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S. G. Mashnik

Publications and source records attributed to S. G. Mashnik.

At least 55 records · Page 3Linked to original sources
arXiv2004

Nuclide Production in 197Au, 208Pb, and natU Irradiated with 0.8-1 GeV Protons: Comparison with other Experiments and with Theoretical Predictions

The ITEP proton synchrotron U10 was used to irradiate isotopically-enriched 208Pb and natU thin targets with 1.0 GeV protons and 197Au thin targets with 0.8 GeV protons. More than 400 cross sections of the nuclides produced were measured using the direct spectrometry method with a high-resolution Ge detector. The measured cross sections are compared with similar data obtained at GSI for kinematically inverse reactions of 1 GeV/nucleon 208Pb, 1 GeV/nucleon 238U, and 0.8 GeV/nucleon 197Au interacting with a hydrogen target and with the ZSR data on natPb and 197Au irradiated with 1 and 0.8 GeV protons, respectively. Our results are on average ~ 10 to 20% higher than the GSI data. The measured data are analyzed with the LANL codes CEM2k+GEM2 and LAQGSM+GEM2 and with the INCL intranuclear cascade code from Liege merged with the GSI evaporation/fission code ABLA.

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arXiv2004

High-Energy Threshold Reaction Rates on 0.8 GeV Proton-Irradiated Thick W and W-Na Targets

Threshold activation reaction rates in 12C, 19F, 27Al, 59Co, 63Cu, 65Cu, 64Zn, 93Nb, 115In, 169Tm, 181Ta, 197Au, and 209Bi experimental samples placed along the axis inside and outside the 0.8 GeV proton-irradiated 92-cm thick W-Na and 4-cm thick W targets where measured at the ITEP proton synchrotron. 158 reactions of up to +AH4-0.5 GeV thresholds have been measured in 123 activation samples for W-Na target, and 157 reactions in 36 activation samples for W target. The reaction rates were determined using the gamma-spectrometry method. In total, more than 1000 values of activation reactions were determined in the experiments. In both cases the measured reaction rates were compared with the LAHET code simulated rates and using several nuclear databases for the respective excitation functions, namely, ENDF/B6 for cross section of neutrons at energies below 20 MeV and MENDL2 together with MENDL2P for cross sections of protons and neutrons of 20 to 100 MeV energies. A general satisfactory agreement between simulated and experimental data has been found.

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arXiv2003

Analysis of Intermediate-Energy Nucleus-Nucleus Spallation, Fission, and Fragmentation Reactions with the LAQGSM code

The LAQGSM code has been recently developed at Los Alamos National Laboratory to simulate nuclear reactions for proton radiography applications. We have benchmarked our code against most available measured data both for proton-nucleus and nucleus-nucleus interactions at incident energies from 10 MeV to 800 GeV and have compared our results with predictions of other current models used by the nuclear community. Here, we present a brief description of our code and show illustrative results obtained with LAQGSM for neutron spectra measured recently by Nakamura's groups for reactions induced by light and medium nuclei on targets from C to Pb at several incident energies from 95 to 600 MeV/nucleon and with the recent GSI measurements of spallation, fission, and fragmentation yields from A+p and A+A reactions at incident energies near and below 1 GeV/nucleon. Further necessary work is outlined.

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arXiv2003

Evaluation of Production Cross Sections of Li, Be, B in CR

Accurate evaluation of production cross sections of light elements is important for models of CR propagation, galactic chemical evolution, and cosmological studies. However, experimental spallation cross section data are scarce and often unavailable to CR community while semi-empirical systematics are frequently wrong by a significant factor. We use all available data from LANL nuclear database together with modern nuclear codes to produce evaluated production cross sections of isotopes of Li, Be, B suitable for astrophysical applications.

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arXiv2003

Antiprotons in CR: What Do They Tell Us?

Recent measurements of the CR antiproton flux have been shown to pose a problem for conventional propagation models. In particular, models consistent with secondary/primary nuclei ratio in CR produce too few antiprotons, while matching the ratio and the antiproton flux requires ad hoc assumptions. This may indicate an additional local CR component or new phenomena in CR propagation in the Galaxy. We discuss several possibilities which may cause this problem.

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arXiv2003

Propagation of Light Elements in the Galaxy

The origin and evolution of isotopes of the lightest elements H2, He3, Li, Be, B in the universe is a key problem in such fields as astrophysics of CR, Galactic evolution, non-thermal nucleosynthesis, and cosmological studies. One of the major sources of these species is spallation by CR nuclei in the interstellar medium. On the other hand, it is the B/C ratio in CR and Be10 abundance which are used to fix the propagation parameters and thus the spallation rate. We study the production and Galactic propagation of isotopes of elements Z<6 using the numerical propagation code GALPROP and updated production cross sections.

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arXiv2003

Cross Sections for Nuclide Production in 1 GeV Proton-Irradiated 208Pb and 0.8 GeV Proton-Irradiated 197Au

Measured at ITEP (Moscow) cross sections for nuclide production in 1.0 GeV proton-irradiated 208Pb and 0.8 GeV proton-irradiated 197Au targets are presented. The cross sections were measured by direct gamma-spectrometry with a high-resolution Ge detector. The measured cross sections are compared with experimental data of GSI (inverse kinematics, 1 GeV/nucleon 208Pb and 0.8 GeV/nucleon 197Au interacting with a liquid hydrogen target, and the ZSR data (direct kinematics, 1.0 and 0.8 GeV protons on nat-Pb and 197Au, respectively). All experimental data are compared with each other and with results by the Los Alamos codes CEM2k+GEM2, LAQGSM+GEM2, and LAHET (INLC option: Cugnon's INC + Schmidt's evaporation and fission models).

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arXiv2003

Threshold Activation Reaction and Absorption Dose Rates Inside and on the Surface of a Thick W-Na Target Irradiated with 0.8-GeV Proton

Results of measured threshold activation reaction rates in 12C, 19F, 27Al, 59Co, 63Cu, 65Cu, 64Zn, 93Nb, 115In, 169Tm, 181Ta, 197Au, and 209Bi experimental samples placed both along the axis inside and outside a 0.8 GeV proton-irradiated thick W-Na target are presented. Absorption dose rates outside the target are presented as well. The target was irradiated by the proton beam from the ITEP U10 accelerator. The measured reaction rates were compared with the LAHET code simulated rates and using several nuclear databases for the respective excitation functions, namely, ENDF/B6 for cross section of neutrons at energies below 20 MeV and MENDL2 together with MENDL2P for cross section of protons and neutrons of 20 to 100 MeV energies.

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arXiv2003

Nuclide Production Cross Sections for 59Co and nat-Cu Irradiated with 0.2 and 2.6 GeV Protons and 0.2 GeV/Nucleon Carbon Ions

Results of experimental cross sections for residual nuclide production in interactions of 200 MeV/A 12C ions and 0.2 and 2.6 GeV protons with nat-Cu, 59Co, and 27Al targets are presented. The residual products are measured at ITEP (Moscow) by gamma-spectrometry with a detector of 1.8 keV resolution in the 1332 keV 60Co gamma-line. The measured data are compared with predictions by the LANL (Los Alamos) code LAQGSM+GEM2 and JINR (Dubna) code CASCADE.

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arXiv2003

Propagation of secondary antiprotons and cosmic rays in the Galaxy

Recent measurements of the cosmic ray (CR) antiproton flux have been shown to challenge existing CR propagation models. It was shown that the reacceleration models designed to match secondary to primary nuclei ratios (e.g., B/C) produce too few antiprotons. In the present paper we discuss one possibility to overcome these difficulties. Using the measured antiproton flux AND B/C ratio to fix the diffusion coefficient, we show that the spectra of primary nuclei as measured in the heliosphere may contain a fresh local "unprocessed" component at low energies perhaps associated with the Local Bubble, thus decreasing the measured secondary to primary nuclei ratio. The independent evidence for SN activity in the solar vicinity in the last few Myr supports this idea. The model reproduces antiprotons, B/C ratio, and elemental abundances up to Ni (Z<=28). Calculated isotopic distributions of Be and B are in perfect agreement with CR data. The abundances of three "radioactive clock" isotopes in CR, 10Be, 26Al, 36Cl, are all consistent and indicate a halo size z_h~4 kpc based on the most accurate data taken by the ACE spacecraft.

astro-ph↗
arXiv2003

Propagation model for cosmic ray species in the Galaxy

In a recent paper (Moskalenko et al., 2002), it has been shown that the flux of secondary cosmic ray (CR) antiprotons appears to be contradictory to measurements of secondary to primary nuclei ratios in cosmic rays when calculated in the same Galactic propagation model. The contradiction appears as a value of the diffusion coefficient necessary to match the secondary ratios antiproton/proton and B/C. In particlular, it was shown that the reacceleration models designed to match secondary to primary nuclei ratios produce too few antiprotons. It is, however, clear that some reacceleration is unavoidable in the turbulent interstellar medium. Here we discuss an idea of how to improve reacceleration model by allowing for the damping of interstellar turbulences on the small scale by cosmic rays, mostly protons. This would lead to increase in the mean free path lenghts at low energies, the well-known phenomena empirically discovered in the Leaky Box models, thus producing less secondary nuclei. Antiprotons will remain almost non-affected due to their high energy threshold of production cross section.

astro-ph↗
arXiv2002

Challenging cosmic ray propagation with antiprotons. Evidence for a "fresh" nuclei component?

Recent measurements of the cosmic ray (CR) antiproton flux have been shown to challenge existing CR propagation models. It was shown that the reacceleration models designed to match secondary to primary nuclei ratios (e.g., boron/carbon) produce too few antiprotons. Matching both the secondary to primary nuclei ratio and the antiproton flux requires artificial breaks in the diffusion coefficient and the primary injection spectrum suggesting the need for other approaches. In the present paper we discuss one possibility to overcome these difficulties. Using the measured antiproton flux AND B/C ratio to fix the diffusion coefficient, we show that the spectra of primary nuclei as measured in the heliosphere may contain a fresh local "unprocessed" component at low energies perhaps associated with the Local Bubble, thus decreasing the measured secondary to primary nuclei ratio. The independent evidence for SN activity in the solar vicinity in the last few Myr supports this idea. The model reproduces antiprotons, B/C ratio, and elemental abundances up to Ni (Z<=28). Calculated isotopic distributions of Be and B are in perfect agreement with CR data. The abundances of three "radioactive clock" isotopes in CR, 10Be, 26Al, 36Cl, are all consistent and indicate a halo size z_h~4 kpc based on the most accurate data taken by the ACE spacecraft.

astro-ph↗
arXiv2002

CEM2k and LAQGSM as Event Generators for Space-Radiation-Shielding and Cosmic-Ray-Propagation Applications

The CEM2k and LAQGSM codes have been recently developed at Los Alamos National Laboratory to simulate nuclear reactions for a number of applications. We have benchmarked our codes against most available measured data at incident particle energies from 10 MeV to 800 GeV and have compared our results with predictions of other current models used by the nuclear community. Here, we present a brief description of our codes and show illustrative results to show that CEM2k and LAQGSM can be used as reliable event generators for space-radiation-shielding, cosmic-ray-propagation, and other astrophysical applications. Finally, we show the use of our calculated cross sections together with experimental data from our LANL T-16 compilation to produce evaluated files which we use in the GALPROP model of galactic particle propagation to better constrain the size of the CR halo.

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arXiv2002

Fission Parameters Measurements for Np, Pu, Am, and Cm Isotopes Inside a Salt Blanket Micromodel

The MAKET zero-power heavy water reactor has been used at ITEP to measure the fission characteristics of the Np, Pu, Am, and Cm isotopes in the 0.52NaF+0.48ZrF_4 melt-filled salt blanket micromodel. The 237Np(n,f), 238Pu(n,f), 239Pu(n,f), 240Pu(n,f), 241Pu(n,f), 242m^Am(n,f), 243Cm(n,f), 245Cm(n,f), 247Cm(n,f), 238U(n,f), 238U(n,g), 235U(n,f) fission reaction rates have been measured. The neutron spectrum in the isotope irradiation locations was monitored by measuring the rates of the (235U(n,f), 238U(n,g), 55Mn(n,g), 63Cu(n,g), 176Lu(n,g), 197Au(n,g), 115In(n,n'), 27Al(n,4He), and 64Zn(n,p)) reactions whose cross sections have been commonly accepted. The measured functionals are compared with the respective results of MCNP code simulation obtained using the ENDF/B6 and JENDL3.2 neutron databases.

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arXiv2001

New calculation of radioactive secondaries in cosmic rays

We use a new version of our numerical model for particle propagation in the Galaxy to study radioactive secondaries. For evaluation of the production cross sections we use the Los Alamos compilation of all available experimental cross sections together with calculations using the improved Cascade-Exciton Model code CEM2k. Using the radioactive secondary ratios 26Al/27Al, 36Cl/Cl, 54Mn/Mn, we show how the improved cross-section calculations together with the new propagation code allow us to better constrain the size of the CR halo.

astro-ph↗
arXiv2000

Cross sections for nuclide production in 1 GeV proton-irradiated 208-Pb

114 cross sections for nuclide production in a 1.0 GeV proton-irradiated thin 208Pb target have been measured by the direct gamma spectrometry method 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 27Al(p,x)22Na reaction was used to monitor the proton flux. Results of a feasibility study of the auxiliary 27Al(p,x)24Na and 27Al(p,x)7Be monitor reactions in the 0.07-2.6 GeV proton-energy range are presented as well. Most of the experimental data have been analyzed by the LAHET (with ISABEL and Bertini options), CEM95, CEM2k, INUCL, CASCADE, CASCADE/INPE, and YIELDX codes that simulate hadron-nucleus interactions.

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arXiv2000

7-Li(p,n) Nuclear Data Library for Incident Proton Energies to 150 MeV

We describe evaluation methods that make use of experimental data, and nuclear model calculations, to develop an ENDF-formatted data library for the reaction p + Li7 for incident protons with energies up to 150 MeV. The important 7-Li(p,n_0) and 7-Li(p,n_1) reactions are evaluated from the experimental data, with their angular distributions represented using Lengendre polynomial expansions. The decay of the remaining reaction flux is estimated from GNASH nuclear model calculations. The evaluated ENDF-data are described in detail, and illustrated in numerous figures. We also illustrate the use of these data in a representative application by a radiation transport simulation with the code MCNPX.

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