ABCD-Tool, a software suite for the analysis of α/β spectra from liquid scintillation counting

ABCD-Tool, a software suite for the analysisof a/b spectra from liquid scintillation counting

Romolo Remetti • Daniele Franci

Received: 21 November 2011 / Published online: 8 February 2012

� Akademiai Kiado, Budapest, Hungary 2012

Abstract This paper presents the alpha/beta complete

deconvolution tool (ABCD-Tool), a C?? application for

the analysis of spectra from liquid scintillation counting

(LSC) measurements. In addition to the basic algorithms

for standard gross alpha/beta analysis and the determina-

tion of the counting efficiency, the software implements a

recent unfolding technique based on Fourier transforms,

which gives precise and reliable results even in the case of

complex, strongly overlapping spectra. The application is

designed to be used with alpha/beta spectra generated from

Perkin Elmer Wallac Quantulus 1220. However, future

upgrades are scheduled in order to extend the compatibility

to spectra from other LSC instruments in commerce.

Keywords Liquid scintillation counting � Beta spectra �Deconvolution � Alpha/beta separation � Fourier transforms

Introduction

During the last decades, liquid scintillation counting (LSC)

has played a leading role in the field of radiometric

measurements for the characterization of nuclear wastes

produced by industrial facilities. In particular, it represents

the most reliable technique for quantitative determination of

hard to measure radionuclides (HTMR). These radionuclides

have the distinctive feature of being only a/b and low energy

X-rays emitters. For this reason, the traditional radiometric

approach based on c spectrometry is generally useless for

HTMR, while LSC technique provides reliable results [1].

The LSC technique is based on the counting of the light

pulses generated by a mix of the radioactive sample with a

scintillation cocktail, composed of an aromatic organic sol-

vent plus a fluorescent substance, commonly referred to as

scintillator. The scintillator converts the energy released by

charged particles into photons, which are detected with a

system of photomultipliers and then counted by a multi-

channel analyzer. The sample spectrum is finally recorded,

allowing for a rapid and precise determination of the sample

activity [2–4].

The LSC analysis of mixtures of different radionuclides

may result rather hard to perform, due to the presence of

wide, continuous b spectra, which extend from zero up to a

maximum energy characteristic of each radionuclide. In the

case of mix of several a/b emitters, the resulting spectrum

may be affected by significant overlap between the dif-

ferent shapes. In order to avoid expensive radiochemical

separation procedures, different techniques for analytical

deconvolution of LSC spectra have been proposed [5–13].

Recently, a very promising approach based on the use of

Fourier transforms has been presented by Remetti and

Sessa [14], leading to encouraging results.

This paper presents the ‘‘alpha/beta complete deconvo-

lution tool’’ (ABCD-Tool), a software suite oriented to the

analysis of a/b spectra. ABCD-Tool implements the

deconvolution technique discussed in [14], with some

additional features such as the algorithm for the self-choice

of the number of harmonics. In addition to this, ABCD-

Tool allows to perform standard gross a or b analysis and

the determination of the counting efficiency by means of

standard quench parameter [SQP(E)] method [15].

Alpha/beta complete deconvolution tool is a stand-alone

C?? application, running on Microsoft Windows operating

R. Remetti (&) � D. Franci

Department BASE—Basic and Applied Sciences

for Engineering, ‘‘Sapienza’’ University of Rome,

Via Antonio Scarpa 14, 00161 Rome, Italy

e-mail: [email protected]

123

J Radioanal Nucl Chem (2012) 292:1115–1122

DOI 10.1007/s10967-012-1664-7

systems. The software is designed for an optimal visualiza-

tion with a 1,200 9 800 screen resolution. It is founded on

ROOT libraries, the object-oriented framework for particle

physics data analysis developed at European Organization

for Nuclear Research (CERN) [16]. Currently, ABCD-Tool

is able to manage a/b spectra generated from Perkin Elmer

Wallac Quantulus 1220 only. Future upgrades are scheduled

in order to allow ABCD-Tool to analyze spectra from other

LSC instruments.

Software description

The main window of ABCD-Tool (Fig. 1) offers a rapid

access to all the software analysis routines:

• Gross a/b analysis, to determine the total activity in the

case of very simple spectra.

• Alpha/beta separation routine, based on pulse shape

analysis—PSA [17], a method to distinguish between aand b spectra based on the differences between the

pulse shapes. Spectral separation is performed by

Quantulus and the resulting spectra can be analyzed

with ABCD-Tool.

• Determination of counting efficiency, based on

SQP(E) method [15].

• Analytical deconvolution of complex spectra, using

Fourier transform method described in [14].

In the following a detailed description of the deconvo-

lution method is provided. Subsequently, a rapid overview

of the other ABCD-Tool features is presented.

Deconvolution method

Spectral deconvolution is carried out by loading a spectrum

from Quantulus file and specifying the correct multichan-

nel index (e.g., ‘‘11’’, ‘‘12’’, ‘‘21’’ or ‘‘22’’). A count-

per-minute versus channel histogram is shown in the upper-

left canvas (Fig. 2).

A Fourier series fitting is then performed by means of a

dedicated mask where the order of the series, e.g., the

number of harmonics (NH), and the start and stop channels

used for fitting can be defined. Instead of a manual search

with ‘‘Perform fit’’ button, an automatic search algorithm

for the optimal NH value can be invoked. This ‘‘Optimized

NH search’’ is particularly helpful in the case of complex

spectra with shapes strongly affected by quenching effects.

The automatic search algorithm is composed by the fol-

lowing steps:

1. Starting from an user-defined NH value, a 20 steps loop

is performed. For each step, NH is increased by one and

Fourier fit is computed. The procedure is iterated until

the summed squared fit deviation at the (n ? 1)th step

varies less than 5% with respect to the value at the nth

step, for the entire 20 steps loop. The summed squared

deviation is defined as:

S2 ¼X1;024

i¼1

FNHið Þ � c ið Þ½ �2 ð1Þ

where i runs over all the channels of the spectrum and

FNHið Þ and c(i) represent respectively the value of

Fourier fit and the histogram content corresponding to

the ith channel.

2. The algorithm comes back to the starting NH value and

performs a 5 steps loop. For each step, NH is decreased

by one and Fourier fit is computed. The procedure is

iterated until NH is equal to five, or until the value of

the penalty function at the (n - 1)th step is larger than

the value at the nth step, for the entire 5-steps loop.

The penalty function is defined as:

PF ¼ S2 �ffiffiffiffiffiffiffiNH

pð2Þ

3. For each NH, the value of penalty function is stored

(Fig. 3). The NH value that minimizes the penalty

function is chosen as optimal.

The lowermost part of the window is devoted to the

unfolding procedure. Users must enter nuclide name, the

composite channel range in which nuclide is defined

(e.g., [2,20] [ [753,952]) and the start/stop channel for

integral calculation. The resulting nuclide, obtained from an

interpolation through the cubic spline method, can beFig. 1 The main window of ABCD-Tool

1116 R. Remetti, D. Franci

123

checked using ‘‘Try it!’’ button: the lower-left canvas shows

the original spectrum with the deconvoluted nuclide super-

imposed, while the lower-right canvas shows the subtracted

residual spectrum. Moreover, the total cpm of deconvoluted

nuclide is shown in a dedicated text box. When users are

satisfied with the deconvolution results, the current nuclide

can be added to the list of identified nuclides using ‘‘Add to

the nuclide list’’ button.

At the end of the unfolding procedure, a complete result

summary can be printed using ‘‘Show summary’’ button

(Fig. 4). A pop-up canvas will show the experimental

spectrum together with Fourier fitting and all the decon-

voluted nuclides. In addition, a report file is created with

the most important information.

Another interesting feature of ABCD-Tool is the possi-

bility to export Fourier fit or deconvoluted nuclides into a

.001 file, which is the output format for Quantulus files and

the input format for ABCD-Tool.

Experimental tests

To test the capabilities of ABCD-Tool, three different

spectra have been resolved:

1. A mixture of about 12.5 kBq of 90Sr in secular

equilibrium with 90Y.

2. A mixture of about 12.5 kBq of 90Sr in secular

equilibrium with 90Y plus 1 kBq of 241Am.

3. A simulated spectrum, where three alpha peaks have

been added to the 12.5 kBq 90Sr plus 90Y mixture.

Sample 1 and 2 are the same already used in [14].

Fig. 2 Deconvolution window showing both the input spectrum and the results of unfolding procedure

Fig. 3 Penalty function as a function of the number of harmonics NH.

NH value corresponding to the minimum is chosen as optimal

ABCD-Tool, a software suite for the analysis of a/b spectra from liquid scintillation counting 1117

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The first sample is fitted with 20 harmonics, in the range

[10,952]. 90Y is then identified in the range [2,21] [[753,952] and the residual spectrum is assigned to 90Sr. A

summary of unfolding procedure is presented in Fig. 5. The

integrals of the unfolded nuclides are:

– 743.432 cpm for 90Y

– 743.658 cpm for 90Sr

confirming the hypothesis of secular equilibrium.

The second sample is fitted with 52 harmonics, in the range

[35,952]. The mixture of 90Sr plus 90Y is identified and

unfolded in the range [30,665] [ [744,952] The residual

spectrum is assigned to 241Am (Fig. 6). In order to estimate the

individual contribution of 90Sr and 90Y, the alpha spectrum is

subtracted to the original one and the unfolding procedure is

repeated on beta mixture spectrum only. 90Y is identified in the

range [2,43] [ [749,941] and the residual spectrum is

assigned to 90Sr. The integrals of unfolded nuclides are:

– 755.238 cpm for 90Y

– 746.401 cpm for 90Sr

– 78.846 cpm for 241Am

The third sample is fitted with 58 harmonics, in the

range [10,952]. Following a similar approach as before,

beta mixture is unfolded in the range [50,370] [[445,665] [ [735,820] [ [885,960]. The residual spectrum

comprises all the alpha peaks (Fig. 7). Alpha peaks are

then separated, as shown in Fig. 8. 90Y is then identified, in

the range [2,49] [ [750,952] and the residual spectrum is

assigned to 90Sr. The integrals of unfolded nuclides are:

– 738.513 cpm for 90Y

– 739.063 cpm for 90Sr

– 51.347 cpm for alpha1


Fig. 4 Summary from deconvolution procedure. Input spectrum with unfolded nuclides superimposed is shown. A report file with the most

important information is also printed

Fig. 5 Unfolding of the 90Sr ? 90Y mixture


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Secular equilibrium is still respected and the integral of

alpha peaks is in agreement with the simulated values

(alpha1 = 51.7, alpha2 = 63.5, alpha3 = 45.5). The larg-

est deviation from the simulated value is observed for

alpha2. A possible explanation is the strong influence of

both 90Y and 90Sr in the region of alpha3.

Standard gross alpha/beta analysis

In the case of simple spectra composed by only one nuclide

or many well separated nuclides, the traditional approach

of gross spectrum integral gives excellent results. For this

reason, ABCD-Tool implements a window devoted to

standard gross a/b analysis (Fig. 9). This routine is com-

posed by the following steps:

– Loading of the signal spectrum.

– Loading of the background spectrum.

– Definition of the region of interest (ROI) boundaries;

– Definition of counting efficiency.

– Drawing the spectra.

– Calculation of activity, uncertainty and MDA (if any

background had been loaded).

Alpha/beta separation based on PSA method

A distinctive feature of Wallac Quantulus is the possibility

to distinguish between a and b particle thanks to a dedi-

cated analysis of the pulse shapes. This technique is

referred to as PSA [17], it allows to separate a from bevents into their respective spectra within a mixed sample.

ABCD-Tool implements a window that fully exploits

Quantulus capabilities, providing a simple tool for ana-

lyzing mixed samples processed with PSA technique

(Fig. 10). This routine is composed by the following steps:

– Loading of the signal spectrum.

– Loading of the background spectrum.

– Definition of the appropriate multichannel for both aand b.

– Definition of the ROI boundaries.

– Definition of a and b spillover, i.e., the beta (alpha)

fraction wrongly identified as alpha (beta).

– Definition of a and b counting efficiency.

– Drawing the spectra.

– Calculation of activity, uncertainty and MDA (if any

background had been loaded) for both a and b spectra.

Fig. 6 Unfolding of the 90Sr ? 90Y ? 241Am mixture

Fig. 7 Alpha peaks from deconvolution of the 90Sr ? 90Y ? 3 a-

peaks mixture

Fig. 8 Unfolding of the 90Sr ? 90Y ? 3 a-peaks mixture


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Fig. 9 Window for standard gross a/b analysis

Fig. 10 Window for PSA-based a/b separation analysis


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Determination of counting efficiency using

SQP(E) method

Quantulus is equipped with an external high-energy, low

activity external source of 152Eu used to determine the

SQP(E) of the analyzed sample. This approach [15] is one

of the most popular for the determination of counting

efficiency. For this purpose, set of primary standards with

different quenching level are commonly used to extrapo-

late an efficiency versus SQP(E) curve. In this way, the

calculation of SQP(E) index with the 152Eu source permits

to establish the correct value of counting efficiency to be

applied to the unknown sample. ABCD-Tool implements a

window for the determination of the calibration curve

(Fig. 11). Users can add the primary standard spectra,

declaring the reference activity and start/stop channel for

integral calculation. When the SQP(E) index of the ana-

lyzed sample is known, it can be inputted through a text

box. Otherwise, the 152Eu spectrum collected by Quant-

ulus can be loaded as input for the automatic calculation

of quenching index. Experimental points are then fitted

using a third-order polynomial and the counting efficiency

for the unknown sample is shown, together with the fit

parameters.

Conclusions

Alpha/beta complete deconvolution tool is a general pur-

pose software for analysis of LSC spectra from Perkin

Elmer Wallac Quantulus 1220. It is written in C?? using

ROOT libraries and runs on Microsoft Windows operating

systems. At the moment, it is highly recommended a screen

resolution of 1,200 9 800 for an optimal visualization.

Alpha/beta complete deconvolution tool implements the

deconvolution algorithm described in [14], which is based

on Fourier fitting of the experimental spectrum and an

unfolding technique of the single nuclide based on cubic

spline method. ABCD-Tool has been tested with complex

a/b mixed spectra, providing remarkable results.

In addition to this, ABCD-Tool is able to accomplish

other common tasks in LSC analysis such as gross count-

ing, a/b separation with PSA method and efficiency

determination with SQP(E) technique.

Further improvements are scheduled, in order to make

ABCD-Tool able to manage spectra also from the other

LSC instruments in commerce, and to make the visuali-

zation independent from the screen resolution. In addition,

conversion for the other operating systems is planned for

the near future.

Fig. 11 Window for the determination of counting efficiency with SQP(E) method


123

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