- Email: [email protected]
3He-particle-induced reactions on natSb for production of 124I
ARTICLE IN PRESS
Applied Radiation and Isotopes 64 (2006) 409–413 www.elsevier.com/locate/apradiso
3
He-particle-induced reactions on
nat
Sb for production of
124
I
K.F. Hassana,b, S.M. Qaima,, Z.A. Salehb, H.H. Coenena a
Institut fu¨r Nuklearchemie, Forschungszentrum Ju¨lich GmbH, D-52425 Ju¨lich, Germany Cyclotron Facility, Nuclear Research Centre, Atomic Energy Authority, Cairo 13759, Egypt
b
Received 25 April 2005; received in revised form 25 June 2005; accepted 23 August 2005
Abstract Excitation functions of the reactions natSb(3He,xn)124,123,121I were measured from their respective thresholds up to 35 MeV, with particular emphasis on data for the production of the medically important radionuclide 124I. The conventional stacked-foil technique was used. From the experimental data the theoretical yields of the three investigated radionuclides were calculated. The yield of 124I over the energy range E 3 He ¼ 35 ! 13 MeV amounts to 0.95 MBq/mA h. The radionuclidic impurities are discussed. A comparison of 3He- and a-particle-induced reactions on antimony for production of 124I is given. The a-particle-induced reaction on enriched 121Sb and the 3 He-particle-induced reaction on enriched 123Sb would lead to comparable 124I yields, but the level of impurities in the latter case would be somewhat higher. r 2005 Elsevier Ltd. All rights reserved. Keywords: Sb-nat; I-124; Medical radionuclide; (3He; xn); Excitation function; Integral yield
1. Introduction The radionuclide I24I (T 1=2 ¼ 4:18 d; I bþ ¼ 22%; E bþ ¼ 2:13 MeV) is the only longer-lived b+ emitting radioisotope of iodine and finds application both in therapy and diagnosis. It is produced in MBq amounts via the I24Te(d,2n)I24I and I24Te(p,n)I24I reactions, though in recent years the latter reaction has been more commonly used because it leads to the highest purity I24I (cf. Qaim et al., 2003, and references cited therein). I24I can also be produced by irradiating both natural and enriched antimony with a- or 3He-particles, but the hitherto reported studies were all carried out in the context of 123I production, so that the information available on the production of 124I was either controversial or scanty. In a recent article we described some studies on a-particleinduced reactions on natSb and 121Sb (Hassan et al., 2006) and concluded that production of high-purity I24I is possible if highly enriched 121Sb is used as target material; the batch yield is, however, low. Now we report on 3Heparticle-induced reactions on natSb, for which some data were available in the literature (Watson et al., 1973; Corresponding author. Tel.: +49 2461 613282; fax: +49 2461 612535.
E-mail address: [email protected] (S.M. Qaim). 0969-8043/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2005.08.013
Wiktorsson and Brenner, 1976). The radionuclides of iodine which could be formed in the interactions of 3 He-particles with natSb are listed in Table 1, together with their main decay characteristics (cf. Browne and Firestone, 1986). The possible contributing processes and their Q-values are also given. 2. Experimental Cross-sections were measured using the conventional stacked-foil technique. Each stack contained several properly prepared antimony samples, as well as aluminium and titanium foils as absorbers and monitors, respectively. The information on the purity of materials used and the method of sample preparation via the sedimentation technique have already been given (Hassan et al., 2006). Irradiations were done with 3He-particle beams at the compact cyclotron CV 28 of the Forschungszentrum Ju¨lich GmbH. The energy range covered was from 8 to 35.4 MeV. The current was registered by an integrator. In addition, Ti monitor foils placed in the stacks were used to calculate the actual beam current during the irradiation. For this purpose, the recently evaluated cross-section data of the nat Ti(3He,x)48V reaction (cf. Ta´rka´nyi et al., 2001) were
ARTICLE IN PRESS K.F. Hassan et al. / Applied Radiation and Isotopes 64 (2006) 409–413
410
Table 1 Possible contributing processes to the formation of some radionuclides of iodine in the interactions of 36 MeV 3He-particles with Nuclide
Decay dataa T1/2
126
13.1 d
125
59.4 d
I I
124
I
123
I
4.18 d 13.2 h
I
3.6 min
Eg (keV)
Ig (%)
Reaction
Q-value (MeV)
Remarks
389 666
32.0 29.1
123
+13.62
hsip0 5 mb
35.5
6.7
123
60.1 10.1
123
82.9
123
603 723 159
3
Sb( He,g) Sb(3He,n)
+6.48
3
Sb( He,2n) Sb(3He,g)
121
3
Sb( He,3n) Sb(3He,n)
564
18.0
123
3
Sb( He,4n) Sb(3He,2n)
121 121
I
2.1 h
Sb
Possible contributing processes
121 122
nat
212
84.0
123
Sb(3He,5n) Sb(3He,3n)
121
hsip5 mb
3.07 +12.70
b
10.53 +5.24
b
20.41 4.64
Short-lived Short-lived
28.52 12.75
c
hsip0 5 mb hsip5 mb
b
a
Taken from Browne and Firestone, 1986. Main reaction of interest. c Possibly some contribution from this reaction. b
used. Well-detectable radioactivity was produced after an irradiation of 2 h with beam currents of 100 nA. The energy degradation in the stack was calculated using the tables of Williamson et al. (1966). The irradiated samples and monitor foils were measured using a high-purity Ge (HPGe) detector of 145 cm3 active volume. The resulting spectra were analysed as described earlier (Hassan et al., 2006). The decay rates of the reaction products were determined using the decay data given in Table 1. From the measured activities the cross-sections were calculated using the well-known activation formula. The total uncertainty in the measured cross-section was in the range 10–14% depending on the detector efficiency, counting statistics and beam current. The uncertainty in the 3He-particle energy that was effective at a sample ranged between 0.5 and 1.8 MeV. 3. Results and discussion 3.1. Cross-section data and excitation functions The experimentally determined cross-sections for the He-particle-induced reactions on natSb are given in Table 2. The estimated uncertainties of energy and cross-section values are also presented. The data refer to the natural composition of antimony, and are thus elemental crosssections. In the thin irradiated samples the radionuclides 126I (T 1=2 ¼ 13:1 d) and 125I (T 1=2 ¼ 59:4 d) were not detected. This is understandable since the respective contributing reactions 123Sb(3He,g)126I and 123Sb(3He,n)125I are expected to have very low cross-sections (cf., e.g., Carlson and Daly, 1967; Fassbender et al., 1994; Skakun and Qaim, 2005). Among the four radionuclides of iodine formed in
3
Table 2 Cross-sections of 3He-particle-induced reactions on 3 He-particle energy (MeV)
Sb
Reaction cross-section (mb) Sb(3He,xn)124I
7.071.5 11.071.7 12.071.5 12.370.9 14.170.8 16.170.6 17.471.8 17.571.1 18.070.5 20.671.7 21.170.4 21.370.5 22.370.9 24.471.1 25.071.3 26.070.7 27.470.4 28.570.7 29.071.0 29.771.7 30.471.3 31.370.5 32.070.9 33.270.4 33.771.0 34.271.6 35.070.8 35.470.5
nat
nat
nat
Sb(3He,xn)123I
1.470.3 5.070.6 5.970.7 18.173.3 26.573.3 29.873.5 30.374.4 33.774.2 35.876.1 59.476.8 60.778.5 63.077.5 58.976.8 55.276.3 58.077.4 46.079.5 48.075.8 38.075.6 27.173.4 34.373.9 39.874.5 37.673.7 31.874.0 30.673.2 23.272.8 24.872.8 21.072.4 24.572.9
13.371.5 17.274.3 22.974.2 26.773.0 41.974.7 44.375.0 57.377.2 59.676.7 129714 122713 140717 206723 281732 321736 378742 405737 463752 337738 342738 338738 266730 182720 149717 153718 151717 113713 126714
nat
Sb(3He,xn)121I
4.870.6 1872.0 2973.7 3874.3 4775.3 95711 152717 252728 369741 638772 606768 9847111 800790 676774 764786 518758 340738 324736 263730 199722 225725
measurable quantities, 122I is very short-lived (T 1=2 ¼ 3:6 min). Thus in all measurements started about 40 min after EOB, the three major activities encountered were
ARTICLE IN PRESS K.F. Hassan et al. / Applied Radiation and Isotopes 64 (2006) 409–413 121
Cross section (mb)
This work Watson et al ,1973 Wiktorsson, Brenner,1976 Eye guide
400
200
0 0
10
20 Energy (MeV)
Fig. 2. Excitation function of the guide is through our data points.
This work Watson et al, 1973 Eye guide
80
60
40
20
0 0
10
20
30
40
Energy (MeV) Fig. 1. Excitation function of the guide is through our data points.
nat
Sb(3He,xn)124I reaction. The eye
30
40
nat
Sb(3He,xn)123I reaction. The eye
1200
This work Watson et al,1973 Eye guide
800
400
0 0
10
20 Energy (MeV)
Fig. 3. Excitation function of the guide is through our data points.
100
Cross section (mb)
600
Cross section (mb)
I (T 1=2 ¼ 2:1 h), 123I (T 1=2 ¼ 13:2 h) and 124I (T 1=2 ¼ 4:18 d). From their possible contributing reactions listed in Table 1, and considering that the (3He,g) and (3He,n) reactions on 121Sb also should have negligibly small crosssections, it is concluded that 124I is formed mainly via the 123 Sb(3He,2n) reaction, and 123I and 121I via the 123 Sb(3He,3n) and 121Sb(3He,3n) reactions, respectively. On the basis of the Q-value, in the case of 121I some contribution from the 123Sb(3He,5n) reaction may also be expected. The measured cross-sections are plotted as a function of the 3He-particle energy, and the excitation curves thus obtained up to 36 MeV are compared with the experimental data available in the literature up to 27 MeV. Our data for the formation of 124I (Fig. 1) show considerable discrepancy with the result of Watson et al. (1973). The latter work shows a maximum cross-section of about 40 mb at 17.5 MeV as compared to a value of about 65 mb at approximately 21.5 MeV in this work. Thus, there appears to be an energy shift of about 4 MeV in the two measurements. A similar shift of about 3 MeV was observed between our recent data (Hassan et al., 2006) and those of Watson et al. (1973) in the case of a-particleinduced reactions on natSb. On the basis of other literature data and nuclear model calculations, we demonstrated that our data and energy scale relevant to the formation of 124I in a-particle-induced reactions on natSb were more consistent (Hassan et al., 2006). We assume that a similar situation exists in the case of 3He-particle-induced reactions. Considering some (3He,2n) reactions on target nuclei in the mass region 95–140 (cf., e. g., Montgomery and Porile, 1969; Qaim and Do¨hler, 1984; Fassbender et al., 1994; Hilgers et al., 2005) the shape and magnitude of the excitation function reported in this work appear to be more plausible than the results of Watson et al. (1973). Our data for 123I (Fig. 2) are in agreement with Watson et al. (1973) in the low-energy region up to 14 MeV, and between 23 and 25 MeV. Similarly, our data agree with Wiktorsson and Brenner (1976) up to 23 MeV, but not at
411
30
40
nat
Sb(3He,xn)121I reaction. The eye
higher energies. Our cross-sections for 121I (Fig. 3) are in fairly good agreement with Watson et al. (1973), except for the energy region between 16 and 22 MeV. For a direct comparison of the excitation functions of the three 3He-particle-induced reactions on natural antimony investigated in this work, we reproduce the trend curves in Fig. 4. The maximum of the excitation curve for the formation of 124I occurs at about 21.5 MeV, and those for 123I and 121I at about 28 MeV. This observation suggests that the radionuclides 123I and 121I are produced via a similar type of reaction and 124I via a lower energy reaction (cf. discussion above). There is no optimum energy range for the production of 124I of high purity, though the range E 3 He ¼ 28 ! 13 MeV appears to be
ARTICLE IN PRESS K.F. Hassan et al. / Applied Radiation and Isotopes 64 (2006) 409–413
412
Cross section (mb)
1200
121I
800
123 I 400
124 I 0 10
20
30
40
Energy (MeV) Fig. 4. Trend curves for the excitation functions of the reactions leading to formation of 124I, 123I and 121I.
nat
Sb(3He,xn)
useful. The production may possibly be also carried out using the almost full energy range E 3 He ¼ 35 ! 13 MeV, provided the level of impurities is carefully investigated (see below).
Fig. 5. Calculated integral yields of 121,123,124I plotted as a function of the incident 3He-particle energy.
1000
From the excitation curves for the production of I in 3He-particle-induced reactions on natSb given in Fig. 4, differential and integral yields were calculated using the standard formalism, and the results on integral yields are shown in Fig. 5 as a function of the 3He-particle energy. The integral yield of 124I over the energy range E 3 He ¼ 35 ! 13 MeV amounts to 0.95 MBq/mA h. It is considerably lower than the yield of 123I (36.83 MBq/mA h) as well as that of 121I (358.2 MBq/mA h), since the reactions leading to the formation of 123I and 121I are stronger than that for the production of 124I, and the half-lives of both 123 I and 121I are much shorter than that of 124I. With a view to ascertaining whether 124I could be produced in acceptable radionuclidic purity at all via interaction of 3He-particles with natSb, the yield of each radionuclidic impurity relative to that of 124I was calculated for the range 3 He ¼ 35 ! 13 MeV, and the ratio is plotted as a function of the decay time after EOB (Fig. 6). The curves show that if 124I is separated 5 days after EOB, the 123I impurity would have decayed out to a level of about 14%, and 121I completely. The longer-lived 121 Te (T 1=2 ¼ 16:8 d), formed in the decay of 121I, would be easily removed via the chemical separation process. The levels of 126I and 125I impurities could not be calculated accurately due to the lack of thin sample data. They were, however, roughly estimated from the cross-sections deduced from the systematics of the respective reactions, and also determined in a thick target experiment; in each case a level of about 0.6% (at EOB) was obtained. If a decay time of about 5 d is allowed prior to the separation of 124I, the levels of the short-lived 121I and 123I would decrease, but 124,123,121
Ratio of impurity to 124I
3.2. Calculated yields 100
10
123I/124I
121I/124I
1
0.1
0
1
2 3 4 5 Decay time after EOB (days)
6
Fig. 6. Ratios of the yields of radionuclides 121I and 123I to 124I over the energy range E 3 He ¼ 35 ! 13 MeV plotted as a function of the decay time after EOB.
those of the longer-lived 125I and 126I would increase. From these data it is estimated that in a 10 h irradiation at a nominal current of about 10 mA about 42 MBq 124I could be obtained (value 5 d after EOB). For practical application this batch yield is rather low and the product is not of high purity (see below). 3.3. Comparison of production possibility of 124I via 3Heand a-particle-induced reactions on antimony A summary of the information now available on the production of 124I via a-particle-induced reactions on natSb and 121Sb (Hassan et al., 2006) and 3He-particle-induced reactions on natSb (this work) is given in Table 3. All values
ARTICLE IN PRESS K.F. Hassan et al. / Applied Radiation and Isotopes 64 (2006) 409–413 Table 3 Comparison of 3He- and a-particle-induced reactions on antimony for production of Nuclear reaction
Suitable energy range (MeV)
124
124
I (MBq/mA h)a
I Radionuclidic impurities (%)a 123
125
126
14 4 o4
1.3 27 o0.2
1.2 27 o0.2
I
nat
3
124
Sb( He,xn) I Sb(a,xn) 124I 121 Sb(a,n) 124Ib nat
a
35-13 22-13 22-13
0.42 0.45 0.92
413
I
I
Values at 5 d after EOB. Using 99.45% enriched 121Sb as target material.
b
correspond to the separation of radioiodine 5 d after EOB. As discussed earlier (Hassan et al., 2006), the a-particleinduced reactions on natSb are not suitable for production of 124I due to high levels of 125I and 126I impurities. The aparticle-induced reaction on highly enriched 121Sb, on the other hand, leads to high-purity 124I; the overall yield, however, is rather low. As regards the 3He-particle-induced reactions, the present study shows that 124I can be produced using natSb as target material, but the yield is low and the product is not of high purity. The yield could be increased by a factor of 2.34 if highly enriched 123Sb would be used as target material. It will then be comparable to that from the (a,n) reaction on enriched 121 Sb. However, the levels of the 126I, 125I and 123I impurities would not decrease, since like 124I they are all formed from 123Sb. For general comparison it may be pointed out that, because of their low yields, the 3He- and a-particle-induced reactions on natural or enriched antimony cannot compete with the 124Te(p,n)124I process commonly used today (cf. Qaim et al., 2003). Acknowledgements We thank the operators of the compact cyclotron (CV 28) at Ju¨lich for performing the irradiations. This work was done under an Egyptian–German bilateral agreement, and we are grateful to the concerned authorities in both countries for their support. References Browne, E., Firestone, R.B., 1986. Table of Radioactive Isotopes. Wiley, New York. Carlson, R.V., Daly, P.J., 1967. Excitation functions for (3He,g) and (4He,g) reactions. Nucl. Phys. A 102, 161.
Fassbender, M., Novgorodov, A.F., Ro¨sch, F., Qaim, S.M., 1994. Excitation functions of 93Nb(3He,xn)93m,gTc, 94m,gTc, 95m,gTc processes from threshold up to 35 MeV: possibility of production of 94mTc in high radiochemical purity using a thermochromatographic separation technique. Radiochim. Acta 65, 215. Hassan, K.F., Qaim, S.M., Saleh, Z.A., Coenen, H.H., 2006. Alphaparticle induced reactions on natSb and 121Sb with particular reference to production of the medically interesting radionuclide 124I. Appl. Radiat. Isot. 64, 101. Hilgers, K., Qaim, S.M., Shubin, Yu. N., Coenen, H.H., 2005. Experimental measurements and nuclear model calculations on the excitation functions of natCe(3He,xn) and 141Pr(p,xn) reactions with special reference to production of the therapeutic radionuclide 140Nd. Radiochim. Acta 93, 553. Montgomery, D.M., Porile, N.T., 1969. Reactions of 116Cd with intermediate energy 3He and 4He ions. Nucl. Phys. A 130, 65. Qaim, S.M., Do¨hler, H., 1984. Production of carrier-free 117mSn. Int. J. Appl. Radiat. Isot. 35, 645. Qaim, S.M., Hohn, A., Bastian, Th., El-Azony, K.M., Blessing, G., Spellerberg, S., Scholten, B., Coenen, H.H., 2003. Some optimisation studies relevant to the production of high-purity 124I and 120gI at a small-sized cyclotron. Appl. Radiat. Isot. 58, 69. Skakun, Y., Qaim, S.M., 2005. Excitation functions of helion-induced nuclear reactions for the production of the medical radioisotope 103Pd. In: Haight, R.C., Chadwick, M.B., Kawano, T., Talon, P. (Eds.), International Conference on Nuclear Data for Science and Technology, September/October 2004, Santa Fe, USA. AIP Conference Proceedings, vol. 769, p. 1634. Ta´rka´nyi, F., Taka`cs, S., Gul, K., Hermanne, A., Mustafa, M.G., Nortier, M., Oblozinsky, P., Qaim, S.M., Scholten, B., Shubin, Yu., Zhuang, Y., 2001. Beam monitor reactions. In: Charged Particle Cross Section Database for Medical Radioisotope Production. IAEA-TECDOC1211, pp. 49–152. Watson, I.A., Waters, S.L., Silvester, D.J., 1973. Excitation functions for the reactions producing 121I,123I and 124I from irradiation of natural antimony with 3He and 4He-particles with energy up to 30 MeV. J. Inorg. Nucl. Chem. 35, 3047. Williamson, C.F., Boujot, J.P., Picard, J., 1966. Tables of Range and Stopping Power of Chemical Elements for Charged Particles of Energy 0.5–500 MeV. Report CEA-R 3042. Wiktorsson, C., Brenner, M., 1976. Excitation function for the reaction 123 Sb(3He,3n)123I. The Accelerator of A˚bo Akademi Annual Report 1975, p. 19.
Applied Radiation and Isotopes 64 (2006) 409–413 www.elsevier.com/locate/apradiso
3
He-particle-induced reactions on
nat
Sb for production of
124
I
K.F. Hassana,b, S.M. Qaima,, Z.A. Salehb, H.H. Coenena a
Institut fu¨r Nuklearchemie, Forschungszentrum Ju¨lich GmbH, D-52425 Ju¨lich, Germany Cyclotron Facility, Nuclear Research Centre, Atomic Energy Authority, Cairo 13759, Egypt
b
Received 25 April 2005; received in revised form 25 June 2005; accepted 23 August 2005
Abstract Excitation functions of the reactions natSb(3He,xn)124,123,121I were measured from their respective thresholds up to 35 MeV, with particular emphasis on data for the production of the medically important radionuclide 124I. The conventional stacked-foil technique was used. From the experimental data the theoretical yields of the three investigated radionuclides were calculated. The yield of 124I over the energy range E 3 He ¼ 35 ! 13 MeV amounts to 0.95 MBq/mA h. The radionuclidic impurities are discussed. A comparison of 3He- and a-particle-induced reactions on antimony for production of 124I is given. The a-particle-induced reaction on enriched 121Sb and the 3 He-particle-induced reaction on enriched 123Sb would lead to comparable 124I yields, but the level of impurities in the latter case would be somewhat higher. r 2005 Elsevier Ltd. All rights reserved. Keywords: Sb-nat; I-124; Medical radionuclide; (3He; xn); Excitation function; Integral yield
1. Introduction The radionuclide I24I (T 1=2 ¼ 4:18 d; I bþ ¼ 22%; E bþ ¼ 2:13 MeV) is the only longer-lived b+ emitting radioisotope of iodine and finds application both in therapy and diagnosis. It is produced in MBq amounts via the I24Te(d,2n)I24I and I24Te(p,n)I24I reactions, though in recent years the latter reaction has been more commonly used because it leads to the highest purity I24I (cf. Qaim et al., 2003, and references cited therein). I24I can also be produced by irradiating both natural and enriched antimony with a- or 3He-particles, but the hitherto reported studies were all carried out in the context of 123I production, so that the information available on the production of 124I was either controversial or scanty. In a recent article we described some studies on a-particleinduced reactions on natSb and 121Sb (Hassan et al., 2006) and concluded that production of high-purity I24I is possible if highly enriched 121Sb is used as target material; the batch yield is, however, low. Now we report on 3Heparticle-induced reactions on natSb, for which some data were available in the literature (Watson et al., 1973; Corresponding author. Tel.: +49 2461 613282; fax: +49 2461 612535.
E-mail address: [email protected] (S.M. Qaim). 0969-8043/$ - see front matter r 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.apradiso.2005.08.013
Wiktorsson and Brenner, 1976). The radionuclides of iodine which could be formed in the interactions of 3 He-particles with natSb are listed in Table 1, together with their main decay characteristics (cf. Browne and Firestone, 1986). The possible contributing processes and their Q-values are also given. 2. Experimental Cross-sections were measured using the conventional stacked-foil technique. Each stack contained several properly prepared antimony samples, as well as aluminium and titanium foils as absorbers and monitors, respectively. The information on the purity of materials used and the method of sample preparation via the sedimentation technique have already been given (Hassan et al., 2006). Irradiations were done with 3He-particle beams at the compact cyclotron CV 28 of the Forschungszentrum Ju¨lich GmbH. The energy range covered was from 8 to 35.4 MeV. The current was registered by an integrator. In addition, Ti monitor foils placed in the stacks were used to calculate the actual beam current during the irradiation. For this purpose, the recently evaluated cross-section data of the nat Ti(3He,x)48V reaction (cf. Ta´rka´nyi et al., 2001) were
ARTICLE IN PRESS K.F. Hassan et al. / Applied Radiation and Isotopes 64 (2006) 409–413
410
Table 1 Possible contributing processes to the formation of some radionuclides of iodine in the interactions of 36 MeV 3He-particles with Nuclide
Decay dataa T1/2
126
13.1 d
125
59.4 d
I I
124
I
123
I
4.18 d 13.2 h
I
3.6 min
Eg (keV)
Ig (%)
Reaction
Q-value (MeV)
Remarks
389 666
32.0 29.1
123
+13.62
hsip0 5 mb
35.5
6.7
123
60.1 10.1
123
82.9
123
603 723 159
3
Sb( He,g) Sb(3He,n)
+6.48
3
Sb( He,2n) Sb(3He,g)
121
3
Sb( He,3n) Sb(3He,n)
564
18.0
123
3
Sb( He,4n) Sb(3He,2n)
121 121
I
2.1 h
Sb
Possible contributing processes
121 122
nat
212
84.0
123
Sb(3He,5n) Sb(3He,3n)
121
hsip5 mb
3.07 +12.70
b
10.53 +5.24
b
20.41 4.64
Short-lived Short-lived
28.52 12.75
c
hsip0 5 mb hsip5 mb
b
a
Taken from Browne and Firestone, 1986. Main reaction of interest. c Possibly some contribution from this reaction. b
used. Well-detectable radioactivity was produced after an irradiation of 2 h with beam currents of 100 nA. The energy degradation in the stack was calculated using the tables of Williamson et al. (1966). The irradiated samples and monitor foils were measured using a high-purity Ge (HPGe) detector of 145 cm3 active volume. The resulting spectra were analysed as described earlier (Hassan et al., 2006). The decay rates of the reaction products were determined using the decay data given in Table 1. From the measured activities the cross-sections were calculated using the well-known activation formula. The total uncertainty in the measured cross-section was in the range 10–14% depending on the detector efficiency, counting statistics and beam current. The uncertainty in the 3He-particle energy that was effective at a sample ranged between 0.5 and 1.8 MeV. 3. Results and discussion 3.1. Cross-section data and excitation functions The experimentally determined cross-sections for the He-particle-induced reactions on natSb are given in Table 2. The estimated uncertainties of energy and cross-section values are also presented. The data refer to the natural composition of antimony, and are thus elemental crosssections. In the thin irradiated samples the radionuclides 126I (T 1=2 ¼ 13:1 d) and 125I (T 1=2 ¼ 59:4 d) were not detected. This is understandable since the respective contributing reactions 123Sb(3He,g)126I and 123Sb(3He,n)125I are expected to have very low cross-sections (cf., e.g., Carlson and Daly, 1967; Fassbender et al., 1994; Skakun and Qaim, 2005). Among the four radionuclides of iodine formed in
3
Table 2 Cross-sections of 3He-particle-induced reactions on 3 He-particle energy (MeV)
Sb
Reaction cross-section (mb) Sb(3He,xn)124I
7.071.5 11.071.7 12.071.5 12.370.9 14.170.8 16.170.6 17.471.8 17.571.1 18.070.5 20.671.7 21.170.4 21.370.5 22.370.9 24.471.1 25.071.3 26.070.7 27.470.4 28.570.7 29.071.0 29.771.7 30.471.3 31.370.5 32.070.9 33.270.4 33.771.0 34.271.6 35.070.8 35.470.5
nat
nat
nat
Sb(3He,xn)123I
1.470.3 5.070.6 5.970.7 18.173.3 26.573.3 29.873.5 30.374.4 33.774.2 35.876.1 59.476.8 60.778.5 63.077.5 58.976.8 55.276.3 58.077.4 46.079.5 48.075.8 38.075.6 27.173.4 34.373.9 39.874.5 37.673.7 31.874.0 30.673.2 23.272.8 24.872.8 21.072.4 24.572.9
13.371.5 17.274.3 22.974.2 26.773.0 41.974.7 44.375.0 57.377.2 59.676.7 129714 122713 140717 206723 281732 321736 378742 405737 463752 337738 342738 338738 266730 182720 149717 153718 151717 113713 126714
nat
Sb(3He,xn)121I
4.870.6 1872.0 2973.7 3874.3 4775.3 95711 152717 252728 369741 638772 606768 9847111 800790 676774 764786 518758 340738 324736 263730 199722 225725
measurable quantities, 122I is very short-lived (T 1=2 ¼ 3:6 min). Thus in all measurements started about 40 min after EOB, the three major activities encountered were
ARTICLE IN PRESS K.F. Hassan et al. / Applied Radiation and Isotopes 64 (2006) 409–413 121
Cross section (mb)
This work Watson et al ,1973 Wiktorsson, Brenner,1976 Eye guide
400
200
0 0
10
20 Energy (MeV)
Fig. 2. Excitation function of the guide is through our data points.
This work Watson et al, 1973 Eye guide
80
60
40
20
0 0
10
20
30
40
Energy (MeV) Fig. 1. Excitation function of the guide is through our data points.
nat
Sb(3He,xn)124I reaction. The eye
30
40
nat
Sb(3He,xn)123I reaction. The eye
1200
This work Watson et al,1973 Eye guide
800
400
0 0
10
20 Energy (MeV)
Fig. 3. Excitation function of the guide is through our data points.
100
Cross section (mb)
600
Cross section (mb)
I (T 1=2 ¼ 2:1 h), 123I (T 1=2 ¼ 13:2 h) and 124I (T 1=2 ¼ 4:18 d). From their possible contributing reactions listed in Table 1, and considering that the (3He,g) and (3He,n) reactions on 121Sb also should have negligibly small crosssections, it is concluded that 124I is formed mainly via the 123 Sb(3He,2n) reaction, and 123I and 121I via the 123 Sb(3He,3n) and 121Sb(3He,3n) reactions, respectively. On the basis of the Q-value, in the case of 121I some contribution from the 123Sb(3He,5n) reaction may also be expected. The measured cross-sections are plotted as a function of the 3He-particle energy, and the excitation curves thus obtained up to 36 MeV are compared with the experimental data available in the literature up to 27 MeV. Our data for the formation of 124I (Fig. 1) show considerable discrepancy with the result of Watson et al. (1973). The latter work shows a maximum cross-section of about 40 mb at 17.5 MeV as compared to a value of about 65 mb at approximately 21.5 MeV in this work. Thus, there appears to be an energy shift of about 4 MeV in the two measurements. A similar shift of about 3 MeV was observed between our recent data (Hassan et al., 2006) and those of Watson et al. (1973) in the case of a-particleinduced reactions on natSb. On the basis of other literature data and nuclear model calculations, we demonstrated that our data and energy scale relevant to the formation of 124I in a-particle-induced reactions on natSb were more consistent (Hassan et al., 2006). We assume that a similar situation exists in the case of 3He-particle-induced reactions. Considering some (3He,2n) reactions on target nuclei in the mass region 95–140 (cf., e. g., Montgomery and Porile, 1969; Qaim and Do¨hler, 1984; Fassbender et al., 1994; Hilgers et al., 2005) the shape and magnitude of the excitation function reported in this work appear to be more plausible than the results of Watson et al. (1973). Our data for 123I (Fig. 2) are in agreement with Watson et al. (1973) in the low-energy region up to 14 MeV, and between 23 and 25 MeV. Similarly, our data agree with Wiktorsson and Brenner (1976) up to 23 MeV, but not at
411
30
40
nat
Sb(3He,xn)121I reaction. The eye
higher energies. Our cross-sections for 121I (Fig. 3) are in fairly good agreement with Watson et al. (1973), except for the energy region between 16 and 22 MeV. For a direct comparison of the excitation functions of the three 3He-particle-induced reactions on natural antimony investigated in this work, we reproduce the trend curves in Fig. 4. The maximum of the excitation curve for the formation of 124I occurs at about 21.5 MeV, and those for 123I and 121I at about 28 MeV. This observation suggests that the radionuclides 123I and 121I are produced via a similar type of reaction and 124I via a lower energy reaction (cf. discussion above). There is no optimum energy range for the production of 124I of high purity, though the range E 3 He ¼ 28 ! 13 MeV appears to be
ARTICLE IN PRESS K.F. Hassan et al. / Applied Radiation and Isotopes 64 (2006) 409–413
412
Cross section (mb)
1200
121I
800
123 I 400
124 I 0 10
20
30
40
Energy (MeV) Fig. 4. Trend curves for the excitation functions of the reactions leading to formation of 124I, 123I and 121I.
nat
Sb(3He,xn)
useful. The production may possibly be also carried out using the almost full energy range E 3 He ¼ 35 ! 13 MeV, provided the level of impurities is carefully investigated (see below).
Fig. 5. Calculated integral yields of 121,123,124I plotted as a function of the incident 3He-particle energy.
1000
From the excitation curves for the production of I in 3He-particle-induced reactions on natSb given in Fig. 4, differential and integral yields were calculated using the standard formalism, and the results on integral yields are shown in Fig. 5 as a function of the 3He-particle energy. The integral yield of 124I over the energy range E 3 He ¼ 35 ! 13 MeV amounts to 0.95 MBq/mA h. It is considerably lower than the yield of 123I (36.83 MBq/mA h) as well as that of 121I (358.2 MBq/mA h), since the reactions leading to the formation of 123I and 121I are stronger than that for the production of 124I, and the half-lives of both 123 I and 121I are much shorter than that of 124I. With a view to ascertaining whether 124I could be produced in acceptable radionuclidic purity at all via interaction of 3He-particles with natSb, the yield of each radionuclidic impurity relative to that of 124I was calculated for the range 3 He ¼ 35 ! 13 MeV, and the ratio is plotted as a function of the decay time after EOB (Fig. 6). The curves show that if 124I is separated 5 days after EOB, the 123I impurity would have decayed out to a level of about 14%, and 121I completely. The longer-lived 121 Te (T 1=2 ¼ 16:8 d), formed in the decay of 121I, would be easily removed via the chemical separation process. The levels of 126I and 125I impurities could not be calculated accurately due to the lack of thin sample data. They were, however, roughly estimated from the cross-sections deduced from the systematics of the respective reactions, and also determined in a thick target experiment; in each case a level of about 0.6% (at EOB) was obtained. If a decay time of about 5 d is allowed prior to the separation of 124I, the levels of the short-lived 121I and 123I would decrease, but 124,123,121
Ratio of impurity to 124I
3.2. Calculated yields 100
10
123I/124I
121I/124I
1
0.1
0
1
2 3 4 5 Decay time after EOB (days)
6
Fig. 6. Ratios of the yields of radionuclides 121I and 123I to 124I over the energy range E 3 He ¼ 35 ! 13 MeV plotted as a function of the decay time after EOB.
those of the longer-lived 125I and 126I would increase. From these data it is estimated that in a 10 h irradiation at a nominal current of about 10 mA about 42 MBq 124I could be obtained (value 5 d after EOB). For practical application this batch yield is rather low and the product is not of high purity (see below). 3.3. Comparison of production possibility of 124I via 3Heand a-particle-induced reactions on antimony A summary of the information now available on the production of 124I via a-particle-induced reactions on natSb and 121Sb (Hassan et al., 2006) and 3He-particle-induced reactions on natSb (this work) is given in Table 3. All values
ARTICLE IN PRESS K.F. Hassan et al. / Applied Radiation and Isotopes 64 (2006) 409–413 Table 3 Comparison of 3He- and a-particle-induced reactions on antimony for production of Nuclear reaction
Suitable energy range (MeV)
124
124
I (MBq/mA h)a
I Radionuclidic impurities (%)a 123
125
126
14 4 o4
1.3 27 o0.2
1.2 27 o0.2
I
nat
3
124
Sb( He,xn) I Sb(a,xn) 124I 121 Sb(a,n) 124Ib nat
a
35-13 22-13 22-13
0.42 0.45 0.92
413
I
I
Values at 5 d after EOB. Using 99.45% enriched 121Sb as target material.
b
correspond to the separation of radioiodine 5 d after EOB. As discussed earlier (Hassan et al., 2006), the a-particleinduced reactions on natSb are not suitable for production of 124I due to high levels of 125I and 126I impurities. The aparticle-induced reaction on highly enriched 121Sb, on the other hand, leads to high-purity 124I; the overall yield, however, is rather low. As regards the 3He-particle-induced reactions, the present study shows that 124I can be produced using natSb as target material, but the yield is low and the product is not of high purity. The yield could be increased by a factor of 2.34 if highly enriched 123Sb would be used as target material. It will then be comparable to that from the (a,n) reaction on enriched 121 Sb. However, the levels of the 126I, 125I and 123I impurities would not decrease, since like 124I they are all formed from 123Sb. For general comparison it may be pointed out that, because of their low yields, the 3He- and a-particle-induced reactions on natural or enriched antimony cannot compete with the 124Te(p,n)124I process commonly used today (cf. Qaim et al., 2003). Acknowledgements We thank the operators of the compact cyclotron (CV 28) at Ju¨lich for performing the irradiations. This work was done under an Egyptian–German bilateral agreement, and we are grateful to the concerned authorities in both countries for their support. References Browne, E., Firestone, R.B., 1986. Table of Radioactive Isotopes. Wiley, New York. Carlson, R.V., Daly, P.J., 1967. Excitation functions for (3He,g) and (4He,g) reactions. Nucl. Phys. A 102, 161.
Fassbender, M., Novgorodov, A.F., Ro¨sch, F., Qaim, S.M., 1994. Excitation functions of 93Nb(3He,xn)93m,gTc, 94m,gTc, 95m,gTc processes from threshold up to 35 MeV: possibility of production of 94mTc in high radiochemical purity using a thermochromatographic separation technique. Radiochim. Acta 65, 215. Hassan, K.F., Qaim, S.M., Saleh, Z.A., Coenen, H.H., 2006. Alphaparticle induced reactions on natSb and 121Sb with particular reference to production of the medically interesting radionuclide 124I. Appl. Radiat. Isot. 64, 101. Hilgers, K., Qaim, S.M., Shubin, Yu. N., Coenen, H.H., 2005. Experimental measurements and nuclear model calculations on the excitation functions of natCe(3He,xn) and 141Pr(p,xn) reactions with special reference to production of the therapeutic radionuclide 140Nd. Radiochim. Acta 93, 553. Montgomery, D.M., Porile, N.T., 1969. Reactions of 116Cd with intermediate energy 3He and 4He ions. Nucl. Phys. A 130, 65. Qaim, S.M., Do¨hler, H., 1984. Production of carrier-free 117mSn. Int. J. Appl. Radiat. Isot. 35, 645. Qaim, S.M., Hohn, A., Bastian, Th., El-Azony, K.M., Blessing, G., Spellerberg, S., Scholten, B., Coenen, H.H., 2003. Some optimisation studies relevant to the production of high-purity 124I and 120gI at a small-sized cyclotron. Appl. Radiat. Isot. 58, 69. Skakun, Y., Qaim, S.M., 2005. Excitation functions of helion-induced nuclear reactions for the production of the medical radioisotope 103Pd. In: Haight, R.C., Chadwick, M.B., Kawano, T., Talon, P. (Eds.), International Conference on Nuclear Data for Science and Technology, September/October 2004, Santa Fe, USA. AIP Conference Proceedings, vol. 769, p. 1634. Ta´rka´nyi, F., Taka`cs, S., Gul, K., Hermanne, A., Mustafa, M.G., Nortier, M., Oblozinsky, P., Qaim, S.M., Scholten, B., Shubin, Yu., Zhuang, Y., 2001. Beam monitor reactions. In: Charged Particle Cross Section Database for Medical Radioisotope Production. IAEA-TECDOC1211, pp. 49–152. Watson, I.A., Waters, S.L., Silvester, D.J., 1973. Excitation functions for the reactions producing 121I,123I and 124I from irradiation of natural antimony with 3He and 4He-particles with energy up to 30 MeV. J. Inorg. Nucl. Chem. 35, 3047. Williamson, C.F., Boujot, J.P., Picard, J., 1966. Tables of Range and Stopping Power of Chemical Elements for Charged Particles of Energy 0.5–500 MeV. Report CEA-R 3042. Wiktorsson, C., Brenner, M., 1976. Excitation function for the reaction 123 Sb(3He,3n)123I. The Accelerator of A˚bo Akademi Annual Report 1975, p. 19.