Light Particle Spectra Research Articles

Recoil and charged particle energy spectra from the natSi(n,x) reaction and the Si semiconductor detector response to the 14 MeV neutrons

The energy spectra of light and heavy charged particles generated by the 14 MeV neutrons in silicon nuclei and in the Si semiconductor detector (SSD) were analysed. The existing measurements were used to validate the corresponding energy differential cross sections from major evaluations ENDF/B-VIII.0 and JEFF-3.3. The required data were extracted by the various codes: NJOY21, SPKA and MCNP6. It was shown that both evaluations underestimate the high energy part of the 28Si(n,x)p- and α-particle spectra by ≤50%, whereas at smaller emission energies no experimental data even exist. The calculation of the atom displacement damage in SSD reveals that the secondary protons produce additionally ≈15% of damage, whereas the contribution from secondary alphas is impossible to estimate since the Si(α,x) recoil data are not available.The single experiment, carried out by K. Yageta and co-workers in 1988, reported the energy spectra in the Si semiconductor down to the rather low energy of ≈0.3 MeV, at which the production of reaction recoils dominates over the light ions. The Monte Carlo simulation of this experiment was performed by MCNP6. The generation and transport of all relevant ions were taken in account. The energy depositions from protons or alphas were summed with their associated recoils after correction for non-ionization losses. The neutron reactions in the dead layer of the SSD were shown to increase the counts in active layer by (1–20)% depending on sort of ions. The impact of the field funneling effect was studied. Consideration of all these underlying processes has eventually allowed a reasonable reproduction of this experiment.

The $U$-plane of rank-one 4d $\mathcal{N}=2$ KK theories

The simplest non-trivial 5d superconformal field theories (SCFT) are the famous rank-one theories with E_nEn flavour symmetry. We study their UU-plane, which is the one-dimensional Coulomb branch of the theory on \mathbb{R}^4 \times S^1ℝ4×S1. The total space of the Seiberg-Witten (SW) geometry – the E_nEn SW curve fibered over the UU-plane – is described as a rational elliptic surface with a singular fiber of type I_{9-n}I9−n at infinity. A classification of all possible Coulomb branch configurations, for the E_nEn theories and their 4d descendants, is given by Persson’s classification of rational elliptic surfaces. We show that the global form of the flavour symmetry group is encoded in the Mordell-Weil group of the SW elliptic fibration. We study in detail many special points in parameters space, such as points where the flavour symmetry enhances, and/or where Argyres-Douglas and Minahan-Nemeschansky theories appear. In a number of important instances, including in the massless limit, the UU-plane is a modular curve, and we use modularity to investigate aspects of the low-energy physics, such as the spectrum of light particles at strong coupling and the associated BPS quivers. We also study the gravitational couplings on the UU-plane, matching the infrared expectation for the couplings A(U)A(U) and B(U)B(U) to the UV computation using the Nekrasov partition function.

Study of $$p_{T}$$ spectra of light particles using modified Hagedorn function and cosmic rays Monte Carlo event generators in proton–proton collisions at $$\sqrt{s}$$ = 900 GeV

Study of $$p_{T}$$ spectra of light particles using modified Hagedorn function and cosmic rays Monte Carlo event generators in proton–proton collisions at $$\sqrt{s}$$ = 900 GeV

Dark matter in Hidden Valley models with stable and unstable light dark mesons

It is a distinct possibility that a Hidden Valley sector would have a spectrum of light particles consisting of both stable and unstable dark mesons. The simultaneous presence of these two types of particles can lead to novel mechanisms for generating the correct dark matter relic abundance, which in turn can reflect themselves into new exotic signatures at colliders. We study the viability of such sectors for various Hidden Valley models and map the valid parameter space to possible collider signatures. Mediators studied include various scalar bifundamentals and a heavy Z′. It is shown that in general bounds from direct and indirect detection can easily be avoided. In most of the allowed parameter space, the relic density is determined by stable mesons annihilating to unstable ones which in turn decay quickly to Standard Model particles. Dark mesons that decay mainly to heavier Standard Model fermions allow for more valid parameter space, though dark mesons are still allowed to decay exclusively to some of the lighter fermions. Possible exotic collider signatures include displaced vertices, emerging jets and semivisible jets.

Study on reaction mechanism by analysis of kinetic energy spectra of light particles and formation of final products

The sensitivity of reaction mechanism in the formation of compound nucleus (CN) by the analysis of kinetic energy spectra of light particles and of reaction products are shown. The dependence of the PCN fusion probability of reactants and Wsur survival probability of CN against fission at its deexcitation on the mass and charge symmetries in the entrance channel of heavy-ion collisions, as well as on the neutron numbers is discussed. The possibility of conducting a complex program of investigations of the complete fusion by reliable ways depends on the detailed and refined methods of experimental and theoretical analyses.

Identified Light and Strange Hadron Spectra at [formula omitted] and Systematic Study of Baryon/Meson Effect at Intermediate Transverse Momentum with STAR at RHIC BES I

With the recently measured Au+Au collisions at sNN=14.5 GeV, STAR completed its first phase of the Beam Energy Scan (BES) program at RHIC. The main motivation of the BES program is the study of the QCD phase diagram and the search for a conjectured critical point. Amongst the various collision energies of 7.7, 11.5, 19.6, 27, and 39 GeV, that have been previously presented by STAR, collisions at 14.5 GeV will provide data set in the relatively large chemical potential gap between the 11.5 and 19.6 GeV center-of-mass energies. In this contribution, we report new STAR measurements of Au+Au at sNN=14.5 GeV that include identified light particle RCP and spectra, as well as measurements of the strange hadrons (Ks0,Λ,Ξ,Ω, and ϕ). The spectra from both light and strange particles cover a significant range of the intermediate transverse momentum (2<pT<5 GeV/c) in all beam energies. This provides a unique set of data for a systematic study of the baryon-to-meson ratio at intermediate pT from BES Phase I. We will discuss its physics implications and whether hadronic interactions at late stage dominate the collision dynamics.

Identified Light and Strange Hadron Spectra at √sNN = 14.5 GeV with STAR at RHIC BES I

With the recently measured Au+Au collisions at √sNN=14.5 GeV, RHIC completed its first phase of the Beam Energy Scan (BES) program. The main motivation of the BES program is the search for a conjectured critical point and possible first order phase transition. Amongst the various collision energies of 7.7, 11.5, 19.6, 27, and 39 GeV, that have been previously presented by STAR, collisions at 14.5 GeV will provide data set in the relatively large chemical potential gap between the 11.5 and 19.6 GeV center-of-mass energies. In this contribution, we report new STAR measurements of Au+Au at √sNN=14.5 GeV that include identified light particle RCP and spectra, as well as measurements of the strange hadrons (K0s, A, ξ, and ω). The spectra from both light and strange particles cover a significant range of the intermediate transverse momentum (2 < pT < 5 GeV/c) in all beam energies. We will discuss the physics implications of these observables and whether hadronic or partonic interactions dominate the collision dynamics at a given center-of-mass energy.

Fully Dynamical Simulation of Central Nuclear Collisions

We present a fully dynamical simulation of central nuclear collisions around midrapidity at LHC energies. Unlike previous treatments, we simulate all phases of the collision, including the equilibration of the system. For the simulation, we use numerical relativity solutions to anti-de Sitter space/conformal field theory for the preequilibrium stage, viscous hydrodynamics for the plasma equilibrium stage, and kinetic theory for the low-density hadronic stage. Our preequilibrium stage provides initial conditions for hydrodynamics, resulting in sizable radial flow. The resulting light particle spectra reproduce the measurements from the ALICE experiment at all transverse momenta.

Kinematical coincidence method in transfer reactions

A new method to extract high resolution angular distributions from kinematical coincidence measurements in binary reactions is presented. Kinematics is used to extract the center of mass angular distribution from the measured energy spectrum of light particles. Results obtained in the case of 10Be+p→9Be+d reaction measured with the CHIMERA detector are shown. An angular resolution of few degrees in the center of mass is obtained. The range of applicability of the method is discussed.

Reduced discretization error in HZETRN

The deterministic particle transport code HZETRN is an efficient analysis tool for studying the effects of space radiation on humans, electronics, and shielding materials. In a previous work, numerical methods in the code were reviewed, and new methods were developed that further improved efficiency and reduced overall discretization error. It was also shown that the remaining discretization error could be attributed to low energy light ions (A < 4) with residual ranges smaller than the physical step-size taken by the code. Accurately resolving the spectrum of low energy light particles is important in assessing risk associated with astronaut radiation exposure. In this work, modifications to the light particle transport formalism are presented that accurately resolve the spectrum of low energy light ion target fragments. The modified formalism is shown to significantly reduce overall discretization error and allows a physical approximation to be removed. For typical step-sizes and energy grids used in HZETRN, discretization errors for the revised light particle transport algorithms are shown to be less than 4% for aluminum and water shielding thicknesses as large as 100 g/cm2 exposed to both solar particle event and galactic cosmic ray environments.

Assessment of galactic cosmic ray models

Among several factors involved in the development of a manned space mission concept, the astronauts' health is a major concern that needs to be considered carefully. Galactic cosmic rays (GCRs), which mainly consist of high‐energetic nuclei ranging from hydrogen to iron and beyond, pose a major radiation health risk in long‐term space missions. It is therefore required to assess the radiation exposure of astronauts in order to estimate their radiation risks. This can be done either by performing direct measurements or by making computer based simulations from which the dose can be derived. A necessary prerequisite for an accurate estimation of the exposure using simulations is a reliable description of the GCR spectra. The aim of this work is to compare GCR models and to test their applicability for the exposure assessment of astronauts. To achieve this, commonly used models capable of describing both light and heavy GCR particle spectra were evaluated by investigating the model spectra for various particles over several decades. The updated Badhwar‐O'Neill model published in the year 2010, CREME2009 which uses the International Standard model for GCR, CREME96 and the Burger‐Usoskin model were examined. Hydrogen, helium, oxygen and iron nuclei spectra calculated by the different models are compared with measurements from various high‐altitude balloon and space‐borne experiments. During certain epochs in the last decade, there are large discrepancies between the GCR energy spectra described by the models and the measurements. All the models exhibit weaknesses in describing the increased GCR flux that was observed in 2009–2010.

Validation of nuclear reaction models of 180 MeV proton-induced fragmentation of 27Al

Kinetic energy, angular distribution, and isobaric cross section data for A = 7–25 fragments formed in p + 27Al reaction at bombarding energy of 180 MeV are compared with the calculations of the Binary Cascade Model (BIC), the Cascade Exciton Model (CEM), JQMD/PHITS, as well as the Statistical Model with Final State Interaction (SMFSI). For completeness, the kinetic energy spectra of light particles (n, p, α) formed in p + 27Al reaction at bombarding energy of 156 MeV are also presented. A general agreement between the data and predictions of these models is found. However, disagreement with the data for the yields of light-mass fragments as well as near-target fragments is also found and discussed. The importance of this comparative study to simulation and analysis of radiation effects on microscopic electrical components operating in space is also discussed.

PRE-EQUILIBRIUM ALPHA-PARTICLE EMISSION AS A PROBE TO EXPLORE ALPHA CLUSTERING IN NUCLEI

Experimental data of the double-differential spectra of light particles emitted at pre-equilibrium stage of nuclear processes were obtained at Laboratori Nazionali di Legnaro for the heavy-ion reactions 130 and 250 MeV 16 O + 116 Sn . Light charged particles were measured in coincidence with evaporation residues in order to avoid unwanted competing mechanisms. The experimental data were collected in a wide angular range from 29 to 82 degrees in the laboratory system. Theoretical model was developed in order to describe simultaneously evaporative and pre-equilibrium emission of the light particles in heavy-ion reactions. Griffin exciton model was used for the description of the pre-equilibrium stage of the compound nucleus formation, while the equilibrium evaporation processes were analyzed in the framework of the statistical theory of heavy-ion reactions. Experimental data were compared with the results of the model calculations and new approach was suggested to take into account alpha cluster formation in the projectile nucleus by measuring and analyzing pre-equilibrium alpha-particle spectra.

Medium corrections in the formation of light charged particles in heavy ion reactions

Within a microscopic statistical description of heavy ion collisions, we investigate the effect of the medium on the formation of light clusters. The dominant medium effects are self-energy corrections and Pauli blocking that produce the Mott effect for composite particles and enhanced reaction rates in the collision integrals. Microscopic description of composites in the medium follows the Dyson equation approach combined with the cluster mean-field expansion. The resulting effective few-body problem is solved within a properly modified Alt-Grassberger-Sandhas formalism. The results are incorporated in a Boltzmann-Uehling-Uhlenbeck simulation for heavy ion collisions. The number and spectra of light charged particles emerging from a heavy ion collision changes in a significant manner in effect of the medium modification of production and absorption processes.

Cross-Section Evaluations to 150 MeV for Accelerator-Driven Systems and Implementation in MCNPX

New accelerator-driven technologies that utilize spallation neutrons, such as the production of tritium and the transmutation of radioactive waste, require accurate nuclear data to model the performance of the target/blanket assembly and to predict neutron production, activation, heating, shielding requirements, and material damage. To meet these needs, nuclear-data evaluations and libraries up to 150 MeV have been developed for use in transport calculations to guide engineering design. By using advanced nuclear models that account for details of nuclear structure and the quantum nature of the nuclear scattering, significant gains in accuracy can be achieved below 150 MeV, where intranuclear cascade calculations become less accurate. Evaluations are in ENDF-6 format for important target/blanket and shielding materials (isotopes of H, C, N, O, Al, Si, P, Ca, Cr, Fe, Ni, Cu, Nb, W, Hg, and Pb) for both incident neutrons and incident protons. The evaluations are based on measured data as well as predictions from the GNASH nuclear model code, which calculates cross sections using Hauser-Feshbach, exciton, and Feshbach-Kerman-Koonin preequilibrium models. Elastic scattering distributions and direct reactions are calculated from the optical model. All evaluations specify production cross sections and energy-angle correlated spectra of secondary light particles as well as production cross sections and energy distributions of heavy recoils and gamma rays. A formalism developed to calculate recoil energy distributions is presented. The use of these nuclear data in the MCNPX radiation transport code is also briefly described. This code merges essential elements of the LAHET and MCNP codes and uses these new data below 150 MeV and intranuclear cascade collision physics at higher energies. Extensive comparisons are shown between the evaluated results and experimental cross-section data to benchmark and validate the evaluated library. In addition, integral benchmarks of calculated and measured kerma coefficients for neutron energy deposition and neutron transmission through an iron slab compared with MCNPX calculations are provided. These evaluations have been accepted into the ENDF/B-VI library as Release 6.

Breakup temperature of target spectators in 197Au +197Au collisions at E/A = 1000 MeV

Breakup temperatures were deduced from double ratios of isotope yields for target spectators produced in the reaction 197Au + 197Au at 1000 MeV per nucleon. Pairs of 3,4He and 6,7Li isotopes and pairs of 3,4He and H isotopes (p, d and d, t) yield consistent temperatures after feeding corrections, based on the quantum statistical model, are applied. The temperatures rise with decreasing impact parameter from 4 MeV for peripheral to about 10 MeV for the most central collisions. The good agreement with the breakup temperatures measured previously for projectile spectators at an incident energy of 600 MeV per nucleon confirms the universality established for the spectator decayat relativistic bombarding energies. The measured temperatures also agree with the breakup temperatures predicted by the statistical multifragmentation model. For these calculations a relation between the initial excitation energy and mass was derived which gives good simultaneous agreement for the fragment charge correlations. The energy spectra of light charged particles, measured at τlab = 150°, exhibit Maxwellian shapes with inverse slope parameters much higher than the breakup temperatures. The statistical multifragmentation model, because Coulomb repulsion and sequential decay processes are included, yields light-particle spectra with inverse slope parameters higher than the breakup temperatures but considerably below the measured values. The systematic behavior of the differences suggests that they are caused by light-charged-particle emission prior to the final breakup stage.

Breakup temperature of target spectators in 197Au + 197Au collisions at E/A = 1000 MeV

Breakup temperatures were deduced from double ratios of isotope yields for target spectators produced in the reaction Au + Au at 1000 MeV per nucleon. Pairs of $^{3,4}$He and $^{6,7}$Li isotopes and pairs of $^{3,4}$He and H isotopes (p, d and d, t) yield consistent temperatures after feeding corrections, based on the quantum statistical model, are applied. The temperatures rise with decreasing impact parameter from 4 MeV for peripheral to about 10 MeV for the most central collisions. The good agreement with the breakup temperatures measured previously for projectile spectators at an incident energy of 600 MeV per nucleon confirms the observed universality of the spectator decay at relativistic bombarding energies. The measured temperatures also agree with the breakup temperatures predicted by the statistical multifragmentation model. For these calculations a relation between the initial excitation energy and mass was derived which gives good simultaneous agreement for the fragment charge correlations. The energy spectra of light charged particles, measured at $\theta_{lab}$ = 150$^{\circ}$, exhibit Maxwellian shapes with inverse slope parameters much higher than the breakup temperatures. The statistical multifragmentation model, because Coulomb repulsion and sequential decay processes are included, yields light-particle spectra with inverse slope parameters higher than the breakup temperatures but considerably below the measured values. The systematic behavior of the differences suggests that they are caused by light-charged-particle emission prior to the final breakup stage. PACS numbers: 25.70.Mn, 25.70.Pq, 25.75.-q

Double Differential Cross Section Measurements of the (n,px), (n,dx), (n,tx) and (n,alphax) Reactions on 12C: Kerma Determination at Energies Between 30 and 75 MeV

The double-differential cross sections for the (n,px), (n,dx), (n,tx) and (n,alphax) reactions on carbon have been measured at 42.5, 62.7 and 72.8 MeV incident neutron energies at laboratory angles from 20o to 160o in 10o steps. The energy differential cross sections are deduced and consequently the partial and total kerma values. Experimental results are compared with existing data and theoretical calculations. Preliminary results on carbon are also shown concerning the light charged particle spectra induced by neutrons from the low energy tail of the incident neutron spectrum.

Coping with strongly coupled string theory.

String theory, if it describes nature, is probably strongly coupled. As a result, one might despair of making any statements about the theory. In the framework of a set of clearly spelled out assumptions, we show that this is not necessarily the case. Certain discrete gauge symmetries, combined with supersymmetry, tightly constrain the form of the effective action. Among our assumptions are that the true ground state can be obtained from some perturbative ground state by varying the coupling, and that the actual numerical value of the low energy field theoretic coupling ${g^2 \over 4\pi}$ is small. It follows that the low energy theory is approximately supersymmetric; corrections to the superpotential and gauge coupling function are small, while corrections to the Kahler potential are large; the spectrum of light particles is the same at strong as at weak coupling. We survey the phenomenological consequences of this viewpoint. We also note that the string axion can serve as QCD axion in this framework (modulo cosmological problems).

Impact parameter dependence of preequilibrium particle emission.

The energy spectra and angular distributions of protons, deuterons, tritons, and alpha particles from 215 MeV [sup 16]O bombardment of Tb, Ta, and Au have been measured in coincidence with both evaporation residues and fission fragments. The evaporation residue and fission fragment triggers together with the angular momentum dependence of the evaporation residue-fission competition have enabled us to extract the impact parameter dependence of the light charged particle preequilibrium multiplicities within the fusionlike impact parameter domain. The light charged particle spectra can be parametrized as originating from a source with approximately 1/2 to 2/3 of the beam velocity and with a slope parameter of [similar to]5--7 MeV. The proton multiplicities increase with decreasing impact parameter, in agreement with a nucleon exchange transport model prediction. The ratio of the complex particle to proton multiplicities decrease with decreasing impact parameter, suggesting dynamical effects in the complex particle production mechanism.