Pre-equilibrium Research Articles

Investigation of the fusion mechanism in the Li6 -induced reaction on Nb93

We attempt to put forth the competing reaction mechanisms through residual cross section measurement in $^{6}\mathrm{Li}$ fusion with $^{93}\mathrm{Nb}$. The measured residual cross sections in the 24--43 MeV energy range are analyzed with the theoretical estimations from pace4, empire3.2.2, and alice23 statistical model codes. The replication of major $xn$-channel cross sections by empire with enhanced generalized superfluid model (EGSM) level density confirms that the population of $xn$-channel residues is through the complete fusion (CF) mechanism. The preequilibrium (PEQ) emission signatures were witnessed in the case of $^{97}\mathrm{Ru}$ residue populated via the $2n$ channel. Amplification of major experimental $p$- and $\ensuremath{\alpha}$-channel cross sections relative to the optimal theory was interpreted by considering the possibility of an incomplete fusion (ICF) process in addition to CF, owing to the low breakup threshold of the $^{6}\mathrm{Li}$ projectile. Thus, the ICF strength fraction $({F}_{\mathrm{ICF}})$ was estimated. The ${F}_{\mathrm{ICF}}$ turned out to be $\ensuremath{\approx}8--20%$ with an increasing trend and is found to be thoroughly higher than the deduced ${F}_{\mathrm{ICF}}$ for $^{7}\mathrm{Li}$ reaction on $^{93}\mathrm{Nb}$ target. In the case of weakly bound $^{6,7}\mathrm{Li}$-induced reactions, the first attempt is made to understand the influence of entrance channel parameters such as bombarding energy, $\ensuremath{\alpha}$-separation energy, Coulomb factor, mass asymmetry, neutron skin thickness, angular momentum, etc., on ${F}_{\mathrm{ICF}}$. The observed trend of the isomeric cross section ratios from the relative population of isomeric and ground states of $^{96,94}\mathrm{Tc}$ radionuclides is also discussed.

Fusion-fission events in the B11+Ta181 reaction up to 5.7 MeV/nucleon energy

Background: In heavy-ion fusion reactions, the compound nucleus' de-excitation process is observed via two competitive modes, evaporation of particles and fission, at relatively higher excitation energies. Although fusion-fission dynamics have been extensively studied in actinide nuclei, exploration of the same is yet to come for preactinide nuclei.Purpose: The objective is to understand the fusion-fission dynamics involved in the $^{11}\mathrm{B}+^{181}\mathrm{Ta}$ reaction within 4.8--5.7 MeV/nucleon energy by measuring absolute cross sections of the residues, which are mainly populating through complete and incomplete fusion-evaporation (FE), pre-equilibrium (PEQ), and fusion-fission (FF) mechanisms, as well as to infer on the mass and charge distributions of fission fragments.Method: The stacked-foil activation technique was employed, followed by off-line $\ensuremath{\gamma}$-ray spectroscopy, to measure the activity and production cross sections of radionuclides populated through FE and FF. Charge and mass distributions were studied to obtain dispersion parameters of fission fragments.Results: The equilibrium and pre-equilibrium reaction models have been used to analyze residual cross-section data resulting from FE and PEQ processes in the framework of EMPIRE3.2.2 and PACE4 codes. PEQ reaction's strengths in $3n$-channel have been extracted and compared with other systems. The relative distribution of spins between the ground and isomeric state of $^{186}\mathrm{Ir}$ has been discussed in view of the measured isomeric cross-section ratios. Further, 22 fission-fragments have been identified within the mass range $24\ensuremath{\le}A\ensuremath{\le}160$. The variance extracted from the measured isotopic yield distributions of Nd isotopes is in good agreement with the literature values. A well-consistent approach has been employed to determine the isobaric yield distribution of Nd and In isotopes.Conclusion: The combination of Hauser-Feshbach formalism for compound evaporation and the Exciton model for PEQ reaction agrees with the measured data of $xn$-channel residues, which confirms their production from the CF mechanism. Indirect evidence of ICF was observed in the $\ensuremath{\alpha}$- and $p$-emitting channels. Further, fission fragments' mass distribution is broad and symmetric, indicating their production through the compound nuclear mechanism. The variance of fission fragments' mass distribution shows an increasing trend with raising excitation energy.

Excitation function calculations in proton-induced nuclear reactions on Zn and Cu upto 80 MeV

Nuclear reaction model codes like the EMPIRE-3.2, the ALICE-1991 and the TALYS-1.9 have been used to calculate the excitation functions of 63Cu(p,n)63Zn, 65Cu(p,n)65Zn, 66Zn(p,n)66Ga, 67Zn(p,n)67Ga, 67Zn(p,2n)66Ga, 68Zn(p,n)68Ga and 68Zn(p,2n)67Ga reactions for incident proton energy range of 1–80 MeV. These codes compute reaction cross section using the direct, the compound and the pre-equilibrium (PEQ) processes as major nuclear reaction mechanisms. The computed results have been analyzed and compared with the available experimentally measured data and with the evaluated nuclear data files. Good agreements have been found between theoretically calculated and measured data.

New measurement of residual cross sections from $${\alpha }{+}^{93}$$Nb reaction: a comparative study of PEQ models and nuclear level densities

An experimental study of the $${\alpha }{+}^{93}$$Nb reaction has been accomplished within 7–12.5 MeV/nucleon energy. A systematic study of the preequilibrium (PEQ) emission of particles over the compound evaporations has been carried out using the model codes—TALYS1.8 and Alice14. The measured cross sections of $$^{96g,95m+g,94m+g,93g}\hbox {Tc}$$, $$^{93m}\hbox {Mo}$$ and $$^{92m,90g}\hbox {Nb}$$ are found to agree with other reported data within the estimated uncertainties and are grossly reproduced by the theoretical calculations. The variation of isomeric cross-sectional ratio (ICR) of $$^{96,95,94}\hbox {Tc}$$ has been examined up to 100 MeV projectile energy. Additionally, a quantitative analysis of the extent of agreement between measured and theoretical data has been performed for different nuclear level densities using F-deviation factor, which is calculated considering those energies for which experimental cross section is known. Comparison of the measured and theoretical results as well as ICR analysis demonstrates the occurrence of PEQ process in the high-energy tail of excitation functions in all channels, where the compound reaction has a negligible effect.

Measurement and analysis of excitation functions of the residues from C12+Y89 : A major production route for Ru97

Background: $^{97}\mathrm{Ru}$, a good hepatobiliary agent, is used in delayed investigations, diagnostic and therapeutic purposes, due to its favorable physicochemical properties. Various experimental studies have been carried out to investigate its production and chemical separation. However, in the interest of the subject, a lot of investigation is still required to identify the suitable routes for its optimum production, particularly for heavy-ion reactions, and to understand the reaction mechanisms.Purpose: Measurement and analysis of excitation function of the residues from the $^{12}\mathrm{C}+^{89}\mathrm{Y}$ reaction at the low-energy region and to estimate the cross-section of $^{97}\mathrm{Ru}$ expected to be produced through the direct channel, and indirectly via the decay of its short-lived precursors $^{97g,97m}\mathrm{Rh}$.Method: Thin $^{89}\mathrm{Y}$ foils backed by aluminium were bombarded by the $^{12}\mathrm{C}^{6+}$ beam within 40--75 MeV energy range. The excitation functions of the residues have been measured with the help of off-line $\ensuremath{\gamma}$-ray spectroscopy. Experimental cross-sections are compared with the various reaction models to understand the reaction mechanism involved in the production of residual radionuclides.Results: The measured cross-sections of $^{97}\mathrm{Ru}, ^{98,97m+g,96}\mathrm{Rh}, ^{96,95,94,93}\mathrm{Tc},$ and $^{93m}\mathrm{Mo}$ radionuclides show reasonably good agreement with the calculations based on the equilibrium (EQ) and preequilibrium (PEQ) models. The contribution of PEQ emissions is observed in the $3n$ and $\ensuremath{\alpha}xn$ ($x=1,2$) channels.Conclusion: Comparative analysis of the residual cross-sections demonstrates the dominance of compound nuclear process in the energy range considered. The measured cumulative production cross-section of $^{97}\mathrm{Ru}$ is maximum, $\ensuremath{\sim}850$ mb, at 66.6 MeV. The detailed analysis presented in this article would help to optimize the production parameters for $^{97}\mathrm{Ru}$ and also to understand the reliability of the theoretical models.

Excitation function of the [formula omitted] reactions in the energy range 10–22 MeV

The excitation functions of the proton induced Anatg reactions were measured using the stack foil activation followed by the off-line γ-ray spectrometry. The present work was carried out at 14UD BARC-TIFR Pelletron accelerator, Mumbai, India. The proton beam of 22 MeV was used for the irradiation of the samples and was degraded along the stack of silver foils. The measured cross-section data were compared with the existing literature data available in EXFOR. The calculated excitation functions were also compared with the calculated values from TALYS-1.9 model code using a suitable input parameters for the pure compound nucleus (CN) and pre-equilibrium (PE) reaction cross-sections. ALICE-2014 code was also used to validate the present experimental findings as well as the TALYS-1.9 results.

Excitation functions of the [formula omitted] reaction in the energy range 10–22 MeV

Excitation functions of the proton induced reactions on Nb93 were measured using the stack foil activation followed by off-line γ-ray spectrometry at 14UD BARC-TIFR Pelletron accelerator, Mumbai, India. Proton beam of 22 MeV was used for the present analysis and was degraded along the stack of five niobium foils. We have identified Mo93m, Nb92m and Zr89g reaction residues populated through (p,n), (p,pn) and (p,αn) reaction channels, respectively. The measured cross-section data were compared with the existing literature data available in EXFOR and were found to be in a good agreement. The calculated excitation functions were also compared with the theoretical predictions of TALYS-1.9 code using suitable input parameters for the pure compound nucleus (CN) and pre-equilibrium (PE) reaction cross-sections. The PE process was found to be dominant over the CN process at higher incident proton energies. The present work is also essential for the production cross-section and dose estimation for the medical isotope Zr89g in PET diagnostics procedure.

Spectral and Mechanistic Investigation of Oxidation of Rizatriptan by Silver Third Periodate Complex in Aqueous Alkaline Medium

The oxidation of Rizatriptan by diperiodatoargentate(III) has been studied by spectrophotometry at neutral pH. The kinetics of the reaction of Rizatriptan has been shown to principle of non-complementary oxidation steps. The initial step involves the deprotonated of the diperiodatoargentate(III) with the alkali; this rearranges during the displacement of a ligand to give free periodate and takes up another ligand monoperiodateargentate(III), combines with a substrate to endow with an intermediate complex which decomposes within a slow step to provide the final product in the following step with a first-order rate constant. The main product was identified by spot test, Fourier- transform infrared spectroscopy, Nuclear magnetic resonance and Liquid chromatography-mass spectrometry spectrum. A conceivable mechanism including pre equilibrium of adducts development between the complex and reductant was planned from the kinetics study. The rate conditions got from system can clarify all exploratory phenomena, and the activation parameters alongside rate constants of the rate determining step were ascertained.

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.

Preequilibrium neutron emission from O + Al at 7.5 MeV/nucleon and 8.8 MeV/nucleon

The thick target neutron yield from a ${}^{16}{\mathrm{O}}^{6+}$ beam on a thick $^{27}\mathrm{Al}$ target at 120- and 142-MeV (7.5- and 8.8-MeV/nucleon, respectively) incident energies is presented and compared with theoretical calculations. The theoretical estimates for the yield of a high-energy neutron was obtained using a preequilibrium (PEQ) heavy-ion reaction model (hion), whereas that for the low-energy part was obtained using the standard evaporation models pace4 and empire 3.2. In the present data a significant PEQ contribution, $\ensuremath{\sim}2%$ to 3% of the evaporation contribution, is observed even at projectile energies below 10 MeV/nucleon. The measured energy spectrum of neutrons for $Eg20\phantom{\rule{0.16em}{0ex}}\mathrm{MeV}$ (the predominant PEQ region) is in good agreement with the PEQ model code hion.

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.

Statistical Neutron Emission Model for Neutrino Nuclear Response

The studies of neutrino fundamental properties are widely investigated by double beta decay and inverse beta decay. Recent muon capture experiment provides promising ways to directly evaluate the neutrino nuclear responses. This study provides theoretical explanation for neutrino nuclear responses by muon capture experiment. The effects of muon binding energy towards nuclear excitation region and pre-equilibrium (PEQ) and equilibrium (EQ) neutron decay mode will be discussed. The interpretation of muon strength model by comparison of calculator output and recent experimental data may provide relevant information towards determination of nuclear matrix element (NME) and its missing parameter.

Preequilibrium neutron emission in heavy ion reaction: Mean field effect and multiple emission

Effects of nuclear mean field and of multiple preequilibrium (PEQ) emission on double differential neutron multiplicity distribution from heavy ion reactions (12C+165Ho and 20Ne+165Ho) at 10–30 MeV/u have beeninvestigated in the framework of the semiclassical formalism for heavy ion reaction (henceforth termed “HION”)developed earlier. HION follows the equilibration of a target+projectile composite system through the kinematics of two-body scattering. In the present work nuclear density distribution in the composite system is estimated in the relativistic mean field (RMF) approach. The nucleon-nucleon collision rates and subsequently the nucleon emission probability are calculated from this density distribution. A second approach based on a semiphenomenological formalism is also used for nuclear density distribution. Energy-angle distribution of neutron multiplicities calculated with this modified HION model coupled with multiple PEQ emission could reproduce the measured data of earlier workers in the projectile energy range of 10–30 MeV/u.

Effect of pre-equilibrium emission on probing postsaddle nuclear dissipation with neutrons**Supported by National Nature Science Foundation of China (11575044)

Using the stochastic Langevin model coupled with a statistical decay model, we study the influence of pre-equilibrium (PE) emission on probing postsaddle friction (β) with neutrons. A postsaddle friction value of (14 − 16.5) × 1021 s−1 and (11 − 13) × 1021 s−1 is obtained from comparing calculated and measured prescission neutron multiplicities of heavy fissioning systems 248Fm and 256Fm in the absence and presence of the deformation factor. Moreover, it is found that a larger β is required to fit multiplicity data after the PE effect is accounted for, and that the effect becomes stronger when more energy is removed by PE particles. Our findings suggest that, to more accurately determine the postsaddle friction strength through the measurement of prescission neutrons, in addition to incorporating the contribution of PE evaporation source into the experimental multi-source analysis for particle energy spectra in coincidence with fission fragments, on the theoretical side, it is very important to make a precise evaluation of the energy that PE emission carries away from excited compound systems produced in heavy-ion fusion reactions.

Production cross–section calculations of medical 32P, 117Sn, 153Sm and 186,188Re radionuclides used in bone pain palliation treatment

Abstract In this study, production cross–section calculations of 32P, 117Sn, 153Sm and 186,188Re radionuclides used in bone pain palliation treatment produced by 30Si(d,γ)32P, 118Sn(γ,n)117Sn, 116Sn(n,γ)117Sn, 150Nd(α,n)153Sm, 154Sm(n,2n)153Sm, 152Sm(n,γ)153Sm, 186W(d,2n)186Re, 187Re(γ,n)186Re, 185Re(n,γ)186Re and 187Re(n,γ)188Re reactions have been investigated in the different incident energy range of 0.003–34 MeV. Two-component exciton and generalised superfluid models of the TALYS 1.6 and exciton and generalised superfluid models of the EMPIRE 3.1 computer codes have been used to pre-equilibrium (PEQ) reaction calculations. The calculated production cross–section results have been compared with available experimental results existing in the experimental nuclear reaction database (EXFOR). Except the 118Sn(γ,n)117Sn, 150Nd(α,n)153Sm and 185Re(n,γ)186Re reactions, the two-component exciton model calculations of TALYS 1.6 code exhibit generally good agreement with the experimental measurements for all reactions used in this present study.

Theoretical study of deuteron induced reactions on 6,7Li, 9Be and 19F targets

Abstract The nuclear reactions of the deuteron particles with light nuclei have been extensively investigated in the history of nuclear physics. In this work, the cross-sections of deuteron reactions 6Li(d,n)7Be, 6Li(d,t)5Li, 7Li(d,2n)7Be, 7Li(d,p)8Li, 7Li(d,t)6Li, 9Be(d,p)10Be, 9Be(d,t)8Be, 19F(d,n)20Ne and 19F(d,p)20F were studied for the investigation of structural fusion materials. Excitation functions of these reactions were determined by using ALICE-ASH code considering equilibrium (EQ) and pre-equilibrium (PEQ) effects. The calculated cross-sections, experimental results and TENDL-2011 library data are presented in graphical form.

Cross-section calculations of proton induced (p,n) and (p,2n) reactions for production of diagnostic 67Ga, 81Rb, 111In, 123,124I, 123Cs and 123Xe radioisotopes

Investigation of pre-equilibrium (PEQ) and equilibrium (EQ) effects on proton induced reactions for production of radioisotopes are very important. Therefore, in this study, we have calculated the PEQ and EQ cross-sections for 67Zn(p,n)67Ga, 68Zn(p,2n)67Ga, 82Kr(p,2n)81Rb, 111Cd(p,n)111In, 112Cd(p,2n)111In, 123Te(p,n)123I, 124Te(p,2n)123I, 124Te(p,n)124I and 124Xe(p,2n)123Cs reactions for production diagnostic radioisotopes. Calculations have been performed by using the hybrid model, geometry dependent hybrid model and full exciton model of PEQ reaction mechanism with 1–40 MeV proton incident energy. We have also investigated the EQ effects on these reactions using the Weisskopf–Ewing model in the same energy range. The excitation functions including the PEQ and EQ effects on these reactions are evaluated by using the ALICE/ASH (2006) and the TALYS 1.4 (2011) codes. Our results have shown that using these codes is suitable for production diagnostic isotopes mentioned above. To obtain excitation functions for producing the diagnostic radioisotopes the PEQ mechanism has been found more dominant than that of the EQ. The results are discussed and compared with the available experimental data.

Microscopic models for direct inelastic scattering and direct preequilibrium emission: nucleon induced reactions

We have developed microscopic models for nucleon induced inelastic scattering and one-step direct preequilibrium emission. These models are based on reliable effective in-medium two-body interactions and a microscopic description of the ground and excited states of target nuclei. No arbitrary renormalization process enters our analyzes and the predictions are directly compar ed to experimental data. The nuclear structure in- formation are obtained in the Random Phase Approximation (RPA) framework with the Gogny force, which provides accurate descriptions of spherical nuclei withou t pairing. For medium energy (50-200 MeV) proton in- duced reactions, this approach gives very good predictions for direct inelastic scattering and for the first-step in direct preequilibrium emission. The one-step preequilibr ium model has also been extended to fast neutron scat- tering (10-20 MeV) for the 90 Zr target described with RPA theory, and for axially deformed nuclei with a simpler description of the excited states (i.e. particle-hole exci tations). Predictions of the reaction model reproduce well experimental data for 90 Zr. For deformed targets ( 232 Th and 238 U), our calculations underestimate the data at high emission energy. The cross section missing for both actinides may stem from the excitation of vibrational states with excitation energies lower than 5 MeV which are not described with incoherent particle-hole excitations. This defect might be cured if the target spectra are described wit hin the Quasi-particle-RPA (QRPA) theory recently implemented with the Gogny force.

Fast-neutron induced pre-equilibrium reactions on 55Mn and 63,65Cu at energies up to 40 MeV

The experimental cross sections for all neutron-induced reactions on the stable isotopes of Mn and Cu at incident energies up to 40 MeV are compared with results of pre-equilibrium (PE) and statistical model calculations. Taking advantage of the large sensitivity of statistical model analysis to residual nuclei parameters, for energies up to 20 MeV, our work was then focused on assessing PE model assumptions by data analysis in the energy range 20–40 MeV. The PE model reliance on the nuclear potential finite-depth correction for description of particle–hole state densities (PSD), nuclear-shell effects within the PSD formula, and single-particle level density is thus discussed with regard to the whole data basis. The related variance of the model results has been found as large as the differences between the global and local model calculations, while the data basis available between 20 and 40 MeV for the Mn and Cu isotopes is however too scarce in this respect.

A study of pre-equilibrium emission in some proton- and alpha-induced reactions

Excitation functions (EFs) for a large number of proton- and alpha-induced reactions in the energy range ≈8–60 MeV have been measured employing stacked foil activation technique. The theoretical calculations of the EFs have been carried out using the semi-classical code, which includes compound nucleus (CN) and pre-equilibrium (PE) emission into consideration. In general, the theoretical calculations agree well with the experimental data. The PE fraction has also been calculated and found to depend strongly on the energy of the incident particle.