Radiochim. Acta 93, 311–326 (2005) by Oldenbourg Wissenschaftsverlag, München Activation cross sections for reactions induced by 14 MeV neutrons on natural tin and enriched 112Sn targets with reference to 111In production via radioisotope generator 112Sn(n,2n)111Sn → 111In By Emil Betˇ ak´ 1,2,∗, Renata Mikołajczak3 , Joanna Staniszewska3, Stefan Mikołajewski4 and Edward Rurarz4 1 Institute of Physics, Slovak Academy of Sciences, 84511 Bratislava, Slovakia 2 Faculty of Philosophy and Sciences, Silesian University, 74601 Opava, Czech Rep. 3 Radioisotope Centre, 05-400 Otwock-Swierk,´ Poland 4 Sołtan Institute for Nuclear Studies, 05-400 Otwock-Swierk,´ Poland (Received March 20, 2004; accepted in final form January 10, 2005) Activation cross sections / Ge detector / medicine. Due to the short half-life of 113mIn its application Neutron-induced reactions / γ-ray spectroscopy / is limited to rapid physiological studies that can be scanned Tin region / Neutron generator within a maximum of 4 to 8 hours. It is still in use, because it also allows repeated investigations within few hours. The preparation of 113Sn → 113mIn generator requires the use of γ Summary. We measured activation cross sections via -ray high-flux reactor and a strongly enriched 112Sn target in the spectroscopy using high-purity germanium detectors for 16 reaction 112Sn(n,γ)113Sn. reactions induced by (14.4 ±0.2) MeV neutrons on isotopes of tin. The cross sections are: An alternative is the use of the longer-lived (carrier- free) 111In. Medical investigators have shown that 111In is σ(112 ( , )111 ) = ( ± ) Sn n 2n Sn 1104 43 mb, an important radionuclide for locating and imaging cer- σ(112Sn(n, p)112mIn) = (33.6 ±2.1) mb, tain tumors, visualization of the lymphatic system etc., σ(112Sn(n, p)112gIn) = (42.7±3.1) mb, σ(114Sn(n, 2n)113Sn) = (1270 ±115) mb, and is applied in myriad of labeling. For several in-vivo σ(114Sn(n, p)114m2In) = (20.5 ±1.1) mb, studies (e.g. the study of slow biological processes, for σ(115Sn(n, p)115mIn) = (35.2 ±2.6) mb, which the observation periods of 1 to 3 days after the σ(116Sn(n, p)116m2In) = (11.1 ±0.5) mb, administration are necessary), 111In has very favourable σ(117Sn(n, np)116m2In) = (1.35 ±0.11) mb, decay characteristics [1–3]. Its half-life is 2.8 days. The σ(117Sn(n, p)117mIn) = (4.5 ±0.4) mb, 100% electron-capture decay leads to an excited state σ(117Sn(n, p)117gIn) = (12.8±0.7) mb, of 111Cd. This state is deexcited by the cascade of the σ(117 ( , )117m ) = ( ± ) Sn n n Sn 246 21 mb, 171.3 keV and 245.4 keV gamma-rays having intensities σ(118 ( , )117m ) = ( ± ) Sn n 2n Sn 816 70 mb, of 90.3% and 94%, respectively. The relevant average en- σ(118Sn(n,α)115gCd) = (1.26 ±0.16) mb, σ(120 ( ,α)117m ) = ( . ± . ) ergies (and intensities) of conversion electrons are low, Sn n Cd 0 27 0 04 mb, . σ(120Sn(n,α)117gCd) = (0.29 ±0.06) mb and namely 144 6 keV (10%) and 218 6 keV (6%). The energy σ(124Sn(n, 2n)123mSn) = (590 ±26) mb. of the Auger electrons is only about 20 keV. These gamma- ray energies are in the optimum range of the photo-peak Two 112Sn targets enriched to 62.5% and 84%, respectively, were used for these measurements in addition to the natural efficiency for commercially available gamma cameras or tin. The cross sections were compared with experimental data scanners. They can be imaged either separately or jointly found in the literature, with published empirical formulae and (184 photons per 100 EC disintegrations). In the latter case with model calculations including also the pre-equilibrium an improved statistics or more rapid data accumulation is contribution. For reactions which do not involve protons from achieved. below the closed Z = 50 shell, the agreement to the data is As summarized in Table 11, the isotope 111In can be pro- reasonable, it is somewhat weaker for the (n, p) reactions duced either directly or indirectly via precursors: 111Sb and and still worse in the case of (n,α), where, however, the 111Sn. The list of reactions given in this table is not exhaus- pre-equilibrium component is not described properly by the tive; other reactions, may come into use in the future. models included so far. The possibility of production of The isotope 111In is usually produced by 4He bombard- 111Sn → 111In generator system is considered. ment of a silver target via the 109Ag(4He, 2n)111In reaction, by deuteron bombardment of a cadmium target (natural or 1. Introduction enriched), the nuclear reactions are there 110Cd(d, n)111In 111 ( , )111 113m and Cd d 2n In, or by proton bombardment of cad- Carrier-free In, which is commercially available from mium (natural and enriched), the nuclear reactions in this 113 = → the radioisotope generator system Sn (T1/2 115 d) 111,112,113,114 ( , )111 = 113m case are Cd p xn In (x 1–4) [6, 7]. In (T1/2 = 100 min), is being used extensively in nuclear *Author for correspondence (E-mail: [email protected]). 1 Table 1 has been constructed using the data of Refs. [4, 5]. 312 E. Betˇ ak´ et al. Table 1. Thresholds and Coulomb barri- ers for reactions leading to production of Reaction Nat. abund. Q-value Threshold Coulomb 111In. of target energy barrier (per cent) (MeV) (MeV) (MeV) 111Cd(p, n)111In 12.75 −1.644 1.66 8.49 112Cd(p, 2n)111In 24.07 −11.039 11.14 8.47 113Cd(p, 3n)111In 12.26 −17.579 17.73 8.45 114Cd(p, 4n)111In 28.86 −26.622 26.86 8.43 110Cd(d, n)111In 12.39 3.107 0 8.15 111Cd(d, 2n)111In 12.75 −3.868 3.94 8.13 109Ag(3He, n)111In 48.65 6.533 0 15.52 109Ag(4He, 2n)111In 48.65 −14.044 14.56 15.17 + + EC,β EC,β 112Sn(p, 2n)111Sb −→ 111Sn −→ 111In 0.95 −16.627 16.78 8.82 75 s 35 m 110Cd(3He, 2n)111Sn → 111In 12.39 −5.619 5.77 15.82 112Sn(γ, n)111Sn → 111In 0.95 −10.788 10.79 − 112Sn(n, 2n)111Sn → 111In 0.95 −10.788 10.89 − The yields of 111In from nuclear reactions induced However, 109Ag(3He, n)111In reaction is unsuitable for the by 4He on Ag are much lower than from reactions in production of 111In because its yield is too low [about which Cd (irrespective of whether enriched or natural) is 7.4 × 104 Bq (2 µCi)/µA h at EOB] for 40 MeV bombard- bombarded by protons [2.22 × 106 Bq (60 µCi)/µAh for ing 3He particles [6]. Comparative study on the above ways 109 4 111 111 Ag( He, 2n) In reaction at E4He = 24 MeV compared leading to In for a medium size medical cyclotrons shows to 2.22 × 108 Bq (6000 µCi)/µAh for 112Cd(p, 2n)111In that the highest yield is obtained in the two reactions on reaction with cadmium target enriched to 97% and to highly enriched 112,113Cd targets, namely 112Cd(p, 2n)111In 7 113 111 3.7 × 10 Bq (1000 µCi)/µA h for natural cadmium target (Ep ≤ 30 MeV) and Cd(p, 3n) In (Ep ≤ 60 MeV) [6]. at Ep = 22 MeV] [6]. The reason for our choice of an en- Due to the lack of relevant nuclear data, not much can be riched 113Cd target is the advantage of a larger yield, namely said about indirect methods of the 111In production (the last 6.1 × 108 Bq (16 500 µCi)/µAh forthe(p, 3n) reaction at four reactions in Table 1). 65 MeV compared to the yield of the (p, 2n) reaction on the The radionuclide 111In can be produced by 112Sn(γ, n) enriched 112Cd at 26 MeV and to the yield of the (p, n) reac- 111Sn → 111In using medium-energy electron accelerators. tion on an enriched 111Cd target using 16 MeV protons [6, 7]. The achieved production scale of tens of MBq of no- When preparation of 111In is carried out by bombard- carrier-added (NCA) 111In per several hours run [8 × 107 Bq ing the cadmium target with protons (deuterons), the 111In (2.2mCi)/µA h] is sufficient for many types of applica- activity at the end of bombardment (EOB) contains undesir- tions [9]. Small scale production of 111In (tens of kBq) has able contaminations of other indium radionuclides, namely been reported [10] for reactor irradiations utilizing the fast 109 110m 114m 112 111 In (T1/2 = 4.3h), In (T1/2 = 4.9h),and In (T1/2 = component of the neutron spectrum in the Sn(n, 2n) Sn 49.5 d). The first two of them have relatively short half-lives → 111In reaction. Another potential possibility of 111In pro- and a suitable waiting period is required after EOB to let di- duction is to make use of fast neutrons produced by neutron minish drastically their activities. The chemical separation generators, which are commonly used in many laboratories. of 111In from irradiated cadmium target cannot be performed The aim of this work is to obtain information on 111In before at least 99% of these radioisotopes has decayed. activities induced by 14 MeV neutrons bombarding 112Sn 114m The third mentioned nuclide In (with major Eγ in keV targets. Production rates and achievable radionuclidic pu- and Iγ in per cent: 191.6 (16.7), 558 (3.6), 725.2 (3.5)) has rity after chemical separation were determined.