M. Zamani

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.

An individual neutron dosemeter with (n,α) and (n,p) converters

Abstract An individual neutron dosemeter based on the CR-39 SSNT detector was investigated during the Eurados-Cendos Joint Irradiation Programs 1990 and 1992. A polyethylene moderator was used as the (n,p) converter. 6 Li-enriched LiF as well as Li 2 B 4 O 7 with natural B were used as additional radiators. The important characteristics of an individual dosemeter, such as its energy response, angular response and linearity, are presented. The lowest detectable dose is also discussed.

Secondary neutron production from thick Pb target by light particle irradiation

Abstract Neutron multiplicities from spallation neutron sources were measured by Solid State Nuclear Track Detectors. Light particles as protons, deuterons and alphas in the GeV range were used on Pb targets. For neutron thermalization the targets were covered by 6 cm paraffin moderator. Neutron multiplicity distributions were studied inside and on the moderator surface. Comparison of SSNTDs results were made for thermal-epithermal neutrons with 139 La activation method as well as with Dubna DCM/CEM code. Discussion including previous 12 C results are given.

Application of activation methods on the Dubna experimental transmutation set-ups.

High spallation neutron fluxes were produced by irradiating massive heavy targets with proton beams in the GeV range. The experiments were performed at the Dubna High Energy Laboratory using the nuclotron accelerator. Two different experimental set-ups were used to produce neutron spectra convenient for transmutation of radioactive waste by (n,x) reactions. By a theoretical analysis neutron spectra can be reproduced from activation measurements. Thermal-epithermal and fast-super-fast neutron fluxes were estimated using the 197Au, 238U (n,gamma) and (n,2n) reactions, respectively. Depleted uranium transmutation rates were also studied in both experiments.

High flux neutron production from 12C beams on heavy targets

Abstract Spallation neutrons produced from 12 C ions at 18 and 44 GeV on Cu and Pb targets were studied as well as thermalization in appropriate moderators. The irradiation were performed at the Dubna LHE Synchrophasotron. Results are given for thermal and fast neutrons estimated and compared with different experimental methods.

Dose measurements around spallation neutron sources.

Neutron dose measurements and calculations around spallation sources appear to be of great importance in shielding research. Two spallation sources were irradiated by high-energy proton beams delivered by the Nuclotron accelerator (JINR), Dubna. Neutrons produced by the spallation sources were measured by using solid-state nuclear track detectors. In addition, neutron dose was calculated after polyethylene and concrete, using a phenomenological model based on empirical relations applied in high-energy physics. The study provides an analytical and experimental neutron benchmark analysis using the transmission factor and a comparison between the experimental results and calculations.

Shielding around spallation neutron sources.

Spallation neutron sources provide more intense and harder neutron spectrum than nuclear reactors for which a substantial amount of shielding measurements have been performed. Although the main part of the cost for a spallation station is the cost of the shielding, measurements regarding shielding for the high energy neutron region are still very scarce. In this work calculation of the neutron interaction length in polyethylene moderator for different neutron energies is presented. Measurements which were carried out in Nuclotron accelerator at the Laboratory of High Energies (Joint Institute for Nuclear Research, Dubna) and comparison with calculation are also presented. The measurements were performed with Solid State Nuclear Track Detectors (SSNTDs).

Measurement of inelastic cross sections in relativistic deuteron-on-lead reactions

The inelastic cross section of deuterons hitting a lead target has been determined by the beam attenuation technique. A spallation neutron source based on a lead target was irradiated with 1.6- and 2.5-GeV deuterons. Solid-state nuclear track detectors as well as the activation method were used to obtain the neutron and proton distribution along the surface of the source. The attenuation coefficient was estimated by fitting the experimental data and taking into account the buildup effect and the beam attenuation. Using the attenuation coefficient, the interaction length and then the inelastic cross section of deuterons on lead reaction were determined.

Ternary events measured with CR-39 in the 238U + 197Au reaction at 15 MeV/nucleon

Abstract We report the study of the reaction 15 MeV/nucleon 238 U + 197 Au , in which up to 7 final heavy fragments have been detected, using a CR-39 plastic nuclear track detector. The measured multiplicity distributions indicate that the binary fission of one (U-like) or both (U-like and Au-like) primary products clearly dominates for peripheral and intermediate impact parameters exhausting more than 80% of the total cross section. Multifragment emission sets in for the most central collisions. Reactions with 3 heavy final fragments, accounting for half of the total cross section, have been analysed event-by-event after measuring the geometrical parameters of each detected track, assuming momentum conservation and using empirical range-energy-charged curves. Most of these ternary processes originate in a two-step mechanism: a initial peripheral projectile-target interaction plus a deep-inelastic process followed by the subsequent fission-like decay of one of the fragments (mainly the quasiprojectile). Indeed, the relative velocity between the two fastest fragments are clearly peaked at values close to the Viola systematics for the fission of a very-heavy nucleus.

Nuclear physicsTernary events measured with CR-39 in the 238U + 197Au reaction at 15 MeV/nucleon

Abstract We report the study of the reaction 15 MeV/nucleon 238 U + 197 Au , in which up to 7 final heavy fragments have been detected, using a CR-39 plastic nuclear track detector. The measured multiplicity distributions indicate that the binary fission of one (U-like) or both (U-like and Au-like) primary products clearly dominates for peripheral and intermediate impact parameters exhausting more than 80% of the total cross section. Multifragment emission sets in for the most central collisions. Reactions with 3 heavy final fragments, accounting for half of the total cross section, have been analysed event-by-event after measuring the geometrical parameters of each detected track, assuming momentum conservation and using empirical range-energy-charged curves. Most of these ternary processes originate in a two-step mechanism: a initial peripheral projectile-target interaction plus a deep-inelastic process followed by the subsequent fission-like decay of one of the fragments (mainly the quasiprojectile). Indeed, the relative velocity between the two fastest fragments are clearly peaked at values close to the Viola systematics for the fission of a very-heavy nucleus.