S. Mashnik - Academia.edu (original) (raw)

Papers by S. Mashnik

Physics of Atomic Nuclei, 2010

The recoil properties of the product nuclei from the interaction of 2.2 GeV/nucleon 12 C ions fro... more The recoil properties of the product nuclei from the interaction of 2.2 GeV/nucleon 12 C ions from Nuclotron of the Laboratory of High Energies (LHE), Joint Institute for Nuclear Research (JINR) at Dubna with a 118 Sn target have been studied using catcher foils.

Advanced Monte Carlo for Radiation Physics, Particle Transport Simulation and Applications, 2001

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2014

Fragmentation reactions induced on light target nuclei by protons and light nuclei of energies ar... more Fragmentation reactions induced on light target nuclei by protons and light nuclei of energies around 1 GeV/nucleon and below are studied with the latest Los Alamos Monte Carlo transport code MCNP6 and with its cascade-exciton model (CEM) and Los Alamos version of the quark-gluon string model (LAQGSM) event generators, version 03.03, used as stand-alone codes. Such reactions are involved in different applications, like cosmic-ray-induced single event upsets (SEU's), radiation protection, and cancer therapy with proton and ion beams, among others; therefore, it is important that MCNP6 simulates them as well as possible. CEM and LAQGSM assume that intermediate-energy fragmentation reactions on light nuclei occur generally in two stages. The first stage is the intranuclear cascade (INC), followed by the second, Fermi breakup disintegration of light excited residual nuclei produced after INC. Both CEM and LAQGSM account also for coalescence of light fragments (complex particles) up to 4 He from energetic nucleons emitted during INC. We investigate the validity and performance of MCNP6, CEM, and LAQGSM in simulating fragmentation reactions at intermediate energies and discuss possible ways of further improving these codes.

Accurate evaluation of production cross sections of light elements is important for models of CR ... more 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.

An extended version of the Cascade-Exciton Model (CEM) of nuclear reactions is applied to analyze... more An extended version of the Cascade-Exciton Model (CEM) of nuclear reactions is applied to analyze nucleon-induced fission cross sections for 209 Bi and 208 Pb nuclei in the 45-500 MeV energy range. The available data on linear momentum transfer are analyzed as well. The results are compared with analytical approximations resulting from a comparative critical analysis of all available experimental data. Systematic discrepancies between calculations and experimental data are revealed. A modification of the CEM is proposed, which significantly improves the model predictions for projectile energies above 100 MeV.

Journal of Nuclear Science and Technology, 2002

Emission of light fragments (LF) from nuclear reactions is an open question. Different reaction m... more Emission of light fragments (LF) from nuclear reactions is an open question. Different reaction mechanisms contribute to their production; the relative roles of each, and how they change with incident energy, mass number of the target, and the type and emission energy of the fragments is not completely understood. None of the available models are able to accurately predict emission of LF from arbitrary reactions. However, the ability to describe production of LF (especially at energies > 30 MeV) from many reactions is important for different applications, such as cosmic-ray induced Single Event Upsets (SEUs), radiation protection, and cancer therapy with proton and heavy-ion beams, to name just a few. The Cascade-Exciton Model (CEM), version 03.03 and the Los Alamos version of the Quark-Gluon String Model (LAQGSM), version 03.03 event generators in Monte Carlo N-Particle Transport Code version 6 (MCNP6), describe quite well the spectra of fragments with sizes up to 4He across a b...

Emission of light fragments (LF) from various nuclear reactions is an interesting unsolved scient... more Emission of light fragments (LF) from various nuclear reactions is an interesting unsolved scientific question. Different reaction mechanisms contribute to their production; with different dependencies on incident particle, incident energy, mass number of the target, and the type and emission energy of the fragments. Available models cannot accurately predict emission of LF from arbitrary reactions. However, the emission of LF, especially of intermediate and high energies, is important for many applications, such as cosmic-ray induced Single Event Upsets, radiation protection, and cancer therapy with proton and heavy-ion beams, to name just a few. The Cascade-Exciton Model (CEM) and the Los Alamos version of the Quark-Gluon String Model (LAQGSM) as implemented in the CEM03.03 and LAQGSM03.03 event generators used in the Los Alamos Monte Carlo transport code MCNP6 describe quite well the spectra of fragments with sizes up to 4He across a broad range of target masses and incident ener...

The "condensation" probability, gammaj\gamma_jgammaj , is an important variable in the preequilib... more The "condensation" probability, gammaj\gamma_jgammaj , is an important variable in the preequilibrium stage of nuclear spallation reactions. It represents the probability that pjp_jpj excited nucleons (excitons) will "condense" to form complex particle type jjj in the excited residual nucleus. It has a significant impact on the emission width, or probability of emitting fragment type jjj from the residual nucleus. This paper explores the formulation of a new model for gammaj\gamma_jgammaj, one which is energy-dependent, and which provides improved fits compared to experimental fragment spectra.

The LAQGSM code has been recently developed at Los Alamos National Laboratory to simulate nuclear... more 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.

A relativistic kinetic equation (RKE) is obtained in the nucleon sector of the relativistic nucle... more A relativistic kinetic equation (RKE) is obtained in the nucleon sector of the relativistic nuclear Walecka model on the dynamical basis using the non-equilibrium operator method. The correspondence of different forms of Vlasov-type integrals to collision integrals (CI) is analyzed. It is shown that the integral of the Vlasov-type in the mean-field approximation must be conformed to a CI of the Bloch type while the integral of the Vlasov-type in the Hartree-Fock approximation corresponds to a CI of the Boltzmann-Uehling-Uhlenbeck type. The RKE of the Vlasov type in the Hartree-Fock approximation obtained here includes all basic relativistic quantum effects typical of the Walecka model, in particular, spin effects and negative-energy states. The problem of "alive" mesons is discussed as well.

The present report is devoted to the development of a kinetic approach for the description of a n... more The present report is devoted to the development of a kinetic approach for the description of a non-equilibrium nuclear matter at intermediate energies. A relativistic kinetic equation (RKE) of the Vlasov-type for the nucleon sector of the quantum hadrodynamics is obtained taking into account the exchange effects and the strong averaged nuclear field ones. This RKE is analyzed for the case of a spin-saturated nuclear matter. Calculations are carried out in the framework of the co-variant version of the non-equilibrium statistical operator method. A kinetic effect of suppression and amplification of the quasi-particle states with positive and negative energies was revealed.

ABSTRACT The relativistic kinetic equations describing nuclear reactions at intermediate energies... more ABSTRACT The relativistic kinetic equations describing nuclear reactions at intermediate energies are obtained on the dynamical basis. These equations are analyzed and realized in several versions of the Cascade Exciton Model (CEM). The CEM assumes That reactions occur in three stages: the intranuclear cascade, pre-equilibrium and the evaporative ones. A large variety of experimental data on hadron- and photo-nuclear reactions in the bombarding energy range up to several GeV are analyzed in this approach. The contributions of different pion and photon absorption mechanisms in these reactions are estimated. The CEM describes adequately nuclear reactions at intermediate energies and has one of the best predictive powers as compared to other available modern models.

Il Nuovo Cimento A

A comparison of two methods in the relativistic kinetic theory of the Fermi systems is carried ou... more A comparison of two methods in the relativistic kinetic theory of the Fermi systems is carried out by assuming, as an example, the simplest σω-version of quantum hadrodynamics with allowance for strong mean meson fields. It is shown that the Vlasov-type relativistic kinetic equation (VRKE) obtained by means of the procedure of squaring at an intermediate step is responsible for unphysical features. A direct method of derivation of kinetic equations is proposed. This method does not contain such drawback and gives rise to VRKE in hadrodynamics of a non-contradictory form in which both spin degrees of freedom and states with positive and negative energies are taken into account.

A cascade model has been developed to study pion induced multichannel reactions (quasielastic, SC... more A cascade model has been developed to study pion induced multichannel reactions (quasielastic, SCX, DCX, absorption and pion production) at pion energies above 0.5 GeV. Special attention has been paid to pion double charge exchange. Pion production is a determinant feature in the high energy pion nucleus reactions, and the DCX signal not related to pion production is sizeable only at forward angles and for high energy outgoing pions. The contribution to DCX of the conventional mechanism, with two quasielastic SCX steps decreases very fast as a function of the energy and reaches very low values at energies above 0.7 GeV. This opens the opportunity of having sizeable contributions of exotic mechanisms that are negligible at the delta resonance energies. Comment: 17 pages, 8 figures, LaTeX

Physics of Atomic Nuclei, 2010

The recoil properties of the product nuclei from the interaction of 2.2 GeV/nucleon 12 C ions fro... more The recoil properties of the product nuclei from the interaction of 2.2 GeV/nucleon 12 C ions from Nuclotron of the Laboratory of High Energies (LHE), Joint Institute for Nuclear Research (JINR) at Dubna with a 118 Sn target have been studied using catcher foils.

Advanced Monte Carlo for Radiation Physics, Particle Transport Simulation and Applications, 2001

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2014

Fragmentation reactions induced on light target nuclei by protons and light nuclei of energies ar... more Fragmentation reactions induced on light target nuclei by protons and light nuclei of energies around 1 GeV/nucleon and below are studied with the latest Los Alamos Monte Carlo transport code MCNP6 and with its cascade-exciton model (CEM) and Los Alamos version of the quark-gluon string model (LAQGSM) event generators, version 03.03, used as stand-alone codes. Such reactions are involved in different applications, like cosmic-ray-induced single event upsets (SEU's), radiation protection, and cancer therapy with proton and ion beams, among others; therefore, it is important that MCNP6 simulates them as well as possible. CEM and LAQGSM assume that intermediate-energy fragmentation reactions on light nuclei occur generally in two stages. The first stage is the intranuclear cascade (INC), followed by the second, Fermi breakup disintegration of light excited residual nuclei produced after INC. Both CEM and LAQGSM account also for coalescence of light fragments (complex particles) up to 4 He from energetic nucleons emitted during INC. We investigate the validity and performance of MCNP6, CEM, and LAQGSM in simulating fragmentation reactions at intermediate energies and discuss possible ways of further improving these codes.

Accurate evaluation of production cross sections of light elements is important for models of CR ... more 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.

An extended version of the Cascade-Exciton Model (CEM) of nuclear reactions is applied to analyze... more An extended version of the Cascade-Exciton Model (CEM) of nuclear reactions is applied to analyze nucleon-induced fission cross sections for 209 Bi and 208 Pb nuclei in the 45-500 MeV energy range. The available data on linear momentum transfer are analyzed as well. The results are compared with analytical approximations resulting from a comparative critical analysis of all available experimental data. Systematic discrepancies between calculations and experimental data are revealed. A modification of the CEM is proposed, which significantly improves the model predictions for projectile energies above 100 MeV.

Journal of Nuclear Science and Technology, 2002

Emission of light fragments (LF) from nuclear reactions is an open question. Different reaction m... more Emission of light fragments (LF) from nuclear reactions is an open question. Different reaction mechanisms contribute to their production; the relative roles of each, and how they change with incident energy, mass number of the target, and the type and emission energy of the fragments is not completely understood. None of the available models are able to accurately predict emission of LF from arbitrary reactions. However, the ability to describe production of LF (especially at energies > 30 MeV) from many reactions is important for different applications, such as cosmic-ray induced Single Event Upsets (SEUs), radiation protection, and cancer therapy with proton and heavy-ion beams, to name just a few. The Cascade-Exciton Model (CEM), version 03.03 and the Los Alamos version of the Quark-Gluon String Model (LAQGSM), version 03.03 event generators in Monte Carlo N-Particle Transport Code version 6 (MCNP6), describe quite well the spectra of fragments with sizes up to 4He across a b...

Emission of light fragments (LF) from various nuclear reactions is an interesting unsolved scient... more Emission of light fragments (LF) from various nuclear reactions is an interesting unsolved scientific question. Different reaction mechanisms contribute to their production; with different dependencies on incident particle, incident energy, mass number of the target, and the type and emission energy of the fragments. Available models cannot accurately predict emission of LF from arbitrary reactions. However, the emission of LF, especially of intermediate and high energies, is important for many applications, such as cosmic-ray induced Single Event Upsets, radiation protection, and cancer therapy with proton and heavy-ion beams, to name just a few. The Cascade-Exciton Model (CEM) and the Los Alamos version of the Quark-Gluon String Model (LAQGSM) as implemented in the CEM03.03 and LAQGSM03.03 event generators used in the Los Alamos Monte Carlo transport code MCNP6 describe quite well the spectra of fragments with sizes up to 4He across a broad range of target masses and incident ener...

The "condensation" probability, gammaj\gamma_jgammaj , is an important variable in the preequilib... more The "condensation" probability, gammaj\gamma_jgammaj , is an important variable in the preequilibrium stage of nuclear spallation reactions. It represents the probability that pjp_jpj excited nucleons (excitons) will "condense" to form complex particle type jjj in the excited residual nucleus. It has a significant impact on the emission width, or probability of emitting fragment type jjj from the residual nucleus. This paper explores the formulation of a new model for gammaj\gamma_jgammaj, one which is energy-dependent, and which provides improved fits compared to experimental fragment spectra.

The LAQGSM code has been recently developed at Los Alamos National Laboratory to simulate nuclear... more 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.

A relativistic kinetic equation (RKE) is obtained in the nucleon sector of the relativistic nucle... more A relativistic kinetic equation (RKE) is obtained in the nucleon sector of the relativistic nuclear Walecka model on the dynamical basis using the non-equilibrium operator method. The correspondence of different forms of Vlasov-type integrals to collision integrals (CI) is analyzed. It is shown that the integral of the Vlasov-type in the mean-field approximation must be conformed to a CI of the Bloch type while the integral of the Vlasov-type in the Hartree-Fock approximation corresponds to a CI of the Boltzmann-Uehling-Uhlenbeck type. The RKE of the Vlasov type in the Hartree-Fock approximation obtained here includes all basic relativistic quantum effects typical of the Walecka model, in particular, spin effects and negative-energy states. The problem of "alive" mesons is discussed as well.

The present report is devoted to the development of a kinetic approach for the description of a n... more The present report is devoted to the development of a kinetic approach for the description of a non-equilibrium nuclear matter at intermediate energies. A relativistic kinetic equation (RKE) of the Vlasov-type for the nucleon sector of the quantum hadrodynamics is obtained taking into account the exchange effects and the strong averaged nuclear field ones. This RKE is analyzed for the case of a spin-saturated nuclear matter. Calculations are carried out in the framework of the co-variant version of the non-equilibrium statistical operator method. A kinetic effect of suppression and amplification of the quasi-particle states with positive and negative energies was revealed.

ABSTRACT The relativistic kinetic equations describing nuclear reactions at intermediate energies... more ABSTRACT The relativistic kinetic equations describing nuclear reactions at intermediate energies are obtained on the dynamical basis. These equations are analyzed and realized in several versions of the Cascade Exciton Model (CEM). The CEM assumes That reactions occur in three stages: the intranuclear cascade, pre-equilibrium and the evaporative ones. A large variety of experimental data on hadron- and photo-nuclear reactions in the bombarding energy range up to several GeV are analyzed in this approach. The contributions of different pion and photon absorption mechanisms in these reactions are estimated. The CEM describes adequately nuclear reactions at intermediate energies and has one of the best predictive powers as compared to other available modern models.

Il Nuovo Cimento A

A comparison of two methods in the relativistic kinetic theory of the Fermi systems is carried ou... more A comparison of two methods in the relativistic kinetic theory of the Fermi systems is carried out by assuming, as an example, the simplest σω-version of quantum hadrodynamics with allowance for strong mean meson fields. It is shown that the Vlasov-type relativistic kinetic equation (VRKE) obtained by means of the procedure of squaring at an intermediate step is responsible for unphysical features. A direct method of derivation of kinetic equations is proposed. This method does not contain such drawback and gives rise to VRKE in hadrodynamics of a non-contradictory form in which both spin degrees of freedom and states with positive and negative energies are taken into account.

A cascade model has been developed to study pion induced multichannel reactions (quasielastic, SC... more A cascade model has been developed to study pion induced multichannel reactions (quasielastic, SCX, DCX, absorption and pion production) at pion energies above 0.5 GeV. Special attention has been paid to pion double charge exchange. Pion production is a determinant feature in the high energy pion nucleus reactions, and the DCX signal not related to pion production is sizeable only at forward angles and for high energy outgoing pions. The contribution to DCX of the conventional mechanism, with two quasielastic SCX steps decreases very fast as a function of the energy and reaches very low values at energies above 0.7 GeV. This opens the opportunity of having sizeable contributions of exotic mechanisms that are negligible at the delta resonance energies. Comment: 17 pages, 8 figures, LaTeX