the evolution of the liquid scintillation technique: a ... · late 1940’s- 1950’s marked...

1 1 © 2009 PerkinElmer © 2009 PerkinElmer © 2009 PerkinElmer © 2013 PerkinElmer © 2011 PerkinElmer

Chuck Passo

Associate Product Leader PerkinElmer

The Evolution of the Liquid Scintillation Technique: A personal perspective

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Scintillators and the Scintillation Process

LS Development Drivers

Technological LS advances

The Evolution of Instrumentation – Timeline

Liquid Scintillation Counters – Today

Table of Contents

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1903 W. Croakes “spinthariscope” (a small tube) lens at one end; alpha particles

detected by a zinc sulfide screen; flashes of light detected in a dark room by

human eye

Liquid scintillation counting stimulated by 2 events:

Importance of organic compounds as scintillators

Development of photomultiplier tubes

Late 1940’s- 1950’s marked beginning of organic scintillator investigation

Broser, I; Kallmann, H and Herforth, L: first experiments with aromatic solvents &

fluors

Kallmann and Reynolds (1950) origin of LSA technique - light produced from flours detected

by PMT

Birth of alpha counting by LSC

Hayes and coworkers, Los Alamos discovered PPO (2,5 diphenyl oxazole as primary)

and POPOP (1,4 bis—2(5 phenyloxazole) benzene) as best for performance, cost and

solubility

Concluded several conjugated aromatic rings in linear array are good scintillators

Organic scintillators advance the LS technique


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The quest for new and better scintillators continued with scintillators emission

spectrum closely matching the absorption spectrum of the photocathode

Scintillation Solvents

Early ones include benzene, p-dioxane, toluene, xylene

Some miscible with aqueous samples and biological specimens - methanol, ethylene glycol

and glycol ethers

An early cocktail (~1959-1970) – Brays solution

Dioxane solution of naphthalene, ethylene glycol, methyl alcohol PPO and POPOP

Birth of solvent extraction scintillators (alpha counting) K.B Brown Oak Ridge National

Lab

Later cocktails based on toluene or xylene mixed with Triton - a non-ionic surfactant

Increase capacity for aqueous samples

1965 Real “modern” cocktails appeared on the market

Insta-Gel & Pico-Fluor, (from Packard)

NE-233 & NE-250, (Nuclear Enterprises)

Aquasol (New England Nuclear)

PCS (Amersham)

The evolution continues


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Todays formulations

Solvents evolved to todays safer formulations based on Pseudocumene (tri-methyl

benzene), (LAB linear alkyl benzene), PXE (Phenyxylylethane) and DIN (Di-isopropyl

naphthalene)

Fluors (Dimethyl-POPOP - more soluble than POPOP)

(bis-MSB - even more soluble than DM-POPOP)



0

50

100

150

200

250

300

1950 1955 1960 1965 1970 1975 1980 1985 1990

Fla

sh P

oin

t (°F

)

LSC Solvents Evolution Timeline

BenzeneDioxane Toluene

Xylene

Pseudocumen

LAB DIN/PXE

USA=100 F

ROW=149 F

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1984

First Safer Cocktail (Opti-Fluor)

Current safer cocktails

Packard Ultima Gold (DIN), Opti-Fluor (LAB) Wallac OptiPhase Hi-Safe (DIN) ICN EcoLume & EcoLite (LAB+PXE) ND EcoScint (PXE) RPI Bio-Safe (LAB) Zinsser AquaSafe & QuickSafe (DIN) Lumac LumaSafe (PXE)

Take Away Goes Here


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First commercial LSC counters in 60’ & 70’s were essentially freezers/refrigerators

and were kept at around 5 °C.

Early PMT’s were subject to noise and the only way to reduce this was to cool the

PMT to around 5 °C.

Backgrounds were around 100 to 150 cpm.

Consequence was that all LSC cocktails at that time had to work down to 5 °C.

Later developments in PMT technology reduced the noise and they were then able to

work effectively at room temperature (~20 °C) with significantly lower backgrounds.

Driver for simplifying counter design - no need for it to be housed in a

freezer/refrigerator.

Driver for Chill Pack and UG LLT working down to 14 °C.

This improved performance at low temperature was retrospectively applied to low level

counters and cocktails as they were found to perform better at lower temperatures.

Advance the LS technique

Early Development Drivers for Liquid Scintillation

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Advent of Nuclear Power stations in 1950’s through 1970’s

First working unit was in Russia in 1954

First commercial unit was in the UK (Calder Hall) in 1956

As of January 2013 – 437 operational worldwide

Testing requirements:

work environment (safety)

effluents and discharges (legislation)

personnel (bioassay - safety)

Development of radiocarbon dating method; Willard Frank Libby 1960 Nobel

laureate

On-going development included beta/alpha/gross alpha/beta testing.

Driver for alpha/beta discrimination in LSC.

Nuclear disaster at Chernobyl in 1986 focused attention on environmental low level

counting - driver for development of low level counters and specialist LSC cocktails

Additional Development drivers for environmental monitoring/safety

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1953 The first fast coincidence LS Hiebert and Watts, Los Alamos

~1953 1st commercial LS counter Packard Instrument Company, Tri-Carb 314;

dominate in the 50’s; 2 counting channels; coincidence detection

Technical Measurement Corporation (TMC); never marketed; similar to Los Alamos

instrument

1962 Nuclear Chicago (later Searle-Analytic) introduced a counter with channels

ratio as a quench monitor - eliminating the need to correct by internal

standardization

1960-1970s Many domestic and foreign manufacturers enter the market including

Beckman Instruments USA; Intertechnique France 1968; Nuclear Chicago; 1961

Wallac 1970s; Phillips Holland 1963 and others

Today Just a few major commercial LS manufacturers remain

PerkinElmer

Hidex

Aloka

Take Away Goes Here

The Evolution of Instrumentation - Timeline

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Early advances in the 60’s included pulse summation (reduced geometrical location

effects of scintillation pulses)

1964-1965 logarithmic amplification (eliminates need for independent channel

amplifiers)

As a result of LSA conferences, (1970s) microprocessors and some multi-channel

analyzer capability were recommended as inclusion into LSC

1970-1980 advances

Internal 12 bit processor

ACSS Automatic continuous stabilization (calibration with an LED)

Deionizer (static removal)

1971 2nd generation counter built-in processor

1977 1st rack based counter 1215 RackBeta; PAC (PMT crosstalk discriminator)

1980 Pulse height spectrum analysis

Computers enhance the power of LSA

Technological LS advances

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1980s Computer controlled

1984 Dual MCAs; anticoincidence guard

1985 Pulse discrimination circuitry evolves (TR-LSC); plastic detector guards

1986 Pulse shape analyzer (alpha/beta discrimination and background reduction)

1987- 1990s plate based counters

advances in scintillating microplates

1995 BGO detector guard introduction (low level counting)

1980 - present Software/hardware becomes more sophisticated

User interfaces evolve – DOS to Windows based

DPM calculations improve and become easier to perform

Various techniques; with and without quench curves…

Efficiency tracing , Direct DPM and DOT Spectrum libraries for DPM ; TDCR

Luminescence detection and correction

Recall and reprocessing data

Worklisting and bar code reading

Advances continue

Technological LS advances - continued

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(QIPs) Quench indicating parameters evolve from channels ratio and external

standard ratio from 1960’s…

Sample

Channels Ratio

to ….

Current Sample QIPs

IC # (center of gravity of spectrum)

SIS (spectral index of the sample, spectral endpoint)

SQP(I) (average energy)

Advances continue


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What caused the evolution of using the external

standard spectrum based on ESR?

Advantages - spectrum produced by same

source and thus fixed discriminators can be used

Disadvantages - limited dynamic range; wall

effect and some volume dependency

Current External Standard QIPs

H# and H# Plus (Horrocks #)

(inflection point of 137Cs Compton spectrum)

SIE and tSIE

(spectral index and transformed spectral index

of external standard 226Ra and 133Ba)

SQP(E) (Spectral Quench Parameter of External

standard; 152Eu)

Advances continue


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Traditional LSAs (vial based):

PerkinElmer

Tri-Carb family

(2810TR, 2910TR, 3110TR, 3180TR/SL)

Research and environmental applications

1220 Quantulus

Ultra Low Level environmental applications

Aloka

LB-5 Environmental focus

Hidex

Triathler (Bioscan Lumi-scint) Research and some environmental applications; manual changer

300SL Research and environmental counting Low level capability

Ordela

Perals (8100-AB; 8400AB-P)

Spectrometer

Single PMT system

Dedicated alpha LSC spectrometry


Liquid Scintillation Counters - Today

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Tri-Carbs

External PC/Easy data storage and

networking

Full 4K MCA/ live spectral display

and analysis

Windows 7 user interface

(QuantaSmart software)/ familiar

easy user interface and logical

dialogue

Spectrabase- spectral storage of

standards and sample data

TR-LSC (time – resolved electronic

background discrimination)/

patented technique

GLP features (IPA) and Enhanced

Security/ Compatibilty with GLP

and 21CFR Part 11

Major Features/Benefits/Advances

1220 Quantulus

External PC control with Windows

interface/ multiple instrument

control/live spectral display/easy

default settings

Passive (lead) and active (detector

guard) rejection of cosmic and

background radiation/improved low

background/ lowest 3H

backgrounds available

Additional electronic background

and noise rejection

4 Programmable MCAs/ enhanced

spectral analysis and data

collection

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Aloka LB-5

PC controlled

Low level applications

Triple coincidence anti-coincidence

shield/ reduced background for

high S/N

Large vial sizes 100mL or 145 mL/

provides increased counting

sensitivity

2 MCAs for spectral analysis

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Triathler

Portable manual system; beta and

luminescence counter

Data can be exported for

additional calculations

Optional alpha/beta pulse shape

discriminator

High energy beta detection with

plastic scintillator adapters to

eliminate cocktail usage

Luminescence capabilities

Hidex 300SL

(TDCR) Triple to double

coincidence ratio counting

DPM w/o external or internal

standard

Additional lead shielding

Small footprint

Low level model with active guard

for background discrimination

Optional alpha/beta discrimination



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Computer controlled with either internal or external PC

Modern Windows software compatible

Dual PMTs in coincidence most common; (Aloka and Hidex) use 3 PMTs; several

use only 1 (Triathler); Kvartett; PERALS

Multiple MCAs for spectral analysis and alpha/beta separation

Enhanced sensitivity due to…

Increased passive shielding (lead /copper); lower noise PMTs

Detector guards (anticoincidence active guard (scintillator) or quasi active guard (solid

scintillator crystal or plastic) PerkinElmer; Hidex

Electronic background and alpha/beta discrimination (pulse shape analyzer); e.g. PSA;

TR-LSC

Safer cocktail formulations based on Di-isopropyl naphthalene (DIN) and

Phenylxylylethane (PXE)

Large vial size capability

So what’s the state of the art- LSC Today?

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Major advances in detectors not likely

Increased sensitivity not likely - current low level instrumentation produce 3H

backgrounds in the 0.5 – 3 CPM range

Mostly software/calculation improvements

Some possibility for hybrid software

Continued application support for new applications such as biofuel; biobased products

Interest in smaller footprints; less sample capacity

Improvements in sample preparation techniques/separation chemistries

Current applications of interest

Biofuel and biobased products

Homeland security

Environmental counting

Alpha counting


Future trends, wants, needs, predictions, ...

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Resources

The History of Liquid Scintillation Counting – A Personal View

Liquid Scintillation Spectrometry Conference Proceedings, 1992 Radiocarbon Dr. C.T. Peng

Mr. James Thomson, Meridian Biochemicals Ltd. Personal communication

Radioactivity Introduction and History, L’Annunziata, Michael F. Elsevier publications;

2007

Handbook of Radioactivity Analysis, 3rd edition, L’Annunziata, Michael F. Elsevier

publications, 2012

Thank you to the conference organizers

Dr. Jose F García

Dr. Alex Tarancón

Acknowledgements - Thank You

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Chuck in the Box

Thank you for your attention!!

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