Laser-induced photoacustic spectroscopy for the speciation of transuranic elements in natural aquatic systems

European Commission Directorate-General For The Information Society And Media Directorate-General For Research And Innovation

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Nuclear energy and safety

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• Publié par: EUROPEAN-COMMISSION-DIRECTORATE-GENERAL-FOR-THE-INFORMATION-SOCIETY-AND-MEDIA-DI
• Nombre de lectures: 6
• Langue: English
• Poids de l'ouvrage: 2 Mo

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Commission of the European Communities
nuclear science
and technology
Laser-induced photoacoustic spectroscopy
for the speciation of transuranic elements
in natural aquatic systems
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Report
EUR 13180 EN 5
Commission of the European Communities
Laser-induced photoacoustic spectroscopy
for the speciation of transuranic elements
in natural aquatic systems
J. I. Kim, R. Stumpe, R. Klenze
Technische Universität München
Institut für Radiochemie
D-8046 Garching
PARL EUROP. Biblioth.
N.C./COM35555
CL
Final report
Work carried out under cost-sharing contract No FI1W/0202-D
with the European Atomic Energy Community
in the framework of its third R&D programme on
'Management and storage of radioactive waste',
Part A, Task 4, 'Geological disposal studies'
Directorate-General
Science, Research and Development
EUR 13180 EN 1991 '7 Published by the
COMMISSION OF THE EUROPEAN COMMUNITIES
Directorate-General
Telecommunications, Information Industries and Innovation
L-2920 Luxembourg
LEGAL NOTICE
Neither the Commission of the European Communities nor any person acting
on behalf of then is responsible for the use which might be made of
the following information
Cataloguing data can be found at the end of this publication
Luxembourg: Office for Official Publications of the European Communities, 1991
ISBN 92-826-2159-6 Catalogue number: CD-NA-13180-EN-C
© ECSC-EEC-EAEC, Brussels · Luxembourg, 1991
Printed in Belgium SUMMARY
Laser-induced Photoacoustic Spectroscopy (LPAS) is a new elegant in­
strumentation for the chemical speciation of aquatic transuranium
(TRU) ions in very dilute concentrations (> 10"8 mol L"1)· The paper
describes the principle of LPAS and its application to the study of
the chemical behaviour of TRU ions in natural aquatic systems, the
knowledge of which has become increasingly in demand in connection
with the safety analysis of nuclear waste disposal in the geosphere.
The first part of the paper describes the principle, instrumentation
and characteristics of LPAS in aqueous solution, taking particular
examples from our own experience. The theoretical estimation of the
speciation sensitivity is demonstrated and the result is compared
with experiment. The second part deals with the spectral work in aque­
ous solution and then with the application of LPAS for the speciation
of TRU ions in groundwater. Some examples demonstrated are hydrolysis
reaction, complexation and colloid generation of the Am3+ ion. Specia­
tion sensitivities of U, Np, Pu and Am of different oxidation states
in a variety of aqueous solutions are summarized. The application is
of course open to a broad field of microchemistry in which the conven­
tional spectrophotometry method has difficulty with sensitivity.
Ill -CONTENTS
Page
SUMMARY 111
1. INTRODUCTION 1
2. LASER-INDUCED PHOTOACOUSTIC SPECTROSCOPY (LPAS) 3
2.1 General description 3
2.2 Measuring principle 6
2.3 Theoretical description 10
2.4 Piezoelectric detection5
2.5 Calculation ofn limit9
3. INSTRUMENTATION OF SPECTROSCOPY 23
3.1 Apparatus 2
3.2 Piezoelectric detector and photoacoustic cell 28
3.3 Variation of Instrumentation 31
3.3.1 Dual beam single detector system2
3.3.2 Instrumentation for high temperature experiment 3
3.3.3 Dual beam two detector system8
4. CHARACTERIZATION OF SPECTROSCOPIC OPERATION 43
4.1 Data processing 4
4.2 Calibration of signal magnitude5
4.3 Correlation of PA signal to laser pulse energy 47
4.4 Difference method for background compensation8
4.5 Correlation of PA signal to absorber concentration 50
4.6 Simultaneous calibration by a reference standard5 5. APPLICATION TO AQUEOUS SOLUTION 55
5.1 Speciation sensitivity7
5.2 Hydrolysis reactions of Am9
5.3 Carbonate complexation of Am 62
5.4 Humaten of Am5
5.5 High temperature experiment
5.6 Other investigations
6. APPLICATION TO NATURAL AQUIFER SOLUTION 70
6.1 Speciation of Am (III) in groundwater
6.2n of Am-pseudocolloids in groundwater2
6.3 Speciation of Am in saline groundwater 76
7. REFERENCES 81
- V! 1. Introduction
A growing interest has been directed recently to the application of
photoacoustic sensing techniques to the spectroscopic analysis of
various optical absorbers in very dilute concentrations. For this
purpose a laser is commonly used as a light source. Since the dis­
covery of the photoacoustic effect by A.G. Bell in 1880 [1], its ap­
plication has a long history of development [2]. Renewed interest in
photoacoustics has emerged starting with the work of Kreuzer in 1971
[3] who analysed trace amounts of gas molecules by laser­induced photo­
acoustic generation. The theory, instrumentation and application of
laser­induced photoacoustic generation developed in recent years have
been thoroughly reviewed by Patel and Tarn [4] and more recently by
Tarn [5,6]. Other reviews are also available in the literature from
different authors: Pao [7], Somoano [8], Rosencwaig [9,10], Colles et
al. [11], Kirkbright and Castleden [12], Lyamshev and Sedov [13],
Kinney and Stanley [14], West et al. [15] and Zharov [16].
Because of difficulties involved in handling of radioactive prepara­
tives, the photoacoustic sensing technique had not been applied until
some years ago to the spectroscopy of aqueous actinide ions. Recent­
ly, the authors' laboratory [17­19] has introduced a relatively sim­
ple detection apparatus of photoacoustic spectroscopy for the spec­
tral work of actinide ions using pulsed laser as a light source. This
detection apparatus can be used for radioactive α­emitting aqueous
samples without restriction to corrosive solutions and facilitates
the spectroscopic investigation of actinide solutions, particularly
transuranic ions, in very dilute concentrations [19]. The spectros­
copic system has been, since then, introduced to different nuclear
chemical laboratories and further developed for a variety of applica­
tion purposes [20­23]. Most of these developments are confined prima­
rily to the spectroscopic investigation (i.e. speciation) of actini­
des in very dilute solutions [24­27] or natural aquatic systems [28­
34] in which the solubility of actinides is, in general, very low (<
10"6 mol L"1). Optical spectroscopy of high sensitivity is an indis­
pensable tool for the study of the chemical behaviour of actinides in natural aquatic systems, which has a newly developing research field
in connection with the nuclear waste disposal in the geosphere [28],
For this reason, not only photoacoustic spectroscopy attracts great
attention but also thermal lensing spectroscopy [35-37] and fluores­
cence spectroscopy [21,38-41], all using laser light sources, are in
growing use for the same purpose.
Actinides have particular spectroscopic properties which are charac­
terized primarily by the f*f transitions within the partially filled
5f shell [42] and thus by a number of relatively weak but very sharp
absorption bands. The optical spectra of actinides are characteristic
for their oxidation states, and to a lesser degree dependent upon the
chemical environment of the ion [43]. Thus spectroscopic investiga­
tion provides information on the oxidation state of an actinide ele­
ment [42] and also serves to characterize the chemical states, such
as hydrolysis products [44], various complexes [37,45,46] and col­
loids [29,40]. Hence, laser-induced photoacoustic spectroscopy (LPAS)
with its high sensitivity can be conveniently used for the speciation
of aqueous actinides in very dilute concentrations [17-28].
This paper summarizes the present knowledge on laser-induced photo­
acoustic spectroscopy, as regards theoretical backgrounds, instrumen­
tation and radiochemical applications to particular problems in aqua­
tic actinide chemistry. Since there is no other radiochemical applica­
tion known in the literature, except the measurement of tritium decay
by a acoustic sensing technique [47], the present discussion is lim­
ited to application to actinide chemistry, particularly, in aquatic
systems. The most interesting field of application is and will be the
geochemical study of long-lived radionuclide, namely man-made elements
(transuraniums). The main importance for such a study is not only the
detection of a migrational quantity of radioactivity but also the
characterization of their chemical states and hence their chemical
behaviour in a given aquifer systems. Knowledge of this kind will
facilitates a better prediction of the environmental impact of trans­
urani c elements which are being produced in ever growing quantities
and will be disposed of in the geosphere.
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