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The application of high resolution deuteron-induced prompt γ-ray spectrometry to the analysis of some transition elements
Nuclear
Instruments
and Methods
NIOMI B
in Physics Research B 85 (1994) 142-144
North-Holland
Beam Interactions with Materials 8 Atoms
The application of high resolution deuteron-induced prompt y-ray spectrometry to the analysis of some transition elements M. Peisach b,*, C.A. Pineda a, A.E. Pillay b ’ Van de Graaff Group, National Accelerator Centre, Box 72, Faure,
7131 South Africa b Centre for Applied Chemistry, Chemistry Department, University of the Witwatersrand, P.O. WITS, 2050 South Africa
An assessment has been made deuteron beams of 5 MeV. The originated from (d, n) and (d, p) possibilities of practical application shown by the determination of Co
of the analytical potential of practical nuclear reactions on the transition metals, induced by origin of observed prompt gamma rays was identified. Most of the more intense radiation reactions, but some from (d, (Y) reactions and from Coulomb excitation were noted. The for the determination of transition metals were investigated, and the efficacy of the method was in some standard steels.
1. Introduction The demand for analysis of the transition metals at all levels of concentration is widespread. These metals are widely distributed and occur in almost every matrix ranging from biological samples to specimens from archaeological excavations. Various techniques such as atomic and emission spectrometry, PIXE, XRF and thermal neutron activation have been applied for the determination of these elements. Some of these methods suffer from interferences, matrix effects and timeconsuming sample preparation. The spectrometry of prompt gamma rays with protons [l] and alpha particles [2] have been used for such purposes. This method minimises interferences, and, in particular, is non-destructive. The present study evaluates the analytical potential of deuteron-induced prompt gamma rays from thick targets of the metals of the first transition series.
2. Experimental 2.1. Preparation
of samples
Discs of 13 mm diameter and about 2 mm thick were cut from sheets of the pure metals Ti, V, Fe, Co, Ni, Cu and Zn. Similar discs were prepared from lumps of pure Cr and Mn. The steel samples, which were used for analysis and were cut to similar dimen-
* Corresponding 643 480.
author,
phone
+ 27 21 689 1243, fax + 27 21
0168-583X/94/$07.00 0 1994 - Elsevier SSDI 0168-583X(93)E0443-K
Science
sions, consisted of Standard Reference Materials steel samples obtained from the US National Institute for Standards and Technology, Gaithersburg, Maryland, USA.
2.2. Irradiation
and measurement
The samples were mounted on a vertical ladder [3], remotely controlled by a stepping motor, which enabled each sample in turn to be positioned accurately in the path of the bombarding beam. The ladder fitted into a multi-purpose scattering chamber [4] at the 6 MV Faure Van de Graaff accelerator. The targets were viewed with a horizontally mounted dipstick Ge(Li) detector, protected from excessive neutron damage by layers of paraffin wax about 5 cm thick. Background radiation from the beam tubes was shielded by standard lead bricks. Each target was irradiated with 5 MeV deuterons with beam currents adjusted so that the dead time of measurement did not exceed 15%. The beam diameter was collimated to 6 mm. To minimise activation of the aluminium walls of the scattering chamber, a cylindrical liner of Perspex, with a single entry hole for the beam, was positioned to surround the target area. After the end of the irradiation, the beam was switched off and a second measurement was taken to distinguish between the prompt -y-radiation, and that from radioactivity generated during the bombardment. Thereafter the target was removed and a third measurement was taken to obtain the contribution of the background and any activity generated in the target ladder by neutrons from (d, n) reactions on the target.
B.V. All rights reserved
143
M. Peisach et al. /Nucl. Instr. and Meth. in Phys.Res. B 85 (1994) 142-144
3. Results and discussion
Table 1 Assignments of the gamma rays labelled in Figs. 1 and 2
3.1. Gamma ray spectrometry
Number
deuteron-induced reactions are usually highly exoergic, it was expected that the number of gamma rays observed from each element would be relatively large. Although this was indeed the case, most of the gamma rays were not intense, so that their use for analysis would be limited. As typical examples, the gamma ray energy spectrum from the bombardment of iron is shown in Fig. 1 and that of cobalt in Fig. 2. The more intense peaks in the spectra have been numbered and their assignments are listed in Table 1. Prompt gamma rays are emitted from the product nucleus of a reaction, but the analyst is really concerned with that component of the sample on which the nuciear reaction was carried out. Accordingly, for analytical purposes, it is more meaningful to label spectrum peaks with the target nuelide. In defining the conditions of analysis the nature of the bombarding beam is known and need not be repeated. Thus, the reaction is uniquely identified if the light product particle is also stated. Accordingly the Analysts’ Convention is used for peak assignment [5]. Because
3.2. Possibilities for practical application The gamma ray spectra showed that for every element studied there were some gamma rays sufficiently intense for analytical use. However, the intensity of the background against which a gamma ray has to be measured will determine the sensitivity for analysis. The minimum detection limit (MDL), where qualitative analysis becomes unreliable is given [6] by 1.64&, where C, is the integrated background count over the
Fig. 1. Energy spectrum of the prompt gamma rays obtained from the irradiation of iron with 5 MeV deuterons. The assignments of the numbered peaks are given in Table 1.
Iron
Cobalt
E, [keVl
Assignment
E, [keVl
Assignment
352 511 673 1223 1378 1758 1919 2095
56Fe ~(3, 1) B’ s6Fe n(6,1> *(jFe n(l, Of 56Fe nt2,O) 56Fe n(5,O) 56Fe n(7,O) 56Fe d(4, 1)
230 277 448 467 511 5.56 826 1173 1333
59co
p(3,l) Wo pt2,o) s9co p(5, 11 s9Co n&2) P+ Wo p(7,l) 59Co n(2.1) 59Co n(4,l) -co n(l (0)
energy region of the measured gamma ray. Using this criterion the MDL that could be attained for the transition metals bombarded with 5 MeV deuterons were down to concentration levels of mg/g and are listed in Table 2 for charges of 5 PC and 1 mC and for a matrix of iron-based steels. These values are comparable with sensitivities that could be attained with beams of protons [l] or alpha particles [2]. 3.3. Determination of cobalt As an example of routine analyses, cobalt was determined in some standard steel samples, using the 1333 keV s9Co ml, 01 prompt gamma ray from the bombardment with 5 MeV deuterons and an integrated charge of 5 pC. The results are given in Table 3. Since all the samples were steels, and since the stopping powers of the matrices were very similar, no correction for variation on stopping power was effected. The root mean square error was found to be *0.106% by mass, which reflects the limit of the quantitative analysis. The precision given by the relative standard error was 1.8% for the cobalt concentration range of between about 3 and 12% by mass.
Fig. 2. As Fig. 1, but for cobalt. II. PIXE/PIGE
M. Peisach et al. /Nucl. Imtr. and Meth. in Phys. Res. B 85 (1994) 142-144
144 Table 2 Minimum rays Element
4. Conclusions detection
limits (MDL)
E,
for some
Identity
V
Cr
Mn Fe
Co
Ni
CU Zn
153 595 1585 936 1334 1434 378 564 1290 847 1238 352 1224 1378 826 1173 1333 283 339 878 992 1039 359 752
48Ti n(2,O) 48Ti n(3,2) 48Ti p(3,Ol ‘iv n(2, 1) “V n(4, 1) ‘lV ml, 0) ‘*Cr ml, 0) “Cr p&O) “Cr p(3,O) 55Mn n(1, 0) 55Mn n(2, 1) 56Fe ~(3, 11 56Fe ml, 01 56Fe n(2,O) 59Co n(2,l) s9Co n(4,l) 59Co ml, 0) 60Ni p(2,O) 58Ni ~(1, 0) “Ni p(3,O) 63Cu ml, 0) “Cu ml, 0) @Zn n(2,O) @Zn 1X6,2) 64Zn n(5, 1) @Zn p(7,Ol 64Zn n(4,O)
911
5cLC
1mC
7.1 14.6 9.6 3.8 4.3 0.6 3.0 9.6 7.7 1.6 3.3 4.9 8.4 5.5 7.3 4.0 1.8 6.5 3.6 5.7 2.8 4.5 19.5 21.1
0.51 1.03 0.68 0.27 0.31 0.04 0.21 0.68 0.54 0.11 0.23 0.35 0.60 0.39 0.52 0.28 0.12 0.46 0.26 0.40 0.20 0.32 1.38 1.50
22.1
1.56
Table 3 Determination of cobalt in some standard keV, Charge = 5 uC, Ed = 5 MeV Steel
Count
gamma
MDL hWg1
LkeVl Ti
prompt
Known
Found
[%I
[%I
2.9 4.9 7.8 11.8
2.92 4.77 7.72 11.90
steels,
E, = 1333
Error
Relative error
+ 0.02 -0.13 - 0.08 + 0.10
0.68 2.65 1.03 0.85
[%I D D D D
837 838 839 840
5031 8316 13544 20982
Root mean square
error = 1.75%
It has been shown that prompt photon spectrometry during bombardment with deuterons of a few MeV can usefully be applied to the determination of the transition metals in a matrix such as steel. Moreover, a single bombardment will supply information on the content of every transition metal in the sample where their concentrations exceed 10m3 g/g. Analyses are non-destructive, require little sample preparation and can be carried out relatively quickly. The duration of the bombardment will depend on the beam current, the metal content of the sample and the relative precision required.
Acknowledgements
The helpful cooperation of the staff of the Faure Van De Graaff accelerator of the National Accelerator Centre is gratefully acknowledged. The South African Foundation for Research Development is thanked for financial assistance.
References [l] D. Gihwala and M. Peisach, J. Radioanal. Chem. 70 (1982) 287. [2] IS. Giles and M. Peisach, J. Radioanal. Chem. 50 (1979) 307. [3] M. Peisach, Nucl. Instr. and Meth. B 14 (1986) 99. [4] IS. Giles and M. Peisach, J. Radioanal. Chem. 32 (1976) 105. [5] M. Peisach, Radiochem. Radioanal. Lett. 8 (1971) 119; J. Radioanal. Chem. 12 (1972) 251; Z.B. Alfassi (ed.), Activation Analysis (CRC press, Boca Raton, FL, USA, 1990) p. 151. [6] L.A. Currie, Anal. Chem. 40 (1968) 586.
Instruments
and Methods
NIOMI B
in Physics Research B 85 (1994) 142-144
North-Holland
Beam Interactions with Materials 8 Atoms
The application of high resolution deuteron-induced prompt y-ray spectrometry to the analysis of some transition elements M. Peisach b,*, C.A. Pineda a, A.E. Pillay b ’ Van de Graaff Group, National Accelerator Centre, Box 72, Faure,
7131 South Africa b Centre for Applied Chemistry, Chemistry Department, University of the Witwatersrand, P.O. WITS, 2050 South Africa
An assessment has been made deuteron beams of 5 MeV. The originated from (d, n) and (d, p) possibilities of practical application shown by the determination of Co
of the analytical potential of practical nuclear reactions on the transition metals, induced by origin of observed prompt gamma rays was identified. Most of the more intense radiation reactions, but some from (d, (Y) reactions and from Coulomb excitation were noted. The for the determination of transition metals were investigated, and the efficacy of the method was in some standard steels.
1. Introduction The demand for analysis of the transition metals at all levels of concentration is widespread. These metals are widely distributed and occur in almost every matrix ranging from biological samples to specimens from archaeological excavations. Various techniques such as atomic and emission spectrometry, PIXE, XRF and thermal neutron activation have been applied for the determination of these elements. Some of these methods suffer from interferences, matrix effects and timeconsuming sample preparation. The spectrometry of prompt gamma rays with protons [l] and alpha particles [2] have been used for such purposes. This method minimises interferences, and, in particular, is non-destructive. The present study evaluates the analytical potential of deuteron-induced prompt gamma rays from thick targets of the metals of the first transition series.
2. Experimental 2.1. Preparation
of samples
Discs of 13 mm diameter and about 2 mm thick were cut from sheets of the pure metals Ti, V, Fe, Co, Ni, Cu and Zn. Similar discs were prepared from lumps of pure Cr and Mn. The steel samples, which were used for analysis and were cut to similar dimen-
* Corresponding 643 480.
author,
phone
+ 27 21 689 1243, fax + 27 21
0168-583X/94/$07.00 0 1994 - Elsevier SSDI 0168-583X(93)E0443-K
Science
sions, consisted of Standard Reference Materials steel samples obtained from the US National Institute for Standards and Technology, Gaithersburg, Maryland, USA.
2.2. Irradiation
and measurement
The samples were mounted on a vertical ladder [3], remotely controlled by a stepping motor, which enabled each sample in turn to be positioned accurately in the path of the bombarding beam. The ladder fitted into a multi-purpose scattering chamber [4] at the 6 MV Faure Van de Graaff accelerator. The targets were viewed with a horizontally mounted dipstick Ge(Li) detector, protected from excessive neutron damage by layers of paraffin wax about 5 cm thick. Background radiation from the beam tubes was shielded by standard lead bricks. Each target was irradiated with 5 MeV deuterons with beam currents adjusted so that the dead time of measurement did not exceed 15%. The beam diameter was collimated to 6 mm. To minimise activation of the aluminium walls of the scattering chamber, a cylindrical liner of Perspex, with a single entry hole for the beam, was positioned to surround the target area. After the end of the irradiation, the beam was switched off and a second measurement was taken to distinguish between the prompt -y-radiation, and that from radioactivity generated during the bombardment. Thereafter the target was removed and a third measurement was taken to obtain the contribution of the background and any activity generated in the target ladder by neutrons from (d, n) reactions on the target.
B.V. All rights reserved
143
M. Peisach et al. /Nucl. Instr. and Meth. in Phys.Res. B 85 (1994) 142-144
3. Results and discussion
Table 1 Assignments of the gamma rays labelled in Figs. 1 and 2
3.1. Gamma ray spectrometry
Number
deuteron-induced reactions are usually highly exoergic, it was expected that the number of gamma rays observed from each element would be relatively large. Although this was indeed the case, most of the gamma rays were not intense, so that their use for analysis would be limited. As typical examples, the gamma ray energy spectrum from the bombardment of iron is shown in Fig. 1 and that of cobalt in Fig. 2. The more intense peaks in the spectra have been numbered and their assignments are listed in Table 1. Prompt gamma rays are emitted from the product nucleus of a reaction, but the analyst is really concerned with that component of the sample on which the nuciear reaction was carried out. Accordingly, for analytical purposes, it is more meaningful to label spectrum peaks with the target nuelide. In defining the conditions of analysis the nature of the bombarding beam is known and need not be repeated. Thus, the reaction is uniquely identified if the light product particle is also stated. Accordingly the Analysts’ Convention is used for peak assignment [5]. Because
3.2. Possibilities for practical application The gamma ray spectra showed that for every element studied there were some gamma rays sufficiently intense for analytical use. However, the intensity of the background against which a gamma ray has to be measured will determine the sensitivity for analysis. The minimum detection limit (MDL), where qualitative analysis becomes unreliable is given [6] by 1.64&, where C, is the integrated background count over the
Fig. 1. Energy spectrum of the prompt gamma rays obtained from the irradiation of iron with 5 MeV deuterons. The assignments of the numbered peaks are given in Table 1.
Iron
Cobalt
E, [keVl
Assignment
E, [keVl
Assignment
352 511 673 1223 1378 1758 1919 2095
56Fe ~(3, 1) B’ s6Fe n(6,1> *(jFe n(l, Of 56Fe nt2,O) 56Fe n(5,O) 56Fe n(7,O) 56Fe d(4, 1)
230 277 448 467 511 5.56 826 1173 1333
59co
p(3,l) Wo pt2,o) s9co p(5, 11 s9Co n&2) P+ Wo p(7,l) 59Co n(2.1) 59Co n(4,l) -co n(l (0)
energy region of the measured gamma ray. Using this criterion the MDL that could be attained for the transition metals bombarded with 5 MeV deuterons were down to concentration levels of mg/g and are listed in Table 2 for charges of 5 PC and 1 mC and for a matrix of iron-based steels. These values are comparable with sensitivities that could be attained with beams of protons [l] or alpha particles [2]. 3.3. Determination of cobalt As an example of routine analyses, cobalt was determined in some standard steel samples, using the 1333 keV s9Co ml, 01 prompt gamma ray from the bombardment with 5 MeV deuterons and an integrated charge of 5 pC. The results are given in Table 3. Since all the samples were steels, and since the stopping powers of the matrices were very similar, no correction for variation on stopping power was effected. The root mean square error was found to be *0.106% by mass, which reflects the limit of the quantitative analysis. The precision given by the relative standard error was 1.8% for the cobalt concentration range of between about 3 and 12% by mass.
Fig. 2. As Fig. 1, but for cobalt. II. PIXE/PIGE
M. Peisach et al. /Nucl. Imtr. and Meth. in Phys. Res. B 85 (1994) 142-144
144 Table 2 Minimum rays Element
4. Conclusions detection
limits (MDL)
E,
for some
Identity
V
Cr
Mn Fe
Co
Ni
CU Zn
153 595 1585 936 1334 1434 378 564 1290 847 1238 352 1224 1378 826 1173 1333 283 339 878 992 1039 359 752
48Ti n(2,O) 48Ti n(3,2) 48Ti p(3,Ol ‘iv n(2, 1) “V n(4, 1) ‘lV ml, 0) ‘*Cr ml, 0) “Cr p&O) “Cr p(3,O) 55Mn n(1, 0) 55Mn n(2, 1) 56Fe ~(3, 11 56Fe ml, 01 56Fe n(2,O) 59Co n(2,l) s9Co n(4,l) 59Co ml, 0) 60Ni p(2,O) 58Ni ~(1, 0) “Ni p(3,O) 63Cu ml, 0) “Cu ml, 0) @Zn n(2,O) @Zn 1X6,2) 64Zn n(5, 1) @Zn p(7,Ol 64Zn n(4,O)
911
5cLC
1mC
7.1 14.6 9.6 3.8 4.3 0.6 3.0 9.6 7.7 1.6 3.3 4.9 8.4 5.5 7.3 4.0 1.8 6.5 3.6 5.7 2.8 4.5 19.5 21.1
0.51 1.03 0.68 0.27 0.31 0.04 0.21 0.68 0.54 0.11 0.23 0.35 0.60 0.39 0.52 0.28 0.12 0.46 0.26 0.40 0.20 0.32 1.38 1.50
22.1
1.56
Table 3 Determination of cobalt in some standard keV, Charge = 5 uC, Ed = 5 MeV Steel
Count
gamma
MDL hWg1
LkeVl Ti
prompt
Known
Found
[%I
[%I
2.9 4.9 7.8 11.8
2.92 4.77 7.72 11.90
steels,
E, = 1333
Error
Relative error
+ 0.02 -0.13 - 0.08 + 0.10
0.68 2.65 1.03 0.85
[%I D D D D
837 838 839 840
5031 8316 13544 20982
Root mean square
error = 1.75%
It has been shown that prompt photon spectrometry during bombardment with deuterons of a few MeV can usefully be applied to the determination of the transition metals in a matrix such as steel. Moreover, a single bombardment will supply information on the content of every transition metal in the sample where their concentrations exceed 10m3 g/g. Analyses are non-destructive, require little sample preparation and can be carried out relatively quickly. The duration of the bombardment will depend on the beam current, the metal content of the sample and the relative precision required.
Acknowledgements
The helpful cooperation of the staff of the Faure Van De Graaff accelerator of the National Accelerator Centre is gratefully acknowledged. The South African Foundation for Research Development is thanked for financial assistance.
References [l] D. Gihwala and M. Peisach, J. Radioanal. Chem. 70 (1982) 287. [2] IS. Giles and M. Peisach, J. Radioanal. Chem. 50 (1979) 307. [3] M. Peisach, Nucl. Instr. and Meth. B 14 (1986) 99. [4] IS. Giles and M. Peisach, J. Radioanal. Chem. 32 (1976) 105. [5] M. Peisach, Radiochem. Radioanal. Lett. 8 (1971) 119; J. Radioanal. Chem. 12 (1972) 251; Z.B. Alfassi (ed.), Activation Analysis (CRC press, Boca Raton, FL, USA, 1990) p. 151. [6] L.A. Currie, Anal. Chem. 40 (1968) 586.