SE339727B - - Google Patents

Abstract

1332370 X-ray spectrometer MEDINOVA A B 14 May 1971[21 May 1970] 15124/71 Heading G1A [Also in Division H5] An X-ray spectrometer for measuring more than one constituent in a sample comprises an X-ray tube supplied with a high voltage cyclically varying between two levels to provide emission at two different, alternating wavelengths and a filter system arranged to switch in filters in synchronism with the high voltage variation to define more accurately the separate wavelengths. The apparatus of Fig. 1 is suitable for the determination of bone salts and soft parts in a part of the body 5 which may be inserted in the measuring beam. The tube 2 is supplied with a high voltage comprising a pulsating component superposed on a substantially constant D. C. level via transformers and smoothing circuits etc. 1. The tube has a water cooled tungsten target which omits X-ray radiation at an energy proportional to the applied voltage. The emission from the tube is arranged to provide a measuring beam towards detector 6 and a reference beam for compensating for fluctuations in X-ray source intensity to detector 6a. In the path of both beams is the filter system comprising a rotary sector disc having two opposite sectors of thorium and two of samarium. The rotation of the disc is monitored by electrooptical arrangement 3 and is arranged to synchronize the thorium filter with the high voltage part and the samarium with the low constant part of the X-ray supply waveform. In operation, without the test body 5 in position, the positions of wedges 4a, 4b of simulated bone salts and soft tissue, respectively are adjusted to equalize the intensities of the two different alternate energies in the measuring beam, and also to equalize them with the intensity in the reference beam. Bone salts absorbers 7, 4e and soft tissue absorbers 7a, 4f are provided to aid thus calibration. On insertion of the test body, the output of detector 6 changes for both energies. The detector output corresponding to bone is channelled by gating circuits 8 to a first differencing circuit (with the corresponding reference channel signal) and that corresponding to soft tissue to a second differencing circuit, Fig.3 (not shown). The signals comprise pulses which are rendered all of equal amplitude, the pulse rates being representative of intensity (effectively the number of pulses detected during each half cycle). These digital differences are converted by D/A converters to supply motors 4c, 4d to drive the wedges 4a, 4b to balance the intensities once more. The necessary displacements of respective wedges represent the amounts of the respective constituents.