Etude du noyau 63Cu par la reaction 60Ni(α, pγ)63Cu

The level structure and the decay properties of low-lying levels in ⁶³Cu have been investigated via the ⁶⁰Ni(α, pγ)⁶³Cu reaction at E_α = 11.7MeV. Using a Ge(Li) detector, the correlations of twenty-five primary γ-rays in coincidence with protons, stopped in an annular detector at approximatively 180° with respect to the beam direction, were measured. From these measurements, branching ratios, γ-ray mixing ratios and spin assignments have been obtained for most of the levels up to 2.4 MeV excitation.     

Cross sections and thermonuclear reaction rates for 42Ca(p, γ)43Sc, 44Ca(p, γ) 45Sc, 44Ca(p,n) 44Sc and 45Sc(p,n)45Ti

The yield of γ-rays from the reaction ⁴²Ca(p, γ)⁴³Sc has been measured as a function of bombarding energy over the range 0.63–3.01 MeV, from ⁴⁴Ca(p, γ)⁴⁵Sc over the range 0.775–4.00 MeV, from ⁴²Ca(p, p'γ)⁴²Ca over the range 2.24–3.01 MeV, and from ⁴⁴Ca(p, p'γ)⁴⁴Ca over the range 1.90–5.03 MeV. The cross section of the reaction ⁴⁴Ca(p, n)⁴⁴Sc has been measured from threshold to a bombarding energy of 5.05 MeV by observation of the 1157 keV γ-ray associated with the residual ⁴⁴Sc activity, and the cross section of the reaction ⁴⁵Sc(p, n)⁴⁵Ti has been measured from threshold to a bombarding energy of 4.00 MeV both by observation of the annihilation radiation associated with the residual ⁴⁵Ti activity and by measurement of the total neutron yield with a wide-angle BF₃ tube and paraffin detector. All these data are compared with statisticalmodel calculations and satisfactory agreement is achieved. Thermonuclear reaction rates for the (p, γ) and (p, n) reactions are calculated for the temperature range 5 × 10⁸-10¹⁰K and the significance of these results for explosive nucleosynthesis in stars is discussed.     

Nuclear structure of 47Sc: (I). Gamma-ray correlations and lifetime measurements

Levels of ⁴⁷Sc below an excitation energy of 2.7 MeV have been investigated through the ⁴⁴Ca(α, pγ)⁴⁷Sc reaction. Gamma-ray spectra in coincidence with protons were recorded with a Ge(Li) detector positioned at several angles and at α-energies of 10.15 and 11.00 MeV. Level positions, lifetimes, decay modes and spin values were deduced from these measurements. This study was supplemented by a γ-γ coincidence measurement. The electromagnetic properties for the negative parity states are compared with intermediate coupling predictions. A classification of the positive parity states into several rotational bands is proposed.     

Energy levels of 24Na from the 23Na(d,pγ)24Na reaction

Excited states in ²⁴Na have been investigated by means of the ²³Na(d, pγ)²⁴Na reaction at incident deuteron energies of 2.5 and 2.8 MeV. Excitation energies and γ-ray decay for levels up to 4.2 MeV have been determined from proton-gamma coincidence spectra obtained with a surface barrier detector and a Ge(Li) detector on-line with a computer. Two new levels at 3944 ± 2 and 4195 ± 3 keV excitation energies are reported.     

Energy levels of92Nb from 92Zr(p,nγ)92Nb

The energy levels of⁹²Nb were studied by means of the⁹²Zr(p, nγ) reaction. The deexcitation γ-rays were observed with a high-resolution Ge(Li) detector in the proton energy range 3.00–4.80 MeV in steps of about 25 keV. Many new excited states of ⁹²Nb were populated by this reaction. Excitation energies up to 1.77 MeV were determined with high precision, and a level scheme of ⁹²Nb is proposed. From a Hauser-Feshbach analysis, the γ-decay scheme and other information, the spin-parities of many levels were assigned.     

Rotational states in 151Nd populated through thermal neutron capture

The level scheme in the nucleus ¹⁵¹ Nd has been studied following neutron capture by observing the γ-rays and conversion electrons with curved-crystal spectrometers, a Ge(Li) detector and a β-spectrometer. A comprehensive level scheme up to ? 1 MeV was established. It is shown that the present level scheme energies differ from those previously found in a ¹⁵⁰Nd(d, p) reaction study by a systematic shift of 27 keV. The binding energy of the last neutron in ¹⁵¹Nd was deduced. For most levels spin and parity values are proposed and an identification of bands with Nilsson-model configurations is given.     

The (p,nγ) reaction on Al and Si

The reactions ²⁷Al(p, n γ) ²⁷Si and ²⁸Si(p, n γ)²⁸P have been studied at E_p = 16 and 23 MeV, respectively, with a Ge(Li) detector in coincidence with a neutron detector. In ²⁷Si, two new γ-tran- sitions were detected and accurate excitation energies were determined. In ²⁸P, the γ-decay scheme was studied for the first time and new levels were located at 879 and 1602 keV excitation energy. For both nuclei the γ-ray spectra were supplemented by neutron time-of-flight spectra. The excitation energies are compared with those of the analogue nuclei and with the predictions from Coulomb displacement calculations.     

The lifetime of the 266 keV level in 206Tl

The lifetime of the ²⁰⁶Tl 2^? state at 266 keV has been measured by the delayed coincidence technique. The state was populated via the γ-decay of high-lying states excited in the ²⁰⁵Tl (d, p)²⁰⁶Tl reaction at E_d = 9.0 MeV. Delayed coincidences between a Si surface-barrier detector and a Ge(Li) detector resulted in a mean life for the 266 keV level of τ = 3.3(2) ns. The deduced B(E2) value of 171 (11) e² · fm⁴ indicates strong configuration mixing of two-hole states in this level.     

The 6− analog-antianalog states of 28Si

A resonance is observed in the ²⁷Al(p, γ)²⁸Si reaction at E_p=2876±2 keV, which corresponds to an excitation energy of 14356±2 keV. The 14.36 MeV level decays to a new level at 11577±2 keV, which is turn decays to the known level at 9701.8±0.5 keV. With previous information on the 9.70 MeV level and the present γ-ray angular distributions, obtained from singles spectra as recorded by a 40 cm³ Ge(Li) detector, the spins of the three levels can be limited to J=5, 6; J=6; and J=5, respectively. Transition strength arguments based on measurements of the strength of the 2876 keV resonance and the lifetime of the 11.58 MeV level indicate that the 14.36 MeV level has J^π=6^?, T=1 and that the 11.58 MeV level has J^π=6^?, T=0.     

Fusion cross sections for 10,11B+12C at sub-Coulomb energies

Total fusion cross sections for the ¹⁰B + ¹²C and ¹¹B + ¹²C reactions have been determined over a 5 MeV (c.m.) energy range extending to ≈ 3 MeV below the Coulomb barrier. Absolute γ-ray yields for specific transitions in the de-excitation of the heavy products following compound nucleus decay were measured using a Ge(Li) detector. Statistical model calculations of the decay modes of the compound nucleus have been used to deduce, from the γ-ray data, cross sections for single proton, neutron and α-particle emission, and to determine total cross sections for compound nucleus formation. No evidence has been found for sub-Coulomb resonances in either reaction. The total reaction cross sections are compared with optical model calculations using different parameter sets and the observed trend in the very low energy cross sections is discussed relative to other reactions in the same mass region.     

Study of5Li around 20 MeV excitation energy by a radiative capture reaction

The nucleus⁵Li has been investigated within an excitation range of 17.8 – 21.1 MeV by measuring γ-rays from the reaction D(τ, γ _o)⁵Li. In this range, excitation functions and angular distributions have been taken. The excitation functions exhibit broad maxima at 20 MeV which indicate, in agreement with other results, a level or a group of levels. Assuming that there is only one resonance, its properties are discussed. On the basis of the existing and the new experimental results, aJ ^π=1/2⁺ assignment is proposed besides the former resultJ ^π=(3/2, 5/2)⁺.     

Nuclear reaction cross sections of 16O + 16O obtained by γ-ray detection

The partial production cross sections for reaction residues produced by the fusion of ¹⁶O with ¹⁶O have been measured at E_c.m = 9–30 MeV by detecting the characteristic γ-rays with a Ge(Li) detector. The dominant products are ²⁴Mg and ²⁷A1 corresponding to 2α and αp emission from the compound nucleus, respectively. The total γ-producing cross sections σ_R were also derived by summing the partial cross sections after correction for the observed (average) γ-ray angular distributions. The trend in the total cross sections is very similar to the trends derived from an optical model or a statistical-evaporation model calculation. The partial production cross sections were compared with other experimental results at 11.9 MeV and 30 MeV and with the results of the statistical-model calculation. It is concluded that the treatment of angular momentum in the calculation is inadequate for describing the partial cross sections. Structure in the partial and total cross section excitation functions is observed with minima occurring at E_c.m. = 27, 24, 20, 17.5, and possibly 15 MeV. Some of this structure is well established by the statistical accuracy of the data and most, but perhaps not all of it, is correlated in the various channels. This structure is compared with that observed in another experiment and some of its implications are discussed.     

The levels of144Pr from the decay of144Ce

The level scheme of¹⁴⁴Pr has been studied from the decay of¹⁴⁴Ce. The intensities and energies of gamma rays have been determined with a X-ray Ge(Li) detector. TheK-shell internal conversion coefficients for γ-rays have been measured with theK X-ray/γ-ray ratio method using NaI(Tl)—X-ray Ge(Li) coincidence techniques.     

A study of low-lying states of 72As using the 72Ge(p,nγ)72As reaction

Several low-lying states of ⁷²As have been studied via the γ-rays following the bombardment of ⁷²Ge by protons in the energy range 5.1–6.2 MeV. Gamma-ray spectra were obtained using a Ge(Li) detector, and gamma-gamma coincidences between this detector and a NaI crystal were also investigated. Besides the single previously known excited state at 46 keV, 12 additional excited states were determined in ⁷²As at energies of 213, 242, 308, 317, 333, 343, 413, 438, 454, 512, 523 and (561) keV. The angular distributions of the γ-rays from the 213 and 242 keV levels have also been measured, and the results have been analyzed using the compound nucleus statistical model. The excited states at 213 and 242 keV were found to have spins of (2) and 3 respectively.     

A study of the 59Co(n,n′γ)59Co reaction

The ⁵⁹Co(n, n'γ)⁵⁹Co reaction has been studied for incident neutron energies ranging from 1.3 to 3.9 MeV. The pulsed-beam time-of-flight technique was employed to discriminate between the inelastically scattered neutrons and the de-excitation γ-rays, which were detected by means of a true-coaxial Ge(Li) detector. Thirty-five levels were identified in this way, and their excitation functions have been extensively compared with the predictions of the statistical theory of the compound nucleus. Possible spin assignements to the levels of ⁵⁹Co are discussed and compared with the results available from previous works.     

Excited states of 96Nb from the 96Zr(p,nγ)96Nb reaction

The γ-ray spectra of the ⁹⁶Zi(p, nγ)⁹⁶Nb reaction have been measured with Ge(Li) detectors at different bombarding proton energies between 1.3 and 5.1 MeV. γγ coincidences were observed at E_p = 4.7 and 5.0 MeV. On the basis of experimental results a level scheme of ⁹⁶Nb was deduced, and γ-threshold energies and γ-branching ratios were determined. Computed Hauser-Feshbach (p, n′) cross sections have been compared with experimental data obtained from the γ-ray measurements, and level spins and parities have been determined. The energies of ⁹⁶Nb levels were calculated on the basis of the parabolic rule, derived from the cluster-vibration model. The Racah multipole decomposition method was used also for the theoretical interpretation of several ⁹⁶Nb multiplet states.     

The level scheme of91Nb from the reaction90Zr (p, γ)91Nb

The level scheme of⁹¹Nb has been investigated with the reaction⁹⁰Zr(p, γ)⁹¹Nb. Proton energies between 3.0 and 7.2 MeV were used. The γ spectra were taken with Ge(Li) detectors. Primary γ transitions to 36 excited states of⁹¹Nb up to 3.8 MeV excitation energy and many secondary γ transitions from the decay of those states were observed, leading to an extension of the known level scheme. The proton binding energy for⁹¹Nb was determined as (5167± 5) keV. Eleven γ transitions in⁹⁰Zr, part of them new, from the competing reaction⁹⁰Zr(p, p′ γ) were also observed.     

The energy of levels of45Sc up to 3 MeV from the44Ca (p, γ)45Sc reaction

The gamma-ray decay of the 1658 keV resonance, which is a member of the isobaric analogues of the 1904 keV 3/2^? level in⁴⁴Ca, has been studied with a Ge(Li) detector. A number of gamma-ray transitions are described and associated with the decay of 15 levels between 1.50 and 3.05 MeV. These observations have made it possible to deduce spin and parity assignments to some of the levels. By comparing excited levels of⁴³Sc and⁴⁵Sc it has been possible to assign certain levels as members of one negative-parity band and two positive-parity bands withK ^π=1/2⁺ and 3/2⁺.     

Spin-parity assignments for the excited states of 91Nb from the 91Zr(p,nγ)91Nb reaction

The energy levels of ⁹¹Nb were studied by means of the (p, nγ) reaction. The de-excitation γ-rays were observed with a Ge(Li) detector in the proton energy range from 3.25 to 5.51 MeV in steps of about 30 keV. Resonances attributed to isobaric analog states in the compound system ⁹¹Nb were observed in the excitation functions of the de-excitation γ-rays. From an analysis of these analog resonances, a Hauser-Feshbach analysis and the γ-decay scheme, the spin-parities of the levels up to 2792.6 keV (22 levels) were assigned.     

Measurements of the radiative widths of the first T = 1, 2+ state of 20Ne and their relationship to analog β-decays

The radiative widths for decays of the ²⁰Ne T = 1, 2⁺ (10.27 MeV) state were measured by resonance α-capture in the reaction ¹⁶O(α, γ)²⁰Ne. A special windowless gas-cell target yielded a low-background spectrum enabling six γ-branches to be observed with a Ge(Li) detector. The six branches correspond to decays from the 10.27 MeV level to the following levels: 2⁺(7.83 MeV), 2⁺(7.42 MeV), 3^?(5.62 MeV), 2^?(4.97 MeV), 2⁺(1.63 MeV) and 0⁺(g.s.). The branching ratios and radiative widths Γ_γ to these levels are: 7.83 MeV [(0.22 ± 0.06)%, 0.008 ± 0.002 eV], 7.42 MeV [(6.9 ± 0.4)%, 0.31 ± 0.04 eV], 5.62 MeV [(2.1 ± 0.2)%, 0.097 ± 0.014 eV], 4.97 MeV [(1.3 ± 0.1)%, 0.060 ± 0.008 eV], 1.63 MeV [(88.9 ± 0.5)%, 4.08 ± 0.43 eV] and 0.0 MeV [(0.64 ± 0.14)%, 0.029 ± 0.008 eV]. The radiative widths to the 1.63 MeV and 7.42 MeV levels are used to determine the CVC predictions of the weak magnetism form factors and their effects on certain β-decay observables are evaluated.