Synthesis Of Superheavy Elements Research Articles

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.

Possibility to form Z=120 via the Ni64+U238 reaction using the dynamical cluster-decay model

According to different theoretical studies, the next magicity for the proton number should occur at $Z=114$, 120, or 126 and for the neutron number $N=184$. Superheavy nuclei of interest for the forthcoming synthesis of the isotopes with $Z=119$, 120 are investigated. Many reactions have yet to be studied in order to find the possible incoming channels for the formation of $Z=120$. In this work, synthesis of superheavy element 120 in terms of the fission and quasifission cross sections via $^{64}\mathrm{Ni}+^{238}\mathrm{U}$ reaction is evaluated and discussed. We have explored the possibility of formation of $Z=120$ via $^{64}\mathrm{Ni}+^{238}\mathrm{U}$ reaction, using the experimental data from Kozulin , Phys. Lett. B 686, 227 (2010). Some experimental efforts have been made to synthesize $^{302}120$, via Ni-induced and Cr-induced reaction, i.e., $^{64}\mathrm{Ni}+^{238}\mathrm{U}$ reaction at five ${E}^{*}$'s (excitation energies) and the $^{54}\mathrm{Cr}+^{248}\mathrm{Cm}$ reaction at only one energy, respectively. In this work, we have studied the Ni-induced reaction at given energies by including higher multipole deformations ${\ensuremath{\beta}}_{\ensuremath{\lambda}i}$ $(\ensuremath{\lambda}=2,3,4$; $i=1,2)$, and compact orientations ${\ensuremath{\theta}}_{ci}$ using the coplanar degree of freedom $(\mathrm{\ensuremath{\Phi}}={0}^{\ensuremath{\circ}})$ within the framework of the dynamical cluster-decay model (DCM). The neck-length parameter is the only one, which is fixed in reference to the observed data for fission cross section $({\ensuremath{\sigma}}_{\mathrm{ff}})$ calculated for mass region $A/2\ifmmode\pm\else\textpm\fi{}20$, and quasifission cross section $({\ensuremath{\sigma}}_{\mathrm{qf}})$ for the incoming channel of $^{64}\mathrm{Ni}+^{238}\mathrm{U}$ reaction. Our calculations for Ni-induced reaction have shown a good concurrence with the experimental data for quasifission and fission cross sections along with the DCM-calculated estimated and predicted cross sections for evaporation residues (ERs), which can be used for future references. Our results demonstrate the insignificant compound nucleus formation possibility ${P}_{\text{CN}}$ $(\ensuremath{\ll}1)$ for $Z=120$ from Ni-induced reaction because of the very low order of evaporation residues; thus, this work is not supporting this incoming channel for the formation of $Z=120$.

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.

A dynamical study of fusion hindrance with the Nakajima–Zwanzig projection method

Abstract A new framework is proposed for the study of collisions between very heavy ions which lead to the synthesis of Super-Heavy Elements (SHE), to address the fusion hindrance phenomenon. The dynamics of the reaction is studied in terms of collective degrees of freedom undergoing relaxation processes with different time scales. The Nakajima–Zwanzig projection operator method is employed to eliminate fast variables and derive a dynamical equation for the reduced system with only slow variables. There, the time evolution operator is renormalised and an inhomogeneous term appears, which represents a propagation of the given initial distribution. The term results in a slip to the initial values of the slow variables. We expect that gives a dynamical origin for the so-called “injection point $s$” introduced by Swiatecki et al. in order to reproduce absolute values of measured cross sections for SHE. A formula for the slip is given in terms of physical parameters of the system, which confirms the results recently obtained with a Langevin equation, and permits us to compare various incident channels.

Investigation of the cold valley paths for the synthesis of isotopes of Ubh in optimum orientations

Cold valley paths have been investigated for the synthesis of isotopes of superheavy element Unbihexium using quantum mechanical fragmentation theory, which suggests the fusion of fission fragments belonging to the cold valleys in the potential energy surfaces with at least one spherical closed shell nucleus as the reaction partner for the nuclear synthesis. For the suitability of the cold valley fission fragments for the synthesis of isotopes of Ubh, first the fragmentation potentials, preformation probabilities and fission barriers of the fission fragments of 314Ubh and 326Ubh compound systems in their ground states have been compared by keeping the fragments either in hot or cold optimum orientations. The comparison suggests 138Ba + 176Yb and 132Sn + 194Os reactions in hot optimum orientations for the synthesis of isotopes of Ubh due to their highest values of preformation probabilities, lowest values of the fragmentation potentials and relatively good values of the fission barriers. Also, the reactions 68Ni + 246Cf and 70Ni + 256Cf have been considered for the comparison with 138Ba + 176Yb and 132Sn + 194Os reactions due to their relatively smaller values of the Coulomb potential, higher mass-asymmetry and fission barrier, and shell closures next to 48Ca which has been used in most of the experiments for the synthesis of superheavy elements. Finally, the excitation functions for the neutron evaporation from the compound systems formed in these reactions, the probabilities of the formation and survival of the compound nuclei have been compared to suggest the suitable cold valley paths energies for the synthesis of the isotopes of Ubh.

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.

Investigations on the study of entrance channel effects in synthesis of superheavy elements using Cr-induced fusion reactions

We have investigated the synthesis of superheavy elements using Cr-induced fusion reactions. We have studied all possible Cr-induced fusion reactions for the synthesis of super heavy nuclei [Formula: see text]. We have achieved the semi-empirical formula for fusion barrier heights ([Formula: see text]), positions ([Formula: see text]), curvature of the inverted parabola ([Formula: see text]) of Cr-induced fusion reactions for the synthesis of superheavy nuclei with atomic number range [Formula: see text]. The proposed formula produces fusion barriers of Cr-induced fusion reactions for the synthesis of super heavy nuclei with the simple inputs of mass number ([Formula: see text]) and atomic number ([Formula: see text]) of projectile-targets. We have also identified the targets for Cr-induced fusion reactions to synthesis superheavy elements of [Formula: see text]. We have also studied the entrance channel parameters such as mass asymmetry ([Formula: see text]), charge asymmetry ([Formula: see text]), coulomb interaction parameter ([Formula: see text]’), Businaro–Gallone mass asymmetry parameter ([Formula: see text]) and Isospin asymmetry parameter [[Formula: see text]]. We hope that our predictions may be the guide for the future experiments in the synthesis of more superheavy elements using [Formula: see text]Cr-induced fusion reactions.

Estimation of Synthesizing New Superheavy Elements Using Dynamical Model

For the success the synthesis of superheavy elements $$Z>118$$ , it is indispensable to clarify the fusion–fission mechanism, which includes a role of the nuclear structure of colliding nuclei and the deformation in the fusion process. We develop the dynamical model to estimate the probability to produce new superheavy nuclei. To approach Island of Stability and synthesize new elements, we propose the new idea, which takes advantage of the shell structure in fusion and fission process.

Study of Quasielastic Barrier Distributions as a Step towards the Synthesis of Superheavy Elements with Hot Fusion Reactions.

The excitation functions for quasielastic scattering of ^{22}Ne+^{248}Cm, ^{26}Mg+^{248}Cm, and ^{48}Ca+^{238}U are measured using a gas-filled recoil ion separator. The quasielastic barrier distributions are extracted for these systems and are compared with coupled-channel calculations. The results indicate that the barrier distribution is affected dominantly by deformation of the actinide target nuclei, but also by vibrational or rotational excitations of the projectile nuclei, as well as neutron transfer processes before capture. From a comparison between the experimental barrier distributions and the evaporation residue cross sections for Sg (Z=106), Hs (108), Cn (112), and Lv (116), it is suggested that the hot fusion reactions take advantage of a compact collision, where the projectile approaches along the short axis of a prolately deformed nucleus. A new method is proposed to estimate the optimum incident energy to synthesize unknown superheavy nuclei using the barrier distribution.

Study of neutron-rich isotopes near N=152 shell closure using Timepix type detectors integrated into the mass separator MASHA

The MASHA facility [1–3] was developed as a high precision mass-spectrometer for heavy and super heavy elements with masses up to 450 a.m.u. It uses ISOL (Isotope Separation On-Line) method. Its unique properties opens great prospective for the investigation of neutron-rich nuclei produced in multinucleon transfer reactions. Mainly nuclei near the neutron N = 126 and N = 152 shell closures are of great interest. This region of nuclei is not so far thoroughly enough investigated while its research has direct relation to the synthesis of super heavy elements. As is known the island of stability close to super heavy elements (Z = 112–118) exists due to the shell effects in nuclei. More detailed investigation of these shell effects can greatly help in the synthesis of next super heavy elements. Heavy neutron rich radon isotopes were produced in the multinucleon transfer reaction 40Ar + 232Th at Flerov Laboratory of Nuclear Reactions, Dubna. Radon isotopes with given masses were detected using two types of detectors: a multi-strip well-type detector (made in Canberra) and a position-sensitive quantum counting hybrid pixel detector of the Timepix type [1]. The latter detector has an array of 256×256 square pixels each with a pitch size of 55 μm for the full sensitive area 14×14 mm2. Radon isotopes implanted into the detector emit then alpha and beta particles until they reach the stable or long-lived isotopes at the end of their decay chains. The positions of radon isotopes, the tracks, times and energies of the beta particles were measured and analyzed. New software for the particle recognition and data analysis of the results obtained from the experiment was developed and used. It has been proven that MASHA + Timepix setup is a powerful instrument for investigation of neutron-rich isotopes far from stability limits.

High intensity vanadium beam for synthesis of new superheavy elements with well-controlled emittance by using "slit triplet".

To provide a very powerful vanadium (V) beam with an intensity of at least 6 particle μA for synthesizing a new superheavy element (SHE) with atomic number Z = 119, we have developed a high-temperature oven (HTO) system to evaporate the metallic V powder inside the new superconducting (SC) electron cyclotron ion source. We successfully extracted a V13+ beam with a maximum beam intensity of 600 eμA with 2.8-kW microwave power and 900-W heating power of the HTO. Furthermore, from a systematic study of the dependence of the beam intensity on the microwave power and the HTO power, we successfully produced a V13+ beam of 300 eμA at a consumption rate of 3 mg/h, allowing a one-month duration continuous beam to carry out the SHE synthesis. In addition, to avoid serious damage to newly introduced SC acceleration cavities by beam losses, the beam should be transported with a well-controlled emittance. To efficiently limit the beam emittance, we employed a slit triplet consisting of three pairs of slits installed around the focus point of the low-energy beam transport. The first result of the emittance reduction was observed by a pepper-pot type emittance meter as a function of the acceptance of the slit triplet.

Subbarrier fusion reactions of an aligned deformed nucleus

We discuss heavy-ion fusion reactions of a well-deformed odd-mass nucleus at energies around the Coulomb barrier. To this end, we consider the $^{16}$O+$^{165}$Ho reaction and take into account the effect of deformation of $^{165}$Ho using the orientation average formula. We show that fusion cross sections are sensitive to magnetic substates of the target nucleus, and cross sections for the side collision, which are relevant to a synthesis of superheavy elements, may be enhanced by a factor of around two by aligning the deformed target nuclei. We also discuss the effect of alignment on the fusion barrier distribution. We find that, for a particular choice of alignment, the shape of barrier distribution becomes similar to a typical shape of barrier distribution for a deformed nucleus with a negative hexadecapole deformation parameter, $\beta_4$, even if the intrinsic $\beta_4$ is positive in the target nucleus.

A Detail Investigation on the Synthesis of Superheavy Element Z = 119

We have studied the α-decay properties of superheavy nuclei Z = 119 in the range 265 ≤ A ≤ 316. By studying the α-decay properties, we have identified the possible isotopes for superheavy element Z = 119. The nuclei 292–299119 were found to have long half-lives and hence could be sufficient to detect them if synthesized in a laboratory. We hope that our predictions may be guide for the future experiments in the synthesis of more isotopes of super heavy nuclei Z = 119.

Dynamical Approach for Synthesis of Superheavy Elements: Fusion Mechanism and Nuclear Structure

To synthesis of superheavy elements, the shell structure is very important not only in the stability of nuclei, but also the fusion process, especially the cold fusion reaction. We employ the Langevin equation with the microscopic transport coefficients and calculate the fusion cross section for the reaction 70 Zn+ 208 Pb→ 278 Cn. In the dynamical process, the effect of nuclear structure is discussed.

Elimination of fast variables and initial slip: a new mechanism for fusion hindrance in heavy-ion collisions

Synthesis of superheavy elements by fusion–evaporation reactions is limited by extremely low cross-sections. One of the reasons for the reduced cross-sections is the so-called quasifission, which hinders fusion for reactions with heavy systems. It is widely acknowledged that fusion hindrance is due to a conditional saddle that has yet to be overcome in a dissipative environment, in order to reach the compound configuration from the contact point. However, the dynamical description is not yet well established. In this communication we show that elimination of fast variables to reduce the number of degrees of freedom leads to a slip of the initial conditions of the slow variables, which has a significant impact on the amplitude of the hindrance phenomenon. The energy dependence of the slip is similar to the phenomenological shift introduced in the ‘fusion by diffusion’ model.

The effect of deformation and orientation of colliding nuclei on synthesis of superheavy elements

In this paper, we study the evaporation residue cross section for superheavy elements 120295−304 using the phenomenological model taking into account the deformation and orientation effects of the target and the projectile. Calculations are done for the 3n and 4n channels in the reactions 54Cr+244−248,250Cm, 50V+245−250Bk, 55Mn+240−244Am, and 58Fe+240−242,244,246Pu. To test this model, we compared results of the 3n channel cross section in the reactions 48Ca+243Am, 48Ca+248Cm, 48Ca+249Bk and 48Ca+249Cf and the 4n channel cross section in the reactions 48Ca+243Am, 48Ca+248Cm, and 48Ca+249Bk with the experimental data. The agreement between the experimental data and the theoretical results based on deformed target and projectile is better than theoretical results for spherical target and projectile. Using this model, we predicted the maximum value and the corresponding energy of the 3n and 4n channel cross sections for spherical and deformed colliding nuclei for synthesizing Z=120. By applying the deformation effect and averaging over orientation, it is found that the maximum value of the 3n channel is 70.14 fb at 26.04 MeV for the reaction 54Cr+247Cm, whereas the maximum value of the 4n channel is 0.47 fb at 34.61 MeV for the reaction 54Cr+250Cm.

Superheavy elements

Synthesis of superheavy elements predicted by microscopic nuclear theory is investigated. The heaviest elements with Z = 114–118 were synthesized by fusion reactions of actinide nuclei with 48Ca ions accelerated using the U-400 complex at the Flerov Laboratory of Nuclear Reactions (FLNR), one of seven laboratories that comprise the Joint Institute for Nuclear Research (JINR) located in Dubna, Russia. The experiments were carried out in collaboration with physicists and chemists working at the Livermore and Oak Ridge national laboratories in located in California and Tennessee, respectively. Discovery of these elements allowed completion of the seventh period of the periodic table. The microscopic nuclear theory’s fundamental predictions about the possible existence of superheavy elements received the experimental confirmation. A new laboratory, i.e., the "STE Factory" associated with the JINR FLNR, has been established to research superheavy nuclei.

Studies on the synthesis of superheavy element Z = 123

We have studied the α-decay chains of superheavy nuclei Z = 123 in the range 265 ≤ A ≤ 316. The nuclei 303–308123 were found to have longer half-lives and hence could be detected them if synthesized in a laboratory. After identifying the possible isotopes, we have identified the most probable projectile–target combinations by studying the fusion cross section, evaporation residue cross section, compound nucleus formation probability (PCN) and survival probability (PSurv) of different projectile–target combinations to synthesize superheavy element Z = 123. The selected most probable projectile–target combination to synthesize superheavy nuclei with Z = 123 is Mn + Cf. We hope that our predictions may be guide for the future experiments in the synthesis of new superheavy element Z = 123.

Inner-shell ionization duringαdecay of superheavy isotopes from the tennessineTs117293and oganessonOg118294chains

Presented here are calculations of probabilities of the $K$-, $L$-, and $M$-shell ionization during $\ensuremath{\alpha}$ decay of superheavy isotopes $_{117}^{293}\mathrm{Ts}$, $_{115}^{289}\mathrm{Mc}$, and $_{113}^{285}\mathrm{Nh}$ involved in the tennessine decay chain as well as $_{118}^{294}\mathrm{Og}$, $_{116}^{290}\mathrm{Lv}$, and $_{114}^{286}\mathrm{Fl}$ involved in the new oganesson decay chain. The ionization probabilities are of importance for handling data obtained by methods of the combined $\ensuremath{\alpha}$, $\ensuremath{\gamma}$, and conversion-electron spectroscopy used in the superheavy element synthesis analysis. Relativistic calculations are based on the quantum mechanical model. Electron wave functions are determined by the Dirac-Fock method. The $\ensuremath{\alpha}$-particle tunneling through the atomic Coulomb barrier is taken into account. Peculiarities of the $K$-, $L$-, and $M$-shell ionization are considered. Results demonstrate that the effect of tunneling through the Coulomb barrier for the $L$ and $M$ shells is of no significance as distinct from the $K$ shell, where the inclusion of the tunneling leads to a considerable decrease of the ionization probability. The probability of ionization from higher shells is larger than that from inner shells. However, the change from the $K$ shell to $L$ shell is much more significant than the change from the $L$ shell to $M$ shell. It has been found that only monopole and dipole terms of the radiative field $L=0,1$ make a contribution to the $K$- and ${L}_{1}$-shell ionization probabilities while contributions of all multipoles $L\ensuremath{\le}4$ may be important for the ${L}_{2}$, ${L}_{3}$, and particularly for ${M}_{1}\ensuremath{-}{M}_{5}$ subshells.

Investigations on [formula omitted] reactions

We have investigated the almost all possible 64Ni-induced fusion reactions to synthesis of superheavy elements 104≤Z≤123. On rigorous investigations, we have identified the suitable targets to synthesis superheavy elements through 64Ni-induced fusion reactions. To synthesis superheavy elements with atomic number Z>118, the projectiles heavier than 48Ca must be used. Hence this work presents new Physics required for the synthesis of superheavy elements Z>118.