arXiv subjects

Stepan G. Mashnik

Publications and source records attributed to Stepan G. Mashnik.

36 records · Page 2Linked to original sources

arXiv2010

High Energy Activation Data Library (HEAD-2009)

A proton activation data library for 682 nuclides from 1-H to 210-Po in the energy range from 150 MeV up to 1 GeV was developed. To calculate proton activation data, the MCNPX 2.6.0 and CASCADE/INPE codes were chosen. Different intranuclear cascade, preequilibrium, and equilibrium nuclear reaction models and their combinations were used. The optimum calculation models have been chosen on the basis of statistical correlations for calculated and experimental proton data taken from the EXFOR library of experimental nuclear data. All the data are written in ENDF-6 format. The library is called HEPAD-2008 (High-Energy Proton Activation Data). A revision of IEAF-2005 neutron activation data library has been performed: A set of nuclides for which the cross-section data can be (and were) updated using more modern and improved models is specified, and the corresponding calculations have been made in the present work. The new version of the library is called IEAF-2009. The HEPAD-2008 and IEAF-2009 are merged to the final HEAD-2009 library.

nucl-th↗

arXiv2008

Overview and Validation of the CEM and LAQGSM Event Generators for MCNP6, MCNPX, and MARS15

A brief description of the IntraNuclear cascade, preequilibrium, evaporation, fission, coalescence, and Fermi breakup models used by the last versions of our CEM and LAQGSM event generators is presented, with a focus on our latest development of all these models. The recently developed "S" and "G" versions of our codes, that consider multifragmentation of nuclei formed after the preequilibrium stage of reactions when their excitation energy is above 2A MeV using the Statistical Multifragmentation Model (SMM) code by Botvina et al. ("S" stands for SMM) and the fission-like binary-decay model GEMINI by Charity ("G" stands for GEMINI), respectively, are overviewed as well. Examples of benchmarking our models against a large variety of experimental data on particle-particle, particle nucleus, and nucleus-nucleus reactions, involving some very recent measurements of interest to accelerator radiation induced activation, are discussed.

nucl-th↗

arXiv2005

Excitation Functions of Product Nuclei from 40-2600 MeV Proton-Irradiated 206,207,208,natPb and 209Bi

The work is aimed at experimental determination of the independent and cumulative yields of radioactive residual nuclei produced in intermediate-energy proton-irradiated thin targets made of highly isotopic enriched and natural lead (206,207,208,natPb) and 209Bi. 5972 radioactive product nuclide yields have been measured in 55 thin targets induced by 0.04, 0.07, 0.10, 0.15, 0.25, 0.6, 0.8, 1.2, 1.4, 1.6, and 2.6 GeV protons extracted from the ITEP U-10 proton synchrotron. The measured data have been compared with data obtained at other laboratories as well as with theoretical simulations by seven codes. We found that the predictive power of the tested codes is different but is satisfactory for most of the nuclides in the spallation region, though none of the codes agree well with the data in the whole mass region of product nuclides and all should be improved further.

nucl-ex↗

arXiv2003

Proton-Induced Fission Cross Section Calculation with the LANL Codes CEM2K+GEM2 and LAQGSM+GEM2

The improved Cascade-Exciton Model code CEM2k and the Los Alamos version of the Quark-Gluon String Model code LAQGSM, previously merged with the Generalized Evaporation Model code of Furihata (GEM2) were further modified to provide reliable proton-induced fission cross sections for applications. By adjusting two parameters in GEM2 for each measured reaction, we were able to describe very well with CEM2k+GEM2 and LAQGSM+GEM2 all available experimental fission cross sections induced by protons with energies from 20 MeV to 10 GeV both for subactinide and actinide targets. We also successfully tested our approach on several reactions induced by neutrons, pions, and photons.

nucl-th↗

arXiv2003

Merging the CEM2K and LAQGSM Codes with GEM2 to Describe Fission and Light-fragment Production

We present the current status of the improved Cascade-Exciton Model (CEM) code CEM2k and of the Los Alamos version of the Quark-Gluon String Model code LAQGSM. To describe fission and light-fragment (heavier than He4) production, both CEM2k and LAQGSM have been merged with the GEM2 code of Furihata. We present some results on proton- and deuteron-induced spallation, fission, and fragmentation reactions predicted by these extended versions of CEM2k and LAQGSM. We show that merging CEM2k and LAQGSM with GEM2 allows us to describe many fission and fragmentation reactions in addition to the spallation reactions which are already relatively well described. Nevertheless, the standard version of GEM2 does not provide a completely satisfactory description of complex particle spectra, heavy-fragment emission, and spallation yields, and is not yet a reliable tool for applications. We conclude that we may choose to use a model similar to the GEM2 approach in our codes, but it must be significantly extended and further improved. We observe that it is not sufficient to analyze only A and Z distributions of the product yields when evaluating this type of model, as is often done in the literature; instead it is important to study all the separate isotopic yields as well as the spectra of light particles and fragments.

nucl-th↗

arXiv2003

Event Generator Benchmarking for Proton Radiography Applications

We have benchmarked the QGSM code and event generators of the MARS and LAHET3 codes as potential candidates for high-energy programs to be used in simulations for the Proton Radiography (PRad) Project. We have compiled from the literature experimental data on spectra of particles emitted from proton-induced reactions at incident energies from 30 GeV to 70 GeV on different nuclei and have performed calculations for all reactions for which we found data with these three codes without any modifications and using only default parameters and standard inputs. Our results (514 plots) show that all three codes describe reasonably most of the studied reactions, though all of them should be further improved before becoming reliable tools for PRad. We present here our conclusions concerning the relative roles of different reaction mechanisms in the production of specific secondary particles. We comment on the strengths and weaknesses of QGSM, MARS, and LAHET3 and suggest further improvements to these codes and to other models.

nucl-th↗

arXiv2002

Experimental and Theoretical Study of the Residual Product Nuclide Yields in 100-2600 MeV Proton-Irradiated Thin Targets

The work is aimed at experimental determining and computer simulating the independent and cumulative yields of residual product nuclei in the target and structure materials of the transmutation facilities driven by high-current accelerators. The ITEP U-10 accelerator was used in 48 experiments to obtain more than 4000 values of the yields of radioactive residual product nuclei in 0.1-2.6 GeV proton-irradiated thin 182,183,184,186-W, nat-W, 56-Fe, 58-Ni, 93-Nb, 232-Th, nat-U, 99-Tc, 59-Co 63,65-Cu, nat-Hg, 208-Pb, and 27-Al targets. The results of verifying the LAHET, CEM95, CEM2k, CASCADE, CASCADE/INPE, YIELDX, HETC, INUCL, and other simulation codes are presented.

nucl-ex↗

arXiv2002

Recent Developments of the Cascade-Exciton Model of Nuclear Reactions

Recent developments of the Cascade-Exciton Model (CEM) of nuclear reactions are described. The improved cascade-exciton model as implemented in the code CEM97 differs from the CEM95 version by incorporating new approximations for the elementary cross sections used in the cascade, using more precise values for nuclear masses and pairing energies, using corrected systematics for the level-density parameters, and several other refinements. We have improved algorithms used in many subroutines, decreasing the computing time by up to a factor of 6 for heavy targets. We describe a number of further improvements and changes to CEM97, motivated by new data on isotope production measured at GSI. This leads us to CEM2k, a new version of the CEM code. CEM2k has a longer cascade stage, less preequilibrium emission, and evaporation from more highly excited compound nuclei compared to earlier versions. CEM2k also has other improvements and allows us to better model neutron, radionuclide, and gas production in ATW spallation targets. The increased accuracy and predictive power of the code CEM2k are shown by several examples. Further necessary work is outlined.

nucl-th↗

arXiv2002

Benchmarking Ten Codes Against the Recent GSI Measurements of the Nuclide Yields from 208Pb, 197Au, and 238U + p Reactions at 1 GeV/nucleon

A qualitative and quantitative comparison of the recent GSI measurements of the nuclide yields from 208Pb and 238U at 1 GeV/nucleon and 197Au at 800 MeV/nucleon interactions with protons with the codes LAHET (with both ISABEL and Bertini options), CEM95, CEM97, CEM2k, CASCADE, CASCADE/INPE, YIELDX, HETC, and INUCL is presented. The predictive power of these codes is reasonable for nuclides in the near spallation region but is worse for deep spallation and much worse in the fission region. None of these codes agree well with the data in the whole mass region of product nuclides and all must be improved to become reliable tools for accelerator-driven applications.

nucl-th↗

arXiv2002

Complex Particle and Light Fragment Emission in the Cascade-Exciton Model of Nuclear Reactions

A brief description of our improvements and refinements that led from the CEM95 version of the Cascade-Exciton Model (CEM) code to CEM97 and to CEM2k is given. The increased accuracy and predictive power of the code CEM2k are shown by several examples. To describe fission and light-fragment (heavier than 4He) production, the CEM2k code has been merged with the GEM2 code of Furihata. We present some results on proton-induced fragmentation and fission reactions predicted by this extended version of CEM2k. We show that merging CEM2k with GEM2 allows us to describe many fission and fragmentation reactions in addition to the spallation reactions which are already relatively well described. We have initiated another approach to describe fission, complex particles and fragment emission by developing further our CEM2k code addressing specifically these problems. In this effort, we have developed our own universal approximation for inverse cross sections, new routines to calculate Coulomb barriers and widths of emitted particles and to simulate their kinetic energy using arbitrary approximations for the inverse cross sections. To describe fission-fragment production, we have incorporated into CEM2k a thermodynamical model of fission by Stepanov. This extended version of CEM2k allows us to describe much better complex particle emission and many fission fragments, but it is still incomplete and needs further work.

nucl-th↗

arXiv2000

CEM2k - Recent Developments in CEM

Recent developments of the Cascade-Exciton Model (CEM) of nuclear reactions are briefly described. These changes are motivated by new data on isotope production measured recently in "reverse kinematics" at GSI for interactions of 208-Pb and 238-U at 1 GeV/nucleon and 197-Au at 800 MeV/nucleon with liquid 1-H. This study leads us to CEM2k, which is a new version of the CEM code that is still under development. The increased accuracy and predictive power of the code CEM2k are shown by several examples. Further necessary work is outlined.

nucl-th↗

arXiv2000

On Solar System and Cosmic Rays Nucleosynthesis and Spallation Processes

A brief survey of nuclide abundances in the solar-system and in cosmic rays and of the believed mechanisms of their synthesis is given. The role of spallation processes in nucleosynthesis is discussed. A short review of recent measurements, compilations, calculations, and evaluations of spallation cross sections relevant to nuclear astrophysics is given as well. It is shown that in some past astrophysical simulations, old experimental nuclear data and theoretical cross sections that are in poor agreement with recent measurements and calculations were used. New astrophysical simulations using recently measured and reliably calculated nuclear cross sections, further researches in obtaining better cross sections, and production of evaluated spallation cross sections libraries for astrophysics are suggested.

astro-ph↗

arXiv2000

Study of Residual Product Nuclide Yields in 1.0 GeV Proton-Irradiated 208-Pb and 2.6 GeV Proton-Irradiated nat-W Thin Targets

113 residual product nuclide yields in a 1.0 GeV proton-irradiated thin monoisotopic 208-Pb sample and 107 residual product nuclide yields in a 2.6 GeV proton-irradiated nat-W sample have been measured and simulated by 8 different codes. The irradiations were made using proton beams extracted from the ITEP synchrotron. The nuclide yields were gamma-spectrometered directly using a high-resolution Ge-detector. The gamma-spectra were processed by the GENIE-2000 code. The ITEP-developed SIGMA code was used together with the PCNUDAT nuclear decay database to identify the gamma-lines and to determine the cross-sections. The 27-Al(p,x)Na-22 reaction was used to monitor the proton flux. The measured yields are compared with calculation the LAHET (with ISABEL and Bertini options), CEM95, CEM2k, CASCADE, CASCADE/INPE, INUCL, and YIELDX codes. Estimates of the mean deviation factor are used to demonstrate the predictive power of the codes. The results obtained may be of interest in studying the parameters of the Pb and W target modules of the hybrid Accelerator-Driven System (ADS) facilities.

nucl-ex↗

arXiv2000

Study of Residual Product Nuclide Yields from 0.1, 0.2, 0.8, and 2.6 GeV Proton-Irradiated nat-Hg Targets

The direct gamma-spectrometry method is used to measure more than 350 residual product nuclide yields from 0.1, 0.2, 0.8, and 2.6 GeV proton irradiated HgO targets. The gamma-spectrometer resolution is of 1.8 keV at the 1332 keV gamma-line. The resultant gamma-spectra are processed by the GENIE-2000 code. The gamma-lines are identified, and the cross-sections calculated, by the ITEP-designed SIGMA code using the PCNUDAT radioactive database. The 27-Al(p,x)Na-22 reaction is used as monitor. The experimental results are compared with calculations by the LAHET, CEM95, CEM2k, INUCL, CASCADE, and YIELDX codes.

nucl-ex↗

arXiv2000

Spectral Measurements of Neutrons from Pb, W, and Na Targets Irradiated by 0.8 AND 1.6 GeV Protons

Preliminary results of neutron spectra measurements from Pb, W, and Na targets irradiated by 0.8 and 1.6 GeV protons are presented. Measurements have been carried out using the proton beam extracted from the ITEP synchrotron and the TOF technique. Neutron registration has been carried out using BICRON MAB-511 liquid scintillation counters. Spectra measured at angles of 30, 60, 90, 120, and 150 degrees have been compared with results of their simulation using the LAHET code system and the code CEM2k. The results are of interest both from data gathering viewpoint and as a benchmark of the up-to-the-date predictive powers of codes applied to design the hybrid Accelerator Driven Systems (ADS) using lead or lead-bismuth targets and sodium-cooled targets.

nucl-ex↗

arXiv2000

Threshold Reaction Rates Inside and on the Surface of Thick W-Na Target Irradiated with 0.8 GeV Protons

The preliminary results are presented of the experimental determination of threshold reaction rates in experimental samples made of Al, Co, Bi, In, Au, to name but a few, placed both inside and on the surface of extended thick W-Na target irradiated with 0.8 GeV protons. The target consists of 26 alternating discs each 150 mm in diameter: 6 tungsten discs are 20 mm thick, 7 tungsten discs are 40 mm thick, and 13 sodium discs are 40 mm thick. The relative position of discs is matched with the aim of flattening the neutron field along the target surface. The comparison is made of the measured rates with results of their simulation using the LAHET and KASKAD-S codes, and the ENDF/B6, MENDL2, MENDL2P, SADKO-2, and ABBN-93 databases. The results are of interest both in terms of integral data collection and to test the up-to-the-date predictive power of the codes applied in designing of hybrid Accelerator Driven System (ADS) systems that use tungsten targets cooled with sodium.

nucl-ex↗

arXiv1998

Modeling Fission in the Cascade-Exciton Model

Recent developments of the Cascade-Exciton Model (CEM) of nuclear reactions to describe high energy particle induced fission are briefly described. The increased accuracy and predictive power of the CEM are shown by several examples. Further necessary work is outlined.

nucl-th↗

arXiv1998

Improved Cascade-Exciton Model of Nuclear Reactions

Recent improvements to the Cascade-Exciton Model (CEM) of nuclear reactions are briefly described. They concern mainly the cascade stage of reactions and a better description of nuclei during the preequilibrium and evaporation stages of reactions. The development of the CEM concerning fission is given in a separate talk at this conference. The increased accuracy and predictive power of the CEM are shown by several examples. Possible further improvements to the CEM and other models are discussed.

nucl-th↗