Coherent photonuclear isotope transmutation (CPIT) produces exclusively radioactive isotopes (RIs) by coherent photonuclear (γ,n) and (γ,2n) reactions via E1 giant resonances. Photons to be used are medium energy (E(γ) ≈ 12-25 MeV) photons produced by laser photons backscattered off GeV electrons. The cross sections are as large as 0.2 -0.6 b (10 −24 cm 2 ), being independent of individual nuclides. A large fraction (∼ 5%) of photons is effectively used for the photonuclear reactions, while the scattered GeV electrons remain in the storage ring to be re-used. CPIT with medium energy photons around 10 12−15 /sec provides specific/desired RIs with the rate of 10 10−13 /sec and the RI density around 0.05-50 G Bq/mg for nuclear science, molecular biology and for nuclear medicines.Key wards: RI productions, laser photons, Compton backscattering, GeV electrons, photonuclear reactions, EI giant resonance, nuclear medicine,The present letter aims to report that CPIT (coherent photonuclear isotope transmutation) is quite powerful for exclusive RI (radio isotope) productions (transmutations). Nuclear reactions used for CPIT are coherent photonuclear reactions through giant resonances (GR) by means of laser electron photons, i.e. medium energy photons produced by laser photons backscattered off energetic GeV electrons in a storage ring. CPIT is shown to be a very efficient and realistic way to provide various kinds of RIs to be used for nuclear physics, molecular biology, nuclear medicine and for other basic and applied science.So far, (n,γ) reactions and nuclear fissions have been extensively used for RI productions and transmutations. They are caused by the strong (nuclear) interaction, while the photonuclear reactions are by EM interactions. Thus the photonuclear reaction cross section is in general much smaller than typical nuclear cross sections because of the small EM coupling constant.Low energy thermal neutrons used for (n,γ) reactions and/or nuclear fissions are easily obtained by using intense medium energy protons and/or high flux nuclear reactors. On the other hand medium energy photons required for photonuclear RI productions are hardly obtained by conventional methods.RIs produced by (n,γ) reactions and those by nuclear fissions are limited to those with large neutron capture cross sections and those with large fission branches, respectively. Many kinds of fission product RIs, however, are produced in addition to the specific isotope of interest, and thus chemical separation is indispensable for extracting the desired isotope.Laser electron photons for RI productions have been discussed, as given in re- * ) ejiri@rcnp.osaka-u.ac.jp typeset using PTPT E X.cls Ver.0.9
