Light Particle Emission Research Articles

N/Z dependence of decay channels in A=80 compound nuclei

A comparative decay analysis of $^{80}\mathrm{Zr}^{*}$, $^{80}\mathrm{Sr}^{*}$, and $^{80}\mathrm{Kr}^{*}$ isobaric nuclear systems formed in $^{40}\mathrm{Ca}+^{40}\mathrm{Ca}$, $^{16}\mathrm{O}+^{64}\mathrm{Zn}$, and $^{32}\mathrm{S}+^{48}\mathrm{Ca}$ reactions, respectively, has been conducted to investigate the $N/Z$ dependence of different decay modes within a dynamical cluster-decay model based on the collective clusterization approach of quantum mechanical fragmentation theory. The comparative contributions of the emission of light particles (LPs), intermediate mass fragments (IMFs), and symmetric mass fragments (SMFs) in the total fusion cross-sections, ${\ensuremath{\sigma}}_{\mathrm{fusion}}$, have been calculated. The results show that LPs have a major contribution to ${\ensuremath{\sigma}}_{\mathrm{fusion}}$ in the decay of all three compound nuclei (CN). The percentage contribution of LPs is larger for CN with higher $N/Z$ ratio. The IMFs and SMFs cross-section are comparatively low in the total ${\ensuremath{\sigma}}_{\mathrm{fusion}}$ but their emissions are in competition in the decay process. The results show that the shape of mass distribution evolves from symmetric to asymmetric with increasing $N/Z$ ratio. The yield around SMFs is greater for the system having the lowest $N/Z$ ratio. This may be attributed to higher ${P}_{0}$ for the symmetric exit channel, particularly at higher $\ensuremath{\ell}$ values. The calculated fusion cross-sections for all three CN are in good agreement with the experimental data.

Calculation of the Coulomb barrier and the level density parameter at the fission saddle point in spallation nuclear reactions

This work studies the compound nucleus’ de-excitation during spallation nuclear reactions, with focus on the behavior of the Coulomb barrier for emission of charged particles and the level density parameter at the fission saddle point, establishing for the first time a relationship between these magnitudes and the level density. This relationship manifests itself through two differential equations explicitly dependent on the excitation energy and the level density parameter of the nucleus after the emission of light particles. These equations were implemented into the CRISP code and used to simulate proton induced spallation reactions on and 238U, respectively, comparing the results with data coming from GSI experiments as well as from other codes and obtaining satisfactory results that confirm the reliability of the new models.

Role of charged particle emission on the evaporation residue formation in the 82Se+138Ba reaction leading to the 220Th compound nucleus

We present detailed results of a theoretical investigation on the production of evaporation residue nuclei obtained in a heavy ion reaction when charged particles (proton and α-particle) are also emitted with the neutron evaporation along the deexcitation cascade of the formed compound nucleus. The almost mass symmetric 82Se+138Ba reaction has been studied since there are many experimental results on individual evaporation residue (ER) cross sections after few light particle emissions along the cascade of the 220Th compound nucleus (CN) covering the wide 12–70 MeV excitation energy range. Our specific theoretical results on the ER cross sections for the 82Se+138Ba are in good agreement with the available experimental measurements, but our overall theoretical results concerning all possible relevant contributions of evaporation residues are several times greater than the ERs measured in experiment. The discrepancy could be due to the experimental difficulties in the identification of ER nuclei after the emission of multiple neutral and charged particles, nevertheless the analysis of ER data is very important to test the reliability of the model and to stress the importance on the investigation of ER nuclei also obtained after charged particle emissions.

Experimental study of precisely selected evaporation chains in the decay of excited Mg25

The reaction $^{12}\mathrm{C}+^{13}\mathrm{C}$ at $95\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ bombarding energy is studied using the Garfield + Ring Counter apparatus located at the INFN Laboratori Nazionali di Legnaro. In this paper we want to investigate the de-excitation of $^{25}\mathrm{Mg}$ aiming both at a new stringent test of the statistical description of nuclear decay and a direct comparison with the decay of the system $^{24}\mathrm{Mg}$ formed through $^{12}\mathrm{C}+^{12}\mathrm{C}$ reactions previously studied. Thanks to the large acceptance of the detector and to its good fragment identification capabilities, we could apply stringent selections on fusion-evaporation events, requiring their completeness in charge. The main decay features of the evaporation residues and of the emitted light particles are overall well described by a pure statistical model; however, as for the case of the previously studied $^{24}\mathrm{Mg}$, we observed some deviations in the branching ratios, in particular for those chains involving only the evaporation of $\ensuremath{\alpha}$ particles. From this point of view the behavior of the $^{24}\mathrm{Mg}$ and $^{25}\mathrm{Mg}$ decay cases appear to be rather similar. An attempt to obtain a full mass balance even without neutron detection is also discussed.

Deep-inelastic multinucleon transfer processes in the O16+Al27 reaction

The reaction mechanism of deep-inelastic multinucleon transfer processes in the $^{16}$O+$^{27}$Al reaction at an incident $^{16}$O energy ($E_{\rm lab}=134$ MeV) substantially above the Coulomb barrier has been studied both experimentally and theoretically. Elastic-scattering angular distribution, total kinetic energy loss spectra and angular distributions for various transfer channels have been measured. The $Q$-value- and angle-integrated isotope production cross sections have been deduced. To obtain deeper insight into the underlying reaction mechanism, we have carried out a detailed analysis based on the time-dependent Hartree-Fock (TDHF) theory. A recently developed method, TDHF+GEMINI, has been applied to evaluate production cross sections for secondary products. From a comparison between the experimental and theoretical cross sections, we find that the theory qualitatively reproduces the experimental data. Significant effects of secondary light-particle emissions are demonstrated. Possible interplay between fusion-fission, deep-inelastic, multinucleon transfer and particle evaporation processes are discussed.

Role of dynamical deformation in pre-scission neutron multiplicity

The light-particle emission probability from an excited compound nucleus depends explicitly on the time-evolution of the system as the available internal excitation energy and, consequently, the particle decay widths depend on the instantaneous deformation of the nucleus. The Langevin dynamical model for fission is employed to extract this deformation dependence in pre-scission particle multiplicities by following the propagation of fissioning trajectories up to scission. The variation of particle decay widths with nuclear deformation is accounted more precisely in comparison to the existing calculations. The number of neutrons emitted from different configurations of the compound nucleus are calculated for a detailed analysis. The deformation dependence of particle emission widths is found to be relevant for highly fissile systems where the dynamics is primarily governed by the saddle to scission motion. This dynamical effect essentially predicts the nuclear shape evolution through evaporated light particles and, for a heavy compound system, simultaneous measurement of neutron multiplicities for fission and evaporation residue events can reveal its intricate nature.

Ternary fission of 260No in equatorial configuration

Spontaneous ternary fission is one of the observed decay modes of heavy nuclei. We systematically investigate the equatorial ternary fission of the 260No isotope. In the framework of the three-cluster model, the three-body interaction potential is calculated in terms of the folded M3Y-Reid nucleon-nucleon force and the Coulomb one. The relative orientations of the deformed heavy nuclei participating in the fragmentation process are taken into account. All possible emitted light particles with even mass numbers $A = 4$ -52 are considered. The favored fragmentation channels are estimated as the ones characterized with peaks in the Q-value and local minima in the fragmentation potential. In the absence of nuclear deformations, the closed shell effects are found to play the key role in determining the channels of minimum fragmentation potential and the involved two heavier fragments tend to be of comparable sizes. Inclusion of nuclear deformations manifest the participation of highly deformed prolate nuclei, with large mass asymmetry, as heavy fragment partners in the estimated favored fragmentation channels. The results indicate that the equatorial ternary fission of 260No is most favored with the light emitted nuclei 4,6,8 2He and 10 4Be through the fragmentation channels 155 60Nd + 4 2He + 101 0Zr, 153 60Nd + 6 2He + 101 40Zr, 152 60Nd + 8 2He + 100 40Zr, and 152 0Nd + 10 4Be + 98 38Sr, respectively.

A statistical model for simulating the emission of light particles from excited nuclei

The algorithms and basic equations of a novel evaporation model that have been implemented in the program package EVAP15 are detailed. The level density of an excited nucleus is described by the composite Gilbert–Cameron formula with parameter values as suggested by the IAEA working group RIPL-3. Special attention is paid to the cross sections of inverse reactions and, in particular, to those for the interactions of low-energy neutrons with nuclei and for crossing of the Coulomb barrier by low-energy charged particles. The model predictions are compared with a large volume of experimental data on the spectra of particles emitted in the reactions (n, xn), (n, xp), and (n, xα) induced by neutrons with energy near 14 MeV and on the four spectra for the reaction (p, xp) induced by 62-MeV protons.

Quasifission and fusion-fission processes in the reactionsKr78+Ca40andKr86+Ca48at 10 MeV/nucleon bombarding energy

Within the dinuclear system model the charge, mass, and isotopic distributions of the products in the reactions $^{78}\mathrm{Kr}+^{40}\mathrm{Ca}$ and $^{86}\mathrm{Kr}+^{48}\mathrm{Ca}$ are predicted at bombarding energy 10 MeV/nucleon. The heavy-ion phase-space exploration code is applied to take into consideration the pre-equilibrium emission of light particles. The competition is treated between complete fusion followed by the decay of compound nucleus and quasifission channels. The possible explanation of the odd-even staggering in the yield of the final reaction products at high excitation energies is discussed.

KEWPIE2: A cascade code for the study of dynamical decay of excited nuclei

KEWPIE–a cascade code devoted to investigating the dynamical decay of excited nuclei, specially designed for treating very low probability events related to the synthesis of super-heavy nuclei formed in fusion–evaporation reactions–has been improved and rewritten in C++ programming language to become KEWPIE2. The current version of the code comprises various nuclear models concerning the light-particle emission, fission process and statistical properties of excited nuclei. General features of the code, such as the numerical scheme and the main physical ingredients, are described in detail. Some typical calculations having been performed in the present paper clearly show that theoretical predictions are generally in accordance with experimental data. Furthermore, since the values of some input parameters cannot be determined neither theoretically nor experimentally, a sensibility analysis is presented. To this end, we systematically investigate the effects of using different parameter values and reaction models on the final results. As expected, in the case of heavy nuclei, the fission process has the most crucial role to play in theoretical predictions. This work would be essential for numerical modeling of fusion–evaporation reactions. Program summaryProgram title: KEWPIE2Catalogue identifier: AEZB_v1_0Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEZB_v1_0.htmlProgram obtainable from: CPC Program Library, Queen’s University, Belfast, N. IrelandLicensing provisions: GNU General Public License, version 3No. of lines in distributed program, including test data, etc.: 41230No. of bytes in distributed program, including test data, etc.: 259652Distribution format: tar.gzProgramming language: C++.Computer: All Linux based workstations, Apple machines.Operating system: Linux, OS X.RAM: Depending on the size of system and calculated quantities.Classification: 17.8, 17.10, 17.23.External routines: The latest version of the GSL library, available on http://www.gnu.org/software/gsl/Nature of problem: Estimating evaporation-residue cross-sections and average fission times related to the synthesis of super-heavy elements.Solution method: A specific algorithm based on the Bateman equations and the spectral discretization method.Restrictions: The main area of application is the study of the de-excitation of heavy or super-heavy nuclei.Running time: A few seconds up to several hours, depending on the calculated quantities (evaporation-residue cross-section or average fission time).

Correlation between the fragmentation modes and light charged particles emission in heavy ion collisions

The correlation between the shape of rapidity distribution of the yield of light charged particles and the fragmentation modes in semi-peripheral collisions for 70Zn+70Zn, 64Zn+64Zn and 64Ni+64Ni at the beam energy of 35 MeV/nucleon is investigated based on ImQMD05 code. Our studies show there is an interplay between the binary, ternary and multi-fragmentation break-up modes. The binary and ternary break-up modes more prefer to emit light charged particles at middle rapidity and give larger values of R yield mid compared with the multi-fragmentation break-up mode does. The reduced rapidity distribution for the normalized yields of p, d, t, 3He, 4He and 6He and the corresponding values of R yield mid can be used to estimate the probability of multi-fragmentation break-up modes. By comparing to experimental data, our results illustrate that ≥40% of the collisions events belong to the multifragmentation break-up mode for the reactions we studied.

Pre-equilibrium Emission and α-clustering in Nuclei

The study of nuclear states built on clusters bound by valence neutrons in their molecular configurations is a field of large interest, which is being renewed by the availability of exotic beams: clustering is, in fact, predicted to become very important at the drip-line, where weakly bound systems will prevail. Although for light nuclei at an excitation energy close to the particle separation value there are experimental evidences of such structure effects, this is still not the case for heavier nuclear systems. Many attempts have been done using preformation alpha clustering models, but there is still a lack of experimental data capable to give a direct feedback. In particular, searching for alpha clustering effects in medium mass systems is still a challenge, which can give new hints in this subject. In the past we have studied the reactions 250, 192 and 130 MeV 16O + 116Sn, observing a significant increase in the fast emitted α-particle yield. This effect was ascribed to the presence of preformed a-clusters in the 16O projectile nucleus. In order to investigate these aspects, in a model independent way, a new experimental campaign has been performed with the GARFIELD + RCo set up, to compare results from two different reactions: a double magic a-cluster (16O) and a non-magic α-cluster projectile (19F) at the same beam velocity (16AMeV) have been chosen, impinging respectively on 65Cu and 62Ni targets, thus leading to the same 81Rb* compound nucleus. The angular distributions and the light charged particles emission spectra in coincidence with evaporation residues have been measured and analyzed. The preliminary results of the data analysis and the main features of the theoretical model used for their interpretation are presented.

Competition between Coulomb and symmetry potential in semi-peripheral heavy ion collisions

The anisotropy of angular distributions of emitted nucleons and light charged particles for the asymmetric reaction system, $^{40}$Ar+$^{197}$Au, at b=6fm and $E_{beam}$=35, 50 and 100MeV/u, are investigated by using the Improved Quantum Molecular Dynamics model. The competition between the symmetry potential and Coulomb potential shows large impacts on the nucleons and light charged particles emission in projectile and target region. As a result of this competition, the angular distribution anisotropy of coalescence invariant Y(n)/Y(p) ratio at forward regions shows sensitivity to the stiffness of symmetry energy as well as the value of Y(n)/Y(p). This observable can be further checked against experimental data to understand the reaction mechanism and to extract information about the symmetry energy at subsaturation densities.

Role of neck-length parameter in dynamical cluster-decay model for the decay of

The reformulated dynamical cluster-decay model (DCM) is applied to study the role of the neck-length parameter for the decay of even-A and α-structured formed in the reaction at . Experimentally, light particles (LPs, ) emission cross-section and individual fragments (from A = 12 to 28) emission cross-section are measured for this reaction at . In the present work, we have reproduced the measured data of LPs emission cross-section and mass spectra of A = 12–28 fragments by varying the neck-length parameter and the factor , which is present in the hydrodynamical mass calculation. From the fitted values, polynomial relations are obtained for 4n-structured (even and α-fragments, A = 12, 16, 20, 24 and 28), 4n+1-structured odd mass fragments (A = 13, 17, 21, and 25), 4n+2-structured (even and non-α fragments, A = 14, 18, 22, and 26) and 4n+3-structured odd mass fragments (A = 15, 19, 23 and 27). Experimentally, there is no data for fragments A = 5–11 emission cross-section. In order to account for the cross-section information about these fragments, we have extrapolated the values for these fragments with the use of fitted polynomial relations. To fit the calculated LPs emission cross section with the measured data, we kept values of fragments A = 5–28 and tuned the value of LPs alone. The fitted value of LPs is as 1.3146 fm. With the use of fitted values of fragments A = 1–4 and A = 12–28 and extrapolated values of fragments A = 5–11, our calculated overall cross-section values of the LPs emission and individual fragments (A = 12–28) emission cross-section are found to be in better agreement with the experimental data.

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.

Progress in Developing Nuclear Reaction Calculation Code CCONE for High Energy Nuclear Data Evaluation

To adapt the CCONE code to the high energy nuclear data evaluation, the preequilibrium exciton model part of the code has been extended to multiple particle emission. This is realized by sequential calculation of the decay of exciton states for all residual nuclei left by particle emissions. In addition, Iwamoto-Harada cluster coalescence model has been incorporated in the multiple-emission exciton model to improve the accuracy of calculated cluster emission spectra for deuteron, triton, 3He and α particles. The calculated light particle emission spectra are compared with experimental and evaluated data.

Coulomb corrections to the extraction of the density and temperature in non-relativistic heavy ion collisions

We address the role of Coulomb interaction in the determination of densities and temperatures of hot sources produced in heavy ion collisions. Such quantities can be obtained from the quadrupole momentum and multiplicity fluctuations of the emitted light particles. In this paper we modify the method by taking explicitly into account Coulomb corrections. The classical and quantum limits for fermions are discussed. In the classical case we find that the temperatures determined from 3H and 3He, after the Coulomb correction, are very similar to those obtained from neutrons within the constrained molecular dynamics approach. In the quantum case, the proton temperature becomes very similar to neutron’s, while densities are not sensitive to the Coulomb corrections.

Comparison between cross sections, saddle point and scission point barriers for the32S+24Mg reaction

One of the principal characteristics of nuclear multifragmentation is the emis- sion of complex fragments of intermediate mass. The statistical multifragmentation model has been used for many years to describe the distribution of these fragments. An extension of the statistical multifragmentation model to include partial widths and life- times for emission, interprets the fragmentation process as the near simultaneous limit of a series of sequential binary decays. In this extension, the expression describing inter- mediate mass fragment emission is almost identical to that of light particle emission. At lower temperatures, similar expressions have been shown to furnish a good description of very light intermediate mass fragment emission. However, this is usually not considered a good approximation to the emission of heavier fragments. These emissions seem to be determined by the characteristics of the system at the saddle-point and its subsequent dynamical evolution rather than by the scission point. Here, we compare the barriers and decay widths of these different formulations of intermediate fragment emission and analyze the extent to which they remain distinguishable at high excitation energy.

Control of solid tobacco emissions in industrial fact ories applying CDF tools

The emission of light solid aromatic particles from any tobacco industry affects the surrounding inhabitants, commonly causing allergies and eye irritation and, of course, uncomfortable odours, therefore, these emissions to the air must be regulated. An increasing in production must be considered in the sizing of mechanisms used to achieve the precipitation and final filtration, before discharging to the atmosphere. A numerical tool was applied to study the internal behaviour of low velocity precipitation tunnel and discharge chimney of the refuses treatment system. The characterization of the two-phase flow streamlines allows determining the velocity gradient profiles across the whole tunnel; which is intimately related with the particle concentration, and deposition zones locations. The application of CFD techniques gives the bases to find new design parameters to improve the precipitation tunnel behaviour capability to manage the increment of the mass flow of particles, due to changes in mass cigarette production.

Controllable synthesis of ZnO nanoparticles with high intensity visible photoemission and investigation of its mechanism

ZnO is known as a good photoluminescent semiconductor due to its ability to emit visible light. However, the visible emission mechanism is still under debate. In this work, we have successfully synthesized nanoparticles using LiOH, KOH and NaOH as bases and have achieved visible emission of various colours, such as blue, cyan, green and orange. We demonstrate that LiOH is the most efficient base to control the properties of ZnO nanoparticle emission by varying LiOH concentration. Moreover, detailed studies by TEM, UV and XRD show that ZnO particle size plays an important role in the colour of the emitted light and smaller particles tend to emit shorter wavelength photons. The visible emission is suggested to arise from an electron transition from the conduction band to a deep-trapped defect state. Our experimental results suggest the presence of oxygen vacancies on the ZnO nanoparticle surface.