Nuclear reactions of medium and heavy target nuclei with high-energy particles IV. Interpretation of mass fragment yields

Target residue mass distributions in 3·65 A GeV¹²C-ion- and 3·65 GeV proton-induced reactions on medium and heavy target nuclei have been interpreted in the theoretical framework of the intranuclear cascade and abrasion-ablation models. While the intranuclear cascade model gives a good approximation to experimental yields of residues produced in both types of interaction, the abrasion-ablation model was found to overestimate mass-yield distributions in the vicinity of the target mass numbers.     

Nuclear activation studies of heavy ion reactions

The identification of the residues which are produced in a nuclear interaction, and the measurement of their recoil range and angular distribution provides useful information on the reaction mechanism. If the residues are radioactive this information may be easily obtained by measuring off beam the activity they induce both in the target and a suitable set of catchers. This experimental technique is discussed together with the results of a systematic study of the interaction of¹²C and¹⁶O ions, with heavy nuclei at low incident energies.     

Muon content of ultrahigh-energy air showers: Yakutsk data versus simulations

A sample of 33 extensive air showers (EASs) with estimated primary energies above 2 × 10¹⁹ eV and high-quality muon data recorded by the Yakutsk EAS array is analyzed. The observed muon density is compared event-by-event to that expected from CORSIKA simulations for primary protons and iron using SIBYLL and EPOS hadronic interaction models. The study suggests the presence of two distinct hadronic components, “light” and “heavy.” Simulations with EPOS are in good agreement with the expected composition in which the light component corresponds to protons and the heavy component to iron-like nuclei. With SIBYLL, simulated muon densities for iron primaries are a factor of ∼ 1.5 less than those observed for the heavy component for the same electromagnetic signal. Assuming a two-component proton-iron composition and the EPOS model, the fraction of protons with energies E > 10¹⁹ eV is 0.52_−0.20^+0.19 at the 95% C.L. The text was submitted by the authors in English.     

Target Residues from the Interaction of Indium with 42MeV/nucleon 12C Ions

The cross section is measured for 65 target residues produced from the interaction of indium with 42MeV/nucleon ¹²C ions using nuclear chemistry techniques.The experimental mass yield distribution gives a satisfactory agreement with that calculated from Monte Carlo code GEMINI based on the statistical binary decay model. According to the systematics of isotope distributions,the possibility of the production of new neutron-deficient nuclides far from β stability is discussed in the intermediate energy heavy ion reaction.     

‘Slow’ residues observed in the reaction20Ne+208Pb at E/A=8.6, 11.4 and 15.0 MeV/u

Velocity distributions of heavy residuesA _Res>A _tar,Z _Res>Z _tar identified by means ofα spectroscopy, have been investigated at the velocity filter SHIP in reactions²⁰Ne+²⁰⁸Pb at projectile energies E/A=8.6, 11.4 and 15.0 MeV/u. Besides products from complete or nearly complete fusion, characterized by velocity distributions peaking atν/ν _CN?0.8–1.0, heavy residues with mean velocities of about half of the compound nucleus velocity were observed. The Z-distribution of this component was found to peak atZ=87. It is interpreted as residues from fusion of target nuclei with projectile fragments produced by nearly symmetric break-up. The experimental results were compared with predictions of theoretical models: cross sections for incomplete fusion were calculated using the sum-rule model of Wilcynski et al., while residue cross sections were calculated using the evaporation code HIVAP. A fair agreement between experimental and calculated mass distributions of heavy residues and transferred projectile fragments is achieved if an energy dissipation of ?23% (at E/A=8.6 MeV/u) and ?8% (at E/A=11.4 MeV/u) of the incident projectile energy is introduced. The observed peak of theZ-distribution atZ=87 is predominantly effected due to a higher fission probability of products withZ>87 during the deexcitation process and experimental limitations in the identification of products withZ≦86 by means of a spectroscopy, which cause a decrease of the observed production rates towards lowerZ.     

Complete and Incomplete Fusion in the Reaction of 65Cu With 16O Ions

The excitation functions,angular distributions and differential range distributions have been measured for target residues from the reaction of ⁶⁵Cu induced by 45—96MeV ¹⁶O ions with radiochemical techniques.A comparison of the experimental data with Monte-Carlo simulations based on the statistcal model of compound nucleus that the heavy residues are produced by the decay of a compound nucleus formed by complete fusion.Incomplete fusion or massive transfer are the main reaction mechnisms leading to production of the residues with mass number close to that of the target.     

A P-matrix analysis of nucleon-nucleon scattering below 1 GeV inspired by the quark compound bag model

The quark compound bag model was suggested recently as a dynamical model for the hadronic interaction, taking quark degrees of freedom into account. Important parameters of this model are the positions and residues of the Jaffe-Low P-matrix poles. They can be extracted from the experimental data on the S-matrix. The P-matrix is determined for several nucleon-nucleon channels. A realistic long-range interaction is included in this analysis which introduces a small model dependence in P. The Wigner-Breit condition on the P-matrix can be used to detect deficiencies of existing phase-shift analyses at low energies.     

Moments of charge distributions in the reaction92Mo+92Mo at 14.7 MeV/u

First and second moments of primary charge distributions were determined as a function of the total kinetic energy loss in the reaction⁹²Mo+⁹²Mo at an incident energy of 14.7 MeV/u. Up to energy losses of 200 MeV no significant drift of the first moments is observed. The second moments are in agreement with predictions of a stochastic model derived at lower bombarding energies.     

重核大集团发射半衰期的计算

重核大集团（¹⁴C-³⁴Si）发射的半衰期在理论上用Wentzel-Kramers-Brillouin近似进行了计算.利用双折叠模型计算大集团和剩余子核间的核相互作用,在折叠积分中选取了密度依赖的、零力程交换项的核子-核子相互作用.计算得到的半衰期和液滴模型结果、系统公式的结果以及实验数据进行了比较,表明目前的计算能够很好地给出重核大集团（¹⁴C-³⁴Si）发射的寿命.这可为重核其他大集团（¹⁵N, ⁴⁶Ar,⁴⁸Ca等）的发射提供可靠的预测. 关键词： 半衰期 双折叠模型 集团发射     

Heavy fragments emission in the 84Kr on 12C reaction at 35 MeV/nucleon

Heavy residues of collisions of ⁸⁴Kr + ¹²C at 35 MeV/amu were measured using time of flight ΔE?E telescopes. An important part of the total cross section leads to events that have all the characteristics of an equilibrated composite system decaying by heavy fragment emission. The experimental yields are well reproduced using a statistical model.     

Comparisons of fragmentation spectra using 1 GeV/amu 56Fe data and the PHITS model

We present measurements and model calculations of fluence and linear energy transfer in water (${\mathrm{LET}}_{\infty }$) obtained using ⁵⁶Fe beams with 1 GeV/amu kinetic energy incident on aluminum, polyethylene, PMMA, and lead targets. The measured spectra are compared to predictions of the PHITS model. The study is motivated by NASA's need to develop accurate heavy ion transport codes to assess radiation exposures in deep space, where galactic cosmic rays are important. The data were obtained at the Alternating Gradient Synchrotron at the Brookhaven National Laboratory. Distributions of charge and LET depend on the depth and composition of the target. Several of the targets studied are “thick”, defined operationally as a depth that presents at least 50% of an interaction length to the beam ions. In a thick target, the probability of a secondary interaction is significant, tertiary interactions can also be important, and the target-exit fluence and charge distributions depend on unmeasured cross sections that can only be estimated by nuclear interaction models. Comparisons between calculated and measured spectra are therefore of considerable interest. Some targets used in the study are thin, so that secondary and higher interaction probabilities are negligible, allowing more stringent comparisons between the data and the model. We find that PHITS reproduces some aspects of the experimental data well, but fails to accurately reproduce many of the measured fragment fluences.     

D mesic nuclei

The energies and widths of several D⁰$D^0$ meson bound states for different nuclei are obtained using a D  -meson selfenergy in the nuclear medium, which is evaluated in a selfconsistent manner using techniques of unitarized coupled-channel theory. The kernel of the meson–baryon interaction is based on a model that treats heavy pseudoscalar and heavy vector mesons on equal footing, as required by heavy quark symmetry. We find D⁰$D^0$ bound states in all studied nuclei, from ¹²C up to ²⁰⁸Pb. The inclusion of vector mesons is the keystone for obtaining an attractive D  –nucleus interaction that leads to the existence of D⁰$D^0$–nucleus bound states, as compared to previous studies based on SU(4) flavor symmetry. In some cases, the half widths are smaller than the separation of the levels, what makes possible their experimental observation by means of a nuclear reaction. This can be of particular interest for the future P?ANDA@FAIR physics program. We also find a D⁺$D^{+}$ bound state in ¹²C, but it is too broad and will have a significant overlap with the energies of the continuum.     

Interactions of relativistic heavy ions in thick heavy element targets and some unresolved problems

Interactions of relativistic heavy ions with total energies above 30 GeV in thick Cu and Pb targets (≥ 2 cm) have been studied with various techniques. Radiochemical irradiation experiments using thick Cu targets, both in a compact form or as diluted “2π-Cu targets” have been carried out with several relativistic heavy ions, such as 44 GeV ¹²C (JINR, Dubna, Russia) and 72 GeV ⁴⁰Ar (LBL, Berkeley, USA). Neutron measuring experiments using thick targets irradiated with various relativistic heavy ions up to 44 GeV ¹²C have been performed at the JINR. In addition, the number of “black prongs” in nuclear interactions (due to protons with energies less than 30 MeV and emitted from the target-like interaction partner at rest) produced with 72 GeV ²²Ne ions in nuclear emulsion plates has been measured in the first nuclear interaction of the primary ²²Ne ion and in the following second nuclear interaction of the secondary heavy (Z > 1) ion. Some essential results have been obtained. (1) Spallation products produced by relativistic secondary fragments in interactions ([44 GeV ¹²C or 72 GeV ⁴⁰Ar] + Cu) within thick copper yield fewer products close to the target and many more products far away from the target as compared to primary beam interactions. This applies also to secondary particles emitted into large angles (Θ > 10°). (2) The neutron production of 44 GeV ¹²C within thick Cu and Pb targets is beyond the estimated yield as based on experiments with 12 GeV ¹²C. These rather independent experimental results cannot be understood within well-accepted nuclear reaction models. They appear to present unresolved problems. The text was submitted by the authors in English.     

Effect of next-nearest-neighbour interaction on dx2?y2-wave superconducting phase in 2D t-J model

An exact diagonalization calculation of the t-J model on 2D square cluster has been studied for the ground state properties of HTSC. Effect of next-nearest-neighbour hopping and magnetic (both antiferromagnetic and ferromagnetic) interaction on d _x ²−y ²-wave pairing has been shown. Relative strength of the next-nearest-neighbour interaction with respect to that of near-neighbour interaction for the strongest d _x ²−y ²-wave pairing has been estimated. A schematic phase diagram is shown. It is shown that a two-sublattice model with antiferromagnetic interaction between them and a small intra-ferromagnetictype interaction in one sublattice favours d _x ²−y ²-wave superconductivity and moderate negative type NNN hopping adds flavours to this phase.     

Effect of the ionization energy loss density of high-energy bismuth,krypton, and xenon ions on the development of hydrogen blisters in silicon

Radiation-induced athermal hydrogen removal from single-crystal silicon subjected to irradiation by high-energy heavy Bi⁺ (E = 710 MeV), Kr⁺ (E = 85 and 250 MeV), and Xe⁺ (130 MeV) ions is detected experimentally. The decrease in the hydrogen concentration depends on the specific ionization energy losses of high-energy heavy ions. At high specific ionization losses of Bi⁺ ions with E = 710 MeV (22.5 keV/nm), the hydrogen concentration decreases to a level at which blisters cannot be observed in an optical or electron microscope (which is likely to be 1 at % hydrogen at the peak of the calculated hydrogen concentration profile). At medium specific ionization losses of Xe⁺ ions with E = 130 MeV (12.5 keV/nm) and Kr⁺ ions with E = 250 and 85 MeV (9.5 and 8.5 keV/nm, respectively), the hydrogen concentration decreases to a level that does not affect blister formation but determines the blister failure (flaking) conditions.     

Intermolecular Vibrational Coupling A Model Calculation for the Out-of-Plane Vibration of CO3 −- in Compounds with the Aragonite Structure

Abstract

¹³CO₃ ^?- substituted compounds with the aragonite structure show a fine structure of the out-of-plane vibration in the infrared spectra. A simple quantum mechanical model of coupled oscillators is developed to describe quantitatively the observed spectra. The spectra can be interpreted in terms of isolated ^12CO ₃ ^?- and ¹³CO₃ ^?- clusters, whose eigenfunctions interact. The heavy ions have localized vibrations, whereas clusters of the light ion with more than one ion show only localized vibrations at small coupling; stronger coupling results in resonant modes. Intensitytransfer from light to heavy ion bands is explained and the consequences of interaction between different clusters are discussed.     

Characterization of aromatic-thiol π-type hydrogen bonding and phenylalanine-cysteine side chain interactions through ab initio calculations and protein database analyses

In this study, the aromatic-thiol π hydrogen bonding and phenylalanine-cysteine side chain interactions are characterized through both molecular orbital calculations on a C₆H₆-HSCH₃ model complex and database analyses of 609 X-ray protein structures. The aromatic-thiol π hydrogen bonding interaction can achieve a stabilization energy of 2.60 kcal mol^?1, and is stronger than the already documented aromatic-hydroxyl and aromatic-amino hydrogen bonds. However, the occurrence of the aromatic-thiol hydrogen bond is rather rare in proteins. This is because most of the thiol groups participate in the formation of either disulphide bonds or stronger S—H…O (or N) ‘normal’ hydrogen bonds in a protein environment. Interactions between the side chains of phenylalanine and cysteine residues are characterized as the phenyl(Phe)(HSCH₂-)(Cys) interaction. The bonding energy for such interactions is approximately 3.71 kcal mol-¹ and is achieved in a geometric arrangement with an optimal phenyl(Phe)-(HS-)(Cys) π-type hydrogen bonding interaction. The interaction is very sensitive to the orientation of the two lone electron pairs on the sulphur atom relative to the π electron cloud of the phenyl ring. Accordingly, the interaction configurations that can accomplish a significant bonding energy exist only within a narrow configurational space. The database analysis of 609 experimental X-ray protein structures demonstrates that only 268 of the 1620 cysteine residues involve such phenylalanine-cysteine side chain interactions. Most of these interactions occur in the form of π (aromatic)-lone pair(sulphur) attractions, and correspond to a bonding energy less than 1.5 kcal mol^?1. A few were identified as the aromatic-thiol hydrogen bond with a bonding energy of 2.0–3.6 kcal mol^?1.     

Nuclide distributions for Fe-like fragments in the 136Xe + 56Fe reaction

The nuclide distributions of Fe-like reaction products from the reaction 5.9 MeV/u ¹³⁶Xe on. ⁵⁶Fe were measured as a function of total kinetic energy loss at a laboratory angle of 55°. The first and second moments of N, Z and A were obtained in addition to the correlation coefficients and the isobaric variances. We compare these results for the Fe-like fragment to those implied by previous measurements of the secondary distribution of the Xe-like fragment. We incorporate the effects of particle evaporation on both the light and heavy complementary primary distributions. There is overall qualitative agreement, but the variances are somewhat smaller than those obtained previously even after correction for particle evaporation. Evaporation calculations are also performed on the primary distributions predicted by a nucleon exchange model, and yield distributions in good agreement with the present experimental data.     

Potential pockets in the238U+238U system and their possible consequences

Within the double-folding model the separation, shape, and orientation dependence of the interaction potential is studied for two heavy ions. An effective nucleon-nucleon interaction (M3Y) derived fromG-matrix elements and based upon the Reid soft-core potential is used. Deformed Fermi-type matter densities with static quadrupole and hexadecapole deformations were utilized. The model is applied to the²³⁸U+²³⁸U system and shows dramatic dependence on the deformations and orientations.