Incomplete Fusion Fraction Research Articles

Study of incomplete fusion reaction dynamics for the system 14N + 169Tm using the forward Recoil Range distribution technique

Studies in the past have demonstrated that complete fusion and incomplete fusion (ICF) dynamics are both significant just above the Coulomb barrier, yet the dynamics of ICF are elusive since they are so complex below 10 MeV/nucleon. In order to investigate low-energy ICF dynamics, we measured the forward recoil range distribution (FRRD) of evaporation residues (ERs) populated in the system 14N + 169Tm at energy ≈5.9 MeV/nucleon. A stack target-catcher activation technique followed by offline-γ-spectroscopy was used to estimate the FRRD of the ERs. In order to investigate a new parameter for describing ICF dynamics, the ICF fraction (F ICF(%)) for the present system was estimated from the range-integrated cross-sections and compared with other systems in the literature. The FRRD and range integrated cross-sections of seven ERs have been estimated experimentally. These cross-section results agree well with the experimental results obtained from the excitation functions. On re-investigation of entrance channel systematics for Q α -value of projectile, mass-asymmetry (μ MA), and Coulomb factor (Z P Z T), it has been found that the Q α -value systematic for 14N is not valid at all projectile energies. The FRRD measurement is one of the direct methods available to probe the complete and ICF contributions in ERs at low projectile energy. It has also been observed that the dynamics of ICF are not only dependent on the parameters of one entrance channel but on multiple entrance channels. We have also introduced the entrance channel parameter zeta (ζ) for the first time in ICF reactions to see the combined effect of mass-asymmetry (μ MA) and Z P Z T, as this parameter is better suited than μ MA and Z P Z T individually and has a linear dependency on F ICF(%).

Role of the entrance channel in the experimental study of incomplete fusion of 13 C with 93 Nb

We report measured cross-section data of the residues produced in the $^{13}\mathrm{C}$-induced reaction on $^{93}\mathrm{Nb}$ within the 63.7--87.1-MeV energy range. The off-line $\ensuremath{\gamma}$-ray spectroscopy method has been used to measure the cross sections of the radionuclides produced in this system. The analysis of present measured cross-section data has been carried out within the light of well-established statistical model code pace4. The excitation function of residues populated via $xn$ and/or $pxn$ channels are found to be in fair agreement with those estimated by the theoretical model code, which confirms the assembly of these residues via complete fusion process. A considerable enhancement in the measured cross-section data has been observed for the residues involving $\ensuremath{\alpha}$-emitting channels as compared to the theoretical predictions. The observed enhancement in the cross sections has been assigned to the incomplete fusion processes. Furthermore, in order to have a better insight into the onset and strength of incomplete fusion, termed as the incomplete fusion fraction has been deduced for the present paper and is compared with $^{16}\mathrm{O}$ and $^{18}\mathrm{O}$ beams on the same target $^{93}\mathrm{Nb}$. This suggests that the incomplete fusion fraction is strongly influenced by the entrance channel, which may be understood in terms of the projectile ${Q}_{\ensuremath{\alpha}}$ value. The comparison of this paper with literature data also shows that the incomplete fusion probability increases with various entrance channel parameters, such as projectile structure, projectile energy, and mass asymmetry of interacting partners.

Mass-number dependence of statistical model parameters and its impact on incomplete fusion fraction calculations

Incomplete fusion processes and estimation of strength of incomplete fusion in heavy ion induced nuclear reactions have been explored for several combinations of projectile-target nuclei. Dynamics of these reactions is explained using an optical model. Parameters of the optical model affect the shape and depth of nuclear potential and hence influence the theoretical predictions. For heavy ion induced reactions, the optical model potential parameters are not unique and different sets of these parameters may be used for different ranges of mass number $A$ and incident energy $E$. To explore the effect of optical model potential parameters, a comparative study of available experimental data for excitation functions of four systems, $^{16}\mathrm{O}+^{181}\mathrm{Ta}, ^{12}\mathrm{C}+^{165}\mathrm{Ho}, ^{14}\mathrm{N}+^{163}\mathrm{Dy}$, and $^{16}\mathrm{O}+^{74}\mathrm{Ge}$, with corresponding theoretically predicted excitation functions, made by PACE4 using different sets of optical model potential parameters, has been done. It has been observed that a single set of optical model potential parameters is not adequate for all the systems. The variations in these parameters change the theoretical cross-section predictions for various channels considerably, which in turn, change the correspondingly estimated fraction of incomplete fusion $({F}_{\mathrm{ICF}})$. The effect of deformation of target nuclei on fractional incomplete fusion has also been investigated for the above mentioned systems. ${F}_{\mathrm{ICF}}$ has been plotted as a function of deformation parameter $({\ensuremath{\beta}}_{2})$ of the target nuclei and it is found to increase as the deformation parameter of the corresponding target nuclei increases on either side of the intrinsic spherical symmetry.

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.

Examination of break-up fusion in the O16+Nd148 system through measurements of forward recoil range distributions and angular distributions

The forward recoil range distributions and angular distributions of several evaporation residues produced via complete and incomplete fusion (ICF) dynamics in $^{16}\mathrm{O}+^{148}\mathrm{Nd}$ system at energy $\ensuremath{\approx}6$ MeV/nucleon were measured. The measured forward recoil range distributions of various reaction products show the presence of incomplete fusion components apart from complete fusion. Full and partial linear momentum transfer components of reaction products were found in the interaction of $^{16}\mathrm{O}$ with $^{148}\mathrm{Nd}$. These results were also confirmed by the measurements of angular distributions of evaporation residues. The measured angular distributions of the evaporation residues populated through complete and incomplete fusion channels were found to be distinctly different. The evaporation residues populated via complete fusion channels were trapped in the narrow angular zone as compared to incomplete fusion channels. A systematic study of the dependence of incomplete fusion dynamics on well-known entrance channel parameters shows that the incomplete fusion fraction grows exponentially with mass asymmetry $({\ensuremath{\mu}}_{EC}^{AS})$, Coulomb factor $({Z}_{P}{Z}_{T})$ and $\ensuremath{\alpha}\ensuremath{-}Q$ value of the projectile. The present observations suggest an exponential rise of ICF fraction with entrance channel parameters in contrast with the linear pattern reported in some earlier measurements. Further, the correlation of incomplete fusion fraction with the structure of target (T) was investigated employing four different parameters viz. deformation parameter $({\ensuremath{\beta}}_{2}^{T})$, interaction radius $({R}^{T})$, deformation length $({\ensuremath{\beta}}_{2}^{T}{R}^{T})$ and excess of neutrons ${(N\ensuremath{-}Z)}^{T}$ in the target. In the present study, the ICF fraction was found to rise exponentially with these parameters, independently for different projectiles. The three parameters ${\ensuremath{\beta}}_{2}^{T}, {\ensuremath{\beta}}_{2}^{T}{R}^{T}$, and ${(N\ensuremath{-}Z)}^{T}$ were found more sensitive and effective to investigate the entire picture about the influence of projectile and target deformation along with their relative orientations on incomplete fusion dynamics at low projectile energy. Moreover, the interaction radius of target $({R}^{T})$ is suitable to explain the characteristics of ICF dynamics in the spherical-spherical collisions. These present results show that incomplete fusion dynamics is strongly affected by the structure of projectile along with the target.

Investigating entrance channel influences in the fusion of some heavy–ion systems

The dynamics of heavy-ion fusion reaction involved in the interaction of 12C,14N and 16O projectiles with,59Co, 51V,128Te and165Ho targets at≈3-8MeV/nucleon specific energies was studied. This study focus on the correlation between entrance channel properties and incomplete fusion reaction. The experimentally measured excitation functions of various reaction products populated by complete and/or incomplete fusions of 12C+59Co, 128Te,14N+128Teand 16O+ 51V, 165Hoprojectile-target systems available in the literature. Were compared and analyzed with the predicted excitation functions, using the statistical model code PACE4. For representative non-α-emitting channels, the experimentally measured excitation functions were, in general, found to be in good agreement with the theoretical predictions. However, for α-emitting channels in the present systems, the measured excitation functions were higher than the predictions of the theoretical model code, which may be credited to incomplete fusion reactions at these energies. An attempt was made to approximate the incomplete fusion fraction that explains the relative importance of incomplete fusion processes. The incomplete fusion fraction was found to be sensitive to the projectile energy and mass-asymmetry of the entrance channel

Investigating the Influence of Incomplete Fusion on Complete Fusion of 16 O –Induced Reaction ≈ 3-8 MeV/nucleon

The dynamics of heavy-ion fusion reaction elaborate in the interaction of 1616O "> projectiles with 16165Ho "> and 51 V targets at ≈3-8MeV/nucleon specific energies were studied. This study were emphases on the relationship between entrance channel belongings and incomplete fusion reaction. The experimentally measured excitation functions of various reaction products duplicated by complete or incomplete fusions of 1616O "> + 1651V"> , 16165Ho "> projectile-target systems had been compared and analyzed within the predicted excitation functions, using the statistical model code PACE4. For α-emitting channels in the present systems, the measured excitation functions had been highest than the predictions of the theoretical model code, which may focuses at these energies. However for non-alpha emitting channels in this system the measured excitation function had been nice agreement with the theoretical values. An endeavor were made to nearly the incomplete fusion fraction that designates importance of incomplete fusion process. Keywords: Alpha emitted, CF reaction, Entrance channel, Heavy ion fusion, ICF reaction, Non alpha emitted DOI : 10.7176/APTA/79-03 Publication date :September 30 th 2019

Investigation of breakup fusion in 16O + 124Sn system and its correlation with various entrance channel parameters

Forward recoil range distribution of evaporation residues (ERs) populated through complete fusion (CF) and incomplete fusion (ICF) dynamics in [Formula: see text]O + [Formula: see text]Sn system have been measured. Different full and partial linear momentum transfer components have been observed. The results indicate the occurrence of ICF involving break-up of [Formula: see text]O into 4He + [Formula: see text]C and 8Be + 8Be. However, the present data shows that the ERs are populated through both CF and ICF. A systematic study was performed which shows that the ICF fraction rises exponentially with the established entrance channel parameters and their various combinations. Moreover, these present results clearly show that [Formula: see text] is able to explain the ICF dynamics more conclusively than combined parameter [Formula: see text] for the systems having spherical or slightly deformed target. Further, the dependence of ICF dynamics on target structure has also been studied through a new parameter [Formula: see text] of the target. The parameter [Formula: see text] is directly associated with the target structure and has been found more effective and sensitive than existing parameters to investigate the target structure effect on ICF dynamics. Thus, the present observations suggest that [Formula: see text] ratio of the target should also be considered as an important entrance channel parameter which strongly affects the ICF dynamics.

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 incomplete-fusion dynamics below 8 MeV/nucleon energy

An attempt has been made to provide crucial information about the dependence of incomplete-fusion dynamics on various entrance channel parameters below 8 MeV/nucleon energy. The forward recoil range distributions of several evaporation residues produced in the $^{13}\mathrm{C}+^{175}\mathrm{Lu}$ system have been measured at $\ensuremath{\approx}88$-MeV energy and examined in the framework of the code SRIM. Owing to the fractional linear momentum transfer from the projectile to the target nucleus, incomplete-fusion (ICF) products are observed to be trapped at lower cumulative thickness than that of complete fusion products. In order to study the incomplete-fusion behavior with various entrance channel parameters, the incomplete-fusion fraction (${F}_{\mathrm{ICF}}$) has also been deduced and compared with those obtained for the systems available in the literature. The reinvestigation of the Coulomb factor $({Z}_{P}{Z}_{T})$ dependence of incomplete fusion indicates that it is somehow projectile structure dependent. No systematic trend is observed with the target deformation parameter $({\ensuremath{\beta}}_{2})$ dependent study of ICF. A systematic linear growth in the incomplete-fusion probability function (${F}_{\mathrm{ICF}}$) is observed with increasing the parameters ${Z}_{P}{Z}_{T}{\ensuremath{\beta}}_{2}$ and ${Z}_{P}{Z}_{T}/(1\ensuremath{-}{\ensuremath{\beta}}_{2})$, but separately for $\ensuremath{\alpha}$- and non-$\ensuremath{\alpha}$-cluster structured projectiles with different targets. The present findings explore the role of Coulomb interaction on ICF dynamics more effectively. Moreover, the projectile $\ensuremath{\alpha}\ensuremath{-}Q$ value is found to be a suitable parameter which explains effectively the observed trend in the study of ICF with the above-mentioned parameters. The incomplete-fusion existence below critical angular momentum (${\ensuremath{\ell}}_{\mathrm{crit}}$), i.e., $\ensuremath{\ell}\phantom{\rule{0.16em}{0ex}}\ensuremath{\le}\phantom{\rule{0.16em}{0ex}}{\ensuremath{\ell}}_{\mathrm{crit}}$, is also observed for the present $^{13}\mathrm{C}+^{175}\mathrm{Lu}$ system.

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.

Probing of incomplete fusion dynamics and its correlation with various systematic

The study of complete and incomplete fusion dynamics in Ne20+59Co system at projectile energies ≈62–150 MeV using recoil-catcher activation technique followed by offline gamma-ray spectroscopy has been done. The excitation functions for the evaporation residues produced in the reaction channels 63Zn(3αp3n), 62Zn(3αp4n) and 60Cu(4α3n) have been measured. The excitation functions for these evaporation residues have been compared with theoretical predictions based on code PACE-2. The observed enhancements in the measured cross-sections over their theoretical predictions for the α-emitting channels indicate the presence of incomplete fusion. The incomplete fusion fraction (FICF) has also been deduced and compared with those obtained for few earlier measurements. It has been observed that the incomplete fusion contributes significantly along with complete fusion even at lower projectile energies and it increases with increasing the projectile energies. Mass-asymmetry systematic is found to be projectile structure dependent rather than a simple linear growth with increasing the mass-asymmetry between interacting partners. Further, the deformation of the target is also found to affect the incomplete fusion dynamics. The present results show that the incomplete fusion dynamics does not depend completely on a single entrance channel parameter, but it also depends on multi entrance channel parameters namely; entrance channel mass-asymmetry, α-Q-value of the projectile, Coulomb factor (ZPZT) and deformation of the target or deformation parameter (β2). All these parameters are found to play an important role in the dynamics of incomplete fusion.

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.

Low-energy nuclear reaction of the N14+Tm169 system: Incomplete fusion

Excitation functions of reaction residues produced in the $^{14}\mathrm{N}+^{169}\mathrm{Tm}$ system have been measured to high precision at energies above the fusion barrier, ranging from $1.04{V}_{B}$ to $1.30{V}_{B}$, and analyzed in the framework of the statistical model code pace4. Analysis of $\ensuremath{\alpha}$-emitting channels points toward the onset of incomplete fusion even at slightly above-barrier energies where complete fusion is supposed to be one of the dominant processes. The onset and strength of incomplete fusion have been deduced and studied in terms of various entrance channel parameters. Present results together with the reanalysis of existing data for various projectile-target combinations conclusively suggest strong influence of projectile structure on the onset of incomplete fusion. Also, a strong dependence on the Coulomb effect $({Z}_{P}{Z}_{T})$ has been observed for the present system along with different projectile-target combinations available in the literature. It is concluded that the fraction of incomplete fusion linearly increases with ${Z}_{P}{Z}_{T}$ and is found to be more for larger ${Z}_{P}{Z}_{T}$ values, indicating significantly important linear systematics.

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).

Incomplete fusion analysis of the Li7 -induced reaction on Nb93 within 3–6.5 MeV/nucleon

It is understood from the recent experimental studies that prompt/resonant breakup, and transfer followed by breakup in the weakly bound $^{6,7}$Li-induced reactions play a significant role in the complete-incomplete fusion (CF-ICF), suppression/enhancement in the fusion cross section around the Coulomb barrier. Investigation of ICF over CF was done by measuring cross sections of the populated residues in the $^{7}$Li-induced reaction on $^{\text{nat}}$Nb target within 3--6.5 MeV/nucleon energy region. Measured excitation functions of different channels were compared with different equilibrium (EQ) and preequilibrium (PEQ) models. The enhancement in cross sections in the proton ($\sim$ 20--30 MeV) and $\alpha$-emitting channels, which may be ascribed to ICF, was observed in the measured energy range when compared to the Hauser-Feshbach and exciton model calculations using EMPIRE, which satisfactorily reproduces the neutron channels, compared to the Weisskopf-Ewing model and Hybrid Monte Carlo calculations. The increment of the incomplete fusion fraction was observed with rising projectile energy.

Li7 -induced reaction on Monat : A study of complete versus incomplete fusion

Several investigations on the complete-incomplete fusion (CF-ICF) dynamics of $\alpha$-cluster well-bound nuclei has been contemplated above the Coulomb barrier ($\sim$ 4-7 MeV/nucleon) in recent years. It is therefore expected to observe significant ICF over CF in the reactions induced by a weakly bound $\alpha$-cluster nucleus at slightly above the barrier. In order to investigate CF-ICF in the loosely bound system, $^{\text{7}}$Li beam was bombarded on the $^{\text{nat}}$Mo foils, separated by the aluminium (Al) catcher foils alternatively, within $\sim$ 3-6.5 MeV/nucleon. Evaporation residues produced in each foil were identified by the $\gamma$-ray spectrometry. Measured cross section data of the residues were compared with the theoretical model calculations based on the equilibrium (EQ) and preequilibrium (PEQ) reaction mechanisms. The experimental cross section of $^{\text{101m,100,99m,97}}$Rh, $^{\text{97,95}}$Ru, $^{\text{99m,96,95,94,93m+g}}$Tc and $^{\text{93m}}$Mo residues measured at various projectile energies were satisfactorily reproduced by the simplified coupled channel approach in comparison to single barrier penetration model calculation. Significant cross section enhancement in the $\alpha$-emitting channels was observed compared to EQ and PEQ model calculations throughout observed energy region. The ICF process over CF was analyzed by comparing with EMPIRE. The increment of the incomplete fusion fraction was observed with increasing projectile energies. Theoretical model calculations reveal that compound reaction mechanism is the major contributor to the production of residues. Theoretical evaluations substantiate the contribution of ICF over the CF in $\alpha$-emitting channels.

Incomplete fusion studies in theF19+Tb159system at low energies and its correlation with various systematics

The excitation functions of reaction residues populated via the complete fusion and incomplete fusion process in the interaction of the $^{19}\mathrm{F}+^{159}\mathrm{Tb}$ system have been measured at energies $\ensuremath{\approx}4--6$ MeV/nucleon, using off-line $\ensuremath{\gamma}$-ray spectroscopy. The analysis of data was done within the framework of statistical model code pace4 (a compound nucleus model). A significant fraction of incomplete fusion was observed in the production of reaction residues involving $\ensuremath{\alpha}$ particle(s) in the exit channels, even at energies as low as near the Coulomb barrier. The incomplete fusion strength function was deduced from the experimental excitation functions and the dependence of this strength function on various entrance channel parameters was studied. The present results show a strong dependence on the projectile $\ensuremath{\alpha}$-Q value that agrees well with the existing data. To probe the dependence of incomplete fusion on entrance channel mass asymmetry, the present work was compared with the results obtained in the interaction of $^{12}\mathrm{C}, ^{16}\mathrm{O}$, and $^{19}\mathrm{F}$ with nearby targets available in the literature. It was observed that the mass asymmetry linearly increases for each projectile separately and turns out to be a projectile-dependent mass-asymmetry systematics. The deduced incomplete fusion strength functions in the present work are also plotted as a function of ${Z}_{P}{Z}_{T}$ (Coulomb effect) and compared with the existing literature. A strong dependence of the Coulomb effect on the incomplete fusion fraction was observed. It was found that the fraction of incomplete fusion linearly increases with ${Z}_{P}{Z}_{T}$ and was found to be more for larger ${Z}_{P}{Z}_{T}$ values indicating significantly important linear systematics.

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.

Reconciliation of mass-asymmetry systematics for incomplete fusion

The onset and strength of incomplete fusion (ICF) has been studied in the framework of Morgenstern's mass-asymmetry systematics. The fraction of ICF has been deduced in 12C+169Tm system at energies ranging from 1.02Vb to 1.64Vb (Vb = 54.94 MeV from the analysis of excitation functions (EFs). It has been found that the ICF starts influencing complete fusion at noticeably lower, β-values (i.e., 0.025 or 2. 5% of c) than that proposed by Morgenstern (i.e., ≈ 6% of c). The fraction of ICF increases with entrance channel mass-asymmetry for individual projectiles, termed as projectile dependent mass-asymmetry (ProMass-) systematics. The proposed ProMass- systematics has withstood all tests that have been done for fairly large number of systems to verify its validness.