arXiv subjects

K. K. Gudima

Publications and source records attributed to K. K. Gudima.

36 records · Page 2Linked to original sources

arXiv2005

Merging the CEM2k and LAQGSM Codes with GEMINI

An improved version of the Cascade-Exciton Model (CEM) of nuclear reactions contained in the code CEM2k and the Los Alamos version of the Quark-Gluon String Model (LAQGSM) are merged with the well-known sequential-binary-decay model GEMINI by Charity. We present some results on proton-induced fragmentation, fission-product yields and on particle spectra predicted by these extended versions of CEM2k and LAQGSM. We show that merging CEM2k and LAQGSM with GEMINI allows us to describe many fission and fragmentation reactions in addition to the spallation and evaporation reactions which are already described well by these codes. Nevertheless, the current version of GEMINI we use does not provide a completely satisfactory description of some complex-particle spectra, fragment emission, and spallation yields for some reactions, and is not yet a universal tool for applications. Our results show that GEMINI contains a powerful model to describe evaporation/fission/fragmentation reactions and often provides better results when compared to other models, especially for emission of heavy fragments from reactions on medium-heavy nuclei (where most other models simply fail), but it must be further extended and improved in order to properly describe arbitrary reactions.

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arXiv2005

CEM03 and LAQGSM03 - new modeling tools for nuclear applications

An improved version of the Cascade-Exciton Model (CEM) of nuclear reactions realized in the code CEM2k and the Los Alamos version of the Quark-Gluon String Model (LAQGSM) have been developed recently at LANL to describe reactions induced by particles and nuclei for a number of applications. Our CEM2k and LAQGSM merged with the GEM2 evaporation/fission code by Furihata have predictive powers comparable to other modern codes and describe many reactions better than other codes; therefore both our codes can be used as reliable event generators in transport codes for applications. During the last year, we have made a significant improvements to the intranuclear cascade parts of CEM2k and LAQGSM, and have extended LAQGSM to describe photonuclear reactions at energies to 10 GeV and higher. We have produced in this way improved versions of our codes, CEM03.01 and LAQGSM03.01. We present a brief description of our codes and show illustrative results obtained with CEM03.01 and LAQGSM03.01 for different reactions compared with predictions by other models, as well as examples of using our codes as modeling tools for nuclear applications.

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arXiv2005

Formation of Light Isotopes by Protons and Deuterons of 3.65 GeV/nucleon on Separated Tin Isotopes

We measure cross sections for residual nuclide formation in the mass range 6 < A < 97 caused by bombardment with protons and deuterons of 3.65 GeV/nucleon energy of enriched tin isotopes (112-Sn, 118-Sn, 120-Sn, 124-Sn). The experimental data are compared with calculations by the codes FLUKA, LAHET, CEM03, and LAQGSM03. Scaling behavior is observed for the whole mass region of residual nuclei, showing a possible multifragmentation mechanism for the formation of light products (6 < A < 31). Our analysis of the isoscaling dependence also shows a possible contribution of multifragmentation to the production of heavier nuclides, in the mass region 39 < A < 81.

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arXiv2005

Extension of the CEM2k and LAQGSM Codes to Describe Photo-Nuclear Reactions

The improved Cascade-Exciton Model (CEM) code CEM2k+GEM2 and the Los Alamos version of the Quark-Gluon String Model code LAQGSM are extended to describe photonuclear reactions. First, we incorporate into CEM2k+GEM2 new evaluations of elementary cross sections based on the latest experimental data and also make several improvements in the description of the de-excitation of nuclei remaining after the cascade stage of reactions induced by arbitrary projectiles. Next, for photonuclear reactions we include in CEM2k+GEM2 a normalization to evaluated experimental absorption cross sections based on the recent systematics by Kossov. Then, we extend our high-energy code LAQGSM by adding the photonuclear mode which was ignored in all its previous versions, and add to it the photonuclear part from our improved CEM2k+GEM2. In this work we present a short description of the photonuclear mode as incorporated into our codes, show several illustrative results, and point out some unresolved problems.

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arXiv2005

Improved Intranuclear Cascade Models for the Codes CEM2k and LAQGSM

An improved version of the Cascade-Exciton Model (CEM) of nuclear reactions implemented in the codes CEM2k and the Los Alamos version of the Quark-Gluon String Model (LAQGSM) has been developed recently at LANL to describe reactions induced by particles and nuclei at energies up to hundreds of GeV/nucleon for a number of applications. We present several improvements to the intranuclear cascade models used in CEM2k and LAQGSM developed recently to better describe the physics of nuclear reactions. First, we incorporate the photonuclear mode from CEM2k into LAQGSM to allow it to describe photonuclear reactions, not previously modeled there. Then, we develop new approximations to describe more accurately experimental elementary energy and angular distributions of secondary particles from hadron-hadron and photon-hadron interactions using available data and approximations published by other authors. Finally, to consider reactions involving very highly excited nuclei (E* > 2-3 MeV/A), we have incorporated into CEM2k and LAQGSM the Statistical Multifragmentation Model (SMM), as a possible reaction mechanism occurring after the preequilibrium stage. A number of other refinements to our codes developed recently are also listed.

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arXiv2004

Analysis of the JINR p(660 MeV) + 129I, 237Np, and 241Am Measurements with Eleven Different Models

We have analyzed the recent JINR measurements on nuclide production cross sections from interaction of 660 MeV proton beams with radioactive targets of enriched 129I (85% 129I and 15% 127I), 237Np, and 241Am with eleven different models, realized in eight transport codes and event-generators: LAHET (Bertini, ISABEL, INCL+ABLA, and INCL+RAL options), CASCADE, CEM95, CEM2k, LAQGSM+GEM2, CEM2k+GEM2, LAQGSM+GEMINI, and CEM2k+GEMINI. We found out that all these models have problems in a correct description of many of these cross sections, though some of these models describe very well most of the recent measurements done at GSI using inverse kinematics, as well as many other reactions. None of the tested here models is able to reproduce well all the JINR data and all of them should be further improved. Development of a better universal evaporation/fission model should be of a highest priority. We conclude that it is impossible to make a correct choice between fission and fragmentation reaction mechanisms analyzing only measurements on product cross sections; addressing this question would require analysis of two- or multi-particle correlation measurements.

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arXiv2004

Towards a Heavy-ion Transport Capability in the MARS15 Code

In order to meet the challenges of new accelerator and space projects and further improve modelling of radiation effects in microscopic objects, heavy-ion interaction and transport physics have been recently incorporated into the MARS15 Monte Carlo code. A brief description of new modules is given in comparison with experimental data.

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arXiv2004

Recent Enhancements to the MARS15 Code

The MARS code is under continuous development and has recently undergone substantial improvements that further increase its reliability and predictive power in numerous shielding, accelerator, detector and space applications. The major developments and new features of the MARS15 (2004) version described in this paper concern an extended list of elementary particles and arbitrary heavy ions and their interaction cross-sections, inclusive and exclusive nuclear event generators, module for modelling particle electromagnetic interactions, enhanced geometry and histograming options, improved MAD-MARS Beam Line Builder, enhanced Graphical-User Interface, and an MPI-based parallelization of the code.

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arXiv2004

Analysis of the GSI A+p and A+A Spallation, Fission, and Fragmentation Measurements with the LANL CEM2k and LAQGSM codes

The CEM2k and LAQGSM codes have been recently developed at Los Alamos National Laboratory to simulate nuclear reactions induced by particles and nuclei for a number of applications. We have benchmarked our codes against most available measured data at projectile energies from 10 MeV/A to 800 GeV/A 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 obtained with CEM2k and LAQGSM for A+p and A+A spallation, fission, and fragmentation reactions measured recently at GSI compared with predictions by other models. Further necessary work is outlined.

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arXiv2004

Study of Proton Induced Reactions in a Radioactive 129-I Target at Ep=660 MeV

Two NaI (85% 129-I and 15% 127-I) targets were exposed to a beam of 660-MeV protons. Cross sections for formation of 76 residual nuclei were obtained by the induced activity method. The results are compared with other experimental data on 127-I and theoretical calculations by eleven models contained in the codes LAHET3 (using the Bertini+Dresner, ISABEL+Dresner, INCL+Dresner, and INCL+ABLA options), CASCADE, CEM95, CEM2K, LAQGSM+GEM2, CEM2k+GEM2, LAQGSM+GEMINI, and CEM2k+GEMINI. Most of the models describe spallation products with masses close to the target reasonably well while the reliability of the codes differs greatly in the deep spallation and fission/fragmentation regions. The difficulties in describing products with A=40-80 by all of the codes tested here except for CEM2k+GEMINI and LAQGSM+GEMINI is related to the neglect of fission (and fragmentation) processes for targets as light as 129-I.

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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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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

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

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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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

Comparative Study of Multifragmentation of Gold Nuclei Induced by Relativistic Protons, $^4$He, and $^{12}$C

Multiple emission of intermediate-mass fragments has been studied for the collisions of p, $^4$He and $^{12}$C on Au with the $4π$ setup FASA. The mean IMF multiplicities (for the events with at least one IMF) are saturating at the value of $2.2\pm0.2$ for the incident energies above 6 GeV. The observed IMF multiplicities cannot be described in a two-stage scenario, a fast cascade followed by a statistical multifragmentation. Agreement with the measured IMF multiplicities is obtained by introducing an intermediate phase and modifying empirically the excitation energies and masses of the remnants. The angular distributions and energy spectra from the p-induced collisions are in agreement with the scenario of ``thermal'' multifragmentation of a hot and diluted target spectator. In the case of $^{12}$C+Au(22.4 GeV) and $^4$He(14.6 GeV)+Au collisions, deviations from a pure thermal break-up are seen in the energy spectra of the emitted fragments, which are harder than those both from model calculations and from the measured ones for p-induced collisions. This difference is attributed to a collective flow.

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arXiv2001

Fragile Signs of Criticality in the Nuclear Multifragmentation

Deviations from an idealized equilibrium phase transition picture in nuclear multifragmentation is studied in terms of the entropic index. We investigate different heat-capacity features in the canonical quantum statistical model of nuclear multifragmentation generalized in the framework of Tsallis nonextensive thermostatistics. We find that the negative branch of heat capacity observed in quasi-peripheral Au+Au collisions is caused primarily by the non-generic nonextensivity effects.

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arXiv2000

Nuclear Multifragmentation in the Non-extensive Statistics - Canonical Formulation

We apply the canonical quantum statistical model of nuclear multifragmentation generalized in the framework of recently proposed Tsallis non-extensive thermostatistics for the description of nuclear multifragmentation process. The test calculation in the system with A=197 nucleons show strong modification of the 'critical' behaviour associated with the nuclear liquid-gas phase transition for small deviations from the conventional Boltzmann-Gibbs statistical mechanics.

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