Evaporation Residue Excitation Functions Research Articles

Understanding the low-energy incomplete fusion reactions

With a motivation to find out the systematics for the low-energy ($\ensuremath{\approx}4$--7 MeV/nucleon) incomplete fusion reactions, the experimentally measured excitation functions for evaporation residues, which were populated during the interactions of $^{18}\mathrm{O}$ with $^{159}\mathrm{Tb}$ target nuclei, have been studied. The analysis clearly exhibits that the $xn/pxn$ channels are populated to a large extent through the complete fusion processes. Although, the production cross-section of the $\ensuremath{\alpha}$-emitting channels, despite of deducting the precursor decay contribution, found to be significantly under-estimated by the statistical model predictions. The observed enhancement, which may be attributed due to the involvement of break-up fusion processes, is found to be get larger with the incident energy. In addition, the present work in light of the literature data imparts the reliance of incomplete fusion processes on various entrance channel parameters, such as the mass-asymmetry of the interacting partners, fissility parameter and also on the ${Z}_{P}{Z}_{T}$ (Coulomb factor). These systematics inarguably indicates the projectile type dependency of the incomplete fusion reactions, and the results may be explained on the basis of the $\ensuremath{\alpha}\text{\ensuremath{-}}Q$ value of the projectile. Furthermore, an attempt has been made to explain the trends of incomplete fusion fractions through the total asymmetry parameter and the system parameter, where system parameter seems to explain the data more satisfactorily, as it incorporates the Coulomb factor as well as the masses of the interacting partners.

Investigating the fission dynamics of the following neutron shell closed nuclei within a stochastic dynamical approach: 210Po, 212Rn, and 213Fr* *D.A. acknowledges the financial support from the University Grants Commission (UGC), Government of India, received in the form of a research fellowship (Ref. No. 19/06/2016/(i) EU-V, Sr. No. 2061651303)

The dissipative dynamics of nuclear fission is a well confirmed phenomenon that can be either described by a Kramers-modified statistical model or by a dynamical model employing the Langevin equation. Although dynamical models as well as statistical models incorporating fission delays have been found to explain the measured fission observables in several studies, they present conflicting results for shell closed nuclei in the mass region of 200. Notably, an analysis of the recent data on neutron shell closed nuclei in the excitation energy range of 4080 MeV failed to provide a satisfactory description of the data, which was attributed to a mismatch with shell effects and/or entrance channel effects, without reaching a definite conclusion. In the present study, we demonstrate that a well established stochastic dynamical code can simultaneously reproduce the available data for pre-scission neutron multiplicities and fission and evaporation residue excitation functions for the following neutron shell closed nuclei Po and Rn and their isotopes Po and Rn without the need for including any extra shell or entrance channel effects. The relevant calculations are performed by using a phenomenological universal friction form factor with no ad-hoc adjustment of the model parameters. However, we note a significant deviation, beyond experimental errors, for some Fr isotopes.

The Fusion-by-Diffusion model as a tool to calculate cross sections for the production of superheavy nuclei

This article summarizes recent progress in our understanding of the reaction mechanisms leading to the formation of superheavy nuclei in cold and hot fusion reactions. Calculations are done within the Fusion-by-Diffusion (FBD) model using the new nuclear data tables by Jachimowicz et al. (At Data Nucl Data Tables 138, 101393, 2021). The synthesis reaction is treated in a standard way as a three-step process (i.e., capture, fusion, and survival). Each reaction step is analysed separately. Model calculations are compared with selected experimental data on capture, fissionlike and fusion cross sections, fusion probabilities, and evaporation residue excitation functions. The role of the angular momentum in the fusion step is discussed in detail. A set of fusion excitation functions with corresponding fusion probabilities is provided for cold and hot synthesis reactions.

Statistical model calculation of the compound nuclear fission timescale in fusion-fission reactions

In the decay of an excited heavy nucleus, both the fission or evaporation residue (ER) cross sections and the fission time are determined by the competition between the various evaporation channels and fission. Statistical model (SM) calculations for several heavy-ion-induced fusion-fission reactions are presented which reproduce the fission or ER excitation functions. The corresponding calculated fission times are found to depend upon the compound nuclei and their excitation energies. The multichance fission probabilities and the corresponding fission times are also obtained, and they are shown to depend sensitively on the shell correction energies and the neutron separation energies of the compound nuclei involved. The experimental neutron multiplicities are reproduced by adjusting the saddle-to-scission transition time interval. An additional delay time for compound nuclear formation is found necessary to fit the experimental neutron multiplicities for a system with higher entrance channel mass symmetry.

Systematics on production of superheavy nuclei $$Z = 119-122$$ in fusion-evaporation reactions

The fusion dynamics on the formation of superheavy nuclei is investigated thoroughly within the dinuclear system model. The Monte Carlo approach is implemented into the nucleon transfer process for including all possible orientations, at which the dinuclear system is assumed to be formed at the touching configuration of dinuclear fragments. The production cross sections of superheavy nuclei Cn, Fl, Lv, Ts and Og are calculated and compared with the available data from Dubna. The evaporation residue excitation functions in the channels of pure neutrons and charged particles are analyzed systematically. The combinations with $^{44}$Sc, $^{48,50}$Ti, $^{49,51}$V, $^{52,54}$Cr, $^{58,62}$Fe and $^{62,64}$Ni bombarding the actinide nuclides $^{238}$U, $^{244}$Pu, $^{248}$Cm, $^{247,249}$Bk, $^{249,251}$Cf, $^{252}$Es and $^{243}$Am are calculated for producing the superheavy elements with Z=119-122. It is found that the production cross sections sensitively depend on the neutron richness of reaction system. The structure of evaporation residue excitation function is related to the neutron separation energy and fission barrier of compound nucleus.

Effect of non- α -cluster projectile on incomplete-fusion dynamics: Experimental study of the N14+Ta181 system

In order to study incomplete fusion (ICF) reaction dynamics, the present work manifests the role of a non-$\ensuremath{\alpha}$-cluster $^{14}\mathrm{N}$ projectile on $^{181}\mathrm{Ta}$ target at energies $\ensuremath{\approx}4--7$ MeV/nucleon using the offline $\ensuremath{\gamma}$-ray spectroscopy. The excitation functions for 15 reaction residues populated in $^{14}\mathrm{N}+^{181}\mathrm{Ta}$ system have been measured and analyzed within the framework of statistical model code PACE4. The experimentally measured excitation functions of evaporation residues populated via xn/pxn channels are found to be well reproduced by the predictions of code PACE4, which confirms their production solely via complete fusion process. However, an enhancement in the measured excitation function as compared to PACE4 calculations, particularly in tail portion of $^{192}\mathrm{Hg}$ residue ($3n$ channel) has been observed indicating the presence of precompound emission. A significant contribution from precursor decay in pxn channels has also been observed. An enhancement in the measured excitation functions for $\ensuremath{\alpha}$-emitting channels as compared to the PACE4 predictions has been observed and attributed to the incomplete fusion process. Further, the contribution from incomplete fusion process in the $^{14}\mathrm{N}+^{181}\mathrm{Ta}$ system has also been deduced in terms of strength function (${F}_{\mathrm{ICF}}$). The results have been discussed in terms of the parameters which influence the dynamics of ICF process. The ${F}_{\mathrm{ICF}}$ is found to depend strongly on projectile energies, the product of projectile and target charges, and $\ensuremath{\alpha}\ensuremath{-}Q$ value of the projectile.

Fusion studies in Cl35,37+Ta181 reactions via evaporation residue cross section measurements

The fusion evaporation residue (ER) excitation function has been measured for $^{35,37}\mathrm{Cl}+^{181}\mathrm{Ta}$ reactions at energies above the Coulomb barrier. The measurements were performed using the HYbrid Recoil mass Analyzer at IUAC, New Delhi. Comparable ER cross sections have been observed in both reactions and there is no isotopic dependence. Measured ER cross sections were compared with theoretical calculations employing the dinuclear system model at projectile and target nuclei interaction and statistical model for the deexcitation of the formed compound nucleus. Larger ER cross sections at the complete deexcitation cascade of the formed compound nucleus are noticed in both reactions at higher excitation energies $({E}^{*}g80 \mathrm{MeV})$ over the calculated results. Fusion probability varies from $95%$ to $40%$ in the excitation energy range of the study. No appreciable difference in the fusion probability is noticed in the two reactions. Comparison of our results with other reactions populating $^{216}\mathrm{Th}$ shows a very strong entrance channel dependence.

Effect of projectile breakup in the system 19F + 154Sm

An attempt was made to understand the role of various entrance channel parameters on incomplete fusion dynamics by the measurements of excitation functions of evaporation residues populated via complete and incomplete fusion dynamics in the system 19 F + 154 Sm at projectile energy ≈ 4-6 MeV/A. The stacked foil activation technique followed by offline gamma ray spectrometry was employed in these measurements. The measured excitation functions of various evaporation residues populated have been analyzed within the framework of statistical model code PACE-4. It has been observed that the measured excitation functions of xn and pxn emission channels agree well with the theoretical predictions of PACE-4. On the other hand, the measured excitation functions of α-emission channels have been found significantly enhanced over their theoretical predictions. This enhancement may be attributed to the incomplete fusion of the projectile 19 F as the calculations for incomplete fusion are not included in statistical model calculations. The incomplete fusion fraction has been deduced from the present measurements. Further, a systematic study has also been performed, which shows that the incomplete fusion increases significantly with entrance channel mass asymmetry at low projectile energy, differently for different projectiles.

Systematic study of low-energy incomplete-fusion dynamics in the O16+Nd148 system: Role of target deformation

A study of low-energy incomplete fusion was done by the measurements of excitation functions of evaporation residues produced in the $^{16}\mathrm{O}+^{148}\mathrm{Nd}$ system at energies $\ensuremath{\approx}4--7$ MeV/nucleon. The stacked foil activation technique using offline $\ensuremath{\gamma}$-ray spectrometry was employed. Significant enhancements were found in the measured cross sections from the theoretical predictions of pace-4 for the evaporation residues populated through $\ensuremath{\alpha}$-emission channels. This enhancement is attributed to incomplete fusion (ICF) of $^{16}\mathrm{O}$ with $^{148}\mathrm{Nd}$. The comparison of present work with literature data shows that the ICF probability increases exponentially with existing entrance channel parameters. The dependence of ICF dynamics on target deformation was investigated using deformation parameter (${\ensuremath{\beta}}_{2}^{T}$), deformation length (${\ensuremath{\beta}}_{2}^{T}{R}^{T}$) and neutron excess ${(N\ensuremath{-}Z)}^{T}$ of the target. The present analysis indicates that the ICF fraction rises exponentially with ${\ensuremath{\beta}}_{2}^{T}$, ${\ensuremath{\beta}}_{2}^{T}{R}^{T}$, and ${(N\ensuremath{-}Z)}^{T}$. These results show that the ICF fraction follows a systematic exponential pattern rather than a simple linear growth with various entrance channel parameters reported in the literature. However, this study also suggests that the ICF dynamics is strongly influenced by the structure of projectile along with that of the target. Further, the role of deformation parameters on incomplete-fusion dynamics was also investigated through the method of universal fusion function. Analysis of the present data indicates that the experimental fusion functions are suppressed with different factors depending on deformation of the target nuclei. These suppressions are removed by including incomplete-fusion cross sections in the fusion function calculations. The average value of experimental fusion functions deviates from the universal fusion function for deformed targets. However, the average value of the total fusion function for deformed targets shifts towards the average value of the universal fusion function. The present study shows that the effect of target deformation plays an important role in affecting the ICF dynamics, along with various entrance channel parameters for different systems.

Fusion probability of massive nuclei in reactions leading to heavy composite nuclear systems

Reactions between massive nuclei show a considerable reduction in fusion-evaporation cross-sections at the Coulomb barrier according to the comparison of experimental values with those calculated by barrier passing (BP) and statistical model (SM) approximations. Reduced fusion cross-sections corresponding to fusion probability PCN<1 are accompanied by a high probability of deep-inelastic and quasi-fission processes arising on the way to fusion. At the same time, the excitation functions for evaporation residues (ERs) obtained in very mass-asymmetric projectile-target combinations are well described in the framework of the BP model (assuming PCN=1) and SM approximations. In the framework of SM, the survivability of produced heavy nuclei can be described with the use of adjusted macroscopic fission barriers. Fusion suppression appears in less asymmetric combinations, for which PCN values can be estimated using survivability obtained for very asymmetric ones leading to the same CN. An attempt was made to systemize the PCN data derived from different projectile-target combinations leading to ERs in the range from Pb to the most heavies, which are compared withPCN values obtained in fission experiments.

Insights into the low energy incomplete fusion

In the present work, channel-by-channel excitation functions of different evaporation residues populated via complete and/or incomplete fusion in C12+169Tm system have been measured for an energy range Elab≈53–90MeV, using recoil-catcher activation technique followed by off-line γ-spectroscopy. Experimentally measured excitation functions have been analysed in the framework of statistical model code pace. To probe the effect of entrance-channel parameters on the onset and strength of incomplete fusion, relative contributions of complete and incomplete fusion have been deduced from the analysis of experimentally measured excitation functions. The percentage fraction of incomplete fusion deduced from the analysis of excitation functions has been studied in terms of incident energy, entrance-channel mass-asymmetry, ground state alpha-Q-value, neutron skin thickness of target nuclei, and nuclear potential parameters. It has been found that incomplete fusion start competing with complete fusion even at slightly above barrier energies where complete fusion is assumed to the sole contributor. The probability of incomplete fusion increases with incident energy, entrance channel mass-asymmetry, large negative ground state alpha-Q-value, neutron skin thickness, and nuclear potential parameters for individual projectiles.

Deformation effects on sub-barrier fusion cross sections inO16+Yb174,176

Background: Couplings with various reaction channels are known to enhance sub-barrier fusion cross sections by several orders in magnitude. However, a few open questions still remain. For example, the influence of higher order static deformations on sub-barrier fusion cross sections is yet to be comprehensively understood.Purpose: We study the role of hexadecapole nuclear deformation effect on sub-barrier fusion cross sections. Also, this work aims to extract hexadecapole deformation $({\ensuremath{\beta}}_{4})$ in nuclei in the lanthanide region.Method: The evaporation residue (ER) excitation functions for $^{16}\mathrm{O}+^{\phantom{\rule{0.16em}{0ex}}174,176}\mathrm{Yb}$ were measured at laboratory beam energies $({E}_{\mathrm{lab}})$ in the range of 64.6--103.6 MeV. Measurements were carried out by employing the recoil mass spectrometer Heavy Ion Reaction Analyzer (HIRA) at IUAC, New Delhi. Fusion barrier distributions (BDs) were extracted from data. Results from the experiment were subjected to coupled-channels analysis, in which ${\ensuremath{\beta}}_{4}$ was varied as a free parameter.Results: Experimental fusion cross sections at energies below the barrier expectedly showed strong enhancement compared to the predictions from the one-dimensional barrier penetration model. Data were satisfactorily reproduced after inclusion of negative ${\ensuremath{\beta}}_{4}$ for both the targets in the coupled-channels calculation.Conclusions: The significant role of hexadecapole deformation was observed in the sub-barrier fusion of $^{16}\mathrm{O}+^{\phantom{\rule{0.16em}{0ex}}174,176}\mathrm{Yb}$. The proposed value of ${\ensuremath{\beta}}_{4}$ reproduced the measured fusion excitation function reasonably well. The BDs from these data were also extracted but no definitive conclusions could be drawn from them.

Evaporation residue excitation function measurements inTi50- andCr54-induced reactions with lanthanide targets

Evaporation residue excitation function measurements in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi mathvariant="normal">Ti</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>50</mml:mn></mml:mrow></mml:mmultiscripts></mml:math>- and<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi mathvariant="normal">Cr</mml:mi><mml:mprescripts /><mml:none /><mml:mrow><mml:mn>54</mml:mn></mml:mrow></mml:mmultiscripts></mml:math>-induced reactions with lanthanide targets

Fusion probability in heavy nuclei

Background: Fusion between two massive nuclei is a very complex process and is characterized by three stages: (a) capture inside the potential barrier, (b) formation of an equilibrated compound nucleus (CN), and (c) statistical decay of the CN leading to a cold evaporation residue (ER) or fission. The second stage is the least understood of the three and is the most crucial in predicting yield of superheavy elements (SHE) formed in complete fusion reactions.Purpose: A systematic study of average fusion probability, $\ensuremath{\langle}{P}_{\mathrm{CN}}\ensuremath{\rangle}$, is undertaken to obtain a better understanding of its dependence on various reaction parameters. The study may also help to clearly demarcate onset of non-CN fission (NCNF), which causes fusion probability, ${P}_{\mathrm{CN}}$, to deviate from unity.Method: ER excitation functions for 52 reactions leading to CN in the mass region 170--220, which are available in the literature, have been compared with statistical model (SM) calculations. Capture cross sections have been obtained from a coupled-channels code. In the SM, shell corrections in both the level density and the fission barrier have been included. $\ensuremath{\langle}{P}_{\mathrm{CN}}\ensuremath{\rangle}$ for these reactions has been extracted by comparing experimental and theoretical ER excitation functions in the energy range $\ensuremath{\sim}5$%--35% above the potential barrier, where known effects of nuclear structure are insignificant.Results: $\ensuremath{\langle}{P}_{\mathrm{CN}}\ensuremath{\rangle}$ has been shown to vary with entrance channel mass asymmetry, $\ensuremath{\eta}$ (or charge product, ${Z}_{p}{Z}_{t})$, as well as with fissility of the CN, ${\ensuremath{\chi}}_{\mathrm{CN}}$. No parameter has been found to be adequate as a single scaling variable to determine $\ensuremath{\langle}{P}_{\mathrm{CN}}\ensuremath{\rangle}$. Approximate boundaries have been obtained from where $\ensuremath{\langle}{P}_{\mathrm{CN}}\ensuremath{\rangle}$ starts deviating from unity.Conclusions: This study quite clearly reveals the limits of applicability of the SM in interpreting experimental observables from fusion reactions involving two massive nuclei. Deviation of $\ensuremath{\langle}{P}_{\mathrm{CN}}\ensuremath{\rangle}$ from unity marks the beginning of the domain of dynamical models of fusion. Availability of precise ER cross sections over a wider energy range for many more reactions is desired for accurate determination of $\ensuremath{\langle}{P}_{\mathrm{CN}}\ensuremath{\rangle}$ and more insight into the dynamics of fusion in the heavy mass region.

Recent results of measurements of evaporation residue excitation functions for19F+194,196,198Pt and16,18O+198Pt systems with HYRA spectrometer at IUAC

In this talk results of the evaporation residue (ER) cross sections for the 19 F+ 194,196,198 Pt (forming compound nuclei 213,215,217 Fr) and 16,18 O+ 198 Pt (forming compound nuclei 214,216 Rn) systems measured at Hybrid Recoil mass Analyzer (HYRA) spectrometer installed at the Pelletron+LINAC accelerator facility of the Inter University Accelerator Center (IUAC), New Delhi are reported. The survival probabilities of 215 Fr and 217 Fr with neutron numbers N = 126 are found to be lower than the survival probabilities of 215 Fr and 217 Fr with neutron numbers N = 128 and 130 respectively. Statistical model analysis of the ER cross sections show that an excitation energy dependent scaling factor of the finite-range rotating liquid drop model fission barrier is necessary to fit the experimental data. For the case of 214,216 Rn, the experimental ER cross sections are compared with the predictions from the statistical model calculations of compound nuclear decay where Kramer’s fission width is used. The strength of nuclear dissipation is treated as a free parameter in the calculations to fit the experimental data.

Production cross sections of elements near theN=126shell inCa48-induced reactions withGd154,Tb159,Dy162, andHo165targets

Excitation functions for shell-stabilized evaporation residues produced in $^{48}\mathrm{Ca}$-induced reactions with $^{154}\mathrm{Gd},^{159}\mathrm{Tb},^{162}\mathrm{Dy}$, and $^{165}\mathrm{Ho}$ targets have been measured in experiments performed at the Cyclotron Institute at Texas A University. The examined energy range predominantly covers the $3n$ and $4n$ evaporation channels with higher cross sections measured for the $4n$ products. The ${\ensuremath{\sigma}}_{4n}$ are nearly invariant within experimental uncertainty in reactions with $^{159}\mathrm{Tb},^{162}\mathrm{Dy}$, and $^{165}\mathrm{Ho}$ with the maxima at 12.6 \ifmmode\pm\else\textpm\fi{} 1.9, 12.6 \ifmmode\pm\else\textpm\fi{} 1.7, and 9.4 \ifmmode\pm\else\textpm\fi{} 1.3 mb, respectively. For the reaction with $^{154}\mathrm{Gd}$, the maximum is slightly lower at 4.0 \ifmmode\pm\else\textpm\fi{} 0.6 mb. A simple model to describe the measured production cross sections was employed. Capture was estimated by using the ``diffused barrier formula'' from the ``fusion by diffusion'' model proposed by \ifmmode \acute{S}\else \'{S}\fi{}wi\k{a}tecki et al. [Phys. Rev. C 71, 014602 (2005)]. The fusion probability was estimated by using a phenomenological expression presented by Siwek-Wilczy\ifmmode \acute{n}\else \'{n}\fi{}ska et al. [Int. J. Mod. Phys. E 17, 12 (2008)]. The survival probability was calculated according to the formula of Vandenbosch and Huizenga [Nuclear Fission (Academic, New York, 1973)], derived from transition-state theory. The best agreement is reached between calculation and experiment upon inclusion of collective effects in the calculation of the survival probability, shown previously to be important for production of weakly deformed nuclei. This, in turn, challenges the expectation that strong shell stabilization benefits the production cross section. The present data are compared with earlier studies on production of neutron-deficient nuclei in Ca-induced reactions with lanthanide targets.

Measurement of evaporation residue excitation functions for theF19+Pt194,196,198reactions

Experimental measurements of evaporation residue (ER) cross sections for the $^{19}F$ + $^{194,196,198}\mathrm{Pt}$ reactions forming $^{213,215,217}\mathrm{Fr}$ compound nuclei are reported. The cross sections are measured at beam energies in the range of 101--137.3 MeV. The survival probability of the $^{213}\mathrm{Fr}$ compound nucleus with neutron number $N=126$ is found to be lower than the survival probabilities of $^{215}\mathrm{Fr}$ and $^{217}\mathrm{Fr}$ with neutron numbers $N=128$ and 130 respectively. Statistical model analysis of the ER cross sections show that an excitation energy dependent scaling of the finite-range rotating liquid drop model fission barrier is necessary to fit the experimental data. The fitted scaling factors for $^{213}\mathrm{Fr}$ are found to be smaller than those of $^{215}\mathrm{Fr}$ and $^{217}\mathrm{Fr}$ for almost the entire range of excitation energies.

Effects of beam energy distribution on fusion-evaporation excitation functions

A numerical approach has been developed for the calculation of fusion-evaporation excitation functions taking into account the heavy ion beam energy distribution inside the target. The approach uses statistical model approximations of the HIVAP code for the calculations of evaporation residue excitation functions in the ordinary way and the Monte Carlo TRIM simulations for the determination of beam energy distributions inside the target. Several applications of the approach have been considered to evaluate the effect of the beam energy distributions inside the target on fusion-evaporation excitation functions calculated in the ordinary way.

Evaporation residue excitation function and spin distribution for31P + 170Er

Background: Synthesis of a doubly magic spherical nucleus beyond ${}_{82}^{208}$Pb${}_{126}$ is a key question in contemporary nuclear physics. Such nuclei can exist solely because of shell stabilization. As the formation cross section of super heavy elements is prohibitively low, attempts have been made to understand stabilizing effects of closed proton ($Z$) and neutron ($N$) shells in the vicinity of ${}_{82}^{208}$Pb${}_{126}$.Purpose: The present work attempts to elucidate the stabilizing effect of shell closure, in general, and the same of $Z=82$, in particular.Methods: The evaporation residue (ER) excitation function and ER-gated $\ensuremath{\gamma}$-multiplicity distribution have been measured for the reaction ${}^{31}$P + ${}^{170}$Er at a laboratory energy range of 134--172 MeV. The measurements have been carried out using the HYbrid Recoil mass Analyzer (HYRA) in gas-filled mode and a $4\ensuremath{\pi}$ spin spectrometer consisting of 29 NaI(Tl) detectors. Results of the present reaction have been compared with those of the reaction ${}^{30}$Si + ${}^{170}$Er. Statistical model calculation has been performed for both the systems.Results: The two reactions, induced by ${}^{30}$Si and ${}^{31}$P projectiles, resulted in compound nuclei (CN) ${}^{200}$Pb ($Z=82$) and ${}^{201}$Bi ($Z=83$), respectively. To reproduce experimental ER cross sections, the liquid drop fission barrier (${B}_{\mathrm{f}}$) had to be scaled in the statistical model calculation. The scaling factor (${K}_{\mathrm{f}}$) varies from $0.75$ to $1.05$ and $0.90$ to $1.05$ for ${}^{30}$Si and ${}^{31}$P induced reactions, respectively. No significant differences have been found between $\ensuremath{\gamma}$-multiplicity distribution and the distribution moments of the two systems.Conclusions: No clear signature has been observed in favor of extra stability of the ERs with closed proton shell ($Z=82$) as ${K}_{\mathrm{f}}$ values of the two systems match within errors. More exclusive measurements and comparison between more systems forming CN/ER around $Z=82$ are desirable.

Investigation of the48Ca + 249–252Cf reactions synthesizing isotopes of the superheavy element 118

The study of the $^{48}$Ca+$^{249,250,251,252}$Cf reactions in a wide energy interval around the external barrier has been achieved with the aim of investigating the dynamical effects of the entrance channel via the $^{48}$Ca induced reactions on the $^{249-252}$Cf targets and to analyze the influence of odd and even neutron composition in target on the capture, quasifission and fusion cross sections. Moreover, we also present the results of the individual evaporation residue excitation functions obtained from the de-excitation cascade of the various even-odd and even-even $^{297-300}$118 superheavy compound nuclei reached in the studied reactions, and we compare our results of the $^{294}$118 evaporation residue yields obtained in the synthesis process of the $^{48}$Ca+$^{249,250}$Cf reactions with the experimental data obtained in the $^{48}$Ca+$^{249}$Cf experiment carried out at the Flerov Laboratory of Nuclear Reactions of Dubna.