Liquid scintillation unit with low background noise

Claim 2

In a liquid scintillation coincidence counting apparatus having a sample counting chamber with event detecting photodetectors in optical communication therewith, wth said event detecting photodetectors connectd to a coincident pulse detection and registration circuit, the improvement comprising radiation guard circuit employing a solid scintillating materIal and connected in anti-coincident arrangement with said coincident pulse detection and registration circuit, said coincident pulse detection and registration circuit having a timing discrimination means including means associated with each of said event detecting photodetectors for shaping and amplifying pulses from said photodetectors to represent the time interval between pulses from respective photodetectors, and conversion means responsive to said shaping means for generating an information pulse whose amplitude varies as a function of said time interval, whereby pulses induced in said photodetectors due to scintillations from a liquid scintillator in said sample may be discriminated from pulses induced in said photodetectors by other radioactive events.

Claim 3

The apparatus of claim 1 wherein said radiation guard circuit is comprised of a cylindrical scintillation crystal with an axial hole therein, an opaque covering on the surfaces of said crystal with photodetector accommodating apertures located at, at least, one end of said cylindrical scintillation crystal, whereby said sample counting chamber and said event detecting photodetectors are optically isolated from said crystal, and guard photodetectors are positioned at said photodetector accommodating apertures in optical communication with said scintillation crystal, and wherein said event counting photodetectors are aligned in opposing relationship in the axial hole defined in said scintillating crystal, thereby defining the boundaries of said sample counting chamber at the interior of said scintillation crystal.

Claim 4

The apparatus of claim 2 wherein a transverse passageway is defined within said crystal through said sample counting chamber, and a sample transfer means is provided for bringing radioactive samples into said sample counting chamber for sample analysis and for carrying said samples from said sample counting chamber subsequent to analysis.

Claim 5

The apparatus of claim 1 wherein said timing discrimination means further includes first and second timing pulse generating means and event threshold discimination means respectively associated with different ones of said shaping and amplifying means, pulse delay means for delaying pulses from the second timing pulse generating means for a predetermined interval based on the probably proximity in time of the light pulses generated in a liquid scintillator by events of interest, with said conversion means generating said information pulses with an amplitude correlated to the elapsed time interval between pulses received from said first and second timing pulse generating means, said timing discrimination means also including pulse height analyzer means with an upper and lower discriminator for suppressing said information pulse output for pulses from said first and second event detecting photodetectors which differ in time of occurrence by greater than an acceptable time interval.

Claim 6

The apparatus of claim 4 wherein said amplifier means generate bipolar pulses, each such pulse changing polarity after an interval independent of the pulse amplitude, and said conversion means including a pulse generator and generating said information pulse with amplitude increasing as a linear function of elapsed time, and operation of said conversion means being terminated as a result of a pulse from said second event detecting photodetector.

Claim 7

The apparatus of claim 5 wherein said upper and lower level discriminators of said pulse height analyzer means are adjusted to define a pulse amplitude window that includes the time distribution peak of pulses from said first and second timing pulse generating means generated as a result of scintillations occurring in a liquid scintillator in a sample positioned in said sample counting chamber, and excludes all pulse falling beyond said pulse amplitude window.

Claim 8

The apparatus of claim 5 wherein said conversion means is equipped with an anticoincident gate connected to said event detecting photodetectors anD to said guard photodetectors for suppressing the output of said conversion means if an input is received at said anti-coincident gate from any of said guard photodetectors subsequent to the input from said first event detecting photodetector and prior to the input from said second event detecting photodetector.

Claim 9

A liquid scintillation coincidence counting apparatus comprising a sample counting chamber, first and second photodetectors in optical communcation therewith, amplifier means connected to each of said photodetectors, first and second timing pulse generating means connected to said amplifier means and associated respectively with said first and second photodetectors, a pulse delay mechanism in said amplifier means and associated respectively with said first and second photodetectors, a pulse delay mechanism in said second timing pulse generating means set to insure that for coincident pulses from said first and second photodetectors, pulses generated by said second timing pulse generating means are delayed with respect to timing pulses generated by said first timing pulse generating means, conversion means connected to both of said timing pulse generating means, pulse height analyzer means with an upper and lower discriminator connected to said conversion means, solid scintillating radiation guard crystal at least partially surrounding the sample counting chamber and having guard photodetectors in optical communcation therewith, background delay and amplifier means and background threshold discrimination means associated with said guard photodetectors, an anti-coincidence circuit with inputs from said first and second photodetectors and from said guard photodetectors for governing the output of said pulse height analyzer means, and pulse count register means for recording coincident pulses from said first and second photodetectors which are received in anti-coincidence with pulses from said guard photodetectors when said pulse height analyzer means yields an output.

Claim 10

A liquid scintillation coincidence counting apparatus comprising a sample counting chamber, first and second photodetectors in optical communcation therewith, amplifier means connected to each of said photodetectors, first and second timing pulse generating means connected to said amplifier means and associated respectively with said first and second photodetectors, a pulse delay mechanism in said amplifier means and associated respectively with said first and second photodetectors, a pulse delay mechanism in said second timing pulse generating means set to insure that for coincident pulses from said first and second photodetectors, pulses generated by said second timing pulse generating means are delayed with respect to timing pulses generated by said first timing pulse generating means, conversion means connected to both of said timing pulse generating means, pulse height analyzer means with an upper and lower discriminator connected to said conversion means, solid scintillating radiation guard crystal at least partially surrounding the sample counting chamber and having guard photodetectors in optical communcation therewith, background delay and amplifier means and background threshold discrimination means associated with said guard photodetectors, an anti-coincidence circuit with inputs from said first and second photodetectors and from said guard photodetectors for governing the output of said pulse height analyzer means, and pulse count register means for recording coincident pulses from said first and second photodetectors which are received in anti-coincidence with pulses from said guard photodetectors when said pulse height analyzer means yields an output.

Claim 11

In a liquid scintillation coincidence counting apparatus having a sample counting chamber with event detecting photodetectors in optical communication therewith, with said event detecting photodetctors connected to a coincident pulse detection and registration circuit, the improvement comprising a radiation guard circuit employing a solid scintillating material and connected in anti-coincident arrangement with said coincident pulse detection and registration circuit, wherein said coincident pulse detection and registration circuit includes a timing discrimination means for generating a data pulse having an amplitude that is a linear function of time differential between pulses emanating from said event detecting photodetectors and including amplitude discrimination means for defining a pulse amplitude window for discriminating between said data pulses, whereby discrimination is effected between pulses on the basis of the arrival time of pulses induced in said event detecting photodetectors by scintillations from liquid scintillator in said sample counting chamber caued by radioactive events therein, and those pulses induced in said event detecting photodetectors as a result of other radioactive events.

Claim 12

In a liquid scintillation coincidence counting apparatus having a sample counting chamber with event detecting photodetectors in optical communication therewith, with said event detecting photodetctors connected to a coincident pulse detection and registration circuit, the improvement comprising a radiation guard circuit employing a solid scintillating material and connected in anti-coincident arrangement with said coincident pulse detection and registration circuit, wherein said coincident pulse detection and registration circuit includes a timing discrimination means for generating a data pulse having an amplitude that is a linear function of time differential between pulses emanating from said event detecting photodetectors and including amplitude discrimination means for defining a pulse amplitude window for discriminating between said data pulses, whereby discrimination is effected between pulses on the basis of the arrival time of pulses induced in said event detecting photodetectors by scintillations from liquid scintillator in said sample counting chamber caued by radioactive events therein, and those pulses induced in said event detecting photodetectors as a result of other radioactive events.