Projectile-target Combinations Research Articles

Predictions for the synthesis of the Z=119 superheavy element

The optimal projectile-target combination and bombarding energy for the production of the new superheavy element (SHE) $Z=119$ are predicted within the framework of a dinuclear system (DNS) model, in which the evaporation residue cross section (ERCS) is the product of capture cross section, fusion probability, and survival probability. To this end, the effects of mass asymmetry and isospin effect of target nucleus on the ERCS are analyzed. It is found that the ERCS for the production of SHE $Z=119$ is relatively large with the $^{45}\mathrm{Sc}$ projectile, while the ERCS in most cases decreases slowly with increasing neutron number of the target nucleus. We hope these predictions will shed new light timely for the recent experiments on the synthesis of the $Z=119$ superheavy element.

Production of neutron deficient rare earth radionuclides by heavy ion activation

Abstract The attempts to produce neutron deficient radioisotopes of rare Earth elements by heavy ion activation are discussed in this review. The heavy ion induced reaction products have large atomic number difference with that of the target; therefore, radiochemical separation of no-carrier-added radio-lanthanides from the target matrix becomes easier. Heavy ion induced reactions also allow the production of rare Earth radionuclides from non-rare Earth target by tailor-made target-projectile combinations, and in those cases, radiochemical separations become even more easier. In general, the cross sections of heavy ion induced reactions are less than those of light charged particle induced reactions. However, some of the heavy ion induced reactions have comparable cross sections with those of light ion induced reactions. The range of heavy ions is also much smaller in the target matrix than that of lighter charged particles. These points hinder application of heavy ion induced reactions to produce radionuclides for nuclear medicine.

Fusion Dynamics of 16O + 72,76Ge →88,92Zr Reactions using Skyrme Energy Density Formalism

In the fusion of 16O+72,76Ge→ 88,92Zr reactions the significance of structural and bulk properties of projectile-target combination is investigated at energies across the Coulomb barrier. For the purpose, the role of distinct Skyrme interactions (SIII, SKM*, SGII, RATP, T6, SkP), in conjunction with different surface diffuseness parameter (a=0.45-0.99) and nuclear charge radii i.e. iso-spin dependent and iso-spin independent are examined for the studied reaction. These geometrical parameters have their straight effect on the interaction barrier and the fusion excitation function. Thus, the sensitivity of fusion barrier and the cross sections in the sub barrier region of 88,92Zr Compound systems is carefully explored. The estimations of fusion cross sections are done in the framework of Wong formula and are compared with the respective experimental data. The observations implies that SKM* Skyrme interaction in which nuclear radius derived from polynomial fit gives relatively better result than the considered iso-spin dependent and independent nuclear charge radii. Further, the behaviour in the cross sections of Zr isotopes is investigated in terms of surface diffuseness parameter, which depicts that surface width is higher for neutron rich nucleus and lower for the neutron deficient one.

Production of new neutron-rich isotopes with 92≤Z≤100 in multinucleon transfer reactions

To explore the optimum conditions for producing new neutron-rich isotopes in the range $92\ensuremath{\le}Z\ensuremath{\le}100$ by multinucleon transfer reactions, $^{86}\mathrm{Kr}+^{248}\mathrm{Cm}, ^{129}\mathrm{Xe}+^{248}\mathrm{Cm}, ^{132}\mathrm{Xe}+^{248}\mathrm{Cm}, ^{136}\mathrm{Xe}+^{248}\mathrm{Cm}$ and $^{238}\mathrm{U}+^{248}\mathrm{Cm}$ systems with bombarding energies around their respective Coulomb barriers are investigated within an improved dinuclear system (DNS) model, combined with the statistical gemini$++$ model. The calculated production cross sections are in a good agreement with experimental data. It is found that, compared with projectiles $^{86}\mathrm{Kr}$ and $^{136}\mathrm{Xe}$, the projectile $^{238}\mathrm{U}$ can produce larger cross sections of neutron-rich nuclei of interest by bombarding the actinide target $^{248}\mathrm{Cm}$. Actinide projectile-target combination seems to be encouraging for the production of neutron-rich isotopes with $92\ensuremath{\le}Z\ensuremath{\le}100$.

Production of evaporation residues in the O16+Pb208 and Ca48+Yb176 reactions

Cross section data for evaporation residues (ERs) produced in the $^{16}\mathrm{O}+^{208}\mathrm{Pb}$ and $^{48}\mathrm{Ca}+^{176}\mathrm{Yb}$ heavy-ion fusion-evaporation reactions leading to the same $^{224}\mathrm{Th}^{*}$ compound nucleus (CN) were obtained at energies around the fusion reaction barriers with the recoil separator vassilissa. These data for ERs formed in the most probable evaporation channels in both reactions agree with those obtained earlier. ER and fission cross sections for $^{16}\mathrm{O}+^{208}\mathrm{Pb}$ are well reproduced with model calculations using adjustment of respective model parameters. The mutual comparison of the ER cross sections for the very asymmetric ($^{16}\mathrm{O}+^{208}\mathrm{Pb}$) and more symmetric ($^{48}\mathrm{Ca}+^{176}\mathrm{Yb}$) projectile-target combinations allowed us to obtain the fusion probability value (CN formation probability) imposed by the quasifission effect inherent in the $^{48}\mathrm{Ca}+^{176}\mathrm{Yb}$ reaction.

Theoretical study of evaporation residue cross sections in the decay of Cn*286 formed via the U238+Ca48 reaction using Skyrme forces

The dynamical cluster-decay model (DCM) is employed to study the excitation functions and fusion evaporation residue (ER) cross sections for the production of $^{283}\mathrm{Cn}$ and $^{282}\mathrm{Cn}$ isotopes via $3n$ and $4n$ decay channels from the $^{286}\mathrm{Cn}^{*}$ compound nucleus. The study includes quadrupole deformation ${\ensuremath{\beta}}_{2i}$ and hot-optimum orientations ${\ensuremath{\theta}}_{i}$ at various $^{48}\mathrm{Ca}$-beam energies ${E}_{\mathrm{lab}}=233.3\text{--}240\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ (equivalently, excitation energies ${E}^{*}=34.4\text{--}39.8\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$), supporting symmetric fission, which agrees well with the experimental data. The reaction was investigated by using a hot compact configuration. The Skyrme forces used are new forces GSkI and KDE0(v1), and the conventional force SIII. Apparently, the DCM with the pocket formula for nuclear proximity potential reproduces the measured data on fusion ER nicely within single-parameter fitting of $\mathrm{\ensuremath{\Delta}}R$, independently of the nuclear interaction potential and Skyrme force used. We have also calculated the fusion-fission cross section (${\ensuremath{\sigma}}_{ff}^{\mathrm{predicted}}$) at ${E}^{*}=35\phantom{\rule{4pt}{0ex}}\mathrm{MeV}$ and ER cross sections for the experimentally unobserved neutron emission channels $1n$, $2n$, and $4n$ at different excitation energies ${E}^{*}$. Further, we have proposed new target-projectile (t-p) combinations for the synthesis of $^{286}\mathrm{Cn}$ for future experiments.

Quasifission in Kr84,86 -induced reactions populating superheavy elements

Background: Quasifission plays a detrimental role in the synthesis of superheavy elements. Understanding the dynamics of quasifission helps in selecting the optimum target projectile combinations for the synthesis of new superheavy elements.Purpose: The influence of various entrance channel parameters on the quasifission dynamics was explored. Three reactions, $^{84}\mathrm{Kr}+^{198}\mathrm{Pt}$, $^{86}\mathrm{Kr}+^{198}\mathrm{Pt}$, and $^{86}\mathrm{Kr}+^{197}\mathrm{Au}$, expected to be dominated by quasifission, were studied near the Coulomb barrier energies.Methods: The binary fission fragments from the three reactions were detected using the double arm time-of-flight spectrometer CORSET. The mass and total kinetic energy distributions, which are sensitive to the quasifission dynamics, were measured and analyzed for the three reactions.Results: The mass and total kinetic energy distributions of all the three reactions have the characteristics that show the dominance of quasifission. For the reaction $^{84}\mathrm{Kr}+^{198}\mathrm{Pt}$, symmetric quasifission has been found to be relatively more dominant compared to $^{86}\mathrm{Kr}+^{198}\mathrm{Pt}$ reaction. The results have been compared with $^{48}\mathrm{Ca}$- and $^{52}\mathrm{Cr}$-induced reactions, populating nearby nuclei, to understand the evolution of quasifission. An analysis of the timescales in these reactions using a dynamical calculation shows that $^{84}\mathrm{Kr}+^{198}\mathrm{Pt}$ takes a longer time to reach a particular dinuclear shape compared to the other two reactions. The driving potential at the barrier radius also shows a shallower pocket for $^{84}\mathrm{Kr}+^{198}\mathrm{Pt}$ compared to $^{86}\mathrm{Kr}+^{198}\mathrm{Pt}$ and $^{86}\mathrm{Kr}+^{197}\mathrm{Au}$ reactions.Conclusion: The entrance channel isospin difference is found to influence the quasifission dynamics. A higher entrance channel isospin difference may have a larger evolution time, thus driving the systems toward a more symmetric mass split.

Production of unknown neutron-rich transuranium isotopes 245–249Np, 248–251Pu, 248–254Am, and 252–254Cm in multinucleon transfer reactions

The production cross sections of unknown neutron-rich transuranium isotopes of elements Np, Pu, Am and Cm are investigated in multinucleon transfer (MNT) reactions based on the dinuclear system model with GEMINI code. The influence of the incident energy on the production of neutron-rich transuranium nuclei in actinide–actinide collisions is studied. The calculation results show that the final isotopic production cross sections are larger at 1.06–1.10 V cont than at other energies. Considering the high fissility of transuranium nuclides, 1.06 V cont is chosen as the optimal incident energy. The N/Z ratio equilibration mechanism in the nucleon transfer process is also studied in this work. The larger difference of N/Z ratio between projectile and target corresponds to larger neutron diffusion during the nucleon exchange process. The 238U beam with high N/Z ratio and neutron-rich actinide targets are good selections to produce neutron-rich transuranium nuclides. The production cross sections of unknown neutron-rich transuranium isotopes 245–249Np, 248–251Pu, 248–254Am, and 252–254Cm are predicted in 238U-induced actinide-based (249Bk, 249Cf, and 252Cf) MNT reactions. It is found that a large number of these unknown neutron-rich transuranium nuclei could be generated at the level of nb to μb in the reactions 238U + 249Bk and 238U + 252Cf. Our research indicates that the reaction 238U + 249Bk is a suitable projectile-target combination in the current experimental conditions and the reaction 238U + 252Cf could be a promising candidate to produce unknown neutron-rich transuranium nuclides in case that the 252Cf target were to be achieved in the future.

Fusion cross section of the superheavy Z=120 nuclei within the relativistic mean-field formalism

Background: Isotopes of $Z=107\text{--}118$ have been synthesized using cold fusion at GSI, Darmstadt, and hot fusion reactions at JINR, Dubna. Recently theoretical models have predicted $Z=120$ with $N=184$ as an island of stability in the superheavy valley. Hence it is crucial and exciting to predict theoretically the possible combination of projectiles and targets for the synthesis of $Z=120$, which can be informative for upcoming experiments.Purpose: Present theoretical investigations aim to explore the fusion characteristics of various isotopes of $Z=120$ within the relativistic mean-field formalism. We predict the most suitable projectile-target combination for the synthesis of element $Z=120$. The increase in fusion cross section of nuclei in the superheavy island directly signals the nuclear shell effects. Besides these, the analysis will be crucial and relevant for future experiments to synthesize superheavy nuclei.Methods: The microscopic nucleon-nucleon R3Y interaction and the density distributions for targets and projectiles are calculated using a relativistic mean-field formalism with the ${\mathrm{NL3}}^{*}$ parameter set. These densities and R3Y nucleon-nucleon (NN) interaction are then used to calculate the nuclear interaction potential using the double folding approach. Seventeen different projectile-target combinations that allow a high $N$/$Z$ ratio are considered in the present analysis to calculate the capture and/or fusion cross sections of various isotopes of $Z=120$ within the $\ensuremath{\ell}$-summed Wong formula.Results: The nuclear density distributions for the interacting projectile and target nuclei are obtained from relativistic mean-field Lagrangian for the ${\mathrm{NL3}}^{*}$ parameter set. The nucleus-nucleus interaction potential is estimated for seventeen possible projectile-target combinations using the mean-field density and the R3Y NN potential via a double folding approach. The fusion barriers are obtained by adding the Coulomb potential to the nucleus-nucleus interaction potential. Finally, the fusion and/or capture cross section is calculated for all the systems within the $\ensuremath{\ell}$-summed Wong formula. Further, the equivalent surface diffusion parameter is estimated to correlate the surface properties of interacting nuclei with the fusion cross section.Conclusions: The four Ti-based reactions with the heaviest available target $^{\mathrm{x}}\mathrm{Cf}$, namely, $^{46}\mathrm{Ti}+^{248}\mathrm{Cf}$, $^{46}\mathrm{Ti}+^{249}\mathrm{Cf}$, $^{50}\mathrm{Ti}+^{249}\mathrm{Cf}$, and $^{50}\mathrm{Ti}+^{252}\mathrm{Cf}$, and also $^{54}\mathrm{Cr}+^{250}\mathrm{Cm}$ are found to have the most suitable target-projectile combinations for the synthesis of various isotopes $Z=120$. We also notice that $^{48}\mathrm{Ca}$ beams merely provide the required number of protons to synthesize the element with $Z=120$. We established a correlation among the surface properties of interacting nuclei with the fusion characteristics in terms of the equivalent surface diffusion parameter.

The entrance channel effect on the synthesis of a superheavy element 296119

In this study, we investigated the entrance channel effect on the evaporation residue cross section of a superheavy element 296119. Using 29 projectile-target combinations, we investigated the role of the entrance channel on the 3n and 4n evaporation channels in hot combinations. This effect can be evaluated based on the entrance channel asymmetry and Q value of complete fusion. We calculated the variation of the maximum evaporation residue cross sections ( and ) with for the reactions , , , and . With an increase in , and increase. In addition, we studied the role of asymmetry and mean fissility parameters in the synthesis of the superheavy element. The obtained results in this study can be utilized in future studies.

Theoretical study of evaporation-residue cross sections of superheavy nuclei

Based on the empirical coupled-channel model for calculating capture cross section and the statistical model for calculating survival probability, we propose an analytical formula for describing the fusion probability. The cold-fusion and hot-fusion reactions leading to superheavy nuclei have been systematically investigated. For both the cold-fusion and hot-fusion reactions, the measured evaporation-residual (ER) cross sections can be reproduced acceptably well by using the formula with the same parameter set. Simultaneously, the ER cross sections for some reactions producing elements $Z=\phantom{\rule{2pt}{0ex}}119$ and 120 are studied. It is found that the projectile-target combinations $^{50}\mathrm{Ti}$ $+$ $^{249}\mathrm{Bk}$ and $^{50}\mathrm{Ti}$ $+$ $^{249,251}\mathrm{Cf}$ are considered as the most promising reactions for the syntheses of the next two superheavy elements beyond Og. The maximal ER cross section for $^{50}\mathrm{Ti}$ $+$ $^{249}\mathrm{Bk}$ is 48.2 fb at the incident energy ${E}_{\mathrm{c}.\mathrm{m}.}$ = 226 MeV. For $^{50}\mathrm{Ti}$ $+$ $^{249,251}\mathrm{Cf}$, the maximal ER cross section is about 10 fb at the incident energies around ${E}_{\mathrm{c}.\mathrm{m}.}=232$ MeV.

Production of light flavor hadrons in small systems measured by PHENIX at RHIC

With the recent observations of collective behavior of produced particles in small collision systems, measurements of the modification of hadron production in small systems have become increasingly relevant. To study the properties of possible quark-gluon plasma and cold nuclear matter effects PHENIX has performed measurements of light flavor hadrons (π ±, π 0, K *0, φ, and ) in a broad set of projectile-target combinations including p+Al, p+Au, d+Au and 3He+Au collisions at = 200 GeV. The obtained invariant transverse momentum spectra and nuclear modification factors are presented and compared to theoretical model predictions where available. The observation of baryon enhancement in the new experimental data and the comparisons with different calculations confirm that quark-gluon plasma could be formed in small collision systems. However, the volume and the lifetime of the medium produced in small collision systems might be insufficient for observation of strangeness enhancement and jet quenching effects.

An approximate compressible fluid model of long-rod hypervelocity penetration

Long rods are expected to experience higher impact velocities in the future as a result of the further development of new launching systems and ultra-high-energetic materials. It is therefore of considerable importance to investigate the compressible fluid theory of long-rod hypervelocity penetration. Based on the compressible fluid theory and the quasi-steady penetration assumption, an integrated approximate compressible fluid model of long-rod hypervelocity penetration that ignores the influence of shockwaves is established in this study. By comparing the solutions of this theoretical model with the Alekseevskii-Tate model (Alekseevskii (1966), Tate (1967, 1969)), experimental data, and numerical simulations, the validity of the model is verified. Subsequently, we present a compressible hydrodynamic limit after further analyzing the similarities and differences between our model, the Alekseevskii-Tate model, and the hydrodynamic theory. Finally, based on analyses of different projectile–target combinations, the influence of the compressibility of projectile/target materials on the penetration efficiency is discussed. Meanwhile, the proposed model is deemed appropriate for velocities from 1.5 km/s to 12 km/s. In addition, under the conditions that either the projectile and target are similar or both are weakly compressible, we demonstrate that the applicable velocity range of the Alekseevskii-Tate model can be appropriately extended.

Quasifission and fusion-fission lifetime studies for the superheavy element Z=120

We study the quasifission and fusion-fission lifetimes for a number of fusion reactions used to synthesize the superheavy element $Z=120$ using a statistical method within the framework of the dinuclear system model. In particular, influence of the target orientation and angular momentum on such lifetimes have been investigated. The quasifission and fusion-fission lifetimes have been compared very well with that of available experiments on successful superheavy element synthesis. We notice further the predicted quasifission and fusion-fission lifetimes of the projectile-target combinations used for the synthesis of the superheavy element $Z=120$ also show the similar trend. Furthermore, the fusion-fission lifetime is seen to somewhat decrease with the increase of the angular momentum as well as beam energy. Little effect is seen on fusion barrier of the reaction and fission barrier of superheavy compound nucleus. Variation of quasifission lifetime is also not much with orientation angle, beam energy and fission barrier of the superheavy compound nuclei. Hence, this lifetime study does not provide any good reason why the attempted reactions have failed to synthesize the superheavy nuclei $Z=120$. Furthermore, consideration of the fusion barrier, fissility, mass asymmetry, deformation parameter, fission barrier, etc., leads us to reveal that optimal colliding energy is important to have the largest evaporation residue cross section for any chosen reaction so that it is well within the measurable limit for a specific experimental set up.

Energy deposition by nonequilibrium charge states of MeV I127 in Au

The energy loss of iodine ions at initial charge states up to 25+ and energies up to 36 MeV in self-supporting gold foils between 37 and 107 nm of thickness was measured with an electron mirror type time-of-flight detector. An excess energy loss of 130 keV was observed at 36 MeV for charge state 25+ compared to 16+, and an energy loss deficit of 100 keV was observed for charge state 8+. The charge state equilibration length for 36-MeV iodine was estimated to lie between 3 and 7 nm, corresponding to an equilibration time between 0.4 and 0.9 fs. This result is relevant both for nanostructure fabrication with MeV ion beams and for depth profiling based on ion beam analysis data in cases where the charge state of the primary ion is far from the equilibrium value in the sample under study. A comparison to published data on charge state equilibration for various projectile-target combinations and energies from 10 keV to 6 GeV indicated that the energy scaling of the equilibration length observed at high energy is invalid for projectile velocities on the order of the Bohr velocity and below. The measurement further provided equilibrium values of the electronic stopping power for iodine in gold at ten energies between 10 and 36 MeV.

Entrance channel dependent hot fusion reactions for superheavy element synthesis

We have studied the compound nucleus probability, the survival probability, and the evaporation residue cross sections for 6645 projectile-target combinations to synthesize the superheavy nuclei with atomic numbers $Z=110$--126 in the light of the entrance channel effects such as mass asymmetry, charge asymmetry, isospin asymmetry, non-compound nuclear fission probability, and Businaro-Gallone mass asymmetry. The role of quasifission in every reaction has also been considered. Decay chains of various superheavy nuclei produced from the reactions are portrayed as well. The most striking results are that the measured evaporation residue cross sections are of the order of picobarns, whereas the proposed reactions can yield up to microbarn cross sections for the superheavy nuclei with $110\ensuremath{\le}Z\ensuremath{\le}126$. We suggest future experiments may utilize these hot fusion reactions to synthesize new elements ($Zg118$) or to study the properties of the known superheavy nuclei in greater detail. In particular, a proposed reaction containing both projectiles and targets that are naturally abundant, for example, $_{36}^{82}\mathrm{Kr}+_{90}^{232}\mathrm{Th}\ensuremath{\rightarrow}^{314}126+0n$, yields evaporation residue cross sections as high as 31 nb. The presently available experimental setup can test the prediction with ease to make a dream come true by putting a footstep into the eighth row of the periodic table.

Possible syntheses of unknown superheavy 309,312126 nuclei

In this paper, we theoretically investigate 21 projectile-target combinations of stable isotopes for the pre-synthesis parameters and production cross sections of the unknown superheavy 309,312126 nuclei. It is found that 61Ni + 248Cf and 64Ni + 248Cf combinations are the best candidates for the synthesis of the 309,312126 isotopes due to their largest cross sections of 0.03 and 3.6 pb, respectively. Besides, the results in the present and previous works indicate that the uncertainty, from pb to zb, in the synthesis cross sections of superheavy nuclei should be narrowed for a decision of measurements using the presently available facilities. This study, thus, provides valuable data for the synthesis of 126th element.

Examining the entrance channel effects on the synthesis of the double deformed nucleus Hs270 : A theoretical study using the dynamical cluster-decay model including Skyrme forces

The fusion evaporation residue cross sections ${\ensuremath{\sigma}}_{xn}$ for the decay of the compound nucleus (CN) $^{274}\mathrm{Hs}^{*}$ via $3n$- to $5n$-decay channels, synthesized in $^{248}\mathrm{Cm}+^{26}\mathrm{Mg}, ^{238}\mathrm{U}+^{36}\mathrm{S}$, and $^{226}\mathrm{Ra}+^{48}\mathrm{Ca}$ reactions, are studied including deformations ${\ensuremath{\beta}}_{2i}$ for compact hot orientations ${\ensuremath{\theta}}_{i}$ at various excitation energies of ${E}^{*}=40$ to 51 MeV, which support symmetric fission, in agreement with experiments. For the nuclear interaction potentials, we use the Skyrme energy density functional based on the semiclassical extended Thomas-Fermi approach, which means an extension of our earlier study of excitation functions of $^{248}\mathrm{Cm}+^{26}\mathrm{Mg}, ^{238}\mathrm{U}+^{36}\mathrm{S}$, and $^{226}\mathrm{Ra}+^{48}\mathrm{Ca}$ reactions, based on the dynamical cluster-decay model (DCM). In the present work the above reactions have been investigated by using a hot compact configuration. The Skyrme forces used here are the conventional SIII and the newer GSkI and KDE0(v1) given for both normal and isospin-rich nuclei, with densities added in the frozen density approximation. Interestingly, with the inclusion of both conventional and new Skyrme forces, the DCM gives an excellent fit within one parameter fitting of $\mathrm{\ensuremath{\Delta}}R$ to the measured data on the fusion evaporation residue for all three incoming channels at the energy range ${E}^{*}=40$ to 51 MeV, independent of the entrance channel and the Skyrme force used. The possible fusion-fission and quasifission mass-regions of fragments on the DCM are also predicted. The DCM with Skyrme forces is further used to look for all the possible target-projectile combinations forming the ``cold'' CN $^{274}\mathrm{Hs}^{*}$ at the CN excitation energy of ${E}^{*}$ for ``hot compact'' configurations. The role of magic shells is shown in enhancing the evaporation residue cross sections, not only for the entrance channel $^{226}\mathrm{Ra}+^{48}\mathrm{Ca}$ but also for the residue $^{270}\mathrm{Hs}$, compared to its neighboring isotopes ${}^{269\ensuremath{-}271}\mathrm{Hs}$. The fusion evaporation residue cross sections for the proposed new reactions in synthesizing the CN $^{274}\mathrm{Hs}^{*}$ are also estimated for future experiments.

Readjustment of the Bohr stopping force from energies of keV/n to a few tens of MeV/n ions in elemental targets

An analytical approach for the electronic stopping force for non-relativistic energies that has no adjustable parameters has been developed. The approach combines the Bohr model for the close collisions and the Firsov model for the distant collisions. In order to combine the two models, a probabilistic model was introduced. We have applied our model to 16O in 12C, 16O in 27Al, 84 Kr in 27Al, 5Li in 12C, 12C in 12C, and 132Xe in 12C systems and compared with SRIM/MSTAR software, the original Bohr model, the Firsov model and available experimental data. We have found that the calculated electronic stopping force values are in agreement with the general qualitative behaviour of the electronic stopping force as a function of particle velocity reported in the literature. The proposed analytical formula is expected to be valid for other projectile-target combinations but more experimental data are needed to verify this assumption.

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.