You need to calibrate the PSA. The equipment discriminate alpha/beta contributions to the spectra, but the optimum PSA threshold should be found. Please check this paper.

Hi Sarah,

May I ask which radionuclides you want to analyse and what are their activities?

The PSA determination requires a cycle of pure alpha and pure beta standards measurements at different PSA settings (usually a step change every 5-10 units) and then plotting the results on a single graph (see the attached paper for details).

For the optimised value there will always be some spillover from alpha to beta and the other way around. The PSA parameter value depends on the energy of the alpha and beta particles so for different radionuclides it may change.

If your samples are not very active it may be quite hard to use them to determine the PSA value.

If you have access to pure, active standard solutions, I would recommend using them to optimise the PSA and assess the uncertainty it could introduce to your samples.

Regards,

Pawel

Hi Pawel

I'm using:

Am241, added activity 261mBq, expected 15.7cpm

Sr90, 212mBq, expected 12.7cpm

Is there an automatic protocol I can program into the quantulus to run the PSA increment change?

Ta

Sarah

Hi, See our paper listed below:

Determination of 243Am by pulse shape discrimination liquid scintillation spectrometry D.Alamelu, S.P.D.Bhade, P.J.Reddy, K.K.Narayan, P.M.Shah and S.K.Aggarwal

Applied Radiation and Isotopes 64 (2006) 579-583.

This should help you. I suppose. Please let me know. All the best.

Hi Sarah,

I do not know if there is a way of optimising the PSA parameter automatically on Quantulus counters. Years ago I used a EasyScan software to do just that on a 1414 Guardian counter, also a Wallac creation. I do not think this software is compatible with 1220 Quantulus but maybe I am incorrect.

On Quantulus I ended up creating a set of counting protocols with identical MCA setting apart from the PSA value and just queued them - not really an automated procedure as you still need to do all your calculation manually, but at least the counting could be set up and done fairly quickly.

You are using rather low activities so I guess a longish counting time is required. To get a reasonable statistics I'd say at least 2 hrs/std?

Hope that helps.

Pawel

Thank you Ali, Suresh and Pawel, I've read all papers now

The main TCLP containers are spiked with a concentration of 5Bq/L in line with legislation in Australian related to waste leaching. The low activity comes from the direct addition GABW 10mL leaching solution (from 200mL) : 12mL LSC cocktail.

I wanted to avoid depending on evaporation GABW techniques, but maybe this won't be possible to reach the required MDL/resolution.

I will try a longer count time first, have previously been using 1hr.

Hello Sarah,

For optimizing the PSA setting, you can use solutions with larger activities so that you do not have to count each sample at each PSA setting for 1-2 hours. If you use large activities, then you can count each sample for 1 minute or say 5 minutes at each PSA setting and then find out the optimum PSA setting for your work. I did not understand the acronym GABW and TCLP. Could you please expand these two acronyms?

All the best.