R. Odoj

Transmutation of 129I and 237Np using spallation neutrons produced by 1.5, 3.7 and 7.4 GeV protons

Abstract Small samples of 129I and 237Np, two long-lived radwaste nuclides, were exposed to spallation neutron fluences from relatively small metal targets of lead and uranium, that were surrounded with a 6xa0cm thick paraffin moderator, and irradiated with 1.5, 3.7 and 7.4xa0GeV protons. The (n,γ) transmutation rates were determined for these nuclides. Conventional radiochemical La- and U-sensors and a variety of solid-state nuclear track detectors were irradiated simultaneously with secondary neutrons. Compared with results from calculations with well-known cascade codes (LAHET from Los Alamos and DCM/CEM from Dubna), the observed secondary neutron fluences are larger.

Determination of energetic neutron spatial distribution using neutron induced nuclear recoil events

Abstract Neutron induced nuclear recoils were used to determine the spatial distribution of the weakly moderated spallation neutrons produced in the interaction of 1 GeV protons with lead and uranium–lead targets. CR39 plastic track detectors were used to record neutron-induced recoil tracks. The track density measurements were carried out using a fully automated optical microscope. The experimental results were compared with Monte Carlo simulations using MCNPX-2.1.5 code and an extension code that was written for this purpose. A good agreement was found between the experiment and calculations for normalised results. Applicability of the MCNPX-2.1.5 code for absolute recoil track density determination is discussed.

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.

Monitor reactions in Al-foils for high energy proton beams bombarding a thick target

Abstract During the bombardment of U and Pb targets (each 21 cm thick) with protons of energy 1.0 and 1.5 GeV, the reactions 27Al(p, 3pn)24Na and nat.Cu(p, X)24Na were studied as monitor reactions. The influence of 27Al(n, α)24Na on the monitor reaction 27Al(p, 3pn)24Na was investigated experimentally and theoretically. In order to avoid the influence of (n, α) reaction, placing of the Al-monitors 35 cm upstream the massive targets is recommended. This method may be used in Accelerator-Driven-Transmutation (ADT) studies of long-lived nuclear waste, where one always uses a massive heavy element target irradiated with protons at about 1 GeV. The experiments were performed at the Laboratory of High Energies, JINR, Dubna, Russian Federation.

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.

Monte Carlo calculations on transmutation of trans-uranic nuclear waste isotopes using spallation neutrons: difference of lead and graphite moderators

Abstract Transmutation rates of 239 Pu and some minor actinides ( 237 Np, 241 Am, 245 Cm and 246 Cm), in two accelerator-driven systems (ADS) with lead or graphite moderating environments, were calculated using the LAHET code system. The ADS that were used had a large volume (∼32xa0m 3 ) and contained no fissile material, except for a small amount of fissionable waste nuclei that existed in some cases. Calculations were performed at an incident proton energy of 1.5xa0GeV and the spallation target was lead. Also breeding rates of 239 Pu and 233 U as well as the transmutation rates of two long-lived fission products 99 Tc and 129 I were calculated at different locations in the moderator. It is shown that an ADS with graphite moderator is a much more effective transmuter than that with lead moderator.

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.

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.

Interactions of Relativistic Heavy Ions in Thick Heavy Element Targets and Some Unresolved Problems

Interactions of relativistic heavy ions with total energies above 30 GeV in thick Cu and Pb targets (≥ 2 cm) have been studied with various techniques. Radiochemical irradiation experiments using thick Cu targets, both in a compact form or as diluted “2π-Cu targets” have been carried out with several relativistic heavy ions, such as 44 GeV 12C (JINR, Dubna, Russia) and 72 GeV 40Ar (LBL, Berkeley, USA). Neutron measuring experiments using thick targets irradiated with various relativistic heavy ions up to 44 GeV 12C have been performed at the JINR. In addition, the number of “black prongs” in nuclear interactions (due to protons with energies less than 30 MeV and emitted from the target-like interaction partner at rest) produced with 72 GeV 22Ne ions in nuclear emulsion plates has been measured in the first nuclear interaction of the primary 22Ne ion and in the following second nuclear interaction of the secondary heavy (Z > 1) ion. Some essential results have been obtained. (1) Spallation products produced by relativistic secondary fragments in interactions ([44 GeV 12C or 72 GeV 40Ar] + Cu) within thick copper yield fewer products close to the target and many more products far away from the target as compared to primary beam interactions. This applies also to secondary particles emitted into large angles (Θ > 10°). (2) The neutron production of 44 GeV 12C within thick Cu and Pb targets is beyond the estimated yield as based on experiments with 12 GeV 12C. These rather independent experimental results cannot be understood within well-accepted nuclear reaction models. They appear to present unresolved problems.

Experimental and Monte-Carlo studies of the spatial distribution of neutrons around extended Pb-spallation target

Abstract The spatial distribution of thermal and fast neutrons on the surface of a paraffin moderator surrounding a cylindrical lead target, irradiated with 1 GeV protons was studied. The lead target had 8 cm diameter and 20 cm length. The thickness of the paraffin around the target was 6 cm . The slow and fast neutron distributions were determined using LR 115 2B and CR-39 detectors via the 10 B ( n ,α) reaction and neutron induced nuclear recoils, respectively. The observed slow and fast neutron distributions on the surface of the paraffin were compared with Monte-Carlo simulations using the MCNPX-2.1.5 code.