M.I. Krivopustov

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.

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.

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.

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.

Wide angle emission of heavy fragments in relativistic heavy ion collisions and some open problems

Abstract The concept of INFORMATION is reintroduced again and connected to the most recent copper target experiments. The further developments of the “ARBUZOV”-Target using CR-39 detectors and relativistic heavy ions are given.

On the use of SSNTD in relativistic heavy ion physics and the study of open questions

Abstract Taking an historic perspective on the development of relativistic physics in general and relativistic heavy ion physics in particular, it can be shown that many observations were first made with nuclear emulsions and other SSNTD detectors, later confirmed with conventional counter techniques and/or radiochemical techniques. It is quite possible that SSNTD can make similar contributions when studying the open and controversal problems of today. In this article we consider the anomalon phenomenon as to be one such problem.

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.

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.