Silverstein E A. Calculation of the G factor for gas scattering experiments. Nucl. Instrum. Methods 4:53-66, 1959

“As a graduate student at the University of Wisconsin in Madison in low energy nuclear physics, I wished to design a small volume gas scattering chamber with the detector system outside the chamber while at the same time permitting a continuous choice of scattering angle. This could be accomplished by bringing the detector up out of the horizontal plane and pointing it at the center of the chamber, the detector axis thus moving in a cone. However, if I had used the customary arrangement of defining apertures with a straight edged front aperture, it would have been necessary to adjust the rotation angle of the front slits for each scattering angle so that their edges would be perpendicular to the scattering plane. By using a system of circular front and rear apertures, the inconvenience of this adjustment could be avoided and the resulting chamber would have only one rotating seal. “The only problem was that the G factor was not known for this geometry and appeared difficult to calculate. (The C factor, or geometrical efficiency of the system, relates the scattered particle yield to the beam intensity, target density, and scattering cross section and its derivatives.) Before attempting to calculate the C factor for this geometry, I tried to reproduce a calculation1 of the G factor for the simpler vertical front slit case as these results were used in obtaining accurate p-p cross sections at Wisconsin. I was unable to reproduce these results. Furthermore, others2 had obtained different higher terms. After getting this involved, I saw that it would be possible to resolve the differences by undertaking a systematic calculation. It then became apparent that the case of circular front and rear apertures could be treated by the methods developed. “This paper has been highly cited for several reasons. My results were written up in very detailed form with the intent of producing a convenient reference. The analysis and expressions in this paper have been found useful for those involved in gas scattering experiments. The circular front and rear aperture geometry continues3 to be used.” CC/NUMBER 37 SEPTEMBER 14, 1981 This Week’s Citation Classic