Fragment Mass Distributions Research Articles

Multi-parameter global calculations of fission fragments using a simplified two-dimensional scission-point model * *Supported by National Natural Science Foundation of China (11875301, U1832167)

Exploiting the concept of the dinuclear system, the interaction potential energy of two fragments that are quite close to each other is analyzed. A semi-classical method is used to calculate fission fragment yields using a simplified two-dimensional scission-point model. By considering the tip-to-tip orientation at the scission point of the fission process, we investigate the mass, charge, and kinetic-energy distributions of the fission fragments, for excitation energies in the 0-20 MeV range. Our results show that the fission fragment distributions are reproduced quite well, including the recent experimental results for the isotone chain [D Ramos et al. Phys. Rev. C 97, 054612 (2018)]. Thus, the simplified model is useful for multi-parameter global measurements of fission products.

Scaling laws in fragmentation dynamics of rock materials

Dynamic and quasi-static tests for uniaxial compression of cylinders made of quartzite were carried out. The failure of the specimens was accompanied by fractoluminescence. The fractoluminescence was recorded by a photomultiplier tube (PMT) and a high-speed camera. The high-speed camera allowed us to visualize fracture process accompanied with fractoluminescence and PMT provided high temporal resolution for statistical analysis of fracture. A statistical analysis of the mass distribution of quartzite fragments and a statistical analysis of the time intervals between pulses on the signals from the PMT are carried out. The cumulative fragments mass distributions for all samples had two slopes, which were described by power functions. The cumulative time distribution between pulses was also described by a power function, which corresponds to brittle fracture of the material.

Experimental study of fragmentation of fused quartz cylinders under quasi-static loading with the fractoluminescence recording

Quasi-static tests for uniaxial compression of fused silica cylinders have been carried out. The destruction process was accompanied by fractoluminescence, which is typical for quartz. Fractoluminescence was recorded by two methods: a high-speed camera, which, in addition to luminescence, recorded the entire process of destruction of the sample, and using a photomultiplier with a high time resolution to analyze the dynamics of the fragmentation process. In most experiments, two stages of destruction were recorded. Each of which was accompanied by intense fractoluminescence. A statistical analysis of the fragments mass (size) distribution and of the intervals between fractoluminescence pulses has been carried out.

The effect of electron beam incidence angle on the dynamic fracture of metal rings and cylinders

This work investigated how the incidence angle of the electron beam affects the dynamic fracture of metallic cylinder shell. Cylinder shell made of steel was blazed with electron beam and cut into ring and cylinder specimens. Flash X-ray radiography was used to register the fracture of the ring specimen. Fragments from the cylinder specimens under internal explosive loading were recovered and analyzed by SEM, and the fragment mass distribution was derived by statistical analysis. When the incident angle α of the electron beam was 0°, the fracture of the metal ring was along the normal direction of the outer surface. When α was 30° and 45°, the fracture of the metal ring was oblique. The distributions of recovered fragments were similar regardless of α. The fracture of the metallic cylinder shell under explosive loading was well controlled at all α. The recovered fragments from the cylinder specimen with α = 30° or 45° had an oblique quadrangular prism shape, whose the length was 30% larger than the fragments from the cylinder specimen with α = 0°. The fracture near the outer side of the cylinder specimen was along the melting region of the electron beam. The fracture mode of the cylinder specimen was tension-shear mixed fracture when α = 0° but shear fracture when α = 30° or 45°.

Total kinetic energy release in the fast-neutron-induced fission of Np237

The total kinetic energy (TKE) release in the fast neutron-induced fission of $^{237}\mathrm{Np}$ was measured for neutron energies from ${E}_{n}=2.6--100\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ at the Los Alamos Neutron Science Center at the Weapons Neutron Research facility. The post-TKE release decreases nonlinearly with increasing incident neutron energy and can be represented as $\mathrm{TKE}\phantom{\rule{0.16em}{0ex}}(\mathrm{MeV})=(174.38\ifmmode\pm\else\textpm\fi{}0.72)--(5.11\ifmmode\pm\else\textpm\fi{}0.5821){\mathrm{log}}_{10}{E}_{n}$ for ${E}_{n}>1\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$. Analysis of the fragment mass distributions indicates that the decrease in TKE with increasing ${E}_{n}$ is a consequence of the fading out of shell effects at high excitation energies (resulting in an increase of symmetric fission) and the decrease of the total kinetic energy associated with asymmetric fission with increasing ${E}_{n}$.

Fission studies using multinucleon transfer reactions

It is shown that the multinucleon transfer reactions is a powerful tool to study fission of exotic neutron-rich actinide nuclei, which cannot be accessed by particle-capture or heavy-ion fusion reactions. Identification of fissioning nuclei and of their excitation energy is performed on an event-by-event basis, through the measurement of outgoing ejectile particle in coincidence with fission fragments. Fission fragment mass distributions (FFMDs) are measured for each transfer channel, in selected bins of excitation energy. It was found that the mass distributions for all the studied nuclides maintain a double-humped shape up to the high energies that the shell effects are expected to smear out. From a comparison with the dynamical calculation based on the fluctuation-dissipation model, this behavior of the mass distributions was unambiguously attributed to the effect of multichance fission.

Role of higher order deformations in fission fragment mass distribution of Astatine isotopes within collective clusterization approach

The fission fragment mass distribution is used as an investigation tool which assists to disentangle between different modes of fission (symmetric fission and asymmetric fission). In the present work, the fission dynamics of various ‘At*’ isotopes with mass number A=191 to 220 formed in 19F-induced reactions at common centre-of-mass energy Ec.m .=78.5 MeV is explored. The calculations are made within the dynamical cluster-decay model (DCM) using three type of fragmentation such as spherical, (β 2-deformed and (β 2 – β 2-deformed with hot compact optimized orientations. The structural effects come into picture when deformation effects are included in the fragmentation potential. The mass distributions of ‘At*’ isotopes gets significantly modified after inclusion of deformation effects of decaying fragments. The preformation yield shows a drift from symmetric to asymmetric fission with increase in mass of compound nuclei from ACN =191 to 220. The clear signature of fine-structure effects is evident in view of single humped to double humped preformation structure in the fissioning region. However, the mass division of At isotopes is symmetric for spherical choice of fragments. Finally, the analysis of hot (compact) and cold (elongated) configurations of β 2-deformed and oriented fragments is also carried out.

Mass-asymmetric fission of Bi205,207,209 at energies close to the fission barrier using proton bombardment of Pb204,206,208

Background: Recent observation of mass-asymmetric fission in neutron-deficient Hg and Pt nuclei has reignited interest in fission fragment mass distributions close to Pb. Investigations at energies close to the fission barrier, where mass-asymmetric fission is expected to be most obvious and the sensitivity to shell effects is maximized, are limited in this mass region.Purpose: To measure fission mass distributions for $^{205,207,209}\mathrm{Bi}$ nuclei at the lowest possible excitation energies to determine how the mass distributions change with excitation energy and the neutron number of the compound nucleus.Method: Proton beams bombarding targets of $^{204,206,208}\mathrm{Pb}$ were used to study the fission of $^{205,207,209}\mathrm{Bi}$ at energies from just above to 10 MeV above their fission barriers. Fission fragments were measured using the CUBE fission spectrometer. Fission fragment mass distributions were determined using a newly developed time difference analysis method. Mass distributions were characterized by triple-Gaussian fits to determine the systematic trends across each isotope with excitation energy.Results: Measured mass distributions of all three Bi isotopes exhibit a component of mass-asymmetric fission at all energies studied. The probability of mass-asymmetric fission decreases significantly with increasing excitation energy, from $\ensuremath{\approx}70$ to $\ensuremath{\approx}40%$ over a 10-MeV range. Comparisons between the three Bi isotopes hint at an increase in the mass-symmetric fission yield with increasing neutron number, which could be due to a decrease in the difference between the symmetric and asymmetric fission barriers. The centroids of the mass-asymmetric peaks suggest that several deformed shell gaps in the fission fragments could be contributing to the presence of the mass-asymmetric fission mode with ${Z}_{\mathrm{light}}\ensuremath{\simeq}38$, ${Z}_{\mathrm{heavy}}\ensuremath{\simeq}45$, and ${N}_{\mathrm{light}}\ensuremath{\simeq}56$ all present in the fission fragments.Conclusions: Measurements of fission mass distributions at the lowest possible excitation energies above the fission barrier provide an excellent platform to investigate the origins of the mass-asymmetric fission mode. Further systematic measurements at these energies offer an opportunity to rigorously test new models of fission in this mass region.

Ternary Fission Mass Distributions of Superheavy Nuclei Within a Statistical Model

Theoretical models predict the existence of an island of stability at the proton shell closures Z = 114 or 120 or 126 and at the neutron shell closure N = 184 due to the microscopic shell effects. In this article, mass distributions of fragments from ternary fission of superheavy nuclei are investigated with the aid of the statistical theory. We have computed the fission mass distributions for the simultaneous decay into three fragments of nuclei 298Fl, $^{304}_{120}$ X and $^{310}_{126} $ X, at the two excitation energies E∗ = 20 and 50 MeV, with the constraint on one of the fragment to be 50Ca and 72Ni. With the fixed third fragments of mass number A3 = 50, 72, asymmetric breakup (A1 ≠ A2) has a larger ternary fission yield for Z = 114, 120 and 126 isotopes. Predominantly, one of the fragments with the neutron closed-shell nucleus (N ≈ 82, 50) is favoured at higher excitation energies. Subsequently, we have considered the ternary fragmentation of the neutron-rich superheavy elements $^{314}_{120}$ X and $^{320}_{126} $ X again for the same excitation energies and fixed third fragment. Interestingly, for the superheavy nucleus $^{314}_{120}$ X, symmetric fission (A1 ≈ A2) with doubly closed-shell nuclei 132Sn for the third fragment 50Ca is favoured at higher E∗. For the isotope $^{320}_{126} $ X, relative yields of fragments with closed shell increase at higher excitation energy.

Measurement of fragment-mass distributions from fission of At214 following the Be9+Tl205 reaction

Background: The recent surprising experimental discovery of asymmetric fission in the nucleus $^{180}\mathrm{Hg}$ at low excitation energy has renewed interest concerning our understanding of the role of nuclear shell effects in the dynamics of the fission process. New theoretical models have been developed that claim to successfully explain the observed asymmetric fission of $^{180}\mathrm{Hg}$ and also predict the nature of mass distributions of several other preactinide nuclei for which experimental data are scarce.Purpose: We investigated fragment-mass distributions in the fission of the preactinide nucleus $^{214}\mathrm{At}$ at different excitation energies near the Coulomb barrier. The present results were compared with the predictions from a recent state-of-the-art theoretical calculation, as well as with our previous measurement for the nearby nucleus $^{210}\mathrm{Po}$.Methods: A pulsed heavy-ion beam was used in the experiment. Fission fragments were detected with two large-area position-sensitive multiwire proportional counters placed at the folding angle. Mass distributions were extracted from time-of-flight differences and position information ($\ensuremath{\theta},\ensuremath{\phi}$) for the fission fragments.Results: An asymmetry in fragment-mass distribution in the fission of $^{214}\mathrm{At}$ was observed at an excitation energy of $\ensuremath{\approx}31$ MeV, where a shell effect is found to influence the potential energy surface. At higher excitation energies, mass distributions are predominantly symmetric indicating the absence of shell effects.Conclusion: This finding is consistent with the prediction of a recent macroscopic-microscopic dynamical model. However, for the preactinides, static models with nascent fragment shell structure are likely to produce similar results.

Effect of nuclear structure and fissility on quasifission

In order to investigate the interplay between nuclear structure (shell closure) and dynamics, fission fragment mass distributions have been measured for reactions $^{35,37}\mathrm{Cl}+^{206,208}\mathrm{Pb}$. These reactions have similar entrance channel parameters except for the number of closed shell configuration in the entrance channel. Fission fragment mass distributions have been measured for these reactions in the energy region close to the Coulomb barrier. No mass-angle correlation was observed in any of the four reactions, indicating the absence of fast quasifission (QF), but mass distributions were wider than that of compound nucleus (CN) fission, which indicates the presence of slow QF. With comparable fissility and deformation values, extra stability against QF was observed for reactions which have more closed shell configurations in the entrance channel. Mass-angle distributions of these reactions do not follow the systematics with respect to mean fissility. A new systematics has been obtained by considering quadrupole deformation of the heavy reaction partner along with the fissility, which explains the absence of mass-angle correlation in the presently measured reactions.

Heavy-ion-induced fission of $$^{181}$$Ta and $$^{209}$$Bi at intermediate energies by CRISP model

In this work, we study the mechanism of the nuclear reaction of $$^{11}$$ B ion with $$^{181}$$ Ta and $$^{209}$$ Bi targets at intermediate energies and analyze the nuclear reaction processes starting from the initial nucleus–nucleus collision up to the fragments production. The experimental data are derived from the literature Karapetyan et al. (Phys Rev C 94: 024618, 2016). A new branch of CRISP model has been extended in the framework of the rotating liquid drop model to describe heavy-ion-induced reactions. Experimental mass-yield distribution is compared with the results of the Monte Carlo simulation code CRISP using the theoretical model calculations. The experimental data of spallation products are also described by the CRISP model. The fission cross sections, fissility and fragment mass distributions are calculated and compared with experimental data. We conclude that CRISP model provides a good description for the cases analyzed in this study and gives us confidence that it might be applied to other cases as well.

Dynamic disintegration processes accompanying transport of an earthquake-induced landslide

Aiming to understand the dynamic disintegration and transport behavior of an earthquake-induced landslide, a dynamic discrete element method has been employed to analyze the Wangjiayan landslide triggered by the 2008 Ms 8.0 Wenchuan earthquake. Absorbing boundary condition is used for the seismic wave transmission and reflection at the slope base. The numerical results show that under seismic loading, internal rock damage initiates, propagates, and coalesces progressively along the weak solid structure and subsequently leads to fragmentation and pulverization of the slope mass. This can be quantitatively interpreted with the continuously rapid increase of the damage ratio and sudden decline of growth ratio of the number of fragments after the peak seismic shaking. During emplacement evolution, fragmented deformation patterns within the translating joint-defined granular assemblies are affected by the locally high dilatancy with a simultaneous occurrence of highly energetic collisions related to the action of shearing, and this can be quantified by the enhancement of particle kinematic activities (high vibrational and rotational granular temperatures) and intense fluctuations of location-dependent global dispersive stress. In this process, slope destabilized and transports downward in a rapid pulsing motion as friction bonds are locally and continually overcome by the seismic- and gravity-induced shear forces. The joint-determined fragment network before movement initiation and the final fragmented depositions after the rapidly sheared transport have been systematically investigated by fragment statistics (fragment size distribution, fragment mass distribution, and fractal dimension) and morphometric characters (fragment shape isotropy) to offer new insights into the disintegration characteristics of the earthquake-induced catastrophic mass movements.

Zeptosecond contact times for element Z=120 synthesis

The synthesis of new superheavy elements beyond oganesson (Z=118) requires fusion reactions with projectile nuclei with proton numbers larger than that of 48Ca (Z=20), which has been successfully employed for the synthesis of elements with Z=112-118. In such reactions, fusion is drastically hindered by fast non-equilibrated dynamical processes. Attempts to produce nuclei with Z=120 using the 64Ni+238U, 58Fe+244Pu, 54Cr+248Cm, and 50Ti+249Cf reactions have been made, which all result in larger Coulomb forces than for 48Ca-induced reactions, but no discovery has been confirmed to date. In this work, mass and angle distributions of fission fragments from these reactions have been measured with large angular coverage to aid in selection of the most promising projectile-target combination that would favor fusion. The results yield information on reaction contact times, with the longest exhibited by 50Ti+249Cf.

A novel method for determination of lethal radius for high-explosive artillery projectiles

A new model has been defined that enables the estimation of the lethal radius (radius of efficiency) of HE (High Explosive) artillery projectiles against human targets. The model is made of several modules: CAD (Computer Aided Design) modeling, fragment mass distribution estimation, fragment initial velocity prediction, fragment trajectory calculation, effective fragment density estimation, and high explosive projectile lethal radius estimation. The results were compared with the experimental results obtained based on tests in the arena used in our country, and the agreement of the results was good. This model can be used in any terminal-ballistics scenario for high explosive projectiles since it is general, parametric, fast and relatively easy to implement.

Hypervelocity Impact Cratering on Semi-Infinite Concrete Targets of Projectiles with Different Length to Diameter Ratios

Impact cratering experiments were performed on semi-infinite concrete targets with 7 mm-diameter 40CrNiMo steel long-rod projectiles at impact velocities ranging from 2117 m/s to 3086 m/s by using a two-stage combustion light-gas gun. After the impact experiments, the crater diameter and depth as well as the crater volume were carefully measured. The concrete fragments were collected from the target chamber and the fragment mass was measured. The size of the crater (including the volume, diameter, and depth) and the fragment mass increased with increasing impact velocities, while the fragment distributions at different impact velocities were almost the same. Scaling laws for the crater volume impacted by the rod-shaped projectile were discussed and an empirical formula of crater volume was determined by the experimental data from the literature. Through the verification of the present experimental results, the predictive ability of the empirical formula proved to be reliable. Scaling laws for the size distribution of concrete fragments were also discussed. The normalized fragment mass distribution was proportional to the impact velocity raised to the power 1.5.

Examination of coexistence of symmetric mass and asymmetric charge distributions of fission fragments

Examination of coexistence of symmetric mass and asymmetric charge distributions of fission fragments

Experimental studies on fragments of reinforced concrete slabs under close-in explosions

Most of the injuries resulting from an explosion are not caused by the shock waves, but rather by the high-speed flying sharp fragments due to concrete spalling and crushing. The commonly used reinforced concrete (RC) components in building and infrastructure construction suffer this typical damage when subjected to close-in blast loads. The numerous ejecting concrete fragments generated from the crushing and spalling damage would threaten the occupants and equipment inside the building structures. Therefore, it is of great significance to study the local damage and fragments of RC members under close-in explosions. In this paper, five RC slabs in size of 1 × 2 × 0.12 m were tested under blast loads generated by 2kg, 4kg and 6kg TNT charges detonated with 0.4 m standoff distance. Significant local damage such as spalling and crushing of the RC slabs were observed, and a lot of ejecting fragments with different sizes and splattering distances were collected. The fragment mass, fragment size and splash distributions were analyzed in detail with respect to the mass of the TNT charge. It is found that higher charge weight will lead to more fragments and also propel them to a farther distance. The proportion of small fragments increases as the charge weight increases. High-speed camera was used to monitor the projection of fragments and found that the maximum ejecting velocity of fragments from RC slab under close-in blast loads is up to 100 m/s when the mass of TNT charge is 6 kg. The concrete fragment with such high ejecting velocity could be very dangerous to the occupants and equipment.

Formation and Decay of the Composite System Z = 120 in Reactions with Heavy Ions at Energies Near the Coulomb Barrier

The mass, energy and angular distributions of binary fragments formed in the reactions 64Ni + 238U, 58Fe + 244Pu, 52Cr + 248Cm, 54Cr + 248Cm at energies near the Coulomb barrier have been measured. The analysis of energy distributions of the symmetric fragments with mass numbers $${{{{A}_{{{\text{CN}}}}}} \mathord{\left/ {\vphantom {{{{A}_{{{\text{CN}}}}}} 2}} \right. \kern-0em} 2} \pm 20$$ formed in these reactions have been applied to separate compound nucleus fission and quasi-fission. The estimated fusion probability for the reactions Cr, Fe, and Ni ions with actinide targets shows an exponential dependence on the mean fissility parameter of the system and shows also that reaction with Cr ions is more favorable for production of the super heavy element with Z = 120.

Fission of Relativistic Nuclei with Fragment Excitation and Reorientation.

Experimental studies of fission induced in relativistic nuclear collisions show a systematic enhancement of the excitation energy of the primary fragments by a factor of ∼2, before their decay by fission and other secondary fragments. Although it is widely accepted that by doubling the energies of the single-particle states may yield a better agreement with fission data, it does not prove fully successful, since it is not able to explain yields for light and intermediate mass fragments. State-of-the-art calculations are successful to describe the overall shape of the mass distribution of fragments, but fail within a factor of 2-10 for a large number of individual yields. Here, we present a novel approach that provides an account of the additional excitation of primary fragments due to final state interaction with the target. Our method is applied to the ^{238}U+^{208}Pb reaction at 1 GeV/nucleon (and is applicable to other energies), an archetype case of fission studies with relativistic heavy ions, where we find that the large probability of energy absorption through final state excitation of giant resonances in the fragments can substantially modify the isotopic distribution of final fragments in a better agreement with data. Finally, we demonstrate that large angular momentum transfers to the projectile and to the primary fragments via the same mechanism imply the need of more elaborate theoretical methods than the presently existing ones.