Development of novel positron emitters for medical applications: nuclear and radiochemical aspects

In molecular imaging, the importance of novel longer lived positron emitters, also termed as non-standard or innovative PET radionuclides, has been constantly increasing, especially because they allow studies on slow metabolic processes and in some cases furnish the possibility of quantification of radiation dose in internal radiotherapy. Considerable efforts have been invested worldwide and about 25 positron emitters have been developed. Those efforts relate to interdisciplinary studies dealing with basic nuclear data, high current charged particle irradiation, efficient radiochemical separation and quality control of the desired radionuclide, and recovery of the enriched target material for reuse. In this review all those aspects are briefly discussed, with particular reference to three radionuclides, namely Cu-64, I-124 and Y-86, which are presently in great demand. For each radionuclide several nuclear routes were investigated but the (p, n) reaction on an enriched target isotope was found to be the best for use at a small-sized cyclotron. Some other positron emitting radionuclides, such as Co-55, Br-76, Zr-89, (82)mRb, (94)mTc, I-120, etc., were also produced via the low-energy (p, n), (p, a) or (d, n) reaction. On the other hand, the production of radionuclides Fe-52, Se-73, Sr-83, etc. using intermediate energy (p, xn) or (d, xn) reactions needs special consideration, the nuclear data and chemical processing methods being of key importance. In a few special cases, a high intensity He-3- or a-particle beam could be an added advantage. The production of some potentially interesting positron emitters via generator systems, for example Ti-44/Sc-44, Se-72/As-72 and Nd-140/Pr-140 is considered. The significance of new generation high power accelerators is briefly discussed

Excitation Functions of the 50Cr(n, np+pn+d)49V, 58Ni(n,alpha)55Fe, 58Ni(n, alpha.p+p.alpha)54Mn and 62Ni(n,alpha)59Fe Reactions.

Excitation functions were measured for the 50Cr(n,np+pn+d)49V, 58Ni(n,a)55Fe, 58Ni(n,ap+pa)54Mn and 62Ni(n,a)59Fe reactions from 7.5 to 19.4 MeV. Use was made of the activation technique in combination with non-destructive high-resolution g-ray spectrometry or X-ray spectrometry after radiochemical separation and thin sample preparation. Quasi-monoenergetic neutrons produced via the 2H(d,n)3He and 3H(d,n) 4He reactions were used to irradiate samples of metallic natural chromium and nickel, respectively. The neutron fluxdensities were determined via the 27Al(n,a)24Na (for En < 12.5 MeV) and 93Nb(n,2n)92mNb (for En < 12.5MeV) monitor reactions. Apart from the 58Ni(n,ap+pa)54Mn reaction, our results represent the first cross sections beyond 15 MeV. The values for the 58Ni(n,a) 55Fe reaction between 7.5 and 12.3 MeV are lower than those in an earlier activation experiment but support the lower trend of literature values determined via the charged particle detection method. A renormalisation of the earlier activation data with respect to the more recent monitor cross section values reduces the discrepancy. Statistical model calculations incorporating precompound effects were to be in good agreement with the present data, depicting that both first and second chance emission of nucleons are treated satisfactorily in the calculations.JRC.D-Institute for Reference Materials and Measurements (Geel

EXCITATION-FUNCTIONS OF THRESHOLD REACTIONS ON SC-45 AND MN-55 INDUCED BY 6 TO 13 MEV NEUTRONS

Excitation functions were measured for the Sc-45(n,2n)Sc-44(m), Sc-45(n,2n)Sc-44(m+g), and Mn-55(n,2n)Mn-54 reactions from threshold to 13 MeV, and for the Sc-45(n,p)Ca-45, Sc-45(n,alpha)K-42, Mn-55(n,p)Cr-55, and Mn-55(n,alpha)V-52 reactions over the neutron energy range of 6 to 13 MeV. The quasimonoenergetic neutrons were produced via the H-2(d,n)He-3 reaction using a deuterium gas target at a variable energy compact cyclotron. The activation technique in combination with high resolution gamma-ray spectroscopy was used. In the case of the Sc-45(n,p)Ca-45 and Mn-55(n,p)Cr-55 reaction products, ''low-level'' beta(-) counting was applied. The reaction product Ca-45 was separated radiochemically prior to beta(-) counting. Statistical model calculations taking into account precompound effects were performed for all the reactions studied. The experimental excitation functions are reproduced well by the calculation except for the (n,alpha) reaction on the (SC)-S-45 target

A critical survey of experimental cross section data, comparison with nuclear model calculations and estimation of production yields of 77Br and 77Kr in no-carrier-added form via various nuclear processes

Experimentally investigated nuclear reactions for production of no-carrier-added Br-77 and Kr-77 were critically surveyed. The survey covered nine reactions for the formation of Br-77 and six reactions for Kr-77. Both radionuclides are simultaneously produced in many of the studied nuclear processes. The experimental data were compared with the results of nuclear model calculations based on the computer code ALICE-IPPE and the third version of TALYS-based Evaluated Nuclear Data Library, TENDL-2010. Good agreement was found over extended energy regions for the p-, He-3- and alpha-particle induced reactions on several target materials. In case of d-induced reactions, however, considerable discrepancies were noted between the experimental and theoretical data. The concordant sets of experimental cross section data for each reaction were fitted by a polynomial function to obtain a trend curve. From the thus obtained trend curves the yields of both Br-77 and Kr-77 were calculated. A discussion of suitable production routes is given. (C) 2011 Elsevier B.V. All rights reserved

Excitation functions of 3He-particle induced reactions on 101Ru and 102Ru for production of the medically interesting radionuclide 101mRh

Using the stacked-foil technique with thin enriched ruthenium targets, excitation functions of 101Ru(3He,x)101mRh, 102Ru(3He,x)101mRh and several other reactions were measured to study the possibility of production of the medical radioisotope 101mRh in helion induced reactions. The 3He-ion energy region extended up to 34 MeV. The 101Ru(3He,x)101mRh reaction was found to be the most effective one. The integral thick target yield of the product radionuclide 101mRh calculated from the excitation function amounts to 16.1 MBq/µAh with the sum of the long-lived impurities 101gRh, 102mRh, and 102gRh being 0.5% at the maximum bombarding energy

Formation of the isomeric pair 194Irm,g in interactions of alpha-particles with 192Os

Cross sections were measured by the activation technique for the nuclear processes Os-192(alpha,d+pn+np)Ir-194(m,g) up to alpha-particle energies of 39 MeV. From the measured data the isomeric cross-section ratio was deduced as a function of projectile energy. The present experimental data as well as those for the Pt-194(n,p)Ir-194(m,g) reaction, given in the literature, were compared with the results of nuclear model calculations using the code TALYS, which combines the statistical, precompound, and direct interactions. In general, the experimental data were reproduced well by the model calculations, which were done using relatively low values of eta (i.e., Theta(eff)/Theta(rigid)). The results provide more evidence for the mass dependence of eta. The level density parameter for Ir-194 was determined unambiguously