Code PACE4 Research Articles

Systematic study of fusion suppression and its dependency on projectile breakup threshold energy

Measurements of the excitation function (EF) of the observed evaporation residues (ERs) populated in the 20Ne + 93Nb reaction at E lab ≈ 91−145 MeV are carried out to explore the systematic of fusion suppression and its dependency on projectile breakup threshold energy, by employing the offline γ-ray detection method. The EF of the observed ERs populated through complete and/or incomplete fusion processes are analysed in the framework of statistical mode code PACE4. The fusion function, derived from the experimentally measured fusion cross section data, is compared with the universal fusion function (UFF) to estimate the degree of fusion incompleteness. Based on the observed results, an empirical formula is proposed to interrelate the degree of fusion suppression and breakup threshold energy of the incident projectile.

Investigating the influence of input angular momentum on independence hypothesis in heavy-ion induced fusion reactions

The experimental verification of compound nucleus theory has successfully been performed for light ion induced reactions using proton and α-particle beams on different targets. However, such studies using the heavy ion beams are scarce due to the complex nature of heavy ion interaction process. The present work is an attempt to validate the Bohr's independent hypothesis using heavy ion beam of 18O beam on 159Tb targets and 12C on 165Ho targets, forming the same compound nucleus 177Ta. A channel wise analysis of cross section data for evaporation residues produced in 18O+159Tb and 12C+165Ho systems has been performed within the framework of statistical model code PACE4 and found to reasonably agree with the experimental data. Further, a comparison of reaction cross section data for the same evaporation residues produced in the two different systems has been found to follow Bohr's compound nucleus hypothesis at relatively higher excitation energies. However, at relatively lower excitation energies, a significant deviation in the measured cross section data of the same residues in the above mentioned systems have been observed and is attributed to the discrepancies in angular momentum values. Such discrepancies are well explained on the basis of input angular momentum involved in the reactions.

A Study of Reaction Dynamics in the Interaction of 14N+59Co System at 32-56 MeV

The present work was done to investigate the reaction mechanisms involved in the interaction of 14 N projectile with 59 Co target at beam energies ∼32-56 MeV. The experimentally measured excitation functions available in the literature [2] were compared and analyzed with the statistical model code PACE4 calculation. For non-α emitting channels populated via complete fusion reaction, the measured excitation functions, after correcting them for possible contributions coming from higher charge isobaric precursor decays, were in general found to be in good agreement with theoretical predictions. However, for α-emitting channels, the experimentally measured excitation functions had more production cross-sections than what PACE4 predicted. The observed enhancement in the present case may be attributable to process of incomplete fusion from break-up of 14 N projectile. It may be pointed out that incomplete fusion reaction increases with increase in projectile energy. The observation of high incomplete fusion reaction is attributable to the prompt breakup of 14 N projectile into α-cluster. DOI: 10.7176/APTA/86-03 Publication date: October 31 st 2022

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.

Effect of projectile structure on break-up fusion for 14N + 175Lu system at intermediate energies

In the present work, fusion in heavy-ion collisions at energies near the Coulomb barrier to ≈ 33% above it has been studied for 14N + 175Lu system. The excitation functions of several reaction channels expected to be populated via complete fusion and/or the incomplete fusion of the projectile have been measured. The experimental excitation functions have been critically compared with the predictions of the statistical model code PACE4. The observed enhancement in the measured cross-sections with respect to the theoretical model code PACE4 predictions of all the reactions having α-particle(s) in the exit channel is reminiscent of the fact that incomplete fusion (ICF) is at work in populating these channels besides the complete fusion process. The relative probability of incomplete fusion in fusion dynamics, obtained in terms of incomplete fusion strength function FICF has also been deduced. The observed behavior of FICF suggests the increasing probability of ICF contributions with projectile energy. A strong and a dictating dependence of FICF on projectile structure in terms of its Qα-value has been observed. The reduction procedures for the elimination of the geometric and the static effects suggest that the observed variation in the fusion data has a purely static origin i.e., a manifestation of different potential barriers and radii. The analysis done within the framework of universal fusion function indicates the fusion suppression of ≈ 5% for the 14N + 175Lu system.

Evaluating the dependency of neutron spectra and absorbed dose rates on the collimation field size in fast neutron therapy

The aim of this research was to investigate the relationship between the collimator aperture and fast-neutron flux, neutron-energy spectrum and absorbed dose rate. For remote therapy, rather large fluxes of fast neutrons are needed which can create dose levels in the tissues of at least 0.1 Gy/min with a source-patient distance of 1 m. Advantageously for these purposes, the 9Be(d, n) reaction was investigated with deuteron energy of 13.6 MeV. The mean energy of the outgoing neutrons was obtained using the code PACE 4 (LISE++) which gave the value of about 5.2 MeV. The maximum neutron flux was at an energy of about 2.5 MeV. Samples activation analysis was deployed to measure the neutron flux in the energy-region [0–14 MeV]. The experimental works were carried out using Al, Fe, Cu and Cd foils which installed on the collimator apertures. To investigate the neutron spectrum, fluxes, and dose rates absorbed at the position of patients, experiments were conducted for four different neutron irradiation-field sizes, which can be modified by the removable-polyethylene parts. Simulation results obtained by the code MCNP-4C and PACE4 (LISE++) were comparable with the experimental data to some extent with consideration of some uncertainties of PACE4 results. It can be concluded that the neutron flux is depended on the irradiation-field size where the neutron flux output for bigger aperture size was about +25% comparing with the smaller ones. These results could play a significant role in improving the neutron flux and optimizing the collimation system utilized in fast neutron therapy. In addition, this can lead to optimization of irradiation canals installed in the nuclear reactors which employed for production of medical isotopes, material testing and many other applications.

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.

A heavy-ion production channel of 149Tb via 63Cu bombardment of 89Y

The radionuclide 149Tb (t1/2 = 4.1 h) is a potential theranostic isotope which can simultaneously be used for targeted-alpha-particle therapy and positron-emission tomography. Feasibility experiments were performed to test a near-symmetric heavy-ion reaction of 63Cu bombardment on monoisotopic 89Y. The indirect reaction was studied to avoid isomer production. Offline gamma spectroscopy was used to quantify thick-target physical yields and experimental results show modest agreement to the fusion-evaporation code PACE4. A near-symmetric fission yield was also observed.

Effect of neutron excess in the entrance channel on the O18+Nb93 system: An experimental study relevant to incomplete-fusion dynamics

The incomplete fusion dynamics in the $^{18}\mathrm{O}+^{93}\mathrm{Nb}$ system at energies above the Coulomb barrier has been investigated. The experimentally measured cross sections have been compared with the theoretical predictions of the statistical model code pace4. To examine 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 measured excitation functions. The contribution of incomplete fusion deduced from the analysis of excitation functions has been studied in terms of various entrance channel parameters, namely, entrance channel mass asymmetry (${\ensuremath{\mu}}_{A}$) of interacting projectile and target combination, Coulomb factor (${Z}_{P}{Z}_{T}$), ground state $\ensuremath{\alpha}\text{\ensuremath{-}}Q$ value of the reaction, and neutron skin thickness of target nuclei. It has been found that the probability of incomplete fusion depends strongly on entrance channel parameters. Further, the incomplete fusion contribution for the $^{18}\mathrm{O}$ projectile with two excess neutrons is noticed to be relatively larger as compared to $^{16}\mathrm{O}$. This may be due to the larger probability of breakup for the $^{18}\mathrm{O}$ projectile resulting in rather weak binding forces as compared to $^{16}\mathrm{O}$. The existence of incomplete fusion below critical angular momentum (${\ensuremath{\ell}}_{\mathrm{crit}}$), i.e., $\ensuremath{\ell}\ensuremath{\leqslant}\phantom{\rule{4pt}{0ex}}{\ensuremath{\ell}}_{\mathrm{crit}}$, has also been observed for the studied system.

Projectile Break-up Effect on Fusion in 16O + 156Gd Reaction at Energy Range 4.3-6.3 MeV/A

We discuss our present understanding of the incomplete fusion (ICF) reaction dynamics, the excitation function of six evaporation residues (ERs) have been measured in 16O + 156Gd reaction at projectile energy range, E/A ~ 4.3-6.3 MeV/Nucleon. Some of the ERs are produced directly & indirectly (i.e. through pre-cursor), the pre-cursor contributions have been separated out from the measured cumulative cross-section with the help of Cavinato et al.1. After correcting the pre-cursor contribution, the independent yield has been compared with the statistical model code PACE-22, which describes the fusion reaction cross section. In order to optimize the parameter of the code PACE-2 that reproduces the cross section of all the complete fusion (CF) channels like xn and /or pxn-channels. Using the same set of input parameters, cross section of the ERs populated via incomplete fusion (ICF) channels have been measured. The enhancement in the measured cross section of the ERs populated via ICF channels over the PACE-2 prediction have been measured, which indicates the occurrence of the break-up of projectile 16O into (12C+α) and/or (8Be+2α) leading to ICF reaction dynamics.

Temperature and isospin dependence of the level-density parameter in the A≈110 mass region

$\ensuremath{\alpha}$-Particle evaporation spectra were measured at backward angles in $^{16}\mathrm{O}+\phantom{\rule{0.16em}{0ex}}^{94,100}\mathrm{Mo}$ reactions at multiple beam energies. Inverse level-density parameter, $K$, was determined for Cd nuclei of different isospins by simulating high-energy tail of the measured $\ensuremath{\alpha}$-particle evaporation spectra with statistical model code pace2. An overall increasing behavior of the $K$ value is observed with increasing temperature in the range of 1 to 2.5 MeV. It is observed that in the temperature region below 1.8 MeV, the parameter $K$ is higher for the neutron-rich nuclei by around 1 MeV. Semiclassical calculations were performed which treat single-particle level density of neutron and proton on different footing and this can account for the isospin effects. These calculations reproduce the $K$ values as determined from the statistical model analysis of $\ensuremath{\alpha}$-particle evaporation spectra. Present results clearly demonstrate the isospin dependence of the level-density parameter as conjectured by theoretical works.

A systematic experimental study of pre-compound emission in $$\alpha $$-particle induced reactions on odd mass nuclei A = 103–123

The compound and pre-compound emission processes have been established as two main competing de-excitation modes of an excited nucleus by-dint-of evaporation and emission of light fast particles in low energy $$\alpha $$ -induced reactions, respectively. An existence of the plenty experimental data on above established processes for a wide range of mass nuclei coerces to drive for some systematic trends in such reactions with excitation energy and mass number (A). Present work is an attempt to develop a systematics on the pre-compound emission process by analysing consistent experimental cross-section data of $$\alpha $$ -particle induced reactions on odd Z and odd A isotopic target nuclei viz., $$^{103}$$ Rh, $$^{107}$$ Ag, $$^{109}$$ Ag, $$^{113}$$ In, $$^{115}$$ In, $$^{121}$$ Sb, and $$^{123}$$ Sb, respectively. The analysis of data indicates sarcastic deviation in the experimental cross-section data with respect to calculations performed by the statistical Monte-Carlo code pace4 beyond the peak region. Such deviation becomes more prominent towards tail portion of excitation functions, which is regarded as a significant contribution of the pre-compound emission process. Observed energy dependent uniformity of such deviation for all studied reactions gives a clue for existing some systematics on concerning process with atomic mass number (A). Present study is an extension of previous work [Eur. Phys. J. A 54, 205 (2018)], but rather in more precise way for nearby isotopic target mass nuclei $$^{107}$$ Ag, $$^{109}$$ Ag, $$^{113}$$ In, $$^{115}$$ In, $$^{121}$$ Sb, and $$^{123}$$ Sb, respectively, where role of the Coulomb barrier V $$_b$$ and target deformation is found to be significantly important in the systematic decay of excited nuclei through emission of light fast particles in pre-compound process with mass number (A).

Evaporation and fission decay of Er158 composite nuclei within the statistical model

Light charged particles emitted by the compound nucleus $^{158}\mathrm{Er}$ produced in the reaction $^{32}\mathrm{S}$ $(180 \mathrm{MeV})+^{126}\mathrm{Te}$, at the excitation energy ${E}_{x}=92$ MeV, have been measured at Laboratori Nazionali di Legnaro in coincidence with fission fragments and evaporation residues. The $4\ensuremath{\pi}$ detector array $8\ensuremath{\pi}\mathrm{LP}$ coupled to a system of parallel-plate avalanche counters to detect evaporation residues has been used. Data have been analyzed in the framework of the statistical model of evaporation with the code pace2_n11. This enlarged version of the code pace2 has been used to reproduce the large set of observables measured in the fusion-evaporation and fusion-fission channels along with experimental prescission neutron multiplicity and fission cross section taken from literature. It is found that the simultaneous reproduction of the prescission neutron, proton, and $\ensuremath{\alpha}$-particle multiplicities can be obtained with zero fission delay without dynamical effects. However, the same set of model input parameters does not allow us to reproduce proton and $\ensuremath{\alpha}$-particle multiplicities in the evaporation channel. Extensive calculations, with different sets of parameters, show the limits of the statistical model in reproducing the whole set of data. This work evidences the importance of measuring a large set of observables in order to obtain a reliable description of the decay of the compound nucleus, and in particular of the fission process.

The Dominance of Proton/Neutron Evaporation Exit-Channel in a Fusion-Evaporation Reaction: The Effect of Target Nuclear Ratio (N/Z)

Cross section of different evaporation residue have been calculated in 112Sn+16O (Neuron/Proton (N/Z) of the 112Sn target is 1.24) and124Sn+16O reaction (N/Z of the 124Sn is 1.48) with beam energy of 80 MeV using statistical model calculation code PACE4. These calculations predicts that the proton emission channels are predicted to be dominant when the N/Z ratio is small (i.e in the first reaction) whereas the neutron emission outgoing channels dominant in the second reaction when N/Z is large. Experimental phenomenon also revealed the fact that in order to populate the proton or neutron reach nucleus we have to choose the target material accordingly.

Angular Distribution of Neutrons Around Thick Beryllium Target of Accelerator-Based 9Be(d, n) Neutron Source

Abstract An experimental work and simulations were carried out to determine the angular distributions of neutrons and yields of the 9Be(d, n) reaction over all angular range (360 deg) on a thick beryllium target as an accelerator-based neutron source at incident-deuteron energy 13.6 MeV. The neutron activation method was used in the experimental part using aluminum and iron foils as detectors to calculate the neutron flux. The Monte Carlo neutral-particles code (MCNP5) was used to demonstrate and simulate the neutron distribution, also to understand and compare with the experimental results. The neutron energy spectrum was computed using the projection angular-momentum coupled evaporation code PACE4 (LISE++) and the spectrum was adopted in MCNP5 code. Two experimental ways were used, one with beryllium target and another one without the beryllium target, to evaluate the neutron flux emitted only by the beryllium target. Typical computational results were presented and are compared with the previous experimental data to evaluate the computing model as well as the characteristics of emitted neutrons produced by the 9Be(d, n) reaction with a thick Be-target. Moreover, the results can be used to optimize the shielding and collimating system for neutron therapy.

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.

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.

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.

Systematic of fusion incompleteness in reactions induced by α cluster projectiles

In order to investigate the systematic of fusion incompleteness in reactions induced by $\ensuremath{\alpha}$ cluster projectiles, a detailed study was carried out using the $^{20}\mathrm{Ne}+^{165}\mathrm{Ho}$ system at energies above the barrier. Measurements of the excitation function (EF) of the observed evaporation residues (ERs) were carried out by employing the offline characteristic $\ensuremath{\gamma}$-ray detection method. The EFs of the ERs populated through $xn/pxn$ channels were found to be in good agreement with the prediction of the statistical model code pace4, whereas the EF of the ERs populated through the $\ensuremath{\alpha}$ emitting channels shows an enhancement over the pace4 prediction. The degree of fusion incompleteness in the $^{20}\mathrm{Ne}+^{165}\mathrm{Ho}$ reaction is estimated by comparing the fusion EF with coupled channels calculations and the extracted fusion function with the universal fusion function. The influence of input angular momentum on fusion reaction dynamics is explored in light of the sum-rule model. An attempt has also been made to examine the dependence of incomplete fusion probability on various entrance channel parameters.

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