GB1432631A - Radioactivity measuring device with a movable detector head - Google Patents

Abstract

1432631 Measuring radio-activity G D SEARLE & CO 20 July 1973 [21 July 1972] 34716/73 Heading G1A [Also in Division H2] The radio-activity of a plurality of samples suspended in the form of an array from a support structure is measured by a detector head containing a scintillator and a photo-detector, the head being movable laterally to select different samples and vertically to receive the selected sample in a cavity for measuring purposes. As shown, Fig. 1, the console is provided with locations for a plurality of trays provided with two or three columns of apertures to receive sample tubes 15. A measuring head 16 is positioned beneath a particular row of samples in a tray by a co-ordinate drive system and when in position the head is raised to engage the sample tubes. As shown, Fig. 2, the head comprises a shielding block 20 having three passages 21, 22, 23 with flared mouths for receiving the sample tubes, the lower part of each passage being formed in a scintillator comprising a Tl activated NaI crystal 18 provided with an Al shield 80. The scintillations are detected by photo-multipliers 17. Micro-switches 68 are provided in each passage to detect the entry of a sample tube. The trays are located by projections along one edge and each possible tray position is provided with a contact array pad 67 and a micro-switch (72). Each tray is identified by means of a coded contact pad located in line with the first column of sample apertures. The identity of the tray is therefore indicated by the code, the location of the first column by the presence of the contact pad and the width of the tray by the number of micro-switches corresponding to subsequent columns which are closed without the presence of a code pad and this information together with the outputs of the head passage micro-switches is applied to logic circuitry for controlling the movement of the measuring head to analyze each row of samples in turn. The outputs of the detectors are amplified (94) and applied to a pulse height discriminator having a window width corresponding to the isotope to be determined (e.g. 1-125, Tc-99m, or Co-57). A background count is subtracted and correction made for non-specific bonding of the radioisotope (74) and the resulting pulses are counted by registers (75, 76, 77). The count is displayed on the console and tabulated according to tray identification and sample position to produce a hard copy print out. A memory is provided to record the values of reference samples with which the readings can be compared. The reference samples are placed in trays identified by their codes and controls are arranged to stop the machine and retard it, return to the previous reference tray or advance to the next reference tray.