SURVEY INSTRUMENTATION

• A survey meter equipped with a G-M pancake or thin-window probe is effective for detecting the betas from the Ca-45. Typical efficiency for a G-M pancake survey meter is 11%-18%.

• A liquid scintillation counter should be used to detect removable Ca-45 contamination on wipe tests smears. Typical efficiency for a liquid scintillation counter to detect Ca-45 is 90% or greater.

I would recommend a perchloric acid-nitric acid digestion of the rodentia organ tissue since the beta emission Emax energy of Ca-45 is quite low. The only element known to be volatilized in significant quantities with this type of digestion scheme is mercury, so calcium isotopes should remain in solution during the digestion process. Most of the counts from liquid scintillation measurement with an aqueous fluor system will be shifted down energy primarily into the tritium and carbon-14 channels due to chemical, color, and particulate quenching. Because of the unavoidable quenching due to the tissue digestion residues, the smaller the aliquot of digestate, the better. A counting efficiency of a tissue digestate in an aqueous fluor system would most likely be much lower than50%. I believe a tissue homegenate of a qiquid fluor system loading would lead to even lower and a very limiting beta counting efficiency. Utlima Gold is a good example of a high quality aqueous liquid scintillation fluor cocktail. Of course, quenching curve standards using non-radioactive rodentia tissue digestates are essential for accurate estimates of beta counting efficiency. A viable alternate method that would possibly be feasible would be to take very thin tissue slices of the tracer-laden organ(s). Freezing the whole organs in liquid nitrogen would allow the organ tissue to be sliced by a microtome into measurably thin slices that would cause minimal sample self-absorption of the beta particle emissions when placed into a Tennelec (for example) alpha/beta counter connected to a supply of P-10 gas (argon and methane). The thinly sliced tissue samples could be placed in planchettes and counted for various lengths of time in reference to control tissue samples to estimate the beta detection efficiency for each tissue thickness. When tissue thickness is plotted against total beta counts per minute should reach a maximum at some thickness of tissue, then begin to decline or level off. This would probably be the least problematic, safest, and least time-consuming methodology to pursue. You should be able to fashion a Ca-45 standard in one of the planchettes using a known quantity of the Ca-45 in CaCl2 carrier solution and oven drying it at 70 degrees C for determination of maximum counting efficiency of the Tennelec. Trade names mentioned here only for reference purposes and not intended as an endorsement.

Thank you for your valuable input !

Daniel Van Gent Mushtaq Ahmad

My Pleasure! In the early 2000s, I digested and counted methanotrophic mussel tissue using this method to determine Ra-226 concentrations in the tissue and shells of the mussels. It was a lot of work, but yielded great results.Ra226 is primarily an alpha emitter, nut the Beckman 6000 LS counter I used had alpha discrimination capabilities. I was able to age-date the shell and determine growth rates using pb-210/Ra-226 ratios. The summary of that methodology is recorded in detail in our report to the Mineral Management Service:

https://www.boem.gov/ESPIS/3/3099.pdf

Fate and Effects of Barium and Radium-Rich Fluid Emissions from Hydrocarbon Seeps on the Benthic Habitats of the Gulf of Mexico Offshore Louisiana

Radium is a very good calcium analog and tends to behave a lot like calcium in biological systems. It is a so-called "bone-seeker" like calcium and is in the same chemical period of the atomic chart of the elements. We also used a PERALS Spectrometer for increased alpha discrimination during the study. Please feel free to contact me if you have further questions about the methodology on my home page here

I apologize that the publication I provided a reference for was edited by MMS to preclude the Liquid Scintillation methodology because it was not an EPA approved one. I still have some of my earlier drafts that include the Liquid Scintillation methodology for determining radium-226 in methanotrophic mussel digestate. I will locate them if you are interested in that specific methodology. The EPA approved methodologies are summarized in this publication:

"Fate and Effects of Barium and Radium-Rich Fluid Emissions from Hydrocarbon Seeps on the Benthic Habitats of the Gulf of Mexico Offshore Louisiana". This publication is available at no charge on the internet. The authors are Paul Aharon, Dan Van Gent (myeself) Baoshun Fu, and L. Max Scott. The publication date is 2001. Paul Aharon recently retired from the University of Alabama. Please feel free to contact me at my home page here on Research Gate.

Sincerely,

Daniel Van Gent, M.S., MHP