Quench correction in liquid scintillation counting

Abstract

A means for determining counting efficiency in a liquid scintillation system. Pulse amplitudes are accumulated as are the number of pulses contributing thereto. The accumulated pulse amplitude sum is divided by the accumulated number of pulses to produce an average pulse amplitude for the pulses measured. The average pulse amplitude may be correlated to average detection efficiency by an ascertainable function. Through average efficiency of detection the actual rate of radioactive disintegrations may be computed from the count rate measured.

We claim: 
     
       1. A method for determining counting efficiency using a liquid scintillation radiation detecting and counting apparatus having .[.pulse amplitude accumulative means for pulses generated by photodetecting means as a result of.]. .Iadd.photodetecting means responsive to .Iaddend.scintillations caused by radioactive events in a liquid sample containing a known radioactive source .Iadd.to generate pulses having an amplitude spectrum, and pulse amplitude accumulative means, .Iaddend.comprising: passing the aforesaid pulses to said pulse amplitude accumulative means to produce a cumulative integral sum of pulse amplitudes .Iadd.ranging upwardly from a detection threshold, .Iaddend.counting the number of pulses contributing to the cumulative integral sum of pulse amplitudes, dividing the integral sum of pulse amplitudes by the number of pulses to ascertain an average pulse amplitude, and determining average pulse collection efficiency as a function of said average pulse amplitude. 
     
     
       2. The method of claim 1 wherein average pulse collection efficiency is determined from an empirically derived function. 
     
     
       3. The method of claim 1 wherein average pulse collection efficiency is determined from a mathematically derived function using said liquid scintillation radiation detecting and counting apparatus. 
     
     
       4. The method of claim 3 wherein said mathematically derived function has parameters that vary between ranges of pulse amplitude limits. 
     
     
       5. The method of claim 1 wherein said function is a linear function, and wherein the pulse amplitudes of the pulses passed to said pulse amplitude accumulative means are weighted according to a transfer function in arriving at the aforesaid cumulative integral sum of pulse amplitudes, whereby the aforesaid linear function accurately reflects the actual relationship of average pulse collection efficiency to the aforesaid average pulse amplitude. 
     
     
       6. The method of claim 5 wherein said transfer function has terms that vary as between distinct and different pulse amplitude ranges. 
     
     
       7. The method of claim 1 further comprising thereafter determining the rate of occurrence of disintegrations based on the average pulse collection efficiency. 
     
     
       8. A method of compensation for quenching of liquified radioactive scintillation samples using a liquid scintillation radiation detecting and counting apparatus having photodetecting means, a function generating means, and a data output means, comprising: detecting scintillations caused by radioactive events in a liquified radioactive scintillation sample, generating electrical pulses in said photodetecting means .Iadd.having an amplitude spectrum .Iaddend.in response to scintillations caused by radioactive events in said sample, adding and accumulating the pulses .Iadd.ranging upwardly in amplitude from detection threshold .Iaddend.to produce an accumulated integral amplitude sum, dividing said integral amplitude sum by the number of pulses contributing thereto, generating a signal proportional to the resulting quotient representative of an average pulse amplitude, passing said average pulse amplitude signal to a function generating means to produce a signal representative of average pulse collection efficiency, and passing said average pulse collection efficiency signal to said data output means. 
     
     
       9. In a liquid scintillation radiation detecting and counting device having a scintillation chamber, at least one photodetector in optical communication with said scintillation chamber .Iadd.and generating pulses having an amplitude spectrum, .Iaddend.the improvement comprising: an analog to digital converter operatively connected to said photodetector, a pulse amplitude cumulative register connected to said analog to digital converter .Iadd.and responsive to said pulses having amplitudes above a detection threshold, .Iaddend.a pulse count cumulative register connected to said analog to digital converter, and dividing means connected to said pulse amplitude cumulative register and to said pulse count cumulative register for dividing accumulated pulse amplitudes by cumulated pulse counts to produce an average pulse amplitude. 
     
     
       10. In a liquid scintillation radiation detecting and counting device having a scintillation chamber, at least one photodetector in optical communication with said scintillation chamber .Iadd.and generating pulses having an amplitude spectrum, .Iaddend.the improvement comprising: analog to digital converter means operatively connected to said photodetector for producing signals representing pulse amplitudes and signals representing pulse counts, an accumulative register connected to said analog to digital converter for storing the total sum of signals representing .Iadd.all .Iaddend.pulse amplitudes .Iadd.in said spectrum above the detection threshold, .Iaddend.an accumulative register connected to said analog to digital converter for storing the total sum of signals representing pulse counts, dividing means connected said accumulative register for pulse amplitudes and to said accumulative register for pulse counts for dividing cumulated pulse amplitudes by cumulated pulse counts to produce an average pulse amplitude, and a function generator operatively connected to said dividing means for applying a function to said average pulse amplitude to arrive at pulse detection efficiency. 
     
     
       11. The improved device of claim 10 wherein said pulse amplitude analog to digital converter further comprises amplitude sensitive pulse weighting means operative according to a mathematical transfer function with parameters that vary between ranges of pulse amplitude limits, and wherein said function generator applies a linear function to said average pulse amplitude. 
     
     
       12. The improved device of claim 10 further comprising a disintegration register connected to said function generator for determining the rate of radioactive disintegrations based on pulse detection efficiency. 
     
     
       13. In a liquid scintillation radiation detecting and coincidence counting device having a scintillation chamber, a plurality of photodetectors in optical communication with said scintillation chamber .Iadd.and generating pulses having an amplitude spectrum, .Iaddend.and a coincidence detector connected to said photodetector, the improvement comprising: analog to digital converter means operatively connected to said photodetectors  and to said coincidence detector for producing .Iadd.first .Iaddend.signals representing pulse amplitudes .Iadd.ranging upwardly from threshold coincidence .Iaddend.and .Iadd.second .Iaddend.signals representing .Iadd.the corresponding .Iaddend.pulse counts, .[.an.]. .Iadd.a first .Iaddend.accumulative register connected to said analog to digital converter for storing the total sum of .Iadd.said first .Iaddend.signals representing .Iadd.the cumulated value of said .Iaddend..[.pulse.]. amplitudes, .[.an.]. .Iadd.a second .Iaddend.accumulative register connected to said analog to digital converter for storing the total sum of .Iadd.said second .Iaddend.signals representing .Iadd.the cumulated value of said .Iaddend.pulse counts, dividing means connected to said .Iadd.first .Iaddend.accumulative register .[.for pulse amplitudes.]. and to said .Iadd.second .Iaddend.accumulative register .[.for pulse counts.]. for dividing .Iadd.said .Iaddend.accumulated pulse amplitudes by .Iadd.said .Iaddend.cumulated pulse amplitudes by .Iadd.said .Iaddend.cumulated pulse counts to produce an average pulse amplitude, and a function generator operatively connected to said dividing means for applying a function to said average pulse amplitude to arrive at pulse detection efficiency. .Iadd. 14. The improved device of claim 13, wherein said first signals produced by said analog to digital converter means represent pulse amplitudes ranging from threshold coincidence to infinity.