Patent GB-1100931-A (GB)
Title: Method and apparatus for automatic standardization in liquid scintillation spectrometry
IPC: G01T1/204
Filed: 1965-02-03
Abstract: 1,100,931. Measuring radio-activity. PACKARD INSTRUMENT CO. Inc. Feb. 3, 1965 [June 18, 1964], No. 4913/65. Heading G1A. Radio-active samples are estimated automatically by apparatus similar to that described in Specification 1,041,413. Samples in transparent phials, which also contain a scintillator, are moved automatically in succession into a position before a photo-multiplier in a shielded container, the pulses resulting from the scintillations being segregated into categories by height analyzers and counted. The invention is concerned with the effects of "quenching", i.e. a diminution in number or size of the scintillations and the subsequently recorded pulses. This may be due to the presence, in the sample, of substances which prevent the formation of scintillations (heat being generated instead) or to light absorbing substances which absorb part of their energy before it is recorded. The invention provides two counts for each sample, one being of the sample by itself, the other with the addition of stimulated scintillations from a standard radioactive source. The standard source may be beta source which is added to the sample ("internal standardization") or a source of penetrating radiation which brought into proximity to the sample to interact with electrons in the sample by Compton scatter and thereby produce an effect akin to beta decay ("external standardization"). The activity of the sample being known, the expected count is also known and can be compared with the observed count to give a measure of the quenching which can be applied to correct the count from the sample itself.  Various embodiments are described for the use of internal and external standards. Internal standards may be used in the form of pellets which are housed in cavities in the caps of the phials. In one such form each sample is counted with the standard so disposed and the sample then dropped into the phial by actuating a magnetically operated latch, the sample then being counted again. In another form with the standards so disposed all the samples are counted without the standards and returned to their carrier in the form of an annular sample tray as described in Specification 1,041,413. The tray is then tipped to an inclined position and rotated in this plane so that all of the standards drop from the caps of the phials into the samples. In a further form, the standards are kept in a hopper external to the shielded container in which the sample is located for counting and released, one for each sample, to pass down a conduit and through an aperture in the cap of the phial. A similar arrangement may also be used with an external standard. In this case the hopper must provide shielding to contain the penetrating radiation from the pellets which do not enter the samples but are deposited, when required, in depressions on the caps of the phials. A single pellet may be used for all the samples and may be retrieved from each phial as it is returned to the sample carrier. It may be provided with a magnetically attractable coating and retrieved magnetically. A further form uses an external standard in the form of a single pellet which is moved pneumatically, when required, to a position within the shielded container adjacent the sample.