LS User’s Forum 2001 Developments in LSC Andy Pearce CIRM Date: 5th September 2001
Dec 20, 2015
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
“...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- 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