Multiplicity Of Intermediate Mass Fragments Research Articles

Statistical approach of nuclear multifragmentation with a realistic nuclear equation of state

In this work, Canonical Thermodynamical model for nuclear multifragmentation has been updated with realistic nuclear equation of state. Mass distribution, intermediate mass fragment multiplicity as well as isospin sensitive observables have been investigated with semi-microscopic approach of determining nuclear binding and excitation energies. Production of neutron rich isotopes as well as isoscaling and isobaric yield ratio parameters have been significantly modified due to inclusion of this realistic nuclear equation of state.

Hard-photon production and its correlation with intermediate-mass fragments in a framework of a quantum molecular dynamics model

Hard photon provides a unique probe for nuclear reaction dynamics. In this work, we embedded incoherent neutron-proton bremsstrahlung photon production channel in a framework of isospin-dependent quantum molecular dynamics (IQMD) model and performed a systematic study of multiplicities of hard photons and intermediate-mass fragments (IMFs). It is found that the IQMD model with the in-medium nucleon-nucleon cross section can reproduce previous experimental data of hard-photon energy spectra better. By investigating the incident energy and centrality dependencies of multiplicities of hard photons and IMFs of $^{40}\mathrm{Ca}+^{40}\mathrm{Ca}$ collisions, it is found that the multiplicity correlation between thermal photons and IMFs can provide valuable information on nuclear liquid-gas phase transition. Additionally, temperatures from the thermal emitting sources are also investigated. The results indicate that hard photons provide some unique information of the thermodynamical state of multifragmentating nuclear system.

Emission characteristics of intermediate mass fragments by the $${^{84}_{36}{\hbox {Kr}}}$$ projectile in nuclear emulsion detector at 1 GeV per nucleon

This article is focused on the intermediate mass fragments emission induced by the Kr projectile at relativistic energy in nuclear emulsion. The study of correlation between intermediate mass fragments and the total charge confined in fragments for $$Z\ge $$ 2 with different targets (such as H, CNO and AgBr) shows that there is increase in mean multiplicity of intermediate mass fragments with increase in target mass. The observed anti-correlation between the mean multiplicities of particles emitted from the target and the bound system charge $$(Z_{\mathrm{b}})$$ reflects the relation of the $$Z_{\mathrm{b}}$$ to the centrality of the collision.

Finite-size scaling phenomenon of nuclear liquid-gas phase transition probes

Based on the isospin-dependent quantum molecular dynamics model, finite-size scaling effects on nuclear liquid--gas phase transition probes are investigated by studying the de-excitation processes of six thermal sources of different sizes with the same initial density and similar $N/Z$. Using several probes including the total multiplicity derivative ($dM_{tot}/dT$), second moment parameter ($M_2$), intermediate mass fragment (IMF) multiplicity ($N_{IMF}$), Fisher's power-law exponent ($\tau$), and Ma's nuclear Zipf's law exponent ($\xi$), the relationship between the phase transition temperature and the source size has been established. It is observed that the phase transition temperatures obtained from the IMF multiplicity, Fisher's exponent, and Ma's nuclear Zipf's law exponent have a strong correlation with the source size. Moreover, by employing the finite-size scaling law, the critical temperature $T_c$ and the critical exponent $\nu$ have been obtained for infinite nuclear matter.

Isospin effects on the energy of peak mass production

Using the isospin-dependent quantum molecular dynamics model, we study the isospin effects on the peak center-of-mass energy (${E}_{\mathrm{c}.\mathrm{m}.}^{\mathrm{max}}$) and peak multiplicity of intermediate mass fragments (${\ensuremath{\langle}{N}_{\text{IMF}}\ensuremath{\rangle}}^{\mathrm{max}}$). We compare our theoretical calculations (for stable systems) with experimental data and find a good agreement. We further extend this study to neutron-rich colliding pairs. We find that ${E}_{\mathrm{c}.\mathrm{m}.}^{\mathrm{max}}$ is insensitive to neutron content for the isotopic colliding pairs due to the intermixing of mass and isospin effects, while for the isobaric pairs, ${E}_{\mathrm{c}.\mathrm{m}.}^{\mathrm{max}}$ decreases with increase in the $N/Z$ ratio of the system. We also demonstrate clearly the dominance of symmetry energy over Coulomb repulsion. We also find that ${\ensuremath{\langle}{N}_{\text{IMF}}\ensuremath{\rangle}}^{\mathrm{max}}$ increases with the system mass but is insensitive to the isospin degree of freedom.

Investigation of compressibilities using neutron-rich projectileʼs fragmentation at intermediate energy

The present study deals with the determinations of symmetry energy and compressibilities of nuclear matter ( κ 0 , κ asy ) at intermediate energies. The observables, available from GSI, namely the multiplicity of neutrons ( M n ) and the multiplicity of intermediate mass fragments ( M IMFs ), are compared with theoretical results of an isospin quantum molecular dynamics (IQMD) model. The soft symmetry energy with soft equation of state reproduces the data of symmetry energy sensitive observable M n , while hard equation of state is true in the presence of symmetry energy independent observable M IMFs . The correlation between the multiplicity of free neutrons from the projectile spectator fragmentation (PSF) and the reduced multiplicity of bound neutrons within the IMFs (bound neutron number scaled by the multiplicities of intermediate mass fragments) from the projectile fragmentation (PF) is established.

Mass independence and asymmetry of the reaction: Multi-fragmentation as an example

We present our recent calculations on fragmentation by varying the mass asymmetry of the colliding nuclei using the reactions of 26Fe56 +44 Ru96 (η = 0.2), 24Cr50 + 44 Ru102 (η = 0.3), 20Ca40 +50 Sn112 (η = 0.4), 16S32 +50 Sn120 (η = 0.5), 14Si28 +54 Xe124 (η = 0.6), 8O16 +54 Xe136 (η = 0.7) at a fixed center of mass energy Ec.m. = 250 MeV/nucleon. For the present study, total mass of the system is kept constant (ATOT = 152). The measured distributions are given as a function of the total charge of all projectile fragments, Zbound. The well known trend of rise and fall in the multiplicity of intermediate mass fragments for symmetric colliding nuclei is reproduced nicely. Such trends are, however missing for larger asymmetric reactions.

Model ingredients and peak mass production in heavy-ion collisions

We simulate the central reactions of $^{20}$Ne+$^{20}$Ne, $^{40}$Ar+$^{45}$Sc, $^{58}$Ni+$^{58}$Ni, $^{86}$Kr+$^{93}$Nb, $^{129}$Xe+$^{118}$Sn, $^{86}$Kr+$^{197}$Au, and $^{197}$Au+$^{197}$Au at different incident energies for different equations of state, different binary cross sections and different widths of Gaussians. A rise-and-fall behavior of the multiplicity of intermediate mass fragments (IMFs) is observed. The system size dependence of peak center-of-mass energy E$_{c.m.} ^{max}$ and peak IMF multiplicity $<$N$_{IMF}>^{max}$ is also studied, where it is observed that E$_{c.m.}^{max}$ follows a linear behavior and $<$N$_{IMF}>^{max}$ shows a power-law dependence. A comparison between two clusterization methods, the minimum spanning tree and the minimum spanning tree method with binding energy check (MSTB), is also made. We find that the MSTB method reduces the $<$N$_{IMF}>^{max}$, especially in heavy systems. The power-law dependence is also observed for fragments of different sizes at E$_{c.m.} ^{max}$ and the power-law parameter $\tau$ is found to be close to unity in all cases except A$^{max}$.

Variation of mean multiplicity of intermediate mass fragments with the bound charge of the fragmenting system-deviation from the universal behaviour

In this work an attempt has been made to study the variation of normalized mean multiplicity with the normalized Zb for 0.95A GeV 84Kr — Em and 84Kr — AgBr interactions Though the data points of the present investigation exhibit the same pattern of the universal curve of ALADIN group, the maximum value of < NIMF > of the present investigation is found to be about 17 times larger than that of the universal curve.

Variation of mean multiplicity of intermediate mass fragments with the bound charge of the fragmenting system-deviation from the universal behaviour

In this work an attempt has been made to study the variation of normalized mean multiplicity with the normalized Zb for 0.95A GeV 84Kr — Em and 84Kr — AgBr interactions Though the data points of the present investigation exhibit the same pattern of the universal curve of ALADIN group, the maximum value of < NIMF > of the present investigation is found to be about 17 times larger than that of the universal curve.

Production of ternary events in [formula omitted], Bi and Au reactions at 8.8 GeV

Events with three fragments with Z ⩾ 8 in the interactions of 8.8 GeV 4He with U, Bi and Au nuclei are examined using the Makrofol polycarbonate track detector. The sandwich technique is used to enable a direct observation of the multiply charged fragment emission by a single nucleus. Fragments produced in these events are identified and an event-by-event model-free analysis is performed in order to separate different production mechanisms. A classification scheme based on the multiplicity of intermediate-mass fragments 8 ⩽ Z ⩽ 20 is used in order to identify events belonging to the different reaction channels. In the interactions of 4He with U, about 70% of ternary events are registered with the multiplicity of intermediate-mass fragments M IMF obs = 0 , 1 , while in the interactions of 4He with Au, about 60% of ternary events are registered with M IMF obs = 2 , 3 . The analysis shows that these two groups of ternary events are produced by different reaction mechanisms. The cross-sections and experimental features are determined for the various reaction mechanisms, and their variation with the target mass has been investigated.

Influence of a momentum dependent interaction on the isospin dependence of fragmentation and dissipation in intermediate energy heavy ion collisions

We studied the influence of a momentum dependent interaction in the context of isopspin effects on fragmentation and dissipation in intermediate energy heavy ion collisions by using an isospin dependent quantum molecular dynamics model. It is shown that the nuclear stopping, the number of nucleons emitted ,and the multiplicity of intermediate mass fragments are larger with a momentum dependent interaction than without. In particular, the differences for these observables, when using an isospin dependent in-medium nucleon nucleon cross section versus an isospin independent one, are also larger at high energies for a momentum dependent interaction than without one. Therefore,momentum dependence enhances the sensitivities of those observables to the isospin effect of the in-medium nucleon nucleon cross section towards high beam energies

Cluster emission and phase transition behaviours in nuclear disassembly

The features of the emissions of light particles (LP), charged particles (CP), intermediate mass fragments (IMF) and the largest fragment (MAX) are investigated for 129Xe as functions of temperature and ‘freeze-out’ density in the frameworks of the isospin-dependent lattice gas model and the classical molecular dynamics model. Definite turning points for the slopes of average multiplicity of LP, CP and IMF, and of the mean mass of the largest fragment Amax are shown around a liquid–gas phase transition temperature and while the largest variances of the distributions of LP, CP, IMF and MAX appear there. It indicates that the cluster emission rate can be taken as a probe of nuclear liquid–gas phase transition. Furthermore, the largest fluctuation is simultaneously accompanied at the point of the phase transition as can be noted by investigating both the variances of their cluster multiplicity or mass distributions and the Campi scatter plots within the lattice gas model and the molecular dynamics model, which is consistent with the result of the traditional thermodynamical theory when a phase transition occurs.

Multifragmentation of gold nuclei by light relativistic ions: Thermal breakup versus dynamical disintegration

The multiple emission of intermediate-mass fragments (IMF) is studied for collisions of p, 4He, and 12C on Au with the 4π FASA setup. The mean multiplicities of IMF saturate at a value of around 2 for incident energies above 6 GeV. An attempt at describing the observed IMF multiplicities in the two-stage scenario, a fast cascade followed by a statistical multifragmentation, fails. Agreement with the measured IMF multiplicities is obtained by introducing an intermediate expansion phase and modifying empirically the excitation energies and masses of remnants. The angular distributions and energy spectra from p-induced collisions are in agreement with the scenario of “thermal” multifragmentation of a hot and expanded target spectator. In the case of 12C + Au(22.4 GeV) and 4He (14.6 GeV) + Au collisions, deviations from a pure thermal breakup are seen in the fragment energy spectra, which are harder than those both from model calculations and from the measured ones for p-induced collisions. This difference is attributed to a collective flow with the expansion velocity at the surface of about 0.1c (for 12C + Au collisions).

Multifragmentation induced by GeV 4He beams

Multifragmentation of natAg and 197Au induced by 7 and 14.4 GeV 4 He has been investigated by using CR-39 plastic track detectors. Since our experimental technique enables the determination of the multiplicity of intermediate mass fragments (IMFs) with uncertainty of only a few percent, the results obtained pointed out the inconsistency in the data regarding the quantity reported by other authors. We have also studied the behavior of characteristics of IMFs dependent on the reaction parameters (incident energy, atomic number of the target). From this analysis, we made some conclusions about the reaction mechanism of multifragmentation.

Isospin effect on the process of multifragmentation and dissipation at intermediate energy heavy ion collisions

In the simulation of intermediate energy heavy ion collisions by using the isospin dependent quantum molecular dynamics, the isospin effect on the process of multifragmentation and dissipation has been studied. It is found that the multiplicity of intermediate mass fragments $N_{imf}$ for the neutron-poor colliding system is always larger than that for the neutron-rich system, while the quadrupole of single particle momentum distribution $Q_{zz}$ for the neutron-poor colliding system is smaller than that of the neutron-rich system for all projectile-target combinations studied at the beam energies from about 50MeV/nucleon to 150MeV/nucleon. Since $Q_{zz}$ depends strongly on isospin dependence of in-medium nucleon-nucleon cross section and weakly on symmetry potential at the above beam energies, it may serve as a good probe to extract the information on the in-medium nucleon-nucleon cross section. The correlation between the multiplicity $N_{imf}$ of intermediate mass fragments and the total numer of charged particles $N_c$ has the behavior similar to $Q_{zz}$, which can be used as a complementary probe to the in-medium nucleon-nucleon cross section.

Thickness Measurements of Thin CsI(Tl) Scintillators

A γ-activation method for measuring the thickness of thin CsI(Tl) polycrystalline films deposited by evaporation on large-area (∼150 cm2) backings is described. Scintillators specially prepared to be used in the FASA installation as detectors of intermediate-mass fragment multiplicity were measured. It was shown that the distribution of the film thickness along the scintillator surface can be determined by β-activity scanning. It has been shown that the film thickness decreases from the middle of the backing to its periphery by ≈25% for scintillators with a linear size of 140 mm.

Microcanonical studies concerning the recent experimental evaluations of the nuclear caloric curve

The microcanonical multifragmentation model from [Al. H. Raduta and Ad. R. Raduta, Phys. Rev. C 55, 1344 (1997); 56, 2059 (1997); 59, 323 (1999)] is refined and improved by taking into account the experimental discrete levels for fragments with $A \le 6$ and by including the stage of sequential decay of the primary excited fragments. The caloric curve is reevaluated and the heat capacity at constant volume curve is represented as a function of excitation energy and temperature. The sequence of equilibrated sources formed in the reactions studied by the ALADIN group ($^{197}$Au+$^{197}$Au at 600, 800 and 1000 MeV/nucleon bombarding energy) is deduced by fitting simultaneously the model predicted mean multiplicity of intermediate mass fragments ($M_{IMF}$) and charge asymmetry of the two largest fragments ($a_{12}$) versus bound charge ($Z_{bound}$) on the corresponding experimental data. Calculated HeLi isotopic temperature curves as a function of the bound charge are compared with the experimentally deduced ones.

Statistical interpretation of the correlation between intermediate mass fragment multiplicity and transverse energy

Multifragment emission following Xe+Au collisions at 30, 40, 50 and 60 AMeV has been studied with multidetector systems covering nearly 4-pi in solid angle. The correlations of both the intermediate mass fragment and light charged particle multiplicities with the transverse energy are explored. A comparison is made with results from a similar system, Xe+Bi at 28 AMeV. The experimental trends are compared to statistical model predictions.

Decay of hot nuclei formed with energetic antiprotons (PS208)

Energetic antiproton-nucleus interactions allow to build up thermal excitation energies exceeding 800 MeV in nuclei of masses close to 200. We found that for these high excitation energies the fission process still remains a very significant exit channel. At excitation energies close to 800 MeV the fission process approaches 20–50% of the cross section for Ho, Au and U-like nuclei depending on the fission events selection criteria. The average intermediate mass fragment multiplicity at such high excitation energies is equal to about 1 and alpha particle multiplicity is equal to about 5 for all three reactions independently of the exit channel, including fission. A transition towards the multifragmentation is not observed.