Packard Instrument Company, Inc.

Robert J Valenta

John E Noakes

A scintillation measurement system for measuring optical events produced by scintillators in response to the radioactive decay of a constituent or constituents of a sample to be measured comprises a sample support for positioning a sample in a sample well; a bismuth germanate (BGO) scintillation crystal, such as Bi.sub.4 Ge.sub.3 O.sub.12, located adjacent the sample well; a plurality of photodetectors located outside the bismuth germanate crystal for detecting optical events occurring in the sample well or in the bismuth germanate crystal and converting those optical events into electrical pulses; and a pulse analyzing system for receiving the electrical pulses from the photodetectors and determining whether such pulses represent .alpha., .beta. or .gamma. events. This system can be used with samples containing .alpha., .beta. and .gamma. emitters, or any combination thereof.

Scintillation counter

A normalization system for multi-photodetector single photon counting luminescent measuring systems and a standard for use in the same. The method comprises calculating one or more counting ratios for each photodetector in the single photon counting system and multiplying counts of unknown samples by the inverse of the appropriate counting ratio. A counting ratio for a particular photodetector is calculated by dividing the count of a standard measured by the photodetector by the count of the same standard measured by a reference photodetector. The particular standard developed employs calcium tungstate:lead as a scintillator and tritium or carbon-14 thymidine as a means of exciting the scintillator. This standard has the advantages of providing a good model of typical luminescence chemistry and producing an emission pattern which is susceptible to single photon counting.

Normalization technique for photon-counting luminometer

A low-level liquid scintillation measurement system for counting sample optical events resulting from the radioactive decay of a constituent of a sample to be measured while reducing the counting of background optical events which are optical events produced by background radiation and which create electrical pulses other than pulses representing a sample optical event. This system includes a detector located adjacent the sample for detecting optical events and for converting optical events into electrical pulses, a coincidence sensor for receiving the electrical pulses from the detector and producing a trigger pulse when the electrical pulses from the detector coincide with each other, a burst detector for receiving the trigger pulses from the coincidence sensor and the electrical pulses from the detector for determining the number of electrical pulses present in a selected interval following each of the trigger pulses, evaluator connected to the burst detector for determining, in response to the number of pulses detected in the selected interval, the extent to which the optical event represented by the corresponding trigger pulse should be treated as a sample optical event or a background event, and an active guard shield arrangement comprising an auxiliary scintillator optically coupled to the detector. The shield is adapted to be excited by background radiation and to effectively increase the number of electrical pulses present in the selected interval following a trigger pulse generated as a result of the coincident pulses produced due to the background radiation. The axuiliary scintillator is a glass comprising oxides of lithium, magnesium, silicon and cerium.

Liquid scintillation measurement system with active guard shield

A low-level liquid scintillation measurement system for counting sample optical events resulting from the radioactive decay of a constituent of a sample to be measured while reducing the counting of background optical events which are optical events produced by background radiation and which create electrical pulses other than pulses representing a sample optical event. This system includes detection means located adjacent the sample for detecting optical events and for converting optical events into electrical pulses, coincidence sensing means for receiving the electrical pulses from the detection means and producing a trigger pulse when the electrical pulses from the detection means coincide with each other, burst detection means for receiving the trigger pulses from the coincidence sensing means and the electrical pulses from the detection means for determining the number of electrical pulses present in a selected interval following each of the trigger pulses, evaluation means connected to the burst detection means for determining, in response to the number of pulses detected in the selected interval, the extent to which the optical event represented by the corresponding trigger pulse should be treated as a sample optical event or a background event, and an active guard shiled arrangement comprising an auxiliary scintillator optically coupled to the detection means. The shield is adapted to be excited by background radiation and to effectively increase the number of electrical pulses present in the selected interval following a trigger pulse generated as a result of the coincident pulses produced due to the background radiation. This allows the measurement system to accurately evaluate the number of pulses detected in the selected interval and determine the extent to which a trigger pulse is to be treated as a sample optical event.

A method and apparatus for separating background events from valid sample events in a liquid scintillation counter are disclosed. Upon the detection of a coincident event pulse the number of pulses detected during a short time interval immediately thereafter together with the energy level of the event pulse is utilized to determine the probability that the event pulse is a valid sample pulse as opposed to an invalid background pulse. The total count rate is determined by summing pulses over the appropriate energy range where each pulse is counted as one multiplied by the above probability that the pulse is a valid sample pulse.

Reduced background scintillation counting

Method and apparatus for counting nuclear scintillations of a specimen containing tritium. A simple system using a single photomultiplier tube and suitable circuitry segregates the pulses which are emitted from a scintillator due on interaction with a nuclear particle from the pulses attributable to random noise. The system is operable with many scintillation materials as long as the characteristic output from the scintillator is long relative to the duration of a random noise pulse. The preferred embodiment of this radiation assay instrument includes a solid scintillator, a photomultiplier tube whose output is split among a two-path circuit containing a first path for providing an integrated pulse signal as input to a pulse height analyzer and a second path which discriminates based on the number of component pulses in the signal to provide an enable signal to the pulse height analyzer. Also discussed is the response of an apparatus in accordance with the present invention if some relatively high energy isotopes such as carbon-fourteen are tested.

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West Chicago, IL, United States of America

Robert J Valenta