Odd-even staggering in the yields of intermediate mass fragments from p+Ag collisions at Ep = 480 MeV
U. Singh, B. Kamys , S. Sharma, K. Pysz
abstract
The experimental total production cross-sections of intermediate-mass fragments (isotopes of Li, Be, B, C, N, O, F, Ne, Na, and Mg) were extracted by integration of d2s/dOmegadE data measured at several angles for p+Ag collisions at proton beam energy of 480 MeV. The total cross sections show typical odd?even staggering (OES) when presented as a function of the atomic number Z of ejectiles. The effect is the strongest for products with N = Z and N = Z + 2. Similar behaviour is observed for theoretical cross sections evaluated in the two-step model in which the first stage of the reaction is described by intranuclear cascade INCL++ and the second stage by GEMINI++ model or by two other models, namely ABLA07 and SMM. The OES seems to be even more pronounced for theoretical than for the experimental cross sections.
The predictive power of spallation models for isotopic cross sections
U. Singh, D. Filges, F. Goldenbaum, Boguslaw Kamys, Z. Rudy, and S. Sharma
abstract
The experimental cross sections of isotopically identified products of spallation reactions induced
by 136Xe projectiles at 1 GeV/nucleon on hydrogen target were compared with predictions of a two-step
model. The first stage of the reaction was described by the INCL++ model (version 5.3) of an intranuclear
cascade of nucleon-nucleon and pion-nucleon collisions whereas the second stage was analyzed by means
of four different models; ABLA07, GEM2, GEMINI ++ and SMM. Due to the fact that the experimental
data cover a very broad range of elements; from Li (Z=3) to Ba(Z= 56), the analysis could impose severe
constraints on the applied reaction models. The quality of data reproduction by the theoretical models
is discussed. Some systematic deviations of the theoretical predictions from the experimental results are
observed.
Non-equilibrium processes in p + Ag collisions at GeV energies
M. Fidelus,.., B. Kamys, S. Kistryn, A. Magiera, Z. Rudy, S. Sharma et al.,
abstract
The double differential spectra d2?/d?dE of p, d, t, He3,4,6, Li6,7,8,9, Be7,9,10, and B10,11,12 were measured at seven scattering angles, 15.6?, 20?, 35?, 50?, 65?, 80?, and 100?, in the laboratory system for proton induced reactions on a silver target. Measurements were done for three proton energies: 1.2, 1.9, and 2.5 GeV. The experimental data were compared to calculations performed by means of two-step theoretical microscopic models. The first step of the reaction was described by the intranuclear cascade model incl4.6 and the second one by four different models (ABLA07, GEM2, gemini++, and SMM) using their standard parameter settings. Systematic deviations of the data from predictions of the models were observed. The deviations were especially large for the forward scattering angles and for the kinetic energy of emitted particles in the range from about 50 to 150 MeV. This suggests that some important non-equilibrium mechanism is lacking in the present day microscopic models of proton-nucleus collisions in the studied beam energy range.
Ranking and validation of spallation models for isotopic production cross sections of heavy residua
S. Sharma, B. Kamys, F. Goldenbaum, D. Filges
abstract
The production cross sections of isotopically identified residual nuclei of spallation reactions induced by 136Xe projectiles at 500 AMeV on hydrogen target were analyzed in a two-step model. The first stage of the reaction was described by the INCL4.6 model of an intranuclear cascade of nucleon-nucleon and pion-nucleon collisions whereas the second stage was analyzed by means of four different models; ABLA07, GEM2, GEMINI++ and SMM. The quality of the data description was judged quantitatively using two statistical deviation factors; the H-factor and the M-factor. It was found that the present analysis leads to a different ranking of models as compared to that obtained from the qualitative inspection of the data reproduction. The disagreement was caused by sensitivity of the deviation factors to large statistical errors present in some of the data. A new deviation factor, the A factor, was proposed, that is not sensitive to the statistical errors of the cross-sections. The quantitative ranking of models performed using the A-factor agreed well with the qualitative analysis of the data. It was concluded that using the deviation factors weighted by statistical errors may lead to erroneous conclusions in the case when the data cover a large range of values. The quality of data reproduction by the theoretical models is discussed. Some systematic deviations of the theoretical predictions from the experimental results are observed.
Ranking and validation of the spallation models for description of intermediate mass fragment emission from p + Ag collisions at 480 MeV incident proton beam energy
S. Sharma, B. Kamys, F. Goldenbaum, D. Filges
abstract
Double-differential cross-sections d2?/d? dE for isotopically identified intermediate mass frag- ments (6Li up to 27Mg) from nuclear reactions induced by 480MeV protons impinging on a silver target were analyzed in the frame of a two-step model. The first step of the reaction was described by the intranu- clear cascade model INCL4.6 and the second one by four different models (ABLA07,GEM2, GEMINI++, and SMM). The experimental spectra reveal the presence of low-energy, isotropic as well as high-energy, forward-peaked contributions. The INCL4.6 model offers a possibility to describe the latter contribution for light intermediate mass fragments by coalescence of the emitted nucleons. The qualitative agreement of the model predictions with the data was observed but the high-energy tails of the spectra were signif- icantly overestimated. The shape of the isotropic part of the spectra was reproduced by all four models. The GEM2 model strongly underestimated the value of the cross-sections for heavier IMF whereas the SMM and ABLA07 models generally overestimated the data. The best quantitative description of the data was offered by GEMINI++, however, a discrepancy between the data and the model cross-sections still remained for almost all reaction products, especially at forward angles. It indicates that non-equilibrium processes are present which cannot be reproduced by the applied models. The goodness of the data de- scription was judged quantitatively using two statistical deviation factors, the H-factor and the M-factor, as a tool for ranking and validation of the theoretical models.
Angular Asymmetry in the Pro duction of Light and Heavy Recoil Nuclides in Proton Induced Reaction with Au Target at GeV Energies
S. Sharma, B. Kamys
abstract
It is shown that model calculations are able to reproduce main properties in terms of experimental mass
dependence of the forward-backward asymmetry of the emitted reaction products from proton-Au collisions in the
proton beam energy range from 1 GeV to 3 GeV. Qualitative as well as quantitative comparisons are done between
the measurements and the calculations performed by means of the intra nuclear cascade code INCL4.6 coupled
with four different codes: SMM, GEMINI++, ABLA07, and GEM2 with the aim to validate the selected reaction
models.
Validation of Spallation Models for p+Al Reactions at 180 MeV Incident Proton Beam Energy
S. Sharma, B. Kamys, F. Goldenbaum, D. Filges
abstract
Various observables measured at low beam energy of 180 MeV for proton induced reactions on 27 Al targets have been compared with theoretical predictions of different spallation models. These models assume that the reactions proceed in two stages: the intranuclear cascade of nucleon?nucleon collisions followed by the de-excitation of equilibrated, excited remnants of the cascade. The calculations of the intranuclear cascade were performed by means of the INCL4.6 code, whereas the second stage of the reactions was realized using four different models: ABLA07, GEMINI++, GEM2, and SMM. It was found that the main properties of the experimental isobaric total production cross sections are reasonably well reproduced by all these spallation models. The shape of the energy averaged angular distributions of ejectiles with A = 7, 12, 16, 22, 24, and 25 was also well described by the models listed above, however the absolute magnitude of A = 7 and A = 25 data is strongly underestimated and overestimated, respectively. The theoretical energy spectra for A = 7, A = 16, and A = 22 are very similar for all the models and reproduce well the data for heavier ejectiles, whereas the A = 7 data deviate from the model cross sections for energies smaller than ? 10 MeV what may indicate the presence of a reaction mechanism not included in the spallation models. The following ranking of the four used models ? all of them being coupled to the very same INCL4.6 INC model ? was determined using the statistical H-test in a quantitative analysis: (1) GEMINI++, (2) SMM, (3) ABLA07, and (4) GEM2.
Sequential and simultaneous emission of particles from p + Al collisions at GeV energies
M. Fidelus,.., B. Kamys, Z. Rudy, S. Sharma et al.,
abstract
The energy and angular dependence of double differential cross sections
d
2
?/ddE
were measured for
p
,
d
,
t
,
3
,
4
,
6
He,
6
,
7
,
8
,
9
Li,
7
,
9
,
10
Be, and
10
,
11
B produced in collisions of 1.2, 1.9, and 2.5 GeV protons with an Al
target. It was found that the cross sections are almost independent of the beam energy. The spectra and angular
distributions indicate a presence of two contributions: a quasi-isotropic, low-energy one which is attributed
to the emission of particles from excited remnants of the intranuclear cascade, and an anisotropic part which
is interpreted to originate from the first stage of the reaction. The experimental data are compared with an
intranuclear cascade model coupled to evaporation, and to statistical multifragmentation models using their
standard parameter settings. It was found that all applied models produce very similar results describing spectra
of the intermediate mass fragments. All models also reproduce well the low-energy part of the spectra of light
charged particles (below?30 MeV). The description of the higher energy part (50?150 MeV) of the light
charged particles spectra is poorer, deteriorating with decreasing scattering angle and decreasing mass of the
particles.
Dependence and Influence of Projectile Energy and Target Mass on the Production of Light Charged Particles and Intermediate Mass Fragments in Proton Induced Reactions
S. Sharma, D. Filges, F. Goldenbaum, B. Kamys
abstract
Calculations were performed for proton induced spallation reactions over a wide range of atomic masses on the targets: 12C, 27Al, natNi, 108Ag and 197Au using an Intra-nuclear Cascade Model (INCL4.6) with coalescence which includes the emission of protons, light clusters (d?4He), and intermediate mass fragments (up to A=8) formed by the nucleons during the first stage of the reaction. The emission of particles from excited cascade residua are described using three different theoretical models SMM, ABLA07, and GEMINI++. A comparison of calculations with experimental double differential cross?sections for light charged particles and selected intermediate mass fragments was studied at proton beam energies from GeV. Systematic deviations of the simulated cross sections from the experimental data were found for both light charged particles and intermediate mass fragments.
