et al., j. app. cryst., 40, 791–795, 2007 shows a short note on a system capable of measuring the absorption factor of a sample. They measure the attenuated beam by means of a beamstop with a photodiode in it, and the primary beam intensity by means of an ionisation chamber situated before the sample. Unfortunately, the beamstop design seems rather bulky, and would therefore obstruct approximately 1/8th of the complete scattering pattern.

I am reminded at this point of a system designed by Hermans, Heikens and Weidinger c.a. 1959 (Hermans et al., j. pol. sci., 35, 145–165, 1959). They created an apparatus (slit-collimated if I’m not mistaken) that contained no less than three photographic films. The first film would measure the primary beam intensity as it scattered through a thin polymethyl methacrylate film (as a sort of primitive ionisation chamber). The attenuated beam measurement was performed by measuring the backscattered radiation from the beamstop (a tungsten wire). The third film was used to measure the scattering pattern itself.

This allowed them to do a similar determination of all required parameters for a measurement on absolute scale. It is nice to see that a reiteration of this technique has appeared, the newer detectors allowing for less tedious calibrations.

I feel that not enough people measure on an absolute scale at the moment, thereby forfeiting information on their samples that might have proven useful. Hopefully such efforts as described by Morita et al. will initiate more initiatives to allow users to painlessly and effortlessly do measurements on an absolute scale.

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