Liquid Scintillation Counting: External source to determine efficiency

[Chemistlsc]

TL;DR Summary

what are the advantages of using the external source for a Quench Indicating Parameter vs without it? And can the internal standard method be applied with the external source? Why must the same cocktail be used for both the quench set and samples?

Good day,

My background is in chemistry but my work now revolves around the liquid scintillation counter and so I have a couple of couple of questions on the usage of an external source like how typical.

I've read that most Quench Indicating Parameters involve the preparation of a quench set which comprises of a known amount of active standard, and varying amounts of quenching agent such as nitromethane. Then by exposing these quenched standards to the external source a measurement of a Quench Indicating Parameter like QPE, tSIE, etc is achieved and plotted against the efficiency (a quench curve). Following this, when we analyze a sample we measure the sample's Quench Indicating Parameter to determine its efficiency. And then calculate its activity by dividing the measured CPM/efficiency.

I have the following queries:
1. Is this form of Quench Indicating Parameter any better than those without an external source? Mostly because this is an additional standard that incurs additional cost, and so I'm not sure if its worth it. For example, for the HIDEX systems I see that I can plot a quench curve suing TDCR, and this does not require any external source.

2. Instead of using these Quench Indicating Parameters with the external source, is it possible to do it with via the "internal standard" method? Whereby a sample is counted, then a known amount of standard (DPM) is spiked into the sample. Then taking the additional counts/DPM we get the efficiency of the sample. Instead of spiking the standard, can we use the external source to "spike" a known amount of electrons into the system?

3. Must the cocktail I use be the same for the quench set and my samples? My logic is that the "quench" measured with the Quench Indicating Parameter is an all encompassing effect so by plotting a quench curve, I don't have to use the same cocktail anymore. However, I've seen tables from PerkinElmer whereby using a different cocktail from the quench set can result in a large deviations in the determined efficiency. I don't really understand why this is the case since I would think that the Quench Indicating Parameter would take all these compositional differences into account, and so long as the Quench Indicating Parameter of the sample is within the quench set's "calibration range" it should be fine.

 

[gleem]

Check this out https://www.sciencedirect.com/science/article/abs/pii/B9780125223508500155

Edit: Can you get a copy of this book?
Liquid Scintillation: Science and Technology contains the proceedings of the International Conference on Liquid Scintillation: Science and Technology held on June 14-17, 1976 at the Banff Centre in Alberta, Canada. The book presents papers on the mechanisms of the liquid scintillation process; liquid scintillation alpha counting and spectrometry and its application to bone and tissue samples; and measurement by liquid scintillator of labelled compounds (3H or 14C) dropped onto supports. The text also includes papers on the heterogeneous counting on filter support media; liquid scintillation in medical diagnosis; and the theory and application of Cerenkov counting. The radioassay of chlorine using a liquid scintillation spectrometer; some factors influencing external standardization; and the study of the sizes and distributions of colloidal water in water-emulsifier-toluene systems are also considered. The book further tackles the external standard method of quench correction; the liquid scintillation counting of novel radionuclides; and Cerenkov counting and liquid scintillation counting for the determination of fluorine. The text also looks into the absolute disintegration rate determination of beta-emitting radionuclides by the pulse height shift-extrapolation method; automatic data processing in scintillation counting; and the standardization in liquid scintillation counting. Biochemists and scientists involved in the study of chemical biodynamics will find the book invaluable.

 

[Chemistlsc]

Check this out https://www.sciencedirect.com/science/article/abs/pii/B9780125223508500155

Edit: Can you get a copy of this book?
Liquid Scintillation: Science and Technology contains the proceedings of the International Conference on Liquid Scintillation: Science and Technology held on June 14-17, 1976 at the Banff Centre in Alberta, Canada. The book presents papers on the mechanisms of the liquid scintillation process; liquid scintillation alpha counting and spectrometry and its application to bone and tissue samples; and measurement by liquid scintillator of labelled compounds (3H or 14C) dropped onto supports. The text also includes papers on the heterogeneous counting on filter support media; liquid scintillation in medical diagnosis; and the theory and application of Cerenkov counting. The radioassay of chlorine using a liquid scintillation spectrometer; some factors influencing external standardization; and the study of the sizes and distributions of colloidal water in water-emulsifier-toluene systems are also considered. The book further tackles the external standard method of quench correction; the liquid scintillation counting of novel radionuclides; and Cerenkov counting and liquid scintillation counting for the determination of fluorine. The text also looks into the absolute disintegration rate determination of beta-emitting radionuclides by the pulse height shift-extrapolation method; automatic data processing in scintillation counting; and the standardization in liquid scintillation counting. Biochemists and scientists involved in the study of chemical biodynamics will find the book invaluable.

Hi, thank you for the recommendation, I'll read through focusing on this chapter on the external standard method.

 

[Chemistlsc]

Check this out https://www.sciencedirect.com/science/article/abs/pii/B9780125223508500155

Edit: Can you get a copy of this book?
Liquid Scintillation: Science and Technology contains the proceedings of the International Conference on Liquid Scintillation: Science and Technology held on June 14-17, 1976 at the Banff Centre in Alberta, Canada. The book presents papers on the mechanisms of the liquid scintillation process; liquid scintillation alpha counting and spectrometry and its application to bone and tissue samples; and measurement by liquid scintillator of labelled compounds (3H or 14C) dropped onto supports. The text also includes papers on the heterogeneous counting on filter support media; liquid scintillation in medical diagnosis; and the theory and application of Cerenkov counting. The radioassay of chlorine using a liquid scintillation spectrometer; some factors influencing external standardization; and the study of the sizes and distributions of colloidal water in water-emulsifier-toluene systems are also considered. The book further tackles the external standard method of quench correction; the liquid scintillation counting of novel radionuclides; and Cerenkov counting and liquid scintillation counting for the determination of fluorine. The text also looks into the absolute disintegration rate determination of beta-emitting radionuclides by the pulse height shift-extrapolation method; automatic data processing in scintillation counting; and the standardization in liquid scintillation counting. Biochemists and scientists involved in the study of chemical biodynamics will find the book invaluable.

From the book there was this section:
"The Compton spectrum induced in the liquid scintillation sample by a gamma ray source has also been correlated with the counting efficiency of beta emitting radionuclides.
Kaufman et al. combined the external standard technique with the sample channels ratio technique described by Bailie 4 to correlate 57Co channels ratio with 3H efficiency. Fleishman et al. correlated the count rate induced by a 60co source with the counting efficiency of 40K. Similarly, Higashimura 6 correlated the count rate from a 137Cs gamma source with 14Ccounting efficiency."

I believe this is quite close to what I referred to in my 2nd question. I read the Higashimura paper where they used a Cs-137 external source to produce Compton electrons to mimic C-14 emissions. From what I understand, the authors prepared a quench set with three different quenching agents, and measured the transmitted gamma radiation. And the plot of transmitted gamma ray counts vs known C-14 efficiencies show a good relationship.

I believe the practical takeaways from the paper is that the transmitted gamma radiation is a good measure of the sample's efficiency/how quenched the sample is - akin to a quench curve. This works because the gamma source generates a known amount of gamma rays, and a more quenched sample will absorb more gamma rays and so the amount of transmitted gamma rays is related to how quenched a sample is.

Would this idea extend to the usage of Compton electrons in a sample? Meaning would the number of Compton electrons generated always be known, akin to how we would know how much gamma rays is emitted at any point. Because if the number of Compton electrons is going to be fixed, we can calculate the efficiency just by taking the ratio of the actual counts/theoretical Compton electrons generated. For example, the external source will generate 100 CPM of Compton electrons theoretically. Then I measure the sample without exposure to the external source and get 20 CPM, then with the external source I get only 100 CPM. Then I calculate the efficiency as (100-20)/100=80%.

But I have a feeling that it changes from sample to sample depending on the matrix and so we don't have a theoretical DPM (100 CPM in the example) to work with?