Investigation of 50Cr(d,n)51Mn and natCr(p,x)51Mn processes with respect to the production of the positron emitter 51Mn

The positron emitter 51Mn (t1/2 = 46.2 min, Iβ+ = 97%) is of potential interest in positron emission tomography (PET). With a view to optimizing its production route, excitation functions for deuteron induced nuclear reactions on isotopically enriched (~95%) 50Cr were determined radiochemically over the energy range of 3 to 13 MeV and for proton induced nuclear reactions on natCr in the range of 18 to 38 MeV. Cross sections are presented for the reactions: 50Cr(d,2n) 50mMn, 50Cr(d,n) 51Mn, 50Cr(d,t)49Cr, 50Cr(d,p)51Cr, 50Cr(d,a)48V, 52Cr(d,2p)52V, natCr(p,x) 51Mn, natCr(p,x)52Mn, natCr(p,x)52mMn, natCr(p,x)54Mn, natCr(p,x)48Cr, natCr(p,x)49Cr, natCr(p,x) 51Cr, natCr(p,x)48V and natCr(p,x)45Ti. In the case of proton induced reactions on natCr, the isomeric cross section ratio for the isomeric pair 52m,gMn was also determined. The results are interpreted in terms of the spins of the two isomers concerned. Theoretical thick target yields were derived from the corresponding excitation functions. The maximum achievable thick target yield of 51Mn is 1.1 GBq/μAh in the case of the 50Cr(d,n) 51Mn reaction at Ed = 14 → 3 MeV, and 3.2 GBq/μAh in the case of the natCr(p,x)51Mn process for Ep = 40 → 20 MeV. The 50Cr(d,n) 51Mn process is the favourable production route for 51Mn, since the radioisotopic purity is high and a small-sized medical cyclotron is adequate to produce this positron emitter in sufficient quantities.

Spallation processes and nuclear interaction products of cosmic rays

Most cosmic-ray nuclei heavier than helium have suffered nuclear collisions in the interstellar gas, with transformation of nuclear composition. The isotopic and elemental composition at the sources has to be inferred from the observed composition near the Earth. The source composition permits tests of current ideas on sites of origin, nucleosynthesis in stars, evolution of stars, the mixing and composition of the interstellar medium and injection processes prior to acceleration. The effects of nuclear spallation, production of radioactive nuclides and the time dependence of their decay provide valuable information on the acceleration and propagation of cosmic rays, their nuclear transformations, and their confinement time in the Galaxy. The formation of spallation products that only decay by electron capture and are relatively long-lived permits an investigation of the nature and density fluctuations (like clouds) of the interstellar medium. Since nuclear collisions yield positrons, antiprotons, gamma rays and neutrinos, we shall discuss these topics briefly.