- Email: [email protected]
Multielement instrumental activation analysis based on gamma–gamma coincidence spectroscopy
Analytica Chimica Acta 386 (1999) 181±189
Multielement instrumental activation analysis based on gamma±gamma coincidence spectroscopy M. VobeckyÂa,*, J. JakuÊbekb, C. Granja Bustamanteb, J. KonõÂcÏekb, J. PluharÏc, S. PospõÂsÏilb, L. RubaÂcÏekb a Institute of Analytical Chemistry, Academy of Sciences of the Czech Republic, CZ ± 142 20, Praha 4, Czech Republic Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, CZ ± 115 19, Praha 1, Czech Republic c National Veterinary Institute, CZ ± 165 03, Praha 6, Czech Republic
b
Received 14 August 1998; received in revised form 10 December 1998; accepted 14 December 1998
Abstract The methodology of the coincidence instrumental activation analysis (CIAA) based on the three-parameter gamma±gamma coincidence spectrometer with two high-purity germanium (HPGe) detectors is presented. The ¯exible coincidence system was built on NIM spectrometric modules connected to VME or CAMAC data acquisition system, respectively. First results of the application of CIAA for the determination of scandium, cobalt, cesium or iridium contents by means of neutron irradiation are presented. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Trace element analysis; Gamma spectroscopy; Gamma cascades; HPGe detectors; Coincidence techniques; Energy interferences; Instrumental neutron activation analysis
1. Introduction The main advantages of instrumental activation analysis (IAA) in combination with high resolution gamma-ray spectroscopy are the nondestructive procedure and the possibility of simultaneous multielemental determination. These contributed mainly to its extensive application in trace element analysis. Despite the very good energy resolution of germanium detectors, undesirable energy interferences can signi®cantly suppress the capability of IAA, in particular its accuracy in case of the determination of elements at very low concentrations. In the case of measurements *Corresponding author. Fax: 420-2-44472277.
of radionuclides which emit positrons and/or coinciding gamma-rays in cascade, these energy interferences can be suppressed by the application of a coincidence technique. This technique has been previously used and published [1±5]. However, it was limited by the small range of memory (up to 128 by 128 channels) available to store all coincidence events. This limitation was recently overcome by building ¯exible threeparameter gamma±gamma coincidence system [6] with two HPGe (high-purity germanium) detectors which uses NIM (nuclear instrumentation modules) spectrometric modules to VME (Versa module Eurocard) or CAMAC (computer automated measurement and control) standard modules controlled by a com-
0003-2670/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S0003-2670(99)00005-7
182
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
puter for data acquisition. This enables us to store all spectrometric data as measured, event by event. In the current paper the ®rst results of the application of coincidence instrumental activation analysis (CIAA) for the determination of scandium, cobalt, cesium and iridium are presented. 2. Experimental 2.1. Standards and materials, irradiation For the calibration single and multielemental standards were used in this study. For elemental standards preparation, high-purity substances in elemental form or stoichiometrically de®ned stable compounds were used according to previously formulated principles [7,8]. The well-de®ned volume of standard solution was pipetted onto a 10 mm ®lter paper disc, dried and sealed between two polyethylene discs of 25 mm in diameter. The standards and samples were overwrapped with thin aluminium foil for neutron irradiation. In addition we also used three reference materials: Oriental Tobacco Leaves CTA-OTL-1, Institute of Nuclear Chemistry and Technology, Poland; Tea GBW 07604 (GSV-4), Institute of Geophysical and Geochemical Exploration, China; Auto Used Catalyst SRM 2556, National Institute of Standards and Technology, USA. A determination of the element content in analyzed samples was done by comparison of analytical responses of the sample to the elemental standard with an accurately known quantity of the element of interest (the so-called comparative method). The samples and standards were irradiated and measured under the same condition. Activation of samples and standards was carried out in the core of an experimental nuclear reactor LWR-15 Ï ezÏ near Prague) operat(Nuclear Research Institute, R ing at 10 MW output for 2 or 5 h. 2.2. Instrumentation The gamma±gamma coincidence system with two HPGe detectors can operate in two modes, the coincidence mode for CIAA studies, and in the single detector mode for conventional, noncoincidence IAA [6].
The analog part of the coincidence system is based on traditional gamma-spectroscopic and fast/slow NIM modules. Two analog-to-digital converters (ADC) give information about pulse heights, corresponding to the energies the detectors are exposed to. A time-to-amplitude converter (TAC) connected to the third ADC determines the time difference between the detectors signals. Resolutions of both HPGe detectors are 2.0 keV (full width at half maximum at 1.33 MeV), relative ef®ciencies are approximately 20%. The time resolution, as obtained with 22 Na, is 25 ns. An interface between three ADCs and a computer is built in two versions. One, based on standard NIM ADCs connected to a VME crate via simple VME-BVM I/O cards and the other in which CAMAC ADCs are used connected to a Pentium class PC. The VME crate is controlled by a CES-FIC 8234 computer with a Motorola 68040 processor or by a HP 743 workstation. The total system throughput at high resolution is about 25 000 events per second. For each coincidence event, pulse-height information from all three ADCs is stored in an event-by-event ®le on a disk and can be analyzed in off-line or on-line regime. This makes it possible to de®ne a set of conditions on amplitudes and time differences of detected events. In such a way a sum-coincidence technique, coincidence under conditions on pulse height, etc., can be applied. This provides different possibilities of evaluation of coincidence event data by setting conditions on the energies of the pair of coinciding photons. Using the VME controller makes it possible to control measurements via Telnet across Internet. For a more detailed description of the technique see [6]. 3. Results and discussion The determination of some elements using activation analysis is based on measuring characteristic gamma-rays which are emitted after decays of activated radionuclides. If some gamma-rays are emitted in cascades, it is possible to eliminate energy interferences, which often takes place in the gamma spectra of mixtures of radionuclides. The decay scheme of 46 Sc radionuclide (see Fig. 1) gives an example of such a cascade of two gamma photons with energies 889.28 and 1120.55 keV.
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
Fig. 1. Decay scheme of
To assess the analytical applicability of coincidence instrumental neutron activation analysis (CINAA), analytical responses of conventional instrumental and coincidence methods have been compared for analytical gamma lines of some elements. The experimental ratios of spectral gamma yields of conventional and coincidence methods (conv/coinc) for studied radionuclides (activated in the core of LWR-15 reactor) are presented in Table 1 together with their halflives and intensities of analytical lines. The same radionuclides are ordered in Table 2 according to energies of coinciding lines. Analytical applicability of CINAA is illustrated by the determination of scandium, cobalt and cesium in reference materials of plant origin (Oriental Tobacco Leaves CTA-OTL-1 and Tea GBW 07605 (GSW-4)), see Table 3. One ®nds a good agreement of values of determined elements with certi®ed ones for these reference materials. As was discussed above, the application of the coincidence technique decreases signi®cantly the probability of energy interference of analytical lines of different elements. Nevertheless, a nonzero probability of energy interference between coinciding lines still remains. Some of such examples can be found in Table 2. The effect of energy interference can be demonstrated with the determination of iridium in a catalyst of output gas of engine of motorcar, which represents quite complicated elemental matrix. A single detector spectrum of Auto Used Catalyst NIST 2556 is dis-
46
183
Sc radionuclide.
Table 1 Ratio of gamma yieldsa measured by conventional and gamma± gamma coincidence spectroscopy method (ordered according to atomic numbers) Radionuclide
Half-lifeb,c
Gamma line (keV)b
Relative intensity (%)b
46
Sc
83.79 d
889.28 1120.55
99.98 99.99
21.53 20.94
59
Fe
44.503 d
142.65 192.35 1099.25 1291.60
1.02 3.08 56.50 43.20
14.05 9.66 88.53 246.57
58
Cod
70.82 d
510.99 810.78
100.00 99.45
1.50 183.34
60
Co
1173.24 1332.50
99.90 99.98
22.47 22.02
75
Se
119.779 d
121.12 136.00 198.61 264.66 279.54 400.66
17.14 58.27 1.47 58.50 24.79 11.37
112.24 62.12 44.35 38.98 89.30 1197.71
82
Br
35.30 h
221.48 273.48 554.35 606.37 619.72 698.37 776.52 827.83
2.26 0.80 70.72 1.21 43.42 28.47 83.50 24.02
10.55 11.61 9.62 1.79 8.13 6.50 8.41 8.94
5.2714 y
Yields ratio (conv/coinc)
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
184 Table 1 (Continued ) Radionuclide
Half-lifeb,c
Table 1 (Continued ) Gamma line (keV)b
Relative intensity (%)b
952.02 1007.59 1044.00 1081.29 1317.47 1474.88 1650.37 1871.60
0.37 1.27 27.22 0.62 26.47 16.31 0.74 0.03
8.49 10.79 8.38 8.42 9.73 8.99 6.08 14.22
65.94 h
140.51 181.06 352.90 739.50 777.92
4.52 6.08 0.00 12.13 4.28
1362.90 51.70 315.25 35.89 213.00
249.79 d
446.81 620.36 657.76 677.62 687.02 706.68 744.28 763.94 818.03 884.69 937.49 1384.30 1475.79 1505.04
3.72 2.79 94.00 10.28 6.39 16.33 4.70 22.14 7.29 72.19 34.13 24.12 3.97 12.95
6.76 5.77 9.45 6.39 8.29 8.92 9.04 10.01 6.07 9.49 9.45 11.70 11.46 13.39
In
49.51 d
558.43 725.24
4.39 4.39
20.58 20.18
126 e
I
13.11 d
388.63 510.99 666.33
34.09 100.00 33.10
231.59 33.29 121.03
131
Ba
11.50 d
123.81 133.61 249.43 496.33
28.97 2.12 2.81 46.80
9.89 5.81 4.45 7.78
134
Cs
475.35 563.23 569.32 604.70 795.85 801.93 1365.15
1.46 8.38 15.43 97.56 85.44 8.73 3.04
11.48 10.36 9.87 16.93 17.14 10.73 21.14
147
Nd
91.11 120.48
27.90 0.40
3191.62 281.92
99
Mo
110m
114
Ag
2.062 y
10.98 d
Yields ratio (conv/coinc)
Radionuclide
Half-lifeb,c
Gamma line (keV)b
Relative intensity (%)b
Yields ratio (conv/coinc)
196.64 275.37 319.41 398.16
0.20 0.80 1.95 0.87
58.36 26.38 45.04 100.10
152
Eu
13.542 y
121.78 244.70 271.14 295.94 344.28 367.79 411.12 443.98 488.66 564.02 586.29 674.68 678.58 688.68 719.35 756.12 778.90 841.59 867.39 919.40 926.32 964.13 1085.91 1089.70 1112.12 1212.95 1299.12 1408.01 1457.63
28.42 7.49 0.07 0.44 26.58 0.83 2.23 2.78 0.41 0.49 0.46 0.19 0.46 0.83 0.33 0.01 12.96 0.16 4.15 0.44 0.27 14.34 9.91 1.71 13.54 1.40 1.63 20.87 0.49
72.77 22.01 36.57 18.55 30.18 13.29 12.56 17.27 13.12 19.72 12.38 19.86 13.83 30.03 13.66 28.47 20.60 15.30 16.16 15.28 17.84 45.50 113.95 25.30 70.70 14.12 13.69 59.16 66.77
160
Tb
72.3 d
197.04 215.65 298.58 309.56 337.32 392.51 682.31 765.28 879.38 962.32 966.17 1002.88 1115.12 1177.96 1271.88
5.20 4.00 25.51 0.86 0.34 1.34 0.61 2.13 30.01 9.91 25.21 1.04 1.58 15.07 7.46
29.14 26.57 23.17 23.72 17.52 20.00 11.89 15.47 39.89 41.67 34.17 20.63 22.94 233.30 249.34
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189 Table 1 (Continued ) Radionuclide
Half-lifeb,c
169
32.026 d
Yb
Gamma line (keV)b
Relative intensity (%)b
Yields ratio (conv/coinc)
109.78 117.38 130.52 177.21 197.96 261.08 307.74
17.37 0.04 11.25 22.04 35.60 1.71 10.00
140.33 150.49 103.51 138.34 193.96 179.36 820.38
181
Hf
42.39 d
133.02 136.26 136.86 345.93 482.18
43.31 5.85 0.86 15.12 80.50
76.52 52.98 52.98 48.07 85.66
182
Ta
114.43 d
100.11 113.67 116.42 152.43 156.39 179.39 198.35 222.11 229.32 264.08 927.99 959.73 1001.70 1121.30 1189.05 1221.41 1231.02
14.10 1.88 0.43 6.93 2.64 3.08 1.44 7.49 3.63 3.61 0.62 0.35 2.07 34.90 16.23 26.98 11.44
117.24 87.36 47.17 54.70 48.12 34.55 45.93 31.43 22.36 25.92 18.54 12.48 14.16 74.23 105.90 90.37 31.71
192
Ir
295.96 308.46 316.51 468.07
28.67 30.00 82.81 47.83
24.87 17.27 21.31 19.76
73.831 d
a
Defined as peak area. Data from [9]. c d ± day, y ± year. d Product of 58 Ni n; p reaction. e Product of 127 I n; 2n reaction. b
played in Fig. 2(a). The corresponding coincidence spectrum is given in Fig. 2(b), which is still rather complicated. There, the analytical peak of iridium 192 Ir at 296 keV is in¯uenced by the peaks of 152 Eu and 160 Tb. The contributions of interfering peaks to the 296 keV peak of 192 Ir have been revealed using the so-called ``net peak'' coincidence procedure. The ``net peak'' coincidence spectrum can be generated from
185
Table 2 Ratio of gamma yieldsa measured by conventional and gamma± gamma coincidence spectroscopy method (ordered according to photon energies) Gamma line (keV)b
Radionuclide
Half-lifeb,c
Relative intensity (%)b
Yields ratio (conv/coinc)
91.11 100.11 109.78 113.67 116.42 117.38 120.48 121.12 121.78 123.81 130.52 133.02 133.61 136.00 136.26 136.86 140.51 142.65 152.43 156.39 177.21 179.39 181.06 192.35 196.64 197.04 197.96 198.35 198.61 215.65 221.48 222.11 229.32 244.70 249.43 261.08 264.08 264.66 271.14 273.48 275.37 279.54 295.94 295.96 298.58 307.74 308.46 309.56 316.51
147
10.98 d 114.43 d 32.026 d 114.43 d 114.43 d 32.026 d 10.98 d 119.779 d 13.542 y 11.50 d 32.026 d 42.39 d 11.50 d 119.779 d 42.39 d 42.39 d 65.94 h 44.503 d 114.43 d 114.43 d 32.026 d 114.43 d 65.94 h 44.503 d 10.98 d 72.3 d 32.026 d 114.43 d 119.779 d 72.3 d 35.30 h 114.43 d 114.43 d 13.542 y 11.50 d 32.026 d 114.43 d 119.779 d 13.542 y 35.30 h 10.98 d 119.779 d 13.542 y 73.831 d 72.3 d 32.026 d 73.831 d 72.3 d 73.831 d
27.90 14.10 17.37 1.88 0.43 0.04 0.40 17.14 28.42 28.97 11.25 43.31 2.12 58.27 5.85 0.86 4.52 1.02 6.93 2.64 22.04 3.08 6.08 3.08 0.20 5.20 35.60 1.44 1.47 4.00 2.26 7.49 3.63 7.49 2.81 1.71 3.61 58.50 0.07 0.80 0.80 24.79 0.44 28.67 25.51 10.00 30.00 0.86 82.81
3191.62 117.24 140.33 87.36 47.17 150.49 281.92 112.24 72.77 9.89 103.51 76.52 5.81 62.12 52.98 52.98 1362.90 14.05 54.70 48.12 138.34 34.55 51.70 9.66 58.36 29.14 193.96 45.93 44.35 26.57 10.55 31.43 22.36 22.01 4.45 179.36 25.92 38.98 36.57 11.61 26.38 89.30 18.55 24.87 23.17 820.38 17.27 23.72 21.31
Nd Ta 169 Yb 182 Ta 182 Ta 169 Yb 147 Nd 75 Se 152 Eu 131 Ba 169 Yb 181 Hf 131 Ba 75 Se 181 Hf 181 Hf 99 Mo 59 Fe 182 Ta 182 Ta 169 Yb 182 Ta 99 Mo 59 Fe 147 Nd 160 Tb 169 Yb 182 Ta 75 Se 160 Tb 82 Br 182 Ta 182 Ta 152 Eu 131 Ba 169 Yb 182 Ta 75 Se 152 Eu 82 Br 147 Nd 75 Se 152 Eu 192 Ir 160 Tb 169 Yb 192 Ir 160 Tb 192 Ir 182
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
186 Table 2 (Continued )
Table 2 (Continued )
Gamma line (keV)b
Radionuclide
Half-lifeb,c
319.41 337.32 344.28 345.93 352.90 367.79 388.63 392.51 398.16 400.66 411.12 443.98 446.81 468.07 475.35 482.18 488.66 496.33 510.99 510.99 554.35 558.43 563.23 564.02 569.32 586.29 604.70 606.37 619.72 620.36 657.76 666.33 674.68 677.62 678.58 682.31 687.02 688.68 698.37 706.68 719.35 725.24 739.50 744.28 756.12 763.94 765.28 776.52 777.92 778.90 795.85 801.93
147
10.98 d 72.3 d 13.542 y 42.39 d 65.94 h 13.542 y 13.11 d 72.3 d 10.98 d 119.779 d 13.542 y 13.542 y 249.79 d 73.831 d 2.062 y 42.39 d 13.542 y 11.50 d 70.82 d 13.11 d 35.30 h 49.51 d 2.062 y 13.542 y 2.062 y 13.542 y 2.062 y 35.30 h 35.30 h 249.79 d 249.79 d 13.11 d 13.542 y 249.79 d 13.542 y 72.3 d 249.79 d 13.542 y 35.30 h 249.79 d 13.542 y 49.51 d 65.94 h 249.79 d 13.542 y 249.79 d 72.3 d 35.30 h 65.94 h 13.542 y 2.062 y 2.062 y
Nd Tb 152 Eu 181 Hf 99 Mo 152 Eu 126 I 160 Tb 147 Nd 75 Se 152 Eu 152 Eu 110m Ag 192 Ir 134 Cs 181 Hf 152 Eu 131 Ba 58 Co 126 I 82 Br 114 In 134 Cs 152 Eu 134 Cs 152 Eu 134 Cs 82 Br 82 Br 110m Ag 110m Ag 126 I 152 Eu 110m Ag 152 Eu 160 Tb 110m Ag 152 Eu 82 Br 110m Ag 152 Eu 114 In 99 Mo 110m Ag 152 Eu 110m Ag 160 Tb 82 Br 99 Mo 152 Eu 134 Cs 134 Cs 160
Relative intensity (%)b 1.95 0.34 26.58 15.12 0.00 0.83 34.09 1.34 0.87 11.37 2.23 2.78 3.72 47.83 1.46 80.50 0.41 46.80 100.00 100.00 70.72 4.39 8.38 0.49 15.43 0.46 97.56 1.21 43.42 2.79 94.00 33.10 0.19 10.28 0.46 0.61 6.39 0.83 28.47 16.33 0.33 4.39 12.13 4.70 0.01 22.14 2.13 83.50 4.28 12.96 85.44 8.73
Yields ratio (conv/coinc)
Gamma line (keV)b
Radionuclide
Half-lifeb,c
Relative intensity (%)b
45.04 17.52 30.18 48.07 315.25 13.29 231.59 20.00 100.10 1197.71 12.56 17.27 6.76 19.76 11.48 85.66 13.12 7.78 1.50 33.29 9.62 20.58 10.36 19.72 9.87 12.38 16.93 1.79 8.13 5.77 9.45 121.03 19.86 6.39 13.83 11.89 8.29 30.03 6.50 8.92 13.66 20.18 35.89 9.04 28.47 10.01 15.47 8.41 213.00 20.60 17.14 10.73
810.78 818.03 827.83 841.59 867.39 879.38 884.69 889.28 919.40 926.32 927.99 937.49 952.02 959.73 962.32 964.13 966.17 1001.70 1002.88 1007.59 1044.00 1081.29 1085.91 1089.70 1099.25 1112.12 1115.12 1120.55 1121.30 1173.24 1177.96 1189.05 1212.95 1221.41 1231.02 1271.88 1291.60 1299.12 1317.47 1332.50 1365.15 1384.30 1408.01 1457.63 1474.88 1475.79 1505.04 1650.37 1871.60
58
70.82 d 249.79 d 35.30 h 13.542 y 13.542 y 72.3 d 249.79 d 83.79 d 13.542 y 13.542 y 114.43 d 249.79 d 35.30 h 114.43 d 72.3 d 13.542 y 72.3 d 114.43 d 72.3 d 35.30 h 35.30 h 35.30 h 13.542 y 13.542 y 44.503 d 13.542 y 72.3 d 83.79 d 114.43 d 5.2714 y 72.3 d 114.43 d 13.542 y 114.43 d 114.43 d 72.3 d 44.503 d 13.542 y 35.30 h 5.2714 y 2.062 y 249.79 d 13.542 y 13.542 y 35.30 h 249.79 d 249.79 d 35.30 h 35.30 h
99.45 7.29 24.02 0.16 4.15 30.01 72.19 99.98 0.44 0.27 0.62 34.13 0.37 0.35 9.91 14.34 25.21 2.07 1.04 1.27 27.22 0.62 9.91 1.71 56.50 13.54 1.58 99.99 34.90 99.90 15.07 16.23 1.40 26.98 11.44 7.46 43.20 1.63 26.47 99.98 3.04 24.12 20.87 0.49 16.31 3.97 12.95 0.74 0.03
a
Co Ag 82 Br 152 Eu 152 Eu 160 Tb 110m Ag 46 Sc 152 Eu 152 Eu 182 Ta 110m Ag 82 Br 182 Ta 160 Tb 152 Eu 160 Tb 182 Ta 160 Tb 82 Br 82 Br 82 Br 152 Eu 152 Eu 59 Fe 152 Eu 160 Tb 46 Sc 182 Ta 60 Co 160 Tb 182 Ta 152 Eu 182 Ta 182 Ta 160 Tb 59 Fe 152 Eu 82 Br 60 Co 134 Cs 110m Ag 152 Eu 152 Eu 82 Br 110m Ag 110m Ag 82 Br 82 Br 110m
Defined as peak area. Data from [9]. c d ± day, y ± year. b
Yields ratio (conv/coinc) 183.34 6.07 8.94 15.30 16.16 39.89 9.49 21.53 15.28 17.84 18.54 9.45 8.49 12.48 41.67 45.50 34.17 14.16 20.63 10.79 8.38 8.42 113.95 25.30 88.53 70.70 22.94 20.94 74.23 22.47 233.30 105.90 14.12 90.37 31.71 249.34 246.57 13.69 9.73 22.02 21.14 11.70 59.16 66.77 8.99 11.46 13.39 6.08 14.22
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
187
Table 3 Concentration of Sc, Co and Cs determined in the reference materialsa Element
Gamma line (keV)
Oriental Tobacco Leaves CTA-OTL-1
Tea GBW 07605 GSV-4
Measured value
Measured value
Certified value
0.3780.018 0.3680.020
b
(0.38)
0.0910.004 0.0940.005
0.0850.009
1173.24 1332.5
0.8990.034 0.8800.035
0.8790.039
0.2020.012 0.2110.012
0.180.02
563.23 569.32 604.7 795.85 801.93
0.1860.024 0.1850.017 0.1830.008 0.1840.008 0.1820.023
0.1770.022
0.3310.029 0.3080.020 0.2910.014 0.2980.015 0.2600.038
0.290.02
46
Sc ( Sc)
889.28 1120.55
Co (60 Co) Cs (134 Cs)
a
Concentration (mg/kg) Certified value
Oriental Tobacco Leaves CTA-OTL-1 and Tea GBW 07605 GSV-4. Value for information only, not certified.
b
Fig. 2. (a) Single detector spectrum of Auto Used Catalyst NIST 2556. (b) Coincidence spectrum of Auto Used Catalyst NIST 2556.
the event data ®le under the condition that coinciding gamma photons are registered in the second detector in the analytical peak. The ``net peak'' coincidence spectrum, which belongs to the 296 keV peak is displayed in Fig. 3(a). In this simple spectrum, the
peaks of 192 Ir (308.46 and 316.51 keV), 152 Eu (121.78, 244.70, 344.28 and 1112.12 keV) and 160 Tb (878.38 and 966.17 keV) can only be found on a low background. Such a composition of 296 keV is documented in Fig. 3(b)±(d), where ``net peak'' coincidence spec-
188
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
Fig. 3. (a) The ``net 296 keV peak'' coincidence spectrum of Auto Used Catalyst NIST 2556. Peaks which are in coincidence with the 296 keV line (308.46 and 316.51 keV of 192 Ir), (121.78, 244.70, 344.28 and 1112.12 keV of 152 Eu), (878.38 and 966.17 keV of 160 Tb) are marked in the spectrum. (b) The ``net 296 keV peak'' coincidence spectrum measured with iridium standard. (c) The ``net 296 keV peak'' coincidence spectrum measured with europium standard. (d) The ``net 296 keV peak'' coincidence spectrum measured with terbium standard.
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
189
Table 4 Concentration of Ir determined in the reference materiala Gamma line (keV)
Concentration (mg/kg) Conventional
Coincidence
Net 296 keV peak
295.96 308.46 316.51 468.07
0.0440.009 0.0180.005 0.0150.003 0.0170.003
0.0350.002 0.0160.002 0.0170.001 0.0180.004
0.0190.001 0.0190.001
a
NIST 2556.
tra obtained in measurements with 192 Ir, 152 Eu and 160 Tb standards are presented. Then, the determination of iridium in Auto Used Catalyst could be based on the iridium peak (308.46 and 316.51 keV) areas measured in the ``net peak'' coincidence spectrum of 296 keV line without any energy interference. These results are presented in Table 4. 4. Conclusions We demonstrated that the application of the coincidence technique with different kinds of off-line event processing for nondestructive activation analysis decreases the probability of energy interference contribution in the analytical response. In this way a CIAA method gives more accurate results for very low element concentrations. Our ¯exible three parametric coincidence system can be used for coincidence measurements as well as for conventional IAA in the single detector mode. In agreement with the principle of the self-validation philosophy of activation analysis explained in [10], application of both modes (CIAA and IAA) increases the reliability of analytical values for certi®cation of reference materials and for intercomparison analytical studies. Acknowledgements This work has been supported by the Grant Agency of the Czech Republic under Grant project no. 203/95/
0260 ``Coincidence Instrumental Activation Analysis''. References [1] M. VobeckyÂ, L. PavlõÂk, J. BenesÏ, Radiochem. Radioanal. Lett. 29 (1977) 159. [2] Chifang Chai, Jibin Tian, Qinfang Qian, Peiqun Zhang, Qin Xu, Dajun Mao, Biol. Trace Element Res. 43 44 45 (1994) 177. [3] M. VobeckyÂ, J. DeÏdina, L. PavlõÂk, J. ValaÂsÏek, Radiochem. Radioanal. Lett. 38 (1979) 197. [4] L.E. Wangen, E.S. Gladney, W.K. Hensley, Anal. Chem. 52 (1980) 765. [5] G. Meyer, J. Radioanal. Nucl. Chem. Articles 114 (1987) 223. [6] J. JakuÊbek, P. Nuiten, J. PluharÏ, S. PospõÂsÏil, M. SÏinÏor, I. SÏtekl, S. TimorackyÂ, M. VobeckyÂ, Nucl. Instr. Meth. Phys. Res. A 414 (1998) 261. Ï anda, J. Benada, Radioisotopy 14 (1973) [7] M. VobeckyÂ, Z. R 623. Ï anda, M. VobeckyÂ, J. KuncõÂrÏ, J. Benada, J. Radioanal. [8] Z. R Chem. 46 (1978) 95. [9] R.B. Firestone, in: V.S. Shirley (Ed.), Table of Isotopes, 8th ed., Wiley/Interscience, New York, 1996. [10] A.R. Byrne, J. KucÏera, Role of the self-validation principle of NAA in quality assurance of bioenvironmental studies and in the certification of reference materials, in: Harmonization of the Health Related Environmental Measurements Using Nuclear and Isotopic Techniques, Hyderabad, India, 4±7 November, 1996, IAEA-SM-344/8, IAEA, Vienna, 1997, pp. 223±238.
Multielement instrumental activation analysis based on gamma±gamma coincidence spectroscopy M. VobeckyÂa,*, J. JakuÊbekb, C. Granja Bustamanteb, J. KonõÂcÏekb, J. PluharÏc, S. PospõÂsÏilb, L. RubaÂcÏekb a Institute of Analytical Chemistry, Academy of Sciences of the Czech Republic, CZ ± 142 20, Praha 4, Czech Republic Faculty of Nuclear Sciences and Physical Engineering, Czech Technical University, CZ ± 115 19, Praha 1, Czech Republic c National Veterinary Institute, CZ ± 165 03, Praha 6, Czech Republic
b
Received 14 August 1998; received in revised form 10 December 1998; accepted 14 December 1998
Abstract The methodology of the coincidence instrumental activation analysis (CIAA) based on the three-parameter gamma±gamma coincidence spectrometer with two high-purity germanium (HPGe) detectors is presented. The ¯exible coincidence system was built on NIM spectrometric modules connected to VME or CAMAC data acquisition system, respectively. First results of the application of CIAA for the determination of scandium, cobalt, cesium or iridium contents by means of neutron irradiation are presented. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Trace element analysis; Gamma spectroscopy; Gamma cascades; HPGe detectors; Coincidence techniques; Energy interferences; Instrumental neutron activation analysis
1. Introduction The main advantages of instrumental activation analysis (IAA) in combination with high resolution gamma-ray spectroscopy are the nondestructive procedure and the possibility of simultaneous multielemental determination. These contributed mainly to its extensive application in trace element analysis. Despite the very good energy resolution of germanium detectors, undesirable energy interferences can signi®cantly suppress the capability of IAA, in particular its accuracy in case of the determination of elements at very low concentrations. In the case of measurements *Corresponding author. Fax: 420-2-44472277.
of radionuclides which emit positrons and/or coinciding gamma-rays in cascade, these energy interferences can be suppressed by the application of a coincidence technique. This technique has been previously used and published [1±5]. However, it was limited by the small range of memory (up to 128 by 128 channels) available to store all coincidence events. This limitation was recently overcome by building ¯exible threeparameter gamma±gamma coincidence system [6] with two HPGe (high-purity germanium) detectors which uses NIM (nuclear instrumentation modules) spectrometric modules to VME (Versa module Eurocard) or CAMAC (computer automated measurement and control) standard modules controlled by a com-
0003-2670/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S0003-2670(99)00005-7
182
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
puter for data acquisition. This enables us to store all spectrometric data as measured, event by event. In the current paper the ®rst results of the application of coincidence instrumental activation analysis (CIAA) for the determination of scandium, cobalt, cesium and iridium are presented. 2. Experimental 2.1. Standards and materials, irradiation For the calibration single and multielemental standards were used in this study. For elemental standards preparation, high-purity substances in elemental form or stoichiometrically de®ned stable compounds were used according to previously formulated principles [7,8]. The well-de®ned volume of standard solution was pipetted onto a 10 mm ®lter paper disc, dried and sealed between two polyethylene discs of 25 mm in diameter. The standards and samples were overwrapped with thin aluminium foil for neutron irradiation. In addition we also used three reference materials: Oriental Tobacco Leaves CTA-OTL-1, Institute of Nuclear Chemistry and Technology, Poland; Tea GBW 07604 (GSV-4), Institute of Geophysical and Geochemical Exploration, China; Auto Used Catalyst SRM 2556, National Institute of Standards and Technology, USA. A determination of the element content in analyzed samples was done by comparison of analytical responses of the sample to the elemental standard with an accurately known quantity of the element of interest (the so-called comparative method). The samples and standards were irradiated and measured under the same condition. Activation of samples and standards was carried out in the core of an experimental nuclear reactor LWR-15 Ï ezÏ near Prague) operat(Nuclear Research Institute, R ing at 10 MW output for 2 or 5 h. 2.2. Instrumentation The gamma±gamma coincidence system with two HPGe detectors can operate in two modes, the coincidence mode for CIAA studies, and in the single detector mode for conventional, noncoincidence IAA [6].
The analog part of the coincidence system is based on traditional gamma-spectroscopic and fast/slow NIM modules. Two analog-to-digital converters (ADC) give information about pulse heights, corresponding to the energies the detectors are exposed to. A time-to-amplitude converter (TAC) connected to the third ADC determines the time difference between the detectors signals. Resolutions of both HPGe detectors are 2.0 keV (full width at half maximum at 1.33 MeV), relative ef®ciencies are approximately 20%. The time resolution, as obtained with 22 Na, is 25 ns. An interface between three ADCs and a computer is built in two versions. One, based on standard NIM ADCs connected to a VME crate via simple VME-BVM I/O cards and the other in which CAMAC ADCs are used connected to a Pentium class PC. The VME crate is controlled by a CES-FIC 8234 computer with a Motorola 68040 processor or by a HP 743 workstation. The total system throughput at high resolution is about 25 000 events per second. For each coincidence event, pulse-height information from all three ADCs is stored in an event-by-event ®le on a disk and can be analyzed in off-line or on-line regime. This makes it possible to de®ne a set of conditions on amplitudes and time differences of detected events. In such a way a sum-coincidence technique, coincidence under conditions on pulse height, etc., can be applied. This provides different possibilities of evaluation of coincidence event data by setting conditions on the energies of the pair of coinciding photons. Using the VME controller makes it possible to control measurements via Telnet across Internet. For a more detailed description of the technique see [6]. 3. Results and discussion The determination of some elements using activation analysis is based on measuring characteristic gamma-rays which are emitted after decays of activated radionuclides. If some gamma-rays are emitted in cascades, it is possible to eliminate energy interferences, which often takes place in the gamma spectra of mixtures of radionuclides. The decay scheme of 46 Sc radionuclide (see Fig. 1) gives an example of such a cascade of two gamma photons with energies 889.28 and 1120.55 keV.
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
Fig. 1. Decay scheme of
To assess the analytical applicability of coincidence instrumental neutron activation analysis (CINAA), analytical responses of conventional instrumental and coincidence methods have been compared for analytical gamma lines of some elements. The experimental ratios of spectral gamma yields of conventional and coincidence methods (conv/coinc) for studied radionuclides (activated in the core of LWR-15 reactor) are presented in Table 1 together with their halflives and intensities of analytical lines. The same radionuclides are ordered in Table 2 according to energies of coinciding lines. Analytical applicability of CINAA is illustrated by the determination of scandium, cobalt and cesium in reference materials of plant origin (Oriental Tobacco Leaves CTA-OTL-1 and Tea GBW 07605 (GSW-4)), see Table 3. One ®nds a good agreement of values of determined elements with certi®ed ones for these reference materials. As was discussed above, the application of the coincidence technique decreases signi®cantly the probability of energy interference of analytical lines of different elements. Nevertheless, a nonzero probability of energy interference between coinciding lines still remains. Some of such examples can be found in Table 2. The effect of energy interference can be demonstrated with the determination of iridium in a catalyst of output gas of engine of motorcar, which represents quite complicated elemental matrix. A single detector spectrum of Auto Used Catalyst NIST 2556 is dis-
46
183
Sc radionuclide.
Table 1 Ratio of gamma yieldsa measured by conventional and gamma± gamma coincidence spectroscopy method (ordered according to atomic numbers) Radionuclide
Half-lifeb,c
Gamma line (keV)b
Relative intensity (%)b
46
Sc
83.79 d
889.28 1120.55
99.98 99.99
21.53 20.94
59
Fe
44.503 d
142.65 192.35 1099.25 1291.60
1.02 3.08 56.50 43.20
14.05 9.66 88.53 246.57
58
Cod
70.82 d
510.99 810.78
100.00 99.45
1.50 183.34
60
Co
1173.24 1332.50
99.90 99.98
22.47 22.02
75
Se
119.779 d
121.12 136.00 198.61 264.66 279.54 400.66
17.14 58.27 1.47 58.50 24.79 11.37
112.24 62.12 44.35 38.98 89.30 1197.71
82
Br
35.30 h
221.48 273.48 554.35 606.37 619.72 698.37 776.52 827.83
2.26 0.80 70.72 1.21 43.42 28.47 83.50 24.02
10.55 11.61 9.62 1.79 8.13 6.50 8.41 8.94
5.2714 y
Yields ratio (conv/coinc)
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
184 Table 1 (Continued ) Radionuclide
Half-lifeb,c
Table 1 (Continued ) Gamma line (keV)b
Relative intensity (%)b
952.02 1007.59 1044.00 1081.29 1317.47 1474.88 1650.37 1871.60
0.37 1.27 27.22 0.62 26.47 16.31 0.74 0.03
8.49 10.79 8.38 8.42 9.73 8.99 6.08 14.22
65.94 h
140.51 181.06 352.90 739.50 777.92
4.52 6.08 0.00 12.13 4.28
1362.90 51.70 315.25 35.89 213.00
249.79 d
446.81 620.36 657.76 677.62 687.02 706.68 744.28 763.94 818.03 884.69 937.49 1384.30 1475.79 1505.04
3.72 2.79 94.00 10.28 6.39 16.33 4.70 22.14 7.29 72.19 34.13 24.12 3.97 12.95
6.76 5.77 9.45 6.39 8.29 8.92 9.04 10.01 6.07 9.49 9.45 11.70 11.46 13.39
In
49.51 d
558.43 725.24
4.39 4.39
20.58 20.18
126 e
I
13.11 d
388.63 510.99 666.33
34.09 100.00 33.10
231.59 33.29 121.03
131
Ba
11.50 d
123.81 133.61 249.43 496.33
28.97 2.12 2.81 46.80
9.89 5.81 4.45 7.78
134
Cs
475.35 563.23 569.32 604.70 795.85 801.93 1365.15
1.46 8.38 15.43 97.56 85.44 8.73 3.04
11.48 10.36 9.87 16.93 17.14 10.73 21.14
147
Nd
91.11 120.48
27.90 0.40
3191.62 281.92
99
Mo
110m
114
Ag
2.062 y
10.98 d
Yields ratio (conv/coinc)
Radionuclide
Half-lifeb,c
Gamma line (keV)b
Relative intensity (%)b
Yields ratio (conv/coinc)
196.64 275.37 319.41 398.16
0.20 0.80 1.95 0.87
58.36 26.38 45.04 100.10
152
Eu
13.542 y
121.78 244.70 271.14 295.94 344.28 367.79 411.12 443.98 488.66 564.02 586.29 674.68 678.58 688.68 719.35 756.12 778.90 841.59 867.39 919.40 926.32 964.13 1085.91 1089.70 1112.12 1212.95 1299.12 1408.01 1457.63
28.42 7.49 0.07 0.44 26.58 0.83 2.23 2.78 0.41 0.49 0.46 0.19 0.46 0.83 0.33 0.01 12.96 0.16 4.15 0.44 0.27 14.34 9.91 1.71 13.54 1.40 1.63 20.87 0.49
72.77 22.01 36.57 18.55 30.18 13.29 12.56 17.27 13.12 19.72 12.38 19.86 13.83 30.03 13.66 28.47 20.60 15.30 16.16 15.28 17.84 45.50 113.95 25.30 70.70 14.12 13.69 59.16 66.77
160
Tb
72.3 d
197.04 215.65 298.58 309.56 337.32 392.51 682.31 765.28 879.38 962.32 966.17 1002.88 1115.12 1177.96 1271.88
5.20 4.00 25.51 0.86 0.34 1.34 0.61 2.13 30.01 9.91 25.21 1.04 1.58 15.07 7.46
29.14 26.57 23.17 23.72 17.52 20.00 11.89 15.47 39.89 41.67 34.17 20.63 22.94 233.30 249.34
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189 Table 1 (Continued ) Radionuclide
Half-lifeb,c
169
32.026 d
Yb
Gamma line (keV)b
Relative intensity (%)b
Yields ratio (conv/coinc)
109.78 117.38 130.52 177.21 197.96 261.08 307.74
17.37 0.04 11.25 22.04 35.60 1.71 10.00
140.33 150.49 103.51 138.34 193.96 179.36 820.38
181
Hf
42.39 d
133.02 136.26 136.86 345.93 482.18
43.31 5.85 0.86 15.12 80.50
76.52 52.98 52.98 48.07 85.66
182
Ta
114.43 d
100.11 113.67 116.42 152.43 156.39 179.39 198.35 222.11 229.32 264.08 927.99 959.73 1001.70 1121.30 1189.05 1221.41 1231.02
14.10 1.88 0.43 6.93 2.64 3.08 1.44 7.49 3.63 3.61 0.62 0.35 2.07 34.90 16.23 26.98 11.44
117.24 87.36 47.17 54.70 48.12 34.55 45.93 31.43 22.36 25.92 18.54 12.48 14.16 74.23 105.90 90.37 31.71
192
Ir
295.96 308.46 316.51 468.07
28.67 30.00 82.81 47.83
24.87 17.27 21.31 19.76
73.831 d
a
Defined as peak area. Data from [9]. c d ± day, y ± year. d Product of 58 Ni n; p reaction. e Product of 127 I n; 2n reaction. b
played in Fig. 2(a). The corresponding coincidence spectrum is given in Fig. 2(b), which is still rather complicated. There, the analytical peak of iridium 192 Ir at 296 keV is in¯uenced by the peaks of 152 Eu and 160 Tb. The contributions of interfering peaks to the 296 keV peak of 192 Ir have been revealed using the so-called ``net peak'' coincidence procedure. The ``net peak'' coincidence spectrum can be generated from
185
Table 2 Ratio of gamma yieldsa measured by conventional and gamma± gamma coincidence spectroscopy method (ordered according to photon energies) Gamma line (keV)b
Radionuclide
Half-lifeb,c
Relative intensity (%)b
Yields ratio (conv/coinc)
91.11 100.11 109.78 113.67 116.42 117.38 120.48 121.12 121.78 123.81 130.52 133.02 133.61 136.00 136.26 136.86 140.51 142.65 152.43 156.39 177.21 179.39 181.06 192.35 196.64 197.04 197.96 198.35 198.61 215.65 221.48 222.11 229.32 244.70 249.43 261.08 264.08 264.66 271.14 273.48 275.37 279.54 295.94 295.96 298.58 307.74 308.46 309.56 316.51
147
10.98 d 114.43 d 32.026 d 114.43 d 114.43 d 32.026 d 10.98 d 119.779 d 13.542 y 11.50 d 32.026 d 42.39 d 11.50 d 119.779 d 42.39 d 42.39 d 65.94 h 44.503 d 114.43 d 114.43 d 32.026 d 114.43 d 65.94 h 44.503 d 10.98 d 72.3 d 32.026 d 114.43 d 119.779 d 72.3 d 35.30 h 114.43 d 114.43 d 13.542 y 11.50 d 32.026 d 114.43 d 119.779 d 13.542 y 35.30 h 10.98 d 119.779 d 13.542 y 73.831 d 72.3 d 32.026 d 73.831 d 72.3 d 73.831 d
27.90 14.10 17.37 1.88 0.43 0.04 0.40 17.14 28.42 28.97 11.25 43.31 2.12 58.27 5.85 0.86 4.52 1.02 6.93 2.64 22.04 3.08 6.08 3.08 0.20 5.20 35.60 1.44 1.47 4.00 2.26 7.49 3.63 7.49 2.81 1.71 3.61 58.50 0.07 0.80 0.80 24.79 0.44 28.67 25.51 10.00 30.00 0.86 82.81
3191.62 117.24 140.33 87.36 47.17 150.49 281.92 112.24 72.77 9.89 103.51 76.52 5.81 62.12 52.98 52.98 1362.90 14.05 54.70 48.12 138.34 34.55 51.70 9.66 58.36 29.14 193.96 45.93 44.35 26.57 10.55 31.43 22.36 22.01 4.45 179.36 25.92 38.98 36.57 11.61 26.38 89.30 18.55 24.87 23.17 820.38 17.27 23.72 21.31
Nd Ta 169 Yb 182 Ta 182 Ta 169 Yb 147 Nd 75 Se 152 Eu 131 Ba 169 Yb 181 Hf 131 Ba 75 Se 181 Hf 181 Hf 99 Mo 59 Fe 182 Ta 182 Ta 169 Yb 182 Ta 99 Mo 59 Fe 147 Nd 160 Tb 169 Yb 182 Ta 75 Se 160 Tb 82 Br 182 Ta 182 Ta 152 Eu 131 Ba 169 Yb 182 Ta 75 Se 152 Eu 82 Br 147 Nd 75 Se 152 Eu 192 Ir 160 Tb 169 Yb 192 Ir 160 Tb 192 Ir 182
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
186 Table 2 (Continued )
Table 2 (Continued )
Gamma line (keV)b
Radionuclide
Half-lifeb,c
319.41 337.32 344.28 345.93 352.90 367.79 388.63 392.51 398.16 400.66 411.12 443.98 446.81 468.07 475.35 482.18 488.66 496.33 510.99 510.99 554.35 558.43 563.23 564.02 569.32 586.29 604.70 606.37 619.72 620.36 657.76 666.33 674.68 677.62 678.58 682.31 687.02 688.68 698.37 706.68 719.35 725.24 739.50 744.28 756.12 763.94 765.28 776.52 777.92 778.90 795.85 801.93
147
10.98 d 72.3 d 13.542 y 42.39 d 65.94 h 13.542 y 13.11 d 72.3 d 10.98 d 119.779 d 13.542 y 13.542 y 249.79 d 73.831 d 2.062 y 42.39 d 13.542 y 11.50 d 70.82 d 13.11 d 35.30 h 49.51 d 2.062 y 13.542 y 2.062 y 13.542 y 2.062 y 35.30 h 35.30 h 249.79 d 249.79 d 13.11 d 13.542 y 249.79 d 13.542 y 72.3 d 249.79 d 13.542 y 35.30 h 249.79 d 13.542 y 49.51 d 65.94 h 249.79 d 13.542 y 249.79 d 72.3 d 35.30 h 65.94 h 13.542 y 2.062 y 2.062 y
Nd Tb 152 Eu 181 Hf 99 Mo 152 Eu 126 I 160 Tb 147 Nd 75 Se 152 Eu 152 Eu 110m Ag 192 Ir 134 Cs 181 Hf 152 Eu 131 Ba 58 Co 126 I 82 Br 114 In 134 Cs 152 Eu 134 Cs 152 Eu 134 Cs 82 Br 82 Br 110m Ag 110m Ag 126 I 152 Eu 110m Ag 152 Eu 160 Tb 110m Ag 152 Eu 82 Br 110m Ag 152 Eu 114 In 99 Mo 110m Ag 152 Eu 110m Ag 160 Tb 82 Br 99 Mo 152 Eu 134 Cs 134 Cs 160
Relative intensity (%)b 1.95 0.34 26.58 15.12 0.00 0.83 34.09 1.34 0.87 11.37 2.23 2.78 3.72 47.83 1.46 80.50 0.41 46.80 100.00 100.00 70.72 4.39 8.38 0.49 15.43 0.46 97.56 1.21 43.42 2.79 94.00 33.10 0.19 10.28 0.46 0.61 6.39 0.83 28.47 16.33 0.33 4.39 12.13 4.70 0.01 22.14 2.13 83.50 4.28 12.96 85.44 8.73
Yields ratio (conv/coinc)
Gamma line (keV)b
Radionuclide
Half-lifeb,c
Relative intensity (%)b
45.04 17.52 30.18 48.07 315.25 13.29 231.59 20.00 100.10 1197.71 12.56 17.27 6.76 19.76 11.48 85.66 13.12 7.78 1.50 33.29 9.62 20.58 10.36 19.72 9.87 12.38 16.93 1.79 8.13 5.77 9.45 121.03 19.86 6.39 13.83 11.89 8.29 30.03 6.50 8.92 13.66 20.18 35.89 9.04 28.47 10.01 15.47 8.41 213.00 20.60 17.14 10.73
810.78 818.03 827.83 841.59 867.39 879.38 884.69 889.28 919.40 926.32 927.99 937.49 952.02 959.73 962.32 964.13 966.17 1001.70 1002.88 1007.59 1044.00 1081.29 1085.91 1089.70 1099.25 1112.12 1115.12 1120.55 1121.30 1173.24 1177.96 1189.05 1212.95 1221.41 1231.02 1271.88 1291.60 1299.12 1317.47 1332.50 1365.15 1384.30 1408.01 1457.63 1474.88 1475.79 1505.04 1650.37 1871.60
58
70.82 d 249.79 d 35.30 h 13.542 y 13.542 y 72.3 d 249.79 d 83.79 d 13.542 y 13.542 y 114.43 d 249.79 d 35.30 h 114.43 d 72.3 d 13.542 y 72.3 d 114.43 d 72.3 d 35.30 h 35.30 h 35.30 h 13.542 y 13.542 y 44.503 d 13.542 y 72.3 d 83.79 d 114.43 d 5.2714 y 72.3 d 114.43 d 13.542 y 114.43 d 114.43 d 72.3 d 44.503 d 13.542 y 35.30 h 5.2714 y 2.062 y 249.79 d 13.542 y 13.542 y 35.30 h 249.79 d 249.79 d 35.30 h 35.30 h
99.45 7.29 24.02 0.16 4.15 30.01 72.19 99.98 0.44 0.27 0.62 34.13 0.37 0.35 9.91 14.34 25.21 2.07 1.04 1.27 27.22 0.62 9.91 1.71 56.50 13.54 1.58 99.99 34.90 99.90 15.07 16.23 1.40 26.98 11.44 7.46 43.20 1.63 26.47 99.98 3.04 24.12 20.87 0.49 16.31 3.97 12.95 0.74 0.03
a
Co Ag 82 Br 152 Eu 152 Eu 160 Tb 110m Ag 46 Sc 152 Eu 152 Eu 182 Ta 110m Ag 82 Br 182 Ta 160 Tb 152 Eu 160 Tb 182 Ta 160 Tb 82 Br 82 Br 82 Br 152 Eu 152 Eu 59 Fe 152 Eu 160 Tb 46 Sc 182 Ta 60 Co 160 Tb 182 Ta 152 Eu 182 Ta 182 Ta 160 Tb 59 Fe 152 Eu 82 Br 60 Co 134 Cs 110m Ag 152 Eu 152 Eu 82 Br 110m Ag 110m Ag 82 Br 82 Br 110m
Defined as peak area. Data from [9]. c d ± day, y ± year. b
Yields ratio (conv/coinc) 183.34 6.07 8.94 15.30 16.16 39.89 9.49 21.53 15.28 17.84 18.54 9.45 8.49 12.48 41.67 45.50 34.17 14.16 20.63 10.79 8.38 8.42 113.95 25.30 88.53 70.70 22.94 20.94 74.23 22.47 233.30 105.90 14.12 90.37 31.71 249.34 246.57 13.69 9.73 22.02 21.14 11.70 59.16 66.77 8.99 11.46 13.39 6.08 14.22
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
187
Table 3 Concentration of Sc, Co and Cs determined in the reference materialsa Element
Gamma line (keV)
Oriental Tobacco Leaves CTA-OTL-1
Tea GBW 07605 GSV-4
Measured value
Measured value
Certified value
0.3780.018 0.3680.020
b
(0.38)
0.0910.004 0.0940.005
0.0850.009
1173.24 1332.5
0.8990.034 0.8800.035
0.8790.039
0.2020.012 0.2110.012
0.180.02
563.23 569.32 604.7 795.85 801.93
0.1860.024 0.1850.017 0.1830.008 0.1840.008 0.1820.023
0.1770.022
0.3310.029 0.3080.020 0.2910.014 0.2980.015 0.2600.038
0.290.02
46
Sc ( Sc)
889.28 1120.55
Co (60 Co) Cs (134 Cs)
a
Concentration (mg/kg) Certified value
Oriental Tobacco Leaves CTA-OTL-1 and Tea GBW 07605 GSV-4. Value for information only, not certified.
b
Fig. 2. (a) Single detector spectrum of Auto Used Catalyst NIST 2556. (b) Coincidence spectrum of Auto Used Catalyst NIST 2556.
the event data ®le under the condition that coinciding gamma photons are registered in the second detector in the analytical peak. The ``net peak'' coincidence spectrum, which belongs to the 296 keV peak is displayed in Fig. 3(a). In this simple spectrum, the
peaks of 192 Ir (308.46 and 316.51 keV), 152 Eu (121.78, 244.70, 344.28 and 1112.12 keV) and 160 Tb (878.38 and 966.17 keV) can only be found on a low background. Such a composition of 296 keV is documented in Fig. 3(b)±(d), where ``net peak'' coincidence spec-
188
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
Fig. 3. (a) The ``net 296 keV peak'' coincidence spectrum of Auto Used Catalyst NIST 2556. Peaks which are in coincidence with the 296 keV line (308.46 and 316.51 keV of 192 Ir), (121.78, 244.70, 344.28 and 1112.12 keV of 152 Eu), (878.38 and 966.17 keV of 160 Tb) are marked in the spectrum. (b) The ``net 296 keV peak'' coincidence spectrum measured with iridium standard. (c) The ``net 296 keV peak'' coincidence spectrum measured with europium standard. (d) The ``net 296 keV peak'' coincidence spectrum measured with terbium standard.
M. Vobecky et al. / Analytica Chimica Acta 386 (1999) 181±189
189
Table 4 Concentration of Ir determined in the reference materiala Gamma line (keV)
Concentration (mg/kg) Conventional
Coincidence
Net 296 keV peak
295.96 308.46 316.51 468.07
0.0440.009 0.0180.005 0.0150.003 0.0170.003
0.0350.002 0.0160.002 0.0170.001 0.0180.004
0.0190.001 0.0190.001
a
NIST 2556.
tra obtained in measurements with 192 Ir, 152 Eu and 160 Tb standards are presented. Then, the determination of iridium in Auto Used Catalyst could be based on the iridium peak (308.46 and 316.51 keV) areas measured in the ``net peak'' coincidence spectrum of 296 keV line without any energy interference. These results are presented in Table 4. 4. Conclusions We demonstrated that the application of the coincidence technique with different kinds of off-line event processing for nondestructive activation analysis decreases the probability of energy interference contribution in the analytical response. In this way a CIAA method gives more accurate results for very low element concentrations. Our ¯exible three parametric coincidence system can be used for coincidence measurements as well as for conventional IAA in the single detector mode. In agreement with the principle of the self-validation philosophy of activation analysis explained in [10], application of both modes (CIAA and IAA) increases the reliability of analytical values for certi®cation of reference materials and for intercomparison analytical studies. Acknowledgements This work has been supported by the Grant Agency of the Czech Republic under Grant project no. 203/95/
0260 ``Coincidence Instrumental Activation Analysis''. References [1] M. VobeckyÂ, L. PavlõÂk, J. BenesÏ, Radiochem. Radioanal. Lett. 29 (1977) 159. [2] Chifang Chai, Jibin Tian, Qinfang Qian, Peiqun Zhang, Qin Xu, Dajun Mao, Biol. Trace Element Res. 43 44 45 (1994) 177. [3] M. VobeckyÂ, J. DeÏdina, L. PavlõÂk, J. ValaÂsÏek, Radiochem. Radioanal. Lett. 38 (1979) 197. [4] L.E. Wangen, E.S. Gladney, W.K. Hensley, Anal. Chem. 52 (1980) 765. [5] G. Meyer, J. Radioanal. Nucl. Chem. Articles 114 (1987) 223. [6] J. JakuÊbek, P. Nuiten, J. PluharÏ, S. PospõÂsÏil, M. SÏinÏor, I. SÏtekl, S. TimorackyÂ, M. VobeckyÂ, Nucl. Instr. Meth. Phys. Res. A 414 (1998) 261. Ï anda, J. Benada, Radioisotopy 14 (1973) [7] M. VobeckyÂ, Z. R 623. Ï anda, M. VobeckyÂ, J. KuncõÂrÏ, J. Benada, J. Radioanal. [8] Z. R Chem. 46 (1978) 95. [9] R.B. Firestone, in: V.S. Shirley (Ed.), Table of Isotopes, 8th ed., Wiley/Interscience, New York, 1996. [10] A.R. Byrne, J. KucÏera, Role of the self-validation principle of NAA in quality assurance of bioenvironmental studies and in the certification of reference materials, in: Harmonization of the Health Related Environmental Measurements Using Nuclear and Isotopic Techniques, Hyderabad, India, 4±7 November, 1996, IAEA-SM-344/8, IAEA, Vienna, 1997, pp. 223±238.