Complete Fusion Reactions Research Articles

Short-Lived α-Emitting Isotope ^{222}Np and the Stability of the N=126 Magic Shell.

A new, very short-lived neutron-deficient isotope ^{222}Np was produced in the complete-fusion reaction ^{187}Re(^{40}Ar,5n)^{222}Np, and observed at the gas-filled recoil separator SHANS. The new isotope ^{222}Np was identified by employing a recoil-α correlation measurement, and six α-decay chains were established for it. The decay properties of ^{222}Np with E_{α}=10016(33) keV and T_{1/2}=380_{-110}^{+260} ns were determined experimentally. The α-decay systematics of Np isotopes is improved by adding the new data for ^{222}Np, which validates the N=126 shell effect in Np isotopes. The evolution of the N=126 shell closure is discussed in the neutron-deficient nuclei up to Np within the framework of α-decay reduced width.

Could new isotopes of superheavies with Z=112–118 be produced in 48Ca-induced cold fusion reactions?

The excitation functions of the production of new heaviest isotopes of superheavy nuclei with charge numbers 112–118 are predicted in the 1n− and 2n−evaporation channels of the 48Ca-induced actinide-based complete fusion reactions for future experiments.

Optimizing the Solid-State ISOL Technique for Separating Volatile Products of Complete Fusion Reactions

Experiments on measuring the separation efficiency of evaporation residues produced in complete fusion reactions with heavy ions have been performed on the MASHA mass separator. A new design has been developed for a hot catcher based on the use of thin paper from graphite nanotubes and graphene. The catcher is to be used for the synthesis of nuclei at a high intensity of the primary beam to increase the efficiency of separation. A 16-strip silicon detector was used for continuous monitoring during an experiment to measure the mass spectrometer’s efficiency of separation in the intermediate focal plane.

Predictions of identification and production of new superheavy nuclei with Z=119 and 120

Effective single-particle potentials obtained from the established nonrelativistic nuclear energy density functional approach are incorporated into the microscopic-macroscopic method to calculate the ground-state shell corrections, mass excesses, and ${Q}_{\ensuremath{\alpha}}$ values for heaviest nuclei. The low-lying one-quasiparticle states are studied in the isotonic chains with neutron numbers $N=175$, 176, and 177. The isomeric states are discussed in the odd isotopes. The possible $\ensuremath{\alpha}$-decay chains of nuclei $^{295}119$ and $^{295,297}120$ are analyzed and compared with the available experimental data. The termination of the $\ensuremath{\alpha}$-decay chains by spontaneous fission is analyzed. The production cross sections are calculated for superheavy nuclei with $112\ensuremath{\le}Z\ensuremath{\le}120$ in the actinide-based complete fusion reactions with projectiles $^{48}\mathrm{Ca}, ^{48,50}\mathrm{Ti}, ^{54}\mathrm{Cr}, ^{58}\mathrm{Fe}$, and $^{64}\mathrm{Ni}$.

Systematic study of incomplete fusion reactions: Role of various entrance channel parameters

The evaporation residues, populated through complete and incomplete fusion processes in the reaction of 18O+ 165Ho, have been analyzed via excitation function measurements at projectile energies ≈ 4-7 MeV/nucleon. The cross-sections measured experimentally have been compared with the predictions of the compound nucleus model code PACE-4 calculations which only considers complete fusion (CF) reaction cross-sections. The experimental cross-section of the reaction residues populated through xn and pxn channels matches well with the theoretical model code PACE-4 predictions. On the other hand, α-emitting channels show an enhancement in the measured cross-section over PACE-4 calculations which reveals the occurrence of incomplete fusion (ICF) at the studied energy range. The relative percentage of incomplete fusion has been calculated from the experimental data and its dependence on various entrance channel parameters like projectile energy, mass-asymmetry, α-Q value and Coulomb factor (ZPZT) has been studied. The strength of incomplete fusion function obtained in the 18O+ 165Ho interaction has been compared with the previously studied systems. Results of the present study indicate that 18O (two neutron excess) projectile shows more incomplete fusion contribution as compared to 12C,13C and 16O projectiles due to its relatively small negative α-Q value.

Variation of ICF strength function with projectile energy for 12C + 165Ho system at Elab ≤ 7MeV/A

During the last few decades, research in heavy-ion induced nuclear reactions has opened numerous fields, in its theoretical and experimental domains. At energies, from near the Coulomb barrier to well above it, the complete fusion (CF) and incomplete fusion (ICF) reactions compete with each other. The relative contribution of these processes depends on various entrance channel parameters. In order to study the dependence of CF and ICF reaction dynamics on various entrance channel parameters, comparative studies with different parameters of the statistical model codes have been done. In this paper, an attempt has been made to study the dependence of incomplete fusion strength function on incident energy for 12 C + 165 Ho system at energies ≤ 7 MeV/A. The analysis of data has been done within the frame work of statistical model code PACE4, which do not take ICF into account; and thus predicts cross-section values only due to complete fusion process. For the present reaction system, the excitation functions (EFs) of xn/pxn channels, predicted by PACE4 code, well reproduces the experimentally measured values, indicating their production via CF process only. However, for α and 2α-emitting channels, calculated EFs through PACE4 code underpredict the experimentally measured cross-sections by »25-30%, in general. The enhancement of experimental cross-sections for α and 2α-emitting channels as compared to the PACE4 predictions, indicates that the major contribution of their production comes from the ICF of 12 C, if it breaks up into 8 Be and α-fragments, and one of the fragments fuses with the target nucleus. The incomplete fusion strength function (F ICF ), which gives relative importance of ICF processes over CF process has also been deduced and is found to depend sensitively on beam energy.

Study of Complete and Incomplete Fusion Reaction in the Interaction of 12C+ 128 Te and 14N + 128 Te system below 7 MeV/A.

In this paper, an attempt was made to measure the excitation function for the disappearance residues recognized in the interaction of 12 C+ 128 Te and 14 N + 128 Te system with the observation to investigating the complete and incomplete fusion reaction dynamics in heavy ion induced reaction. The incentive of this study was break up of 12 C and 14 N in reaction below 7MeV/A and associate the excitation function for 12 C and 14 N with the same target 128 Te prominent different compound system. PACE-4 were used for analysis of the system, and the measured excitation functions for precise decay channel in two case i.e. ( 12 C+ 128 Te and 14 N + 128 Te) have been associated and established in Bohr assumption in case of complete fusion channels. The properties of coulomb barrier and other entrance channel parameters were established to be relatively significant in decisive the decay mode of composite system. Additionally the incomplete fusion dynamics were also perceived to be of significant importance in present energy section. Keywords : Complete Fusion, Incomplete fusion, non-α-emitting, α-emitting DOI : 10.7176/APTA/81-01 Publication date: December 31 st 2019

Prompt Neutrons from Spontaneous 254Rf Fission

The neutron yield from the spontaneous fission of the short-lived neutron-deficient 254Rf nucleus produced in the complete fusion reaction with the beam of multiply charged ions from the U400 accelerator at the Flerov Laboratory of Nuclear Reactions (FLNR), Joint Institute for Nuclear Research (JINR), is measured using the combined detection system of the SHELS velocity filter. The half-life and the branching ratio of 254Rf are also measured. The data on the multiplicity of prompt neutrons from spontaneous fission of 256Rf ($$\bar {\nu }$$ = 3.87 ± 0.34) are presented for the first time.

On the synthesis of 258Rf via p-deexcitation in the complete fusion reaction 50Ti + 209Bi

Experimental data on evaporation residue production in the reaction 50Ti + 209Bi $\rightarrow$259Db* measured at SHIP in the excitation energy range $ E^{\ast} = 11-31$ MeV were reanalyzed with respect to search for products from pxn-deexcitation channels. While most of the measurements resulted only in upper cross section limits in the range $ \sigma = 5-50$ pb for p- and pn-deexcitation channels, a clear identification of the p-deexcitation channel was obtained at $ E^{\ast} = 21$ MeV. A value of $ \sigma(\mathrm{p}) = 18 \pm 8$ pb was measured.

Systematic study of the break-up fusion process in the C12+Ho165 system and interplay of entrance channel parameters

To understand the low-energy incomplete fusion (ICF) reaction dynamics, the excitation function measurements of $^{12}\mathrm{C}+^{165}\mathrm{Ho}$ system has been performed in the energy region of \ensuremath{\approx} 4--7 MeV/nucleon, by employing the stacked foil activation technique. The cross sections of the measured evaporation residues are compared with the theoretical predictions of statistical model code PACE4, which takes into account only the complete fusion (CF) reaction cross section. It is observed that residues populated via xn and pxn channels are in good agreement with the PACE4 predictions, implying that these residues are populated via CF process. However, in the case of \ensuremath{\alpha}-emission channels a significant enhancement from the PACE4 predictions is observed even after the deduction of precursor contribution, which is accredited to ICF process. The projectile break-up probability is found to increase with increment in the incident projectile energy. Further, the dependence of incomplete fusion dynamics on entrance channel parameters like mass asymmetry, Coulomb effect (${Z}_{\mathrm{P}}{Z}_{\mathrm{T}}$), and projectile ${Q}_{\ensuremath{\alpha}}$ value is systematically studied. The present results reveal that a single entrance channel parameter does not oversee the ICF reaction dynamics but have varying contributions depending upon the projectile-target combination. Moreover, the effect of projectile break-up on complete fusion cross section at energies above the Coulomb barrier is also studied. The suppression in fusion cross section is observed when compared with the universal fusion function.

Effect of the Input Channel of Heavy-Ion Reactions on Fission-Fragment Spins

Within a dynamical approach, the average spins of fission fragments originating from the 12C + 235,236U and 13C + 235U complete fusion reactions at c.m. energies in the range of Ec.m. = (55–75) MeV are analyzed as a function of energy. Particular attention is given to the process of formation of initial distributions for the components of the total angular momentum of compound nuclei. It is shown that substantial distinctions in the behavior of average spins of fission fragments for different fusion reaction channels are expected to be observed in the range of subbarrier energies.

Velocity filter SHELS: Performance and experimental results

Using the GABRIELA (Gamma Alpha Beta Recoil Invetsigations with the ELectromagnetic Analyser) set-up [1] and SHELS recoil separator [2] the experiments aimed to the gamma and electron spectroscopy of the Fm –Db isotopes, formed at the complete fusion reactions 48Ca+207,208Pb→255,256No*, 48Ca+209Bi→257Lr*, 50Ti+206,208Pb→256,258Rf*, 50Ti+209Bi→259Db*, 22Ne+238U→260No* were performed in the last decade.

Measurement of the Production Cross Sections for Isotopes of Transfermium Elements in Complete Fusion Reactions with the Subsequent Evaporation of a Proton and Neutrons

Experiments aimed at synthesizing and investigating the features of radioactive decay of isotopes of superheavy elements (Z ≥ 110) have been conducted in the Flerov Laboratory of Nuclear Reactions at the Joint Institute for Nuclear Research. Complete fusion reactions of an accelerated beam of 48Ca ions with transactinide targets with the subsequent evaporation of several neutrons from excited compound nucleus are typically used in these experiments. “Exotic” reaction channels with the evaporation of protons and several neutrons may be used to produce more neutron-rich isotopes of superheavy elements. The production cross sections were measured in experiments at the SHELS separator for Db and Rf isotopes produced in xn and pxn channels of the 50Ti + 209Bi → 259Db* reaction. The ratio of cross sections σ(xn)/σ(pxn) was on the order of 100.

Special Features of Nuclear Reactions Involving Loosely Bound Cluster Nuclei

Reactions involving loosely bound nuclei have many special features. An enhancement of interaction cross sections in the subbarrier energy region is one of them. This effect is pronounced for nuclei that have a cluster structure. Transfer and complete-fusion reactions are dominant interaction channels for them. Experimental data on the cross sections for fusion reactions induced by such nuclei deviate strongly from the predictions of the statistical compound-nucleus model at energies in the vicinity of the Coulomb barrier. Also, the cross sections for neutron transfer from 3,6,8He and deuteron transfer from 6,9Li were found to grow at deep subbarrier energies. These results are discussed from the point of view of the effect of the cluster structure of nuclei on the probability for their interaction at energies in the vicinity of the Coulomb barrier. A theoretical analysis of relevant experimental data was performed with allowance for the effect of outer neutrons and clusters in loosely bound nuclei of bombarding particles. The results of the present study may be used to solve some problems of astrophysics—in particular, to obtain deeper insight into the mechanism of the production of light elements in the Universe.

Observation of the competing fission modes in 178Pt

Fragment mass distributions from fission of the excited compound nucleus 178Pt have been deduced from the measured fragment velocities. The 178Pt nucleus was created at the JAEA tandem facility in a complete fusion reaction 36Ar + 142Nd, at beam energies of 155, 170 and 180 MeV. The data are indicative of a mixture of the mass-asymmetric and mass-symmetric fission modes associated with higher and lower total kinetic energies of the fragments, respectively. The measured fragment yields are dominated by asymmetric mass splits, with the symmetric mode contributing at the level of ≈1/3. This constitutes the first observation of a multimodal fission in the sub-lead region. Most probable experimental fragment-mass split of the asymmetric mode, AL/AH≈79/99, is well reproduced by nuclear density functional theory using the UNEDF1-HFB and D1S potentials. The symmetric mode is associated by theory with very elongated fission fragments, which is consistent with the observed total kinetic energy/fragment mass correlation.

Development of the Active Correlation Method

At the present time, the Dubna gas-filled separator is the world’s leading physical facility in the field of synthesis of superheavy elements. This is the device where new elements with Z = 114–118 (Fl, Mc, Lv, Ts, Og) were synthesized. The original tools and methods considered in this paper are applied in reactions of complete fusion of actinide target + 48Ca → SHN + xn type. Modification of the active correlation method is planned after the launch of new DC-280 cyclotron developed at the Flerov Laboratory of Nuclear Reactions in 2019.

Short-Lived Isotopes of Transfermium Elements: Studying Characteristics of Spontaneous Fissioning

series of experiments performed in 2014–2015 using the SHELS separator and a beam of multicharged ions from the U-400 accelerator at the Flerov Laboratory of Nuclear Reactions (Joint Institute for Nuclear Research) in Dubna is described. In preparation for a large program of experiments with a beam of highly charged ions of 50Ti, an experiment is performed to study the spontaneous fissioning (SF) of short-lived neutron-deficient isotope 256Rf formed in complete fusion reaction50Ti + 208Pb = 256Rf + 2n. The half-life of 256Rf is measured along with the probability of its SF decay. The average number of neutrons per one event of 256Rf SF ( $$\bar v$$ = 4.47 ± 0.09) is obtained for the first time. The results from experiments to study the SF of short-lived neutron-deficient isotopes synthesized in complete fusion reaction 48Ca + 204Pb → 252No* are presented as well. Two short-lived activities attributed to the SF of the ground and isomeric states of 250No are revealed. The half-life, total kinetic energies of fission fragments, and neutron multiplicities are measured for the obtained short-lived nuclei. The average numbers of neutrons per one SF event are $$\bar v$$ = 4.38 ± 0.13 and $$\bar v$$ = 3.90 ± 0.20, respectively, for SF activity with t1/2 = 5.1 ± 0.3 and t1/2 = 36 ± 3 μs.

Pre-equilibrium Effects of the Hot Nuclei De-excitation via GDR Emission --- Theoretical Approach

The hot rotating nuclei could be formed in the complete and incomplete fusion reaction of two heavy ions. At low bombarding energies the reaction goes via compound nucleus formation and subsequent evaporation of charged particles, neutrons and $\gamma$-rays. However, with increasing the energy of the projectile, the emission of particles during the equilibration process becomes more and more probable. This effect can be estimated by the Heavy-Ion Phase-Space Exploration (HIPSE) code which describes the production of clusters of various size from nucleons initially in the target or projectile. This dynamic evolution finalizes with the compound nuclei, quasi-fission or multi-fragmentation products. The hot rotating nuclei produced in fusion reaction can de-excitate by evaporation of particles and emission of $\gamma$-rays from the Giant Dipole Resonance, or by fission into two fragments. These processes, evaporation and fission, are described within statistical codes such as GEMINI++ or in dynamical approaches by solving the transport equations of Langevin type. In the present article we will concentrate on the possible effect of the pre-equilibrium emission on the strength function of the effective Giant Dipole Resonance, which can be described within Thermal Shape Fluctuation Model (TSFM) approach.

Study of incomplete fusion reaction dynamics in [formula omitted] system and its dependence on various entrance channel parameters

The excitation functions for the evaporation residues populated in the interaction of C13+165Ho system have been measured at projectile energies ≈ 4–7 MeV/nucleon. Stacked foil activation technique followed by off-line γ-ray spectroscopy have been employed in the present work. The experimentally measured cross-sections are analyzed in the frame work of statistical model code PACE4, which takes into account only the complete fusion reaction cross-sections. The evaporation residues populated via xn and pxn channels were found to be in good agreement with the PACE4 predictions, while a significant enhancement in the measured cross-sections over PACE4 predictions is observed in case of α-emitting channels, which may be attributed to the incomplete fusion process. For the better understanding of incomplete fusion dynamics, the incomplete fusion fraction has also been deduced and its sensitivity with various entrance channel parameters like: projectile energy, mass-asymmetry, projectile structure in terms of Qα-value and Coulomb effect has been studied in the present work. The incomplete fusion fraction is found to increase with increasing the projectile energy and a strong projectile structure dependent mass-asymmetry systematic is also observed. The incomplete fusion fraction is also found to be small for more negative Qα-value projectile (13C) induced reactions as compared to less negative Qα-value projectiles (12C, 16O and 20Ne) induced reactions with the same target nucleus 165Ho. An interesting trend is obtained on further investigation of incomplete fusion dependence on Coulomb effect (ZPZT).

β -delayed fission of Am230

The exotic decay process of $\ensuremath{\beta}$-delayed fission ($\ensuremath{\beta}\mathrm{DF}$) has been studied in the neutron-deficient isotope $^{230}\mathrm{Am}$. The $^{230}\mathrm{Am}$ nuclei were produced in the complete fusion reaction $^{207}\mathrm{Pb}(^{27}\mathrm{Al},4n)^{230}\mathrm{Am}$ and separated by using the GARIS gas-filled recoil ion separator. A lower limit for the $\ensuremath{\beta}\mathrm{DF}$ probability ${P}_{\ensuremath{\beta}\text{DF}}(^{230}\mathrm{Am})g0.30$ was deduced, which so far is the highest value among all known $\ensuremath{\beta}\mathrm{DF}$ nuclei. The systematics of $\ensuremath{\beta}\mathrm{DF}$ in the region of $^{230}\mathrm{Am}$ will be discussed.