Transmutation of radioactive waste with the help of relativistic heavy ions

During November 1996 a series of experiments was carried out at the Synchropha-sotron, Laboratory of High Energies, Joint Institute for Nuclear Research, Dubna, Russia, using 3.67 GeV protons and 18 GeV (12) C ion beams. This is in continuation of experiments carried out earlier (Ochs, et al., Radiation Measurements, in print, 1997). At first, massive targets were irradiated: 1) a lead-target, 8 cm diameter, 20 cm length, surrounded by 6 cm paraffin as moderator, 2) an uranium-target, 3.6 cm diameter, surrounded by lead-rings up to 8 cm diameter, both 20 cm length, surrounded by 6 cm paraffin as moderator. The outer surface of the moderator was covered with small U- and La-sensors, to be studied by radiochemistry activation techniques, and also by solid-state nuclear track detector techniques. A first and interesting result will be reported: Both experimental techniques give independently up to about 100 low energy neutrons on the outer surface of the moderator per 3.67 GeV proton hitting the Pb-target. Theoretical estimations based on LAHET and DCM/CEM computer codes give a considerably smaller number of neutrons tall energies) of (34-35) neutrons / proton on the same surface. The DCM/CEM calculations were completed before the LAHET calculations begun. This preliminary result must be studied further. In addition, long-lived radioactive waste nuclides, such as (129) I (1.6 E+7 years) and (237) Np (2 E+6 years) were placed in well-sealed targets of approximately of 1 gram each on top of the paraffin moderator during the 3.67 GeV proton irradiation. The short-lived transmutation products, (130) I (12.4 hours) and (238) Np (2.4 days), could be identified radiochemically. The transmutation rates are substancial: A 1 MA accelerator for 3.67 GeV protons could at least transmute 30% of (237) Np and 1% of (123) I per year under the given geometrical conditions.