In-beam Gamma Research Articles

Levels of the four lowest two-particle configurations in 210Po studied by in-beam gamma -ray and conversion-electron spectroscopy with the 209Bi

We have used the $^{209}\mathrm{Bi}$(t,2n${)}^{210}$Po reaction with standard in-beam \ensuremath{\gamma}-ray and conversion-electron spectroscopic techniques to study the two-proton states in $^{210}\mathrm{Po}$. With the possible , all states of the proton ${\mathit{h}}_{9/2}^{2}$, ${\mathit{h}}_{9/2}$${\mathit{f}}_{7/2}$, ${\mathit{f}}_{7/2}^{2}$, and ${\mathit{h}}_{9/2}$${\mathit{i}}_{13/2}$ configurations have been identified. The level energies agree within 100 keV, typically, with results from shell-model calculations. Relative intensities of M1 and E2 \ensuremath{\gamma} transitions from the ${h}_{9/2}$${f}_{7/2}$ and ${f}_{7/2}^{2}$ configurations are compared with calculated intensities. Published experimental single-proton transition matrix elements were used for the calculations, which were performed both for pure and for mixed states. The results indicate admixture amplitudes of only a few percent or less into the main components of the wave functions.

New excited states of the nucleus129Xe

Excited states of129Xe have been investigated through the126Te(α,n)129Xe reaction at the incident energy E=16MeV by means of in-beam gamma ray spectroscopy. Numerous levels below the excitation energy of 2.5MeV were found. Spin assignments were made from side feeding excitation functions. A new level at 274.2keV, which is suggested as spin 9/2 negtive parity bandhead, was observed for the first time.

Continuum estimation and peak analysis for in-beam gamma ray spectra

An automatic method for the estimation of the continuum in in-beam γ-ray spectra and the subsequent decomposition of overlapping peaks is presented. The continuum estimation starts with a peak identification by means of the correlation technique. The peak-free intervals of the spectrum are taken as parts of the continuum and a logarithmic interpolation is used to find an estimate for the continuum between these intervals. The gross structure of the continuum obtained in this way is controlled by a simple procedure via an inspection of the slope as a function of the γ-ray energy. Modifications of the continuum are automatically carried out when the behaviour of the slope is found in disagreement with empirical rules. In the subsequent decomposition of overlapping peaks new peaks are inserted at those places where peak-like residuals between the measured and the calculated spectrum are detected. The values obtained for the line width and the quality of the fit are taken to control the decomposition using elements of the pattern recognition technique.

Excited states in126Ba

Excited states of126Ba have been investigated via the Sn(13C, 3n)-reaction by means of inbeam gamma ray spectroscopy using compton suppressed germanium detectors of the OSIRIS facility. 37 new levels were observed and spin and parity assignments could be made. Besides the ground and the quasi-gamma band two positive parity superbands and at least 4 more sidebands of presumably negative parity were established.

Excited states of 97Ru and 103Ru.

The /sup 97/Ru and /sup 103/Ru nuclei have been studied via in-beam gamma ray spectroscopy through the /sup 94/Mo(..cap alpha..,n)/sup 97/Ru, /sup 94/Mo(/sup 6/Li,p2n)/sup 97/Ru, and /sup 100/Mo(..cap alpha..,n)/sup 103/Ru reactions. Partial levels schemes can be proposed from ..gamma..-..gamma.. coincidence data, whereas excitation function and angular distribution measurements were used to determine the spins of several excited levels. The results are compared to previous work carried out on these nuclei.

In-beam gamma -ray spectroscopy of excited states in 141Pm.

The level structure of the N = 80 nucleus /sup 141/Pm has been studied in-beam by the /sup 142/Nd(p,2n..gamma..)/sup 141/Pm reaction using a 25-MeV p beam and by the /sup 141/Pr(..cap alpha..,4n..gamma..)/sup 141/Pm reaction using a 47-MeV ..cap alpha.. beam. ..gamma..-ray singles, ..gamma..-..gamma.. coincidence (both prompt and delayed), and angular distribution experiments were performed. We found 42 ..gamma.. rays deexciting 28 states in /sup 141/Pm from the (p,2n..gamma..) reaction and 34 ..gamma.. rays deexciting 22 (generally higher-spin) states from the (..cap alpha..,4n..gamma..) reaction, for a total of 35 known states in /sup 141/Pm. These in-beam experiments, taken together with the results from /sup 141/Sm/sup m/+g decay, yield J/sup ..pi../ assignments for most of the states and have allowed us to deduce the configurations for many of the states. The structures are discussed in terms of single-quasiparticle shell-model and triaxial weak-coupled collective states and are compared with systematics for this nuclear region.

The use of bismuth-backings for in-beam gamma spectroscopy

A method to prepare rolled bismuth foils is described and their advantages as target backings for in-beam γ-ray spectroscopy at beam energies below the Coulomb threshold of bismuth are discussed.

On the irregularities in the band structures of78Kr

Using in-beam gamma -ray spectroscopy techniques experimental information on the presence of two-quasiparticle components in the band structures of 78Kr has been derived. The observation of a second 10+ state decaying by a fast M1 transition of B(M1, 102+ to 101+)=0.8(4) Wu to the 10+ yrast level gives strong evidence for a band crossing between the collective ground-state band and a two-quasiparticle band. The residual interaction between these configurations has been estimated to be V(10+)=130+or-10 keV. The configuration mixing also provides an explanation for the decrease of the B(E2) values in the yrast sequence above the 8+ level.

Rotational band structures and lifetime measurements in130Ce

The deformed nucleus 130Ce has been studied using the techniques of in-beam gamma -ray spectroscopy. Beams of 16O and 18O were used on targets of 116,117,118Sn to obtain excitation energies, mean lifetimes, spins, parities, mixing ratios and branching ratios. The gamma - gamma coincidence data necessary to determine the decay scheme were obtained using an array of five escape-suppressed spectrometers. The yrast band has been extended to Jpi =24+, or possibly Jpi =26+, with mean lifetimes measured for states up to Jpi =22+. Five new bands have been established and a 150 ns isomer has been identified at an excitation energy of 2454 keV. Backbending is observed due to the alignment of two h11/2 protons at the same rotational frequency in both the yrast band and the bands on the isomer. The gamma band based on the 834 keV (Jpi =2+) state can be identified with a triaxial shape corresponding to gamma approximately=-25 degrees . This band backbends at spin 10+ due to the alignment of two h11/2 protons showing softness of the nucleus and the coexistence of different shapes. The data may be interpreted in terms of the cranking model by assuming a prolate deformation with epsilon 2 approximately=0.25. The measured transition strengths in the yrast band generally show a decrease in epsilon 2 or a change in triaxiality from gamma approximately=0 degrees to gamma approximately=30 degrees . The transition rates measured for the 12+ to 10+ and 14+ to 12+ transitions are bigger than expected and are consistent with an increase in deformation to epsilon 2=0.30-0.35.

High spin states inRh97andRh103

High spin states in /sup 97/Rh and /sup 103/Rh have been studied via the /sup 94,100/Mo(/sup 6/Li,3n..gamma..) reaction using in-beam gamma ray spectroscopy techniques. Two cascades based on the (1/2)/sup -/ ground state and the lowest (9/2)/sup +/ state are attributed to /sup 103/Rh. Two cascades based on a proposed (13/2)/sup +/ level are attributed to /sup 97/Rh. Excitation function and angular distribution measurements are used to assign spin values to many of the levels.

Low-lying levels in125Xe and127Xe

The nuclei 125Xe and 127Xe have been studied by the 122Te( alpha ,n)125Xe, 124Te( alpha ,n)127Xe, 125Te( alpha ,2n)127Xe and 123Sb(7Li,3n)127Xe reactions. In-beam gamma -ray spectroscopy measurements largely confirm the level schemes and band structures proposed earlier for these nuclei. The results are compared with recent theoretical calculations and appear to be in good overall agreement with those based on the interacting boson-fermion model, though the electromagnetic decay properties suggest that refinements in the calculations are required.

Band structure in81Sr

The reactions 78Kr( alpha ,n) and 80Kr( alpha ,3n) were used to populate excited states in 81Sr. The de-excitation of these states was studied by in-beam gamma -ray spectroscopy. A number of new high-spin states forming band structures have been observed. Lifetime measurements have also been performed. Theoretical calculations using a particle-rotor approach based on the Nilsson model have been made. The different bands are generally well reproduced.

Medium spin states inRu99andRu101

In-beam gamma ray spectroscopy studies have been performed to deduce the level structure of $^{99}\mathrm{Ru}$ and $^{101}\mathrm{Ru}$ below 3 MeV in excitation energy produced via the $\ensuremath{\alpha}$, n reaction. Excitation functions between 10.0 and 18.0 MeV bombarding energy, together with $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence and angular distribution measurements, were carried out to determine the level energies and spins. The results are compared to previous work and to the available theoretical calculations.NUCLEAR REACTIONS $^{96,98}\mathrm{Mo}(\ensuremath{\alpha}, \mathrm{n})^{99,101}\mathrm{Ru}$ $E=10\ensuremath{-}18$ MeV; measured ${E}_{\ensuremath{\gamma}}$, $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidences, $\ensuremath{\gamma}$-ray angular distributions; $^{99,101}\mathrm{Ru}$ deduced levels, ${J}^{\ensuremath{\pi}}$; enriched targets, Ge(Li) detectors.

Excited states in128Ba

Excited states of128Ba have been investigated via the118Sn (13C, 3n) reaction by means of inbeam gamma spectroscopy. 28 new levels and several spin and parity assignments were established, revealing the existence of two superbands and a tentative new negative parity band.

Excited states in145Gd from the (3He, 2n) reaction

Medium and high spin states in145Gd up to 3.5 MeV excitation energy have been studied by in-beam gamma ray and conversion electron spectroscopy bombarding enriched144Sm target with a3He beam. For a part of the identified levels a configuration is proposed in terms of weak coupling of one neutron hole with the146Gd core or of one neutron particle with the144Gd core.

Evidence for a g9/2decoupled band in85Y

A band of levels has been assigned to the nucleus 85Y by means of in-beam gamma -ray measurements in the reactions 74Ge(14N, 3n gamma ), 72Ge(16O, p2n gamma ) and 73Ge(16O, p3n gamma ). The results of gamma -ray excitation functions and angular distributions are consistent with an interpretation of these levels as a g9/2 proton decoupled band.

Recoil-distance measurements of the lifetimes of high-spin states in83Sr and85Sr

In-beam gamma -ray spectroscopy has been performed for high-spin states of 83Sr and 85Sr, populated through the 74,76Ge(12C, 3n gamma ) reactions, respectively. Gamma-ray angular distributions and recoil-distance Doppler-shift measurements provided branching ratios, multipolarity mixing ratios and lifetimes of the electromagnetic decays of these states. The results are discussed in terms of the existing nuclear model calculations. Also, calculations of positive-parity states are presented, performed on the basis of the asymmetric rotor model (with variable moment of inertia). This model gives a reasonable description of the experimental data for 83Sr, but it fails in the case of 85Sr.

Gamma-ray spectroscopy on87Sr and the energy-B(E2) rule

In-beam gamma -ray measurements following the reaction 84Kr( alpha ,n gamma )87Sr have been undertaken. The level scheme has been established with gamma - gamma coincidence measurements. Mean lifetimes for several levels were obtained with the DSA method. New spin-parity assignments have been made for a number of levels from angular distribution and linear polarisation measurements. The mod g92/-1)(X) mod 88Sr(21+)) quintuplet is discussed in terms of a new energy-B(E2) rule.

Interaction of 80-164 MeV protons with nickel isotopes

Production cross sections of various final nuclei have been determined using the in-beam gamma rays produced during the 80, 100, 136, and 164 MeV proton bombardment of $^{58}\mathrm{Ni}$, $^{60}\mathrm{Ni}$, $^{62}\mathrm{Ni}$, and $^{64}\mathrm{Ni}$ targets. From the systematics of these cross sections it is concluded that (a) typically, 1-2 nucleons are emitted in the fast pre-equilibrium phase leaving a few nuclei excited over a broad range of excitation energy, (b) the bulk of the final nuclei are produced following nucleon evaporation from the excited nuclear residues of the pre-equilibrium phase, (c) the fraction of the incident energy dissipated through fast emission increases from about $\frac{1}{2}$ to $\frac{2}{3}$ over the above energy range, (d) the average excitation energy of the nuclear residues of the pre-equilibrium phase is estimated to increase by only 10 MeV in going from about 40 to 50 MeV over the above energy range, and (e) no evidence is found for significantly preferred removal of alpha particles from the target nucleus. Detailed comparisons of the observed cross sections are made with the cascade and hybrid models. The cascade model yields better overall agreement with the measured results. A hybrid model which includes both multiple pre-equilibrium emission and geometric surface effects is needed if it is to be equally effective.NUCLEAR REACTIONS $^{58,60,62,64}\mathrm{Ni}$($p$,$x\ensuremath{\gamma}$), ${E}_{p}=80, 100, 136, \mathrm{and} 164$ MeV; measured ${E}_{\ensuremath{\gamma}}$, ${\ensuremath{\sigma}}_{\ensuremath{\gamma}}$, $\ensuremath{\sigma}$ production various final nuclei; results compared with cascade and hybrid exciton models including evaporation.

Spin and Parity Assignments of States in 207Bi with J ⩽ 21/2

Levels in 207Bi were studied using the reactions 205Tl(α, 2n)207Bi and 208Pb(d, 3n)207Bi. Spins and parities of levels with J ⩽ 21/2 were determined from conventional in-beam gamma ray and electron spectroscopy. Among these levels the single proton πi13/2v(j-2)0+ level at 1607.5 keV is of particular interest for the question of core polarization.