Ground State Q-value Research Articles

Systematics of multinucleon transfer in heavy-ion reactions

One-neutron pickup reactions for 52 projectile–target combinations were analysed using a systematics between transfer cross-sections and ground-state Q-values. One-neutron pickup transfer shows a good correlation between reduced transfer cross-sections and ground-state Q-values ( $$Q_{gg}$$ ) if one separate the systems into two groups based on their $$Z_{p}Z_{t}$$ product. Also, similar kind of systematics is applied to 2n, 3n and 4n pickup transfer and a good correlation is obtained between reduced transfer cross-sections and $$Q_{gg}$$ values, where no $$Z_{p}Z_{t}$$ dependence is seen.

Interpretation of coincidence data from strip detectors and extraction of absolute cross section using 3-body Monte Carlo simulation method

Accurate knowledge of the response of the detection system is very crucial for unambiguous interpretation of the experimental data. A simulation code has been developed using the Monte Carlo technique involving 3-body kinematics for the analysis of data obtained with segmented large area Si Δ E−E detector telescopes in nuclear reaction measurements. Care was taken in the analysis to maximize the angular coverage and statistics. The emphasis is placed to extract the absolute cross sections of the different reaction processes, for which coincident measurements are unavoidable. The estimated detection efficiency of different coincidence events are found to depend on various parameters, e.g., the relative energy of the breakup fragments, incident beam energy of the projectile, ground state Q-value of the reaction, the excitation of the ejectile as well as target like nuclei, mass asymmetry of the breakup fragments, detection threshold, and geometric solid angle of the detection setup. The interpretation of the various observables from the exclusive measurements of breakup and transfer breakup reactions is reported.

Measurement of multinucleon transfer cross-sections in 58Ni, 56Fe(12C, x); x: 13,11C, 11,10B, 10,9,7Be, 8Beg.s. and 7,6Li at E(12C) = 60 MeV

Cross-sections for one- and multinucleon transfer reactions, namely, 58Ni(12C, 13C), 58Ni(12C, 11C), 58Ni(12C, 11B), 58Ni(12C, 10B), 58Ni(12C, 10Be), 58Ni(12C, 9Be), 58Ni(12C, 8Be g.s.), 58Ni(12C, 7Be), 58Ni(12C, 7Li) and 58Ni(12C, 6Li) have been measured at an incident energy of 60 MeV. The reaction cross-section for the corresponding transfer channels in the system 12C+56Fe have also been measured under the same kinematical conditions. Angular distribution of the elastic scattering cross-section is measured at 60 MeV. The measured elastic scattering angular distributions for these two systems have been analysed using the optical model search code SFRESCO and the potential parameters are extracted. The multinucleon transfer data are analysed to obtain cross-section dependence on the number of nucleons transferred and on the ground state Q-values. The transfer probabilities for multinucleon stripping are extracted. A detailed comparison in the multiparticle stripping and elastic scattering cross-sections between these two systems are made to understand the mechanism of multinucleon transfer and possible role of two extra protons in 58Ni target nucleus as compared to the 56Fe core.

Neutron transfer versus inelastic surface vibrations in the enhancement of sub-barrier fusion excitation function data and the energy dependent Woods–Saxon potential

This work deeply analyzed the relative importance of the neutron transfer channels and inelastic surface vibrations of colliding nuclei in the sub-barrier fusion enhancement of various heavy ion systems using an energy dependent Woods–Saxon potential (EDWSP) model in conjunction with a one-dimensional Wong formula and the coupled channel formulation using the code CCFULL. The multi-phonon vibrational states of colliding nuclei and the nucleon transfer channels are found to be dominant internal degrees of freedom. The coupling between the relative motion of reactants and these relevant channels produces anomalously large sub-barrier fusion enhancement over the expectations of the one-dimensional barrier penetration model. In some cases, the influence of neutron transfer dominates over the couplings to low lying surface vibrational states of collision partners. Furthermore, the effects of coupling to inelastic surface excitations and the impact of neutron transfer channels with positive ground state Q-values are imitated due to energy dependence in the Woods–Saxon potential. In the EDWSP model calculations, a wide range for the diffuseness parameter, which is much larger than the value extracted from the elastic scattering data, is needed to account for the observed fusion enhancement in the close vicinity of the Coulomb barrier.

Studies of multi-nucleon transfer reactions in 90Zr(18O,X) and 90Zr(16O,X)

Multi-nucleon transfer reactions in 18O + 90Zr and 16O + 90Zr have been studied at an incident energy of 90 MeV. The energy spectra and angular distributions are measured. The data have been analyzed to obtain cross-section dependence on the number of nucleons transferred and on the ground-state Q-values. In the 90Zr(18O, X); X = 16O, 17,16,15,14N, 14,13,12C, 12,11,10B, 10,9,7Be and 7,6Li reactions, 2n and 2n-correlated transfer cross-sections are observed to be enhanced as compared to the 16O + 90Zr reaction. A detailed comparison in the multi-particle stripping and elastic-scattering cross-section between these two systems are made in order to investigate the possible influence of the two valence neutrons in 18O nucleus. Diffractional model DWBA calculations, based on the direct surface transfer model, have been performed to understand the reaction mechanism of multi-nucleon transfer to continuum.

Measurement of the ground state 2n pickup probability for 28Si+68Zn and its role in sub-barrier fusion enhancement

The ground state and excited state transfer yields for the 2-neutron pickup channel in the 28Si+68Zn system have been measured explicitly. The recoil mass separator at the nuclear Science Centre, New Delhi was used for the measurement. A NaI(T1) detector was used for detecting the deexcitation γ’s from the transfer products. The kinematic coincidence technique was employed for the transfer measurement. Simplified coupled channels calculations show that out of all transfer channels the major contribution to the sub-barrier enhancement comes from the ground state 2 neutron pickup channel with a ground state Q-value of+1.83 MeV.

Precision measurements of the Q-value for ( p, n) reactions on 37Cl and 59Co

Ground-state Q-values have been measured for ( p, n) reactions on 37Cl and 59Co by determination of the neutron and proton energies associated with near-threshold resonances. The neutron energies were measured by time-of-flight techniques; the energy scale for the protons was calibrated via the well-known Al( p, γ) resonances between 0.6 MeV and 2.2 MeV. By a full covariance analysis the following Q -values were obtained: 37Cl( p, n) 37Ar: −1596.22±0.20 keV, 59Co( p, n) 59Ni: −1855.33±0.20 keV.

A precise measurement of the ground-state q-value for (p, n) reactions on 64Ni and 80Se

Q-values have been measured for (p, n) reactions on 64Ni and 80Se by precise determination of the neutron and the proton energy at pronounced (p, n) resonances near threshold. The following Q-values were obtained using well-established resonances of the reaction Al(p, γ) as calibration standards: 64Ni(p, n)64Cu: −2458.33±0.31 keV; 80Se(p, n)80Br: −2652.93±0.31 keV

Heavy-ion induced transfer reactions with spherical and deformed nuclei

Cross sections for the quasielastic channels have been measured at energies slightly above the Coulomb barrier using 58Ni and 112,116Sn projectiles on targets of 117,118Sn and 161,162,163,164Dy. The deexcitation γ-rays were detected in a 4π NaI array (the Spin Spectrometer of Oak Ridge National Laboratory) in kinematic coincidence with both target-like and projectile-like particles; thus providing a measure of the total energy and multiplicity of the entry state. The reaction channels were identified by characteristic γ-deexcitation transitions measured with Ge detectors substituted for array elements in the Spin Spectrometer. The angular distribution for inelastic scattering is well described by both semiclassical and quantal calculations. Two general features for few-neutron transfer channels are observed; (i) the dependence of the total cross section on the ground-state Q-value, (ii) the “coldness” of the reaction mechanism indicated by the measured entry states. For one-neutron transfer the distorted-wave Born approximation seems to give a correct overall qualitative description of the reaction mechanism for spherical nuclei, and reproduces the cross sections within a factor of two. The ground-to-ground two-neutron transfer probability for the reaction between Sn isotopes was deduced and found to be strongly enhanced ( F ≈ 760), which is consistent with the expectation of strong pairing correlations. Two-neutron transfer to the ground-state band in Dy was partially resolved from transfer to other intrinsic states by using the Spin Spectrometer. The oscillating radial dependence of the probability for populating the ground-state band was found to be related to the nuclear deformation. This leads to an explanation of the “slope anomaly” where the measured radial dependence of the total two-neutron transfer probability has too flat a slope compared to the prediction based on a simple binding energy argument. The probability for two-neutron transfer to the ground-state band is found to be similar to the probability for ground-to-ground transfer in the Sn+Sn system, suggesting a comparable strength for pairing correlations in the two systems.

Structure phenomena in the orbiting 12c + 24Mg system

The backward-angle yield from 12C + 24Mg has been studied with the technique of inverse kinematics, using 24Mg beams with energies from 90 to 126 MeV. In the different exit channels with 5 ⩽ Z ejectile ⩽9 the Q-integrated differential cross sections dσ dθ are consistent with isotropy at 130° ⩽ θ c.m. ⩽ 165°, which is taken as signature of orbiting. The most probable exit energies in the strongly predominant even- Z channels as a function of bombarding energy give evidence for complete damping at angular momenta close to the critical ones for fusion. The results for the weakly populated odd- Z channels suggest that the conditions of damping are affected by the large negative ground-state Q-values. Structures are observed in the Q-value spectra and in the excitation functions at given Q. The former are identified with high-spin states close to the yrast lines, which are shown to be selectively populated due to the matching conditions for deep-inelastic reactions in light heavy-ion systems. An additional selectivity for natural-parity transitions gives evidence for the conservation of the dinuclear parentage. Narrow fluctuations observed in the excitation functions for fixed narrow Q-windows are attributed to the overlapping of unbound states of the intermediate complex. In the Q-integrated excitation functions these fluctuations cancel, but weak gross structure of a few MeV width remains visible. A statistical analysis of the narrow fluctuations yields coherence widths around 400 keV, corresponding to lifetimes of the intermediate dinucleus around 2 × 10 −21 s.

Low-lying states in112In

Low-lying states below 500 keV excitation in112In have been investigated via the112Cd(p, nγ) reaction. New levels have been established atEx=206.5keV and 456.1 keV from the measuredγ-ray excitation functions,γ−γ coincidences and the precision measurements of the (p, n) threshold energy of the ground state and of the 206.5 keV state of112In. Spins and parities of the 206.5 keV state (2+) and the 456.1 keV state (3+) and multipolarities and mixing ratios of the deexcitationγ-rays have been determined from the angular distributions and linear polarizations of the deexcitation γ-rays as well as the excitation functions of the residual levels. Possible configurations of the newly-found levels are discussed. Half-lives of two states have been remeasured:T1/2=15.2±0.1 min for the ground state andT1/2=20.9±0.1 min for the 156.4 keV (4+) state. The ground stateQ-value for the112Cd(p, n)112 In reaction has been measured to be −3.376±0.006 MeV.

The 170Er(t,p)172Er reaction at 15 MeV

Thirty-nine levels have been observed in the 172Er nucleus, for which virtually no nuclear structure information was previously available. The states at 0, 1332, 1470, and 2403 keV have distinctive L = 0 angular distributions and are therefore identified as Iπ = 0+ states. The 76 and 254 keV levels are interpreted as the 2+ and 4+ members, respectively, of the ground state rotational band. The ground state Q-value was measured to be 4.034 ± 0.004 MeV.

Sub-Coulomb transfer and fission in collisions of129Xe,132Xe and136Xe with238U

Integral cross sections for fission and for one- and two-neutron transfer reactions in the system132Xe+238U were measured radiochemically in the energy range 0.7≦E/ECoul≦1. The excitation functions for fission and transfer are found to be essentially parallel below 0.85×ECoul. Even at the lowest energies the transfer cross sections exceed the fission cross section by more than one order of magnitude. With the other projectiles129Xe and136Xe different transfer cross sections illustrating their sensitivity for the ground stateQ-values,Q gg , are observed while the fission cross sections are the same as in the132Xe +238U reaction. The fission data are interpreted in terms of a continuous transition between Coulomb fission and several transfer-induced fission processes.

States in 97, 101Ru observed in the reactions 96,100Ru(d, p)

The neutron single-particle strength distributions for the nuclei 97Ru and 101Ru have been investigated using the (d, p) reaction at a deuteron energy of 11.5 MeV, with an overall experimental resolution of approximately 25 keV. Angular distributions of proton groups leading to sixteen final states in both nuclei were measured in the angular range 15.0 to 67.5°. The measured cross sections are analyzed in the framework of the distorted waves Born approximation to deduce l-values and spectroscopic factors of the states in the residual nuclei. The ground-state Q-value for the 96Ru(d, p) 97Ru reaction has been determined to a much improved accuracy, Q 0 = 5.886 ± 0.003 MeV.

Study of the104Ru(d, p)-reaction at 14 MeV

The reaction104Ru(d, p) was investigated with high resolution (5 keV) at the Munich MP tandem using the Q3D spectrograph in conjunction with the precision time-of-flight system. The ground stateQ-value was determined as Q=3,684.5±1 keV. Proton spectra were measured at 7 angles in the range of 6.1°–65°. 19 levels could be identified in the excitation energy range 0–730 keV. Transferredl-values and spectroscopic factors of these levels were derived with the aid of DWBA calculations.

Energy Levels in 240, 242, 244Am Studied by Deuteron-induced Neutron Transfer

Targets of 241Am and 243Am were bombarded with 12 MeV deuterons in order to study energy levels in 240,242,244Am. The scattered particles were analysed in a broad range magnetic spectrograph. The measured ground state Q-values are -(0.388±0.015) MeV for the 241Am(d,t)240Am-reaction, -(0.111±0.015) MeV for the 243Am(d,t)242Am reaction and (3.308±0.015) MeV for the 241Am(d,p)242Am reaction. The neutron orbitals 631↓ and 501↑ are observed in 240,242Am. The 620↑ orbital is observed in 242,244Am, and the 622↑ orbital is observed in 240,242,244Am. The neutron orbitals are assumed to be coupled to the 523↓ proton orbital.

The ( 18O, 20Ne) reaction on the even Ni isotopes and the mass of 62Fe

The ( 18O, 20Ne) reaction on the even Ni isotopes has been studied at 63.0 MeV with ΔE- E time-of-flight telescopes. From the measured ground-state Q-value for the 64Ni( 18O, 20Ne) 62Fe reaction, −1.97±0.20 MeV, a mass excess −58.87±0.20 MeV is obtained for the 62Fe nucleus. This result is in good agreement with a recent measurement of the β-endpoint energy. Angular distributions for the transitions to the Fe ground states, leaving 20Ne in its ground and 1.63 MeV 2 + excited state, yield relative spectroscopic strengths in fair agreement with DWBA calculations based on simple shell-model estimates.

Structure of 62Zn studied through the (p, t) reaction at 27.5 MeV

Levels of 62Zn were investigated via the (p, t) reaction at 27.5 MeV with excitation energies up to 5.4 MeV being measured for 18 levels, most of which are newly reported. The ground state Q-value was determined to be −12.493±0.010 MeV. Angular distributions were measured in the angular range 8°–110° (lab). Spin-parity assignments are made by comparing the shapes of the angular distributions with zero-range DWBA calculations and with empirical characteristic shapes determined in earlier studies. Of particular interest are the new 0 + states at 3.98 and 4.57 MeV and the strongly excited 4 + states at 3.216, 4.17 and 5.37 MeV. A state at 2.74 MeV is tentatively identified as the low-lying octupole state. A careful search for the 0 + member of the two-phonon triplet near 2 MeV excitation, suggested from other Zn isotopes, revealed no 0 + state below 3.9 MeV excitation.

The 117, 119Sn(p, n) 117, 119Sb reactions near 0 + analogue states

Differential cross sections were measured for the 117,119Sn(p, n) 117,119Sb reactions in the vicinity ( E p ≈ 4.5 MeV) of 0 + analogue states in the compound nuclei 118,120Sb. Three techniques have been used to establish spin-parities of the states in 117,119Sb: (i) the amount of on resonant enhancement for the neutron groups, (ii) the differential cross sections off resonance and (iii) the relative yields off resonance. Energies (in keV) and I π assignments for levels in 117,Sb are 1085 ( I ≧ 7 2 ), 1165 ( I ≧ 7 2 ), 1300 ( I ≧ 7 2 ) and 1355 ( 1 2 − ). Those for 119Sb are 644 ( 1 2 + ), 700 ( 3 2 + ), 975 ( 5 2 − , I≧ 7 2 ) , 1337 ( 1 2 − ), 1416 ( 3 2 − ), 1482 ( 1 2 − ), 1547 ( 5 2 −, I ≧ 7 2 ), 1665 doublet ( 1 2 + and 1 2 +, 5 2 +), 1745 ( 3 2 +), 1822 ( 1 2 +), 1880 doublet ( 3 2 + and 5 2 −, I ≧ 7 2 ), 1970 ( 5 2 − , I ≧ 7 2 ) and 2130 doublet ( 1 2 for one). It is suggested that the observed 1 2 − and 3 2 − states are due to coupling of d 5 2 and g 7 2 single particles to the 3 − core state. The ground state Q-values were found to be −2.525±0.020 MeV for the 117Sn(p, n) reaction and −1.369±0.015 MeV for 119Sn(p,n).

Investigation of the 33S(d,p) 34S reaction

Angular distributions have been measured of proton groups, corresponding to 34S states up to E x = 6.63 MeV excited in the reaction 33S(d, p) 34S at E d = 12 MeV, with the use of a split-pole magnetic spectrograph. The ground state Q-value has been measured as Q o = 9195±6 keV. A DWBA analysis yields l n values and spectroscopic factors. The results of many-particle shell-model calculations for 34S positive-parity states are found to agree well with experiment.