Low Energy Incomplete Fusion Research Articles

A Systematic Study: Some Insights into the Low-energy Incomplete Fusion Reactions

A Systematic Study: Some Insights into the Low-energy Incomplete Fusion Reactions

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.

Low Energy Incomplete Fusion Reactions: Probing of Entrance Channel Effect

Low Energy Incomplete Fusion Reactions: Probing of Entrance Channel Effect

Probing of incomplete fusion dynamics in $${}^{{14}}\text {N} + {}^{{124}}\text {Sn}$$ system and its correlation with various entrance channel effects

Measurements of excitation functions were done for the evaporation residues populated in $${}^{{14}}\text {N}+{}^{{124}}\text {Sn}$$ system at low energy. The present analysis shows the appearance of incomplete fusion by the breakup of non- $$\upalpha $$ cluster structured projectile $$^{{14}}\text {N}$$ into $$\upalpha + {}^{{10}}\text {B}$$ . A correlation between the combined effects of total asymmetry and $$\text {Z}_{\mathrm {P}}\text {Z}_{\mathrm {T}}$$ has been studied through three new parameters total asymmetry ( $$S_{{ TAS}}$$ ), Coulomb asymmetry parameters; $$Z_{P} Z_{T} /S_{{ TAS}} $$ and $$Z_{P} Z_{T} .S_{{ TAS}} $$ . These new parameters were found more sensitive and effective to encounter the combined effects of coulomb interactions and entire asymmetry effect of the system on incomplete fusion dynamics. The complete fusion and total fusion cross-sections of two systems $${}^{{14}}\text {N}+{}^{{124}}\text {Sn}$$ and $${}^{{16}}\text {O}+{}^{124}\text {Sn}$$ have been reduced using two different standard reduction procedures, which shows that the incomplete fusion probability for reactions induced by projectile $${}^{{16}}\text {O}$$ is generally larger than $${}^{{14}}\text {N}$$ induced reactions. The experimental fusion functions are found to be suppressed as compared to universal fusion function for systems $${}^{{14}}\text {N}+{}^{{124}}\text {Sn}$$ and $${}^{{16}}\text {O}+{}^{{124}}\text {Sn}$$ . The different values of suppression factor for projectiles $${}^{{14}}\text {N}$$ and $${}^{{16}}\text {O}$$ indicate that the probability of $$\upalpha $$ -breakup is different for these projectiles. Further, the total fusion functions for systems $${}^{{14}}\text {N}+{}^{{124}}\text {Sn}$$ and $${}^{{16}}\text {O}+{}^{{124}}\text {Sn}$$ agree well with the universal fusion function. However, the present results clearly show that the shell closure of nuclei also affect the low energy incomplete fusion dynamics along with the structure of projectile.

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.

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.

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.

Investigation of Incomplete Fusion events: Recent Results

The dynamics of incomplete fusion processes has been extensively investigated and is found to compete with complete fusion at low incident energies (i.e. ≤ 7.0 MeV/A). Recent reports suggest that the probability of incomplete fusion depends on Qα of the projectile, and found to be originated from the high input angular momentum provided into the system due to non-central collisions. Apart from the well documented existence of low energy incomplete fusion, a strong contradiction on previously established mass-asymmetry systematics has been noticed recently. It has been found that the incomplete fusion fraction increases with entrance channel mass-asymmetry for the individual projectiles. Further, a strong dependence of incomplete fusion on the Coulomb effect (ZP ZT ) has been observed and is found to increase linearly with ZP ZT, a significantly important approach to understand the breakup fusion reactions. For better insights into the onset and strength of incomplete fusion in terms of various entrance channel parameters and to understand the role of high angular momenta in the onset of incomplete fusion, a quality data have been obtained in a variety of experiments performed at the Inter-University Accelerator Center (IUAC), New Delhi, India. Some of the recent results are presented in this paper, conclusively demonstrating the effect of entrance channel parameters on the onset and strength of incomplete fusion, and the usefulness of incomplete fusion to populate high-spin states in final reaction products.

Systematic study of low-energy incomplete fusion: Role of entrance channel parameters

An attempt has been made to investigate the role of various entrance channel parameters in low-energy ($\ensuremath{\approx}4\text{--}7$ MeV/nucleon) incomplete fusion reactions through excitation function measurements. The analysis of measured excitation functions, in the framework of statistical model code pace4, reveals that the $xn$/$pxn$ channels are populated, predominantly, via complete fusion processes. However, in the production of $\ensuremath{\alpha}$-emitting channels, even after correcting for the precursor decay contribution, a significant enhancement as compared to statistical model predictions has been observed, which may be attributed due to the contribution of breakup processes. The observed enhancement is found to increase with projectile energy. Further, the comparison of present work with literature data reveals the dependence of incomplete fusion on mass-asymmetry of interacting partners, $\ensuremath{\alpha}\text{\ensuremath{-}}Q$ value of the projectile, and also on ${Z}_{P}{Z}_{T}$ (the Coulomb factor). From the present analysis, it may be concluded that a single entrance channel parameter (i.e., mass asymmetry or ${Z}_{P}{Z}_{T}$ or $\ensuremath{\alpha}\text{\ensuremath{-}}Q$ value) is not able to explain, completely, the yields of the low-energy incomplete fusion component. Therefore, a combination of these parameters and/or a parameter which can incorporate all gross features of interacting partners should be chosen to get a systematics for such reactions.

Systematics for low energy incomplete fusion: Still a puzzle?

In order to have a better and clear picture of incomplete fusion reactions at energies ≈4-7MeV/nucleon, the excitation function measurements have been performed for 18 O+ 159 Tb system. The experimental data have been analyzed within the framework of compound nucleus decay. The cross-section for xn /p xn -channels are found to be well reproduced by PACE4 predictions, which suggest their production via complete fusion process. However, a significant enhancement in the excitation functions of α -emitting channels has been observed over the theoretical ones, which has been attributed due to the incomplete fusion processes. The incomplete fusion fractions have been deduced at each studied energy and compared with other nearby systems for better insight into the underlying dynamics. The incomplete fusion fraction has been found to be sensitive to the projectile’s energy and α -Q-value.

Low energy incomplete fusion and its relevance to the synthesis of super heavy elements

To study the presence of incomplete fusion at energies around the Coulomb-barrier and to understand its dependence on various entrance-channel parameters, the incomplete fusion fractions have been deduced (i ) from excitation function measurements for 18 O,13,12 C+159 Tb, and (ii ) from forward recoil range measurements for 12 C+159 Tb systems, at low energies ( /pxn -channels via complete fusion, as these are found to be well reproduced by PACE4 predictions, while, a significant enhancement in the excitation functions of α -emitting channels has been observed over the theoretical ones, which has been attributed due to the incomplete fusion processes. Further, the incomplete fusion events observed in case of forward recoil ranges have been explained on the basis of the breakup fusion model, where these events may be attributed to the fusion of 8 Be and/or 4 He from 12 C projectile to the target nucleus. For better insight into the underlying dynamics, the deduced fractions of incomplete fusion have been compared with other nearby systems as a function of various entrance channel parameters. The incomplete fusion has been found to be sensitive to the projectile’s energy and alpha-Q-value of the projectile.

Projectile - Mass asymmetry systematics for low energy incomplete fusion

In the present work, low energy incomplete fusion (ICF) in which only a part of projectile fuses with target nucleus has been investigated in terms of various entrance channel parameters. The ICF strength function has been extracted from the analysis of experimental excitation functions (EFs) measured for different projectile-target combinations from near- to well above- barrier energies in 12 C,16 O(from 1.02Vb to 1.64Vb )+169 Tm systems. Experimental EFs have been analysed in the framework statistical model code PACE4 based on the idea of equilibrated compound nucleus decay. It has been found that the value of ICF fraction (FICF ) increases with incident projectile energy. A substantial fraction of ICF (FICF ≈ 7 %) has been accounted even at energy as low as ≈ 7.5% above the barrier (at relative velocity ν rel ≈0.027) in 12 C+169 Tm system, and FICF ≈ 10 % at ν rel ≈0.014 in 16 O+169 Tm system. The probability of ICF is discussed in light of the Morgenstern’s mass-asymmetry systematics. The value of FICF for 16 O+169 Tm systems is found to be 18.3 % higher than that observed for 12 C+169 Tm systems. Present results together with the re-analysis of existing data for nearby systems conclusively demonstrate strong competition of ICF with CF even at slightly above barrier energies, and strong projectile dependence that seems to supplement the Morgenstern’s systematics.

Low Energy Incomplete Fusion and the Role of Input Angular Momenta

Low Energy Incomplete Fusion and the Role of Input Angular Momenta

Dependence of low energy incomplete fusion on projectile’sα-Q-value

An attempt has been made to understand the effect of entrance-channel parameters on low-energy incomplete fusion and a strong projectile dependence in terms of projectile's α-Q-value has been observed. In the present work, the excitation functions of 16 O, 13,12 C+ 159 Tb systems have been measured and compared with PACE4 predictions to study the involvement of different reaction processes. The strength of incomplete fusion reactions for all the studied systems have been extraced and compared to find out the systematics.

Low energy incomplete fusion: Observation of a significant incomplete fusion fraction atℓ< ℓcrit

To study the low energy incomplete fusion, excitation functions have been measured in the 16O + 165 Ho system using a well-established activation technique. The analysis of the present work has been carried out in the frame work of the statistical model code PACE4. The results show that the yields of complete fusion channels agree well with the theoretical predictions of the model code PACE4. However, α-emitting channels have a significant incomplete fusion fraction even at ℓ < ℓcrit

Influence of a one-neutron-excess projectile on low-energy incomplete fusion

Background: Incomplete fusion has been found to be an important contributor in light heavy-ion ($A\ensuremath{\le}20$) induced reactions even at slightly above barrier energies.Purpose: For better insight into the dynamics of incomplete fusion, the onset and influence of incomplete fusion need to be investigated in terms of projectile energy (${E}_{\mathrm{lab}}$) and entrance channel mass-asymmetry (${\ensuremath{\mu}}_{A}$). A rich set of experimental data on incomplete fusion may be useful to correlate the probability of incomplete fusion with the various entrance channel parameters and eventually to develop a theoretical model code for the same. Presently, there is no theoretical model available which can explain low-energy incomplete fusion data consistently.Methods: The excitation functions of complete and incomplete fusion residues populated in the $^{13}C$+$^{169}\mathrm{Tm}$ system have been measured using the recoil-catcher activation technique followed by offline $\ensuremath{\gamma}$ spectroscopy. The evaporation residues have been identified on the basis of characteristic $\ensuremath{\gamma}$ lines and confirmed through the decay-curve analysis.Results: The excitation functions of $xn$ and $pxn$ channels are found to be in good agreement with the statistical model code pace4; this suggests the population of these channels via complete fusion. Some residues are found to have a contribution from their higher charge isobar precursor decay. The precursor contribution has been deduced from the cumulative cross section using the standard successive radioactive decay formulations. The excitation functions of $\ensuremath{\alpha}$-emitting channels are observed to be significantly enhanced as compared to the statistical model code pace4. This enhancement may be attributed to the contribution from incomplete fusion. The incomplete fusion strength function for $^{13}C$+$^{169}\mathrm{Tm}$ is compared with that obtained in the $^{12}C$+$^{169}\mathrm{Tm}$ system. It has been found that the one-neutron (1$n$) excess projectile $^{13}C$ (as compared to $^{12}C$) results in a less incomplete fusion contribution due to its relatively large negative alpha-$Q$ value. Recently proposed ``alpha-$Q$-value systematics'' seems to explain incomplete fusion data.

Low-energy incomplete fusion and its sensitivity to projectile structure

To study the heavy-ion-induced reactions, particularly complete and incomplete fusion, the excitation functions for ${}^{16}$O$+{}^{165}$Ho interactions at energies $\ensuremath{\approx}$73--105 MeV have been measured using a well-established activation technique. The excitation functions have been compared with the predictions of the statistical model code pace4. The comparison advises that the formation of $xn$ and $pxn$ channels is governed only via complete fusion processes. Even after correction for precursor contribution, a significant enhancement in the production of $\ensuremath{\alpha}$-emitting channels may be attributed to incomplete fusion contribution. Furthermore, in order to understand incomplete fusion reactions in a more conclusive way, the incomplete fusion fraction has been analyzed with the existing data for ${}^{12}$C and ${}^{20}$Ne beams on the same target (${}^{165}$Ho) where a strong projectile structure effect has been observed, which correlates incomplete fusion reaction dynamics with the $\ensuremath{\alpha}$-$Q$ value of the projectile.

Large influence of incomplete fusion in12C+159Tb atElab≈4–7 MeV/nucleon

Low energy incomplete fusion has been studied in ${}^{12}$C+${}^{159}$Tb system at energies $\ensuremath{\approx}$ 4--7 MeV/nucleon. The excitation functions of individual reaction channels have been measured using off-line $\ensuremath{\gamma}$ spectroscopy, and analyzed in the framework of statistical model code pace4 based on the concept of equilibrated compound nucleus decay. A significant fraction of incomplete fusion has been found in the production of residues involving $\ensuremath{\alpha}$ particle(s) in the exit channels. For better insights into the onset and strength of incomplete fusion, the incomplete fusion strength function has been deduced as a function of various entrance channel parameters. Large influence of incomplete fusion has been observed at slightly above barrier energies, and increases smoothly with incident projectile energy. Present results have been compared with the results obtained in the interactions of ${}^{12}$C with nearby targets to probe the dependence of incomplete fusion on entrance channel mass asymmetry. It has been found that the percentage fraction of incomplete fusion increases linearly with mass asymmetry of interacting partners in the studied mass region.