In modern internal radionuclide therapy, Ξ² --emitting radionuclides are often used. For this purpose the relatively high-energy Ξ²-particle emitting radionuclides 32 P (T 1/2 = 14.26 d), 89 Sr (T 1/2 = 50.53 d), and 192 Ir (T 1/2 = 73.83 d) are commonly employed and the Auger electron emitter 169 Yb (T 1/ 2 = 32.03 d) is of great potential interest. The conventional production routes of these radionuclides involve mainly the (n,Ξ³)-reaction at nuclear reactors [1] , leading to high product yields but low specific activities. In the case of 32 P and 89 Sr the (n,p)-reaction with fission neutrons has also been used. The achieved specific activity is then high, but the yield is quite low. In this work we report on new cross section measurements for the production of 32 P and 89 Sr in a fast neutron field. Furthermore, data measurements relevant to the production of 169 Yb and 192 Ir via charged particle induced reactions are also described.
Fast neutrons were produced via breakup of 14 MeV deuterons on a thick Be-target at the compact cyclotron CV 28 in JΓΌlich [2] . Proton bombardments over the energy range of 5 to 18.5 MeV were also carried out at the CV 28 and at the MGC-20E cyclotron in Debrecen. Irradiations with higher proton energies (25 to 45 MeV) were done at the injector of COSY in J ΓΌ lich. For measurement of the neutron spectrum-averaged cross section of the 32 S(n,p) 32 P process, thin sulphur layers were irradiated and the activities determined via Ξ² -counting using a gas flow proportional counter. Similarly, for the investigation of the 89 Y(n,p) 89 Sr reaction, after neutron irradiation of Y 2 O 3 , a clean radiochemical separation was performed and the product analysed via Ξ² -counting as well. Measurements on the 169 Tm(p,n) 169 Yb and 192 Os(p,n) 192 Ir reactions were performed using the stacked-foil technique. Thin samples of 169 Tm 2 O 3 were prepared using a sedimentation technique and those of enriched elemental 192 Os via electrolytic deposition. The measured neutron cross section data were compared with values calculated from the known (n,p) excitation functions and the d(Be)-neutron spectral distribution. This served as an integral test of the differential data. The (n,p) cross sections with the d(Be)-neutrons were found to be about four times higher than those with fission neutrons. No-carrier-added 32 P and 89 Sr can thus be produced more efficiently via the (n,p)-reaction using d(Be)-breakup neutrons than with fission neutrons.
Regarding the production of 169 Yb and 192 Ir via charged particle induced reactions,integral yields were calculated from the measured excitation function of the 169 Tm(p,n) 169 Yb reaction up to 45 MeV and of the 192 Os(p,n) 192 Ir reaction up to 20 MeV. The production possibilities of the two radionuclides at a cyclotron and at a nuclear reactor were evaluated, assuming at both optimum production conditions. The reactor route gives much higher yields. However, the advantage of the cyclotron route would be that a "no-carrier-added" product is obtained.
[1] Manual for reactor produced isotopes.