Energy Spectra Of Fragments Research Articles

Examination of cluster production in excited light systems at Fermi energies from new experimental data and comparison with transport model calculations

Four different reactions, $^{32}$S+$^{12}$C and $^{20}$Ne+$^{12}$C at 25 and 50 MeV/nucleon, have been measured with the FAZIA detector capable of full isotopic identification of most forward emitted reaction products. Fragment multiplicities, angular distributions and energy spectra have been measured and compared with Monte Carlo simulations, i.e. the antisymmetrized molecular dynamics (AMD) and the heavy-ion phase space exploration (HIPSE) models. These models are combined with two different afterburner codes (HF$l$ and SIMON) to describe the decay of the excited primary fragments. In the case of AMD, the effect of including the clustering and inter-clustering processes to form bound particles and fragments is discussed. A clear confirmation of the role of cluster aggregation in the reaction dynamics and particle production for these light systems, for which the importance of the clustering process increases with bombarding energy, is obtained.

Reaction dynamics and in-medium nucleon-nucleon cross section with C12+H1 at 95 MeV/nucleon

Reaction dynamics and effective in-medium nucleon-nucleon $(NN)$ cross section are studied, using the antisymmetrized molecular dynamics (AMD) model with one of the simplest heavy ion collisions, $^{12}\mathrm{C}+^{1}\mathrm{H}$. The roles of different stochastic processes are studied, which are installed in the original AMD. One is the diffusion process as a part of the quantum fluctuation originated from the Fermi motion during the time evolution of the wave packets in the mean field (AMD/D). The second is a coalescence treatment for light clusters with $A\ensuremath{\le}8$ (AMD/D-COALS). The third is the collision process, installed in AMD with different form of the in-medium $NN$ cross sections. These different processes are examined, using the experimental angular distributions and energy spectra of light charged particles and intermediate mass fragments. The effective in-medium $NN$ cross sections are evaluated from the simulated AMD events and compared with the experimentally extracted values. A good agreement is obtained between the AMD values from the $^{12}\mathrm{C}$ $+$ $^{1}\mathrm{H}$ reaction at 95 MeV/nucleon and the experimental results for nuclear matter.

Evolution of the shape of fission fragment energy spectrum with absorber thickness in two different media and effective charge correction

The energy loss behavior of fission fragments (FFs) from [Formula: see text]Cf(sf) in thin Mylar [Formula: see text] and Aluminium absorber foils has been revisited. The aim is to investigate the observed change in the well-known asymmetric energy of spontaneous fission of [Formula: see text]Cf as the fragments pass through increasingly thick absorber foils. Two different types of absorbers have been used: one elemental and the other an organic compound. The stopping powers have been determined as a function of energy for three fragment mass groups with average masses having [Formula: see text], 141.8, 125.8 corresponding to light, heavy and symmetric fragments of [Formula: see text]Cf. The energy loss data have been compared with the predictions of SRIM 2013 code. The best representations of the data have been achieved using the effective Z correction term in the stopping power relation from the classical Bohr theory. Using the effective charge (Z[Formula: see text]) in the stopping power relation in the classical Bohr theory best describes the stopping power data. Spectrum shape parameters, subsequently, have been extracted from the energy spectra of FFs for different foil thicknesses. The effective charge (Z[Formula: see text]) correction term determined from the stopping power data is then used in the simulation for the absorber thickness dependence of the shape parameters of the energy spectrum. The present simulation results are compared with the TRIM prediction. The trends of the absorber thickness dependence of the spectrum shape parameters, for both Mylar and Aluminium, are well reproduced with the present simulation.

Interaction of therapeutic 12C ions with bone-like targets: physical characterization and dosimetric effect at material interfaces

Carbon therapy is a promising treatment option for cancer. The physical and biological properties of carbon ions can theoretically allow for the delivery of curative doses to the tumor, while simultaneously limiting risks of toxicity to adjacent healthy structures. The treatment effectiveness can be further improved by decreasing the uncertainties stemming from several sources, including the modeling of tissue heterogeneity. Current treatment plans employ density-based conversion methods to translate patient-specific anatomy into a water system, where dose distribution is calculated. This approach neglects differences in nuclear interactions stemming from the elemental composition of each tissue. In this work, we investigated the interaction of therapeutic carbon ions with bone-like materials. The study concentrated on nuclear interactions and included attenuation curves of 200 and 400 AMeV beams in different types of bones, as well as kinetic energy spectra of all charged fragments produced up to 29 degrees from the beam direction. The comparison between measurements and calculations of the treatment planning system TRiP98 indicated that bone tissue causes less fragmentation of carbon ions than water. Overall, hydrogen and helium particles were found to be the most abundant species, while heavier fragments were mostly detected within 5 degrees from the beam direction. We also investigated how the presence of a soft tissue-bone interface could affect the depth-dose profile. The results revealed a dose spike in the transition region, that extended from the entry channel to the target volume. The findings of this work indicated that the tissue-to-water conversion method based only on density considerations can result in dose inaccuracies. Tissue heterogeneity regions containing bones can potentially produce dose spikes, whose magnitude will depend on the patient anatomy. Dose uncertainties can be decreased by modeling nuclear interactions directly in bones, without applying the tissue-to-water conversion.

A new type of ground-based simulator of radiation field inside a spacecraft in deep space

The problem of full-scale ground-based modeling of cosmic radiation on heavy-ion accelerators for space radiobiology is very urgent. A new type of space radiation simulator at the 56Fe ion beam with energy 1 GeV/n is proposed. The simulator uses rotating converters consisting of segmented targets with varying thicknesses. When a flat uniform field of primary 56Fe ions is used, this design ensures the uniformity of the fields of all secondary particles behind the targets. The proposed setup with four replaceable converters makes it possible to simulate not only the distribution of linear energy transfers of cosmic radiation but also reproduce continuous energy spectra of all charged fragments of the projectile ion from protons to Co. The results of simulation of the internal radiation field inside the habitable module of a spacecraft with a shell of 15 g/cm2 Al, generated by particles of galactic cosmic rays in the solar activity range from 0 to 190 Wolf numbers, are presented.

Effects of cluster correlations on fragment emission in C12+C12 at 50 MeV/nucleon

The effects of cluster correlations have been studied in the $^{12}\mathrm{C}+^{12}\mathrm{C}$ reaction at 50 MeV/nucleon, using three antisymmetrized molecular dynamics (AMD) models, the AMD (AMD/D) without any additional cluster correlations, AMD/D-COALS with nucleon correlations based on a coalescence prescription for light cluster formations with $A\ensuremath{\le}4$, and AMD-cluster with an extended cluster correlation in two-nucleon collision processes and a special treatment for intermediate fragment formation with $A\ensuremath{\le}9$. The angular distributions and energy spectra of fragments have been simulated and compared with the available experimental data. It is found that the cluster correlations take a crucial role to describe the productions of light charged particles (LCPs) and intermediate mass fragments (IMFs), and the AMD-cluster studied here provides a consistent overall reproduction of the experimental data. It is also shown that the significant effects of the secondary decay processes are involved for the fragment production besides the dynamical productions in the AMD stage. Detailed LCP and IMF production mechanisms involved in the intermediate energy heavy ion collisions are discussed.

Optical Absorption Spectrum of Small Graphene Fragments with Topological Defects

Energy spectra of small graphene fragments with and without topological defects (vacancies, nanopores and Stone–Wales defects) are obtained using the Hubbard model based on the approximation of static fluctuations. Modeling of optical absorption spectra is performed for both defect-free and defective small graphene fragments of the lattice. The analysis is given to optical absorption spectra changing with increasing number of vacancies. It is shown how the energy gap depends on the defect configuration and concentration.

Determination of the number of 238U target nuclei and simulation of the neutron induced fission fragment energy spectrum

A Monte Carlo simulation of the energy spectrum of the α particles emitted from a 238U3O8 sample is performed. Through comparing the simulated and measured energy spectra of the α particles, the non-uniformity of the 238U3O8 sample is obtained, and then the number of 238U target nuclei is determined. Using the obtained non-uniformity, a Monte Carlo simulation is developed to simulate the energy spectrum of neutron induced fission fragments. The simulated and measured energy spectra of neutron induced fission fragments agree well with each other.

Radial Flow in the Interaction of Relativistic Deuterons with a Gold Target

The kinetic energy spectra of intermediate mass fragments (IMF) has been studied for 4.4 GeV d + Au collisions at the Dubna Nuclotron with the 4π detector array FASA. Experimental kinetic energy spectra were compared to that obtained by the multi-body Coulomb trajectory calculations with the initial break-up conditions given by the combined model INC + SMM. It was found good agreement of measured and calculated kinetic energy spectra including a radial flow.

Electron-nuclear correlated multiphoton-route to Rydberg fragments of molecules

Atoms and molecules exposed to strong laser fields can be excited to the Rydberg states with very high principal quantum numbers and large orbitals. It allows acceleration of neutral particles, generate near-threshold harmonics, and reveal multiphoton Rabi oscillations and rich photoelectron spectra. However, the physical mechanism of Rydberg state excitation in strong laser fields is yet a puzzle. Here, we identify the electron-nuclear correlated multiphoton excitation as the general mechanism by coincidently measuring all charged and neutral fragments ejected from a H2 molecule. Ruled by the ac-Stark effect, the internuclear separation for resonant multiphoton excitation varies with the laser intensity. It alters the photon energy partition between the ejected electrons and nuclei and thus leads to distinct kinetic energy spectra of the nuclear fragments. The electron-nuclear correlation offers an alternative visual angle to capture rich ultrafast processes of complex molecules.

Angular distribution measurement for 12C fragmentation via 12C + 12C scattering at 100 MeV/u**Supported by National Natural Science Foundation of China (11705123, 11475013, 11035007, 11175011), China Postdoctoral Science Foundation (2016M591911) and Natural Science Foundation of Jiangsu Province (BK20160306)

The angular distributions and energy spectra of 11B, 10B, and 9Be fragments of 12C in the angular range from 1.0° to 7.5° at 100 MeV/u were obtained via 12C + 12C scattering. Detailed comparisons are presented between the experimental data and the modified antisymmetrized molecular dynamics (AMD-FM), binary intranuclear cascade model (BIC) and Liège intranuclear cascade model (INCL++). The experimental angular distributions and energy spectra are well reproduced by the AMD-FM calculations but fail to be reproduced by the physical models installed in the Geant4 program, including the BIC and INCL++ models.

Light Ion Yields from Bombardment of Thick Targets by Protons, Helium-4 and Iron-56

In March 2016 accelerator-based experiments colliding protons (0.4 and 0.8 GeV), helium (0.4 AGeV) and iron (0.4 and 0.8 AGeV) on thick aluminum targets with surface densities of 20, 40, and 60 g/cm2 were performed at the National Aeronautics and Space Administration Space Radiation Laboratory (NSRL) at Brookhaven National Laboratory. Two targets were utilized in each experimental configuration. Hydrogen and helium ions were detected using organic liquid scintillators in conjunction with thin plastic scintillators at 10°, 30°, 45°, 60°, 80°, and 135° from beam axis. Time-of-flight techniques and pulse shape discrimination were used to identify light ion species in order to generate double differential energy spectra of the light ion fragments. Comparisons of these measured yields were compared with Monte Carlo calculations generated by MCNP6. These yields will be used to quantify uncertainty in radiation transport codes utilized in risk assessment for spaceflight missions with prolonged exposures to galactic cosmic rays.

Small-angle fragmentation of carbon ions at 0.6 GeV/n: a comparison with models of ion-ion interactions

Momentum distributions of hydrogen and helium isotopes from 12C fragmentation at 3.5° were measured at 0.6 GeV/nucleon in the FRAGM experiment at ITEP TWA heavy ion accelerator. The fragments were selected by correlated time of flight and dE/dx measurements with a magnetic spectrometer with scintillation counters. The main attention was drawn to the high momentum region where the fragment velocity exceeds the velocity of the projectile nucleus. The momentum spectra of fragments span the region of the fragmentation peak as well as the cumulative region. The differential cross sections cover six orders of magnitude. The distributions measured are compared to the predictions of three ion-ion interaction models: BC, QMD and LAQGSM03.03. The kinetic energy spectra of fragments in the projectile rest frame have an exponential shape with two temperatures, being defined by their slope parameters.

The effect of nuclear structure in the emission of reaction products in heavy-ion reactions

Study of intermediate mass fragments (IMFs) and light charged particles (LCPs) emission has been carried out for a few reactions involving α-cluster and non- α-cluster systems to see how the emission processes are affected by nuclear clustering. Li, Be, B and α-particles have been studied from α-clustered system 16O + 12C for 117, 125, 145 and 160 MeV bombarding energies respectively. The enhanced yields of near-entrance channel fragment B and large quadrupole deformation of the produced composite 28Si∗ extracted from LCP spectra indicate the survival of orbiting-like process in 16O + 12C system at these energies. The same IMFs emitted from the α-cluster system 12C (77 MeV) + 28Si and nearby non- α cluster 11B (64 MeV) + 28Si and 12C (73 MeV) + 27Al (all having the same excitation energy of ∼67 MeV) have also been studied. The fully energy damped (fusion–fission) and the partially energy damped (deep inelastic) components of the fragment energy spectra have been extracted. It has been found that the yields of the fully energy damped fragments for all the above reactions are in conformity with the respective statistical model predictions. The time-scales of various deep inelastic fragment emissions have been extracted from the angular distribution data. The angular momentum dissipation in deep inelastic collisions has been estimated from the data and it has been found to be close to the corresponding sticking limit value.

Isospin observables from fragment energy spectra

The energy spectra of light charged particles and intermediate mass fragments from ${}^{112}\mathrm{Sn}+{}^{112}\mathrm{Sn}$ and ${}^{124}\mathrm{Sn}+{}^{124}\mathrm{Sn}$ collisions at an incident energy of $E/A=50$ MeV have been measured with a large array of silicon strip detectors. We used charged-particle multiplicities detected in an array with nearly 4$\ensuremath{\pi}$ coverage to select data from the central collision events. We study isospin observables analogous to ratios of neutron and proton spectra, including double ratios and yield ratios of triton/${}^{3}$He and of asymmetries constructed from fragments with $Z=3$--8. Using the energy spectra, we can construct these observables as functions of kinetic energy. Most of the fragment asymmetry observables have a large sensitivity to sequential decays.

Complex-fragment emission in low-energy light-ion reactions

Inclusive energy spectra of the complex fragments (3 $\leq$ Z $\leq$ 5) emitted in the reactions $^{12}$C (77 MeV)+ $^{28}$Si, $^{11}$B (64 MeV)+ $^{28}$Si and $^{12}$C (73 MeV)+ $^{27}$Al (all having the same excitation energy of $ \sim$ 67 MeV), have been measured in the angular range of 10$^\circ$ $\lesssim \theta_{lab} \lesssim$ 60$^\circ$. The fully energy damped (fusion-fission) and the partially energy damped (deep inelastic) components of the fragment energy spectra have been extracted. It has been found that the yields of the fully energy damped fragments for all the above reactions are in conformity with the respective statistical model predictions. The time scales of various deep inelastic fragment emissions have been extracted from the angular distribution data. The angular momentum dissipation in deep inelastic collisions has been estimated from the data and it has been found to be close to the corresponding sticking limit value.

Collective flow in nuclear fragmentation induced by 4.4 GeV deuteron on gold target

Nuclear multifragmentation in d (4.4 GeV) + Au collision was studied with the 4π setup FASA installed at the external beam of the Dubna Nuclotron. Data obtained are analyzed within the statistical model of multifragmentation. It is found that the kinetic energy spectra of intermediate mass fragments deviate from the predicted ones. It is explained by the collective flow caused by the thermal expansion of fragmenting nucleus.

Measurement of the energy spectra of fission fragments using nuclear track detectors and digital image processing

Abstract Energy spectra of fission fragments were determined using a Nuclear Track Methodology (NTM) supported by digital image analysis and numerical data processing using a standard personal computer. The analysis of a californium (252Cf) spectrum with this approach shows improvement compared with the values reported previously using the standard procedure, in terms of resolution and accuracy. This new method adds full automation to the technical advantages and cost effectiveness of an NTM.

Isotopic effect in the broadening of the energy spectra of fragments of hydrogen molecular ions scattered from surface

The effect of broadening of the energy spectra of fragments of different hydrogen molecular ions scattered from a tungsten surface has been investigated experimentally and by computer simulation. The experimental results are approximated within the explosive model. The contributions of different mechanisms to the broadening of the energy spectra of scattered fragments are discussed.

Broadening of energy spectra of molecular ion fragments produced by surface small angle scattering

Relative half-widths of energy spectra of molecular hydrogen ions and their fragments scattered by a tungsten surface have been experimentally studied for various primary molecules and their isotopic analogues in the energy range of 100–4000 eV per nucleon. The spectra of fragments turned out to be broader than the spectra of the same particles that are not fragmentation products. The broadening is interpreted within the “explosion” model, i.e., dissociation of a molecular ion due to the change in the shape of the interaction potential of the fragments. The model of “explosive” dissociation of molecules agrees with the data obtained assuming an effective repulsion energy of 1.1 ± 0.1 eV for all molecules.