LS User’s Forum 2001

Developments in LSC

Andy Pearce

CIRM

Date: 5th September 2001

Intro - LSC at NPL

LSC2001

ICRM2001

Summary

Liquid Scintillation at NPL

4 LS coincidence counting– Absolute standardisation using LSC

– High(ish) activities - or - emitting nuclides– Extension to other nuclides – tracer technique

CIEMAT/NIST efficiency tracing– Secondary standardisation using LSC

– Wide range of activities– Primarily for pure emitting nuclides– Extension to most other nuclides – courtesy of Günter

Liquid Scintillation at NPL (cont’d)

Triple-Double Coincidence Rate (TDCR) Method– Absolute Standardisation using LSC

– Custom built counters – three photomultipliers– Pure and pure EC nuclides– Not coincidence counting!

Other Techniques– “Standard” techniques as familiar to many

– Straightforward secondary counting– Dilution factors– Health physics

LSC2001 – Advances in Liquid Scintillation Spectrometry

LSC2001- Advances in Liquid Scintillation Spectrometry

“...aims at providing a forum for radioanalysts to discuss their most recent findings and future work”

Karlsruhe, Germany 7-11 May 2001

Participants from environmental & life sciences

NIST, PTB, LNHB and NPL

LSC2001- Topics Discussed

Natural Radioactivity

Applications in Bioscience & Medicine

Tritium and Radiocarbon

Low Level Counting

Nuclear Sciences & Environmental Survey

LSC2001- Topics Discussed (cont’d)

Instrumentation & Data Handling

Sample Preparation

Chromatographic Methods

Cocktails

Other Techniques

LSC2001- Scientific Interest

Large amount of interest in Radon and Radium analysis

Some “nuts and bolts” work – particularly by CEA

Alpha-beta pulse shape discrimination

Spectral deconvolution

Scintillant cocktails – nothing new!

LSC2001 – Radium and Radon

A large amount of Chemistry!!!

LSC2001- Nuts and Bolts

Three papers from CEA on underlying principles in LSC

“Understanding the peak asymmetry in -LS with / discrimination”

“Energy Transfer and Fluorescence Mechanism in -LS – Applications to Scintillation Cocktail Composition”

Wall Effect in LSC

LSC2001- Alpha-Beta PSD

A rather popular technique

Some concern (informally raised) that this is often used incorrectly

Commercial systems require careful calibration to give reliable results

LSC2001- Spectral Deconvolution

Another increasingly popular method

Again, some users appear over-optimistic of what can be achieved with this technique

Uncertainty handling and confidence levels seem generally optimistic (personal opinion!)

LSC2001- Scintillant Cocktails

Some sales pitches – but nothing much new?

Interesting “one stage” scintillant with a large Stokes’ Shift (details unavailable)

“Seasonal Variation” of commercial cocktails

Packard LSA Cocktail Guide

Slippery Packard!

1 Shot of rum 1 Orange

Take a bite out of the orange Down the rum Eat the rest of the orange

ICRM2001- International Conference on Radionuclide Metrology and it’s Applications

“... to provide an opportunity for the exchange of information on techniques and applications of radionuclide metrology, and to encourage international co-operation in this field”

Braunschweig, Germany 14-18 May 2001

Representation from NMI’s such as NIST, PTB and NPL

Includes report from ICRM-LSC Working Group

ICRM2001- Topics Discussed

Stability problems with alkaline matrices

Ionisation quench

Wall effect in LSC

Developments in CIEMAT/NIST from PTB

Web Page

ICRM2001 – Alkaline Matrices

A particular problem for NMI’s– Some nuclides not soluble in acids– Example 188W/188Re

Also a problem for user community?– Matrices often more complex– Longer measurement times

ICRM2001- Ionisation Quench

Ionisation quench parameter is used in both CIEMAT/NIST and TDCR techniques

Not significant at high energies – but may be dominant at low energies

Some doubts over best formula and constants to use

Limits precision of CIEMAT/NIST and TDCR

ICRM2001- Wall Effect

LNHB (part of CEA) have investigated wall effect

Used PENELOPE Monte Carlo code

Coupled modelling with experimental observations

Demonstrated that the wall effect is negligible for high-energy beta emitters

ICRM2001- Developments in CIEMAT/NIST

PTB have developed new CIEMAT/NIST code

Extension to standardisation of wider range of nuclides (almost any in fact)

Investigated the best achievable uncertainties

Demonstrated that uncertainties for pure EC nuclides are limited by ionisation quench

ICRM2001- Web Page

www-dta.cea.fr/DAMRI/FR/Pages/radioactivité/scintillation/icrm1.htm

ICRM Working Group web page, containing information on standardisation techniques:

You don’t need to be able to speak French, however...

Your browser does!

Summary – Points

Pulse Shape Discrimination– How well does it really work?– Is it applied properly?

Spectral Deconvolution– Does anybody rely on it?– How much confidence in results?

Summary – Points (cont’d)

Scintillant Cocktails– Variability from one batch to the next– A problem for us – what about the user?

Alkaline Matrices– How to obtain stable solutions– What to use to produce quench curves