V. Bradnova

SSNTD and radiochemical studies on the transmutation of nuclei using relativistic ions

Extended targets were irradiated for transmutation studies with relativistic heavy ions. For this, a metal core was surrounded by a paraffin moderator. The metal is either copper or lead and it was irradiated with deuterium, alpha, or carbon beams of 1.5 or 3.7 GeV/u at the SYNCHROPHASOTRON, LHE, JINR, Dubna, Russia. During this irradiation copious amounts of secondary neutrons are produced and studied with SSNTD detectors and radiochemical sensors, for example: 139 La (n,γ) 140 La→ B- . The yield of reaction products allows an estimation of secondary neutron fluxes. The yields of all kinds of reactions produced with deuterium and alpha beams obey to some extent the law of limiting fragmentation, i.e. they show little influence on the energy and the kind of incoming particles. However, one observes with 44 GeV 12 C ions always enhanced nuclear cross-sections induced by secondary particles. This behavior could not be confirmed with theoretical estimations based on the Dubna Cascade Model in its Cascade Evaporation Model version (DCM-CEM). Finally, some results for transmutation studies on 127 I and Cu will be presented.

Transmutation studies using ssntd and radiochemistry and the associated production of secondary neutrons

Abstract Experiments using 1.5 GeV, 3.7 GeV and 7.4 GeV protons from the Synchrophasotron, LHE, JINR, Dubna, Russia, on extended Pb- and U-targets were carried out using SSNTD and radiochemical sensors for the study of secondary neutron fluences. We also carried out first transmulation studies on the long-lived radwaste nuclei 129I and 237Np. In addition, we carried out computer code simulation studies on these systems using LAHET and DCM/CEM codes. We have difficulties to understand rather large transmutation rates observed experimentally when they are compared with computer simulations. There seems to be a rather fundamental problem understanding the large transmutation rates as observed experimentally in Dubna and CERN, as compared to those theoretical computer simulations mentioned above.

First experiments on transmutation studies of129I and237Np using relativistic protons of 3.7 GeV

First experiments on the transmutation of long-lived129I and237Np using relativistic protons of 3.7 GeV are described. Relativistic protons generate in extended Pb-targets substancial neutron fluences. These neutrons get moderated in paraffin and are used for transmutation as follows:129I(n,γ)130Iβ→ and237Np(n,γ)238Npβ→. The isotopes130I (T1/2-12.36 h) and238Np (T1/2=2.117 d) were identified radiochemically. One can estimate the transmutation cross-section (n,γ) in the given neutron field as σ(129I(n,γ))=(10±2)b and σ(237Np(n,γ))=(140±30)b The experiments were carried out in November 1996 at the Synchrophasotron, LHE, Dubna, Russia. The investigation has been performed at the Laboratory of High Energies, JINR, Dubna.

Transmutation of 239 Pu with spallation neutrons

Incineration studies of plutonium were carried out at the Synchrophasotron of the Joint Institute for Nuclear Research (JINR), Dubna, using proton beams with energies of 0.53 GeV and 1.0 GeV. Solid lead targets (8 cm in diameter and 20 cm long) were surrounded with 6 cm thick paraffin as neutron moderator and then irradiated. The transmutation of 239 Pu and the associated production of fission products 91 Sr, 92 Sr, 97 Zr, 99 Mo, 103 Ru, 105 Ru, 129 Sb, 132 Te, 133 I, 135 I and 143 Ce were studied in the present work. The plutonium samples (each 449 mg) were placed on the outer surface of moderator. For 1.0 GeV proton beam, the fission rate of 239 Pu is 0.0032 atoms per proton in one gram plutonium samples, for 0.53 GeV proton, this value is 0.0022. The experimental uncertainty is about 15%. The experiments are compared to two theoretical model calculations with moderate success, using the Dubna Cascade Model (CEM) and the LAHET code. The practical incineration rate of 239 Pu is very high. For example: if one uses 10 mA, 1 GeV proton beams under the same (fictive) experimental conditions, the incineration rate of 239 Pu via fission is 3 mg out of the 449 mg sample per day. For 0.53 GeV protons the corresponding rate is 2 mg per day.

Studies on neutron production in the interaction of 7.4 GeV protons with extended lead target

Abstract A cylindrical lead target of diameter 8 cm and length 20 cm was irradiated with 7.4 GeV protons along the axis of the cylinder. The lead target was surrounded with a paraffin layer of thickness 6 cm to moderate the neutrons produced in p + Pb reactions. The spatial distribution of the slow and fast neutrons on different surfaces of the moderator were determined using LR 115 2B detectors (through 10 B(n,α) 7 Li reactions) and CR39 detectors (through proton recoils) respectively. Such results can be valuable in the studies and design of Accelerator Driven Subcritical Nuclear Reactors and Nuclear Waste Incinerators.

Determination of spatial and energy distributions of neutrons in experiments on transmutation of radioactive waste using relativistic protons

Abstract The experiments on transmutation of 129 I and 237 Np using uranium-lead targets surrounded by a paraffin moderator were performed at the Joint Institute for Nuclear Research (JINR, Russia). The targets were irradiated by 1.5 GeV and 7.4 GeV protons at the Synchrophasotron of JINR. In the frame of present work spatial and energy distributions of neutrons on the surface of the paraffin moderator were measured using SSNTD technique. It is shown that measured values of spetral indices do not pretend on the energy of incident protons but depend on the target composition. The presence of the uranium insertion softens neutron spectra.

SSNTD studies of lead nuclei fission induced by relativistic p, d, He and 12C projectiles inside massive Pb and U targets

Abstract A series of experiments was carried out with relativistic protons, deuterons, helium and carbon-12 projectiles accelerated at SYNCHOPHASOTRON LHE, Dubna which hit massive Pb and U targets. The beam profiles and intensities of both primary particles and secondary fast neutrons were measured using plastic SSNTD inside the massive cylinder blocks of Cu, Pb and U by counting of fission fragment tracks due to the induced fission of Pb nuclei. The beam diameter increases typically by 20–30% at the depth 10 and 20 cm. With increasing the energy of projectiles the number of secondary neutrons rises with the depth for protons, deutrons and helium ions. Nevertheless, for 12 C ions beams with changing the energy from 18 GeV to 44 GeV we first observe the effect of significant increase both the yield of secondary fast neutrons and the half-width of the beam. The observed enhanced yield of secondary fast neutrons confirms unusual behavior of nuclear interaction cross section of 44 GeV 12 C ions observed earlier in our studies with massive blocks of Cu, Pb and U.

NEUTRON GENERATION IN MASSIVE Cu-TARGETS DURING THE IRRADIATION WITH 22 AND 44 GeV CARBON IONS

AbstractAn extended Cu-target was irradiated with 22 and 44 GeV carbon ions for about 11.3 and 14.7 hours, respectively. The upper side of the target was in contact with a paraffin-block for the moderation of secondary neutrons. Small holes in the moderator were filled with either lanthanum salts or uranium oxide. The reaction

Studies of neutron emission from relativistic nuclear interactions

{}^{139}La(n,\gamma ){}^{140}La\mathop \to \limits^{\beta - }