Method for determining a background count rate in liquid scintillation counting
The present invention provides a method for determining a background count rate in liquid scintillation counting. The method comprises measuring external standard spectra of a sample, determining, from the external standard spectra, a triple to double coincidence ratio and a quench parameter, determining, based on the triple to double coincidence ratio and the quench parameter, a background reference parameter, and determining, based on the background reference parameter, the background count rate from a background reference curve.
1. A method for determining a background count rate in liquid scintillation counting, wherein the method comprises:
measuring external standard spectra of a sample using an external gamma radiation source;
determining, from the external standard spectra, a triple to double coincidence ratio and a quench parameter;
determining, based on the triple to double coincidence ratio and the quench parameter, a background reference parameter; and
determining, based on the background reference parameter, the background count rate from a background reference curve.
2. The method according to claim 1 , wherein the background reference curve is generated by:
using a plurality of background samples having different quenches and performing the following steps for each background sample:
measuring external standard spectra of the background sample;
determining, from the external standard spectra, a triple to double coincidence ratio and a quench parameter;
determining, based on the triple to double coincidence ratio and the quench parameter, a background reference parameter;
measuring an energy spectrum of the background sample; and
determining, from the energy spectrum, a background sample count rate within an energy window;
plotting the background sample count rates against the background reference parameters; and
fitting a curve to datapoints to obtain the background reference curve.
3. The method according to claim 2 , wherein the background sample contains a liquid scintillation cocktail and a quench agent.
4. The method according to claim 2 wherein the number of background samples is at least 6.
5. The method according to claim 2 , wherein a lower limit of the energy window is between 1 and 10 keV, and an upper limit of the energy window is between 30 and 75 keV.
6. The method according to claim 1 , wherein the quench parameter is the spectral endpoint of the external standard spectrum.
7. The method according to claim 1 , wherein the background reference parameter is calculated by an equation:
Ref=TDCR{circumflex over ( )} a *QP{circumflex over ( )} b,
where TDCR is the triple to double coincidence ratio, QP is the quench parameter, and a and b are weight parameters.
8. The method according to claim 1 , wherein the background reference parameter is calculated by an equation:
Ref=TDCR{circumflex over ( )} a *QP{circumflex over ( )} b *Ecounts{circumflex over ( )} c,
where TDCR is the triple to double coincidence ratio, QP is the quench parameter, Ecounts is an external standard count rate within an energy window, and a, b and c are weight parameters.
9. The method according to claim 1 , wherein the sample contains carbon-14.
10. A method for determining a net sample count rate in liquid scintillation counting, comprising:
measuring an energy spectrum of a sample;
determining, from the energy spectrum, a gross sample count rate within an energy window;
wherein the method comprises:
determining a background count rate according to claim 1 ; and
subtracting the background count rate from the gross sample count rate to obtain the net sample count rate.