A study of the states of 30Si with the 28Si(t,p)30Si and 29Si(d,p)30Si reactions

The excitation energies of the levels in ³⁰Si have been measured up to an excitation of 9.46 MeV with the ²⁸Si(t, p)³⁰Si reaction at a triton energy of 6.0 MeV. Angular distributions have been measured of proton groups from the ²⁸Si(t, p)³⁰Si and ²⁹Si(d, p)³⁰Si reactions in a multi-angle magnetic spectrograph. Triton bombarding energies of 10.5 and 12.1 MeV were used and the deuteron incident energy was 10.0 MeV. States in ³⁰Si up to an excitation of 8 MeV were observed. Spins and parities of several states have been assigned using an empirical method for the (t, p) results and using a DWBA analysis for the (d, p) distributions. Spectroscopic factors for twelve states were obtained from the latter analysis. Two of these disagree with theoretical predictions. The state previously reported at an excitation of 6.63 MeV in ³⁰Si was observed to be formed by a strong L = 0 transition in the (t, p) reaction and also by a strong l = 1 transition in the (d, p) reaction. We deduce that there are two closely spaced states at about this excitation, one having a spin and parity of 0⁺ and the other 0^?, 1^? or 2^?.     

The structure of 32S I. Spectroscopy of highly-excited states

Assignments of I, π, T are made to 30 levels in ³²S between 7.35 and 11.76 MeV excitation energy, making the spectroscopy of the T= 0 states rather complete up to 10 MeV and that of the T = 1 states up to 12 MeV. A reassessment of existing data in the light of the new results clarifies the spectrum of I ^π = 1⁺, T = 1 states up to 15 MeV excitation energy. High-spin states (I = 52 - 7) below 10 MeV excitation energy have been investigated by n t γ angular-correlation measurements with the ²⁹Si(α, nγ) reaction at E _α 14.4 MeV. Five g-wave resonances of the ³¹P(p, γ) reaction, leading to the formation of I _π + 4⁺, 5⁺ states in ³²S, have been identified between 10 and 12 MeV excitation energy. The spectrum of T = 1 states between 10.7 and 12 MeV, has been investigated by measurements of γ-ray angular distributions on resonances of the ³¹P(p, γ) reaction and by measurements of resonance strengths. Several ³²S levels between 7.35 and 8.75 MeV excitation energy were studied as final states in resonance decays. Finally a search was performed for I ^π = 0⁺ resonances of the ²⁸Si(α, γ) reaction.     

Study of 94Mo through the (n,n′γ) reaction

The ⁹⁴Mo(n, n′γ) reaction has been studied in the neutron energy range 1.5–4.0 MeV. Neutron inelastic scattering cross sections for levels up to an excitation energy of 2.6 MeV have been measured from 1.5 to 3.0 MeV. The results have been analyzed with the optical-statistical and coupled-channels theories. The 1.74 MeV level has been observed and has been assigned to be 0⁺. The branching ratios for the γ-rays deexciting the levels below the 3.5 MeV excitation have also been obtained.     

The spectroscopy of 13C by inelastic proton scattering

At 135 MeV incident energy, differential proton scattering cross sections have been measured for many states of ¹³C, up to 23 MeV in excitation. These data are supplemented by analysing power data for states up to 10 MeV in excitation, measured at 119 MeV incident energy. Distorted wave analysis using a density-dependent form of the nucleon-nucleon interaction has provided a thorough assessment of the model predictions of the nuclear structure of many of these excited states.     

States in Be studied through the reaction B(p, α)Be with 40 MeV protons

Spectroscopy of the α- and τ-particles from 40 MeV proton bombardment of ¹¹B reveals transitions to ⁸Be states up to 19 MeV. The ratio of excitation of the 16.6 MeV state to the 16.9 MeV state is 2.3 ± 0.4. The ⁸Be(4⁺) state is found at 12.5 MeV with a width of 4.0 ± 0.5 MeV.     

Evidence for critical angular momenta in the formation of 26Al via the 14N + 12C channel

States in ²⁰Ne have been studied through the ¹²C(¹⁴N, ⁶Li)²⁰Ne reaction. Excitation functions have been measured from 20 MeV to 60 MeV in steps of 5 MeV at different angles for ²⁰Ne states up to 10 MeV excitation energy. States of ²⁴Mg have been also populated using the ¹²C(¹⁴N, d)²⁴Mg reaction; excitation functions of ²⁴Mg states up to 9 MeV excitation energies as well as angular distributions at 35 MeV bombarding energy have been obtained. Comparisons of data with Hauser-Feshbach calculations show clearly that the compound nucleus mechanism is the main process for both ¹²C(¹⁴N, ⁶Li)²⁰Ne and ¹²C(¹⁴N, d)²⁴Mg reactions. Strong evidence has been provided for inhibition of the ²⁶Al compound nucleus formation for angular momenta higher than critical values. The location of the yrast line in the ²⁶Al nucleus is discussed.     

New investigation of83Zr and85Zr beta decay

The decay of on-line mass separated⁸³Zr and⁸⁵Zr sources has been studied by singles and coincident X-ray and-ray and conversion electron measurements. The previous level scheme of⁸³Y is confirmed and 5 new levels have been added up to 2.74 MeV excitation. A decay scheme of^85gZr with 40 levels up to 2.66 MeV in⁸⁵Y is deduced. The experimental observation below 2 MeV excitation in⁸⁵Y agrees qualitatively with the predictions of the interacting boson-fermion model.     

Study of new resonances at high excitation energy by the 120Sn(p,t)118Sn reaction at 35 MeV

The ¹²⁰Sn(p,t)¹¹⁸Sn reaction was investigated at 35 MeV incident energy. The ¹¹⁸Sn excitation energy spectrum was reconstructed up to about 16 MeV. Preliminary results show the presence of a broad resonance at high excitation energy, compatible with the predicted population of the Giant Pairing Vibration (GPV).     

Selectivity of the 16O(7Li, α) reaction and states with (sd)3 and (sd)2(fp)1 configurations in 19F

The ¹⁶O(⁷Li, α)¹⁹F reaction has been studied at 35 MeV up to 11 MeV excitation energy. Comparison with the ¹⁶O(⁶Li, ³He)¹⁹F and ¹⁶O(⁶Li, t)¹⁹Ne reactions shows very good agreement up to 5.5 MeV excitation energy and large differences at higher excitation energies which can be explained by different angular momentum matching conditions in the different reactions. The identification of mirror states in A = 19 and of states with (sd)³ and (sd)² (fp)¹ configurations in ¹⁹F are discussed.     

The width of the giant dipole resonance built on excited states of Cu compound nuclei

Continuumγ- ray spectra from the decay of⁵⁹Cu formed at an excitation energy of 100 MeV and angular momenta up to 43? by means of the reaction 190 MeV³²S +²⁷Al have been measured and analyzed. The parameters of the Giant Dipole Resonance (GDR) have been extracted using the statistical model. The derived GDR width confirms the sizeable broadening of this resonance in⁵⁹Cu already reported in our earlier investigation at 77 MeV excitation energy (J_crit=38?). Estimates of the GDR width have been performed in the adiabatic approximation. Predicted values account qualitatively for the experimental data of⁵⁹Cu as well as of the heavier isotope⁶³Cu, in which the broadening was not seen up to 77MeV excitation (J_crit=35?). The present analysis demonstrates the strong sensitivity of the GDR to spin effects in this mass region.     

The study of the (α, α'f) reaction at 120 MeV on 232Th and 238U: (I). Fission probabilities and angular distributions in the region of the giant quadrupole resonances

The fission decay channel of ²³²Th and ²³⁸U has been investigated, using the (α, α'f) reaction at 120 MeV bombarding energy. The angular distributions of the fission fragments and the fission probabilities up to around 15 MeV excitation have been measured. No evidence for the fission decay of the giant quadrupole resonance has been found, although for ²³⁸U, a weakly excited structure is seen in the (α, α'f) spectrum at about 9.5 MeV excitation at backward angles with respect to the recoil axis. This effect is similar to what has been found in a (⁶Li, ⁶Li'f) experiment reported recently. The over-all feature of the fission probability for excitation energies above the fission barrier are well reproduced by statistical calculations.     

Multi-quasiparticle excitations in145Tb

High-spin states in¹⁴⁵Tb have been populated using the¹¹⁸Sn (³²S, 1p4n) reaction at beam energy of 165 MeV. The level scheme of¹⁴⁵Tb has been established up toEx≈7.4 MeV. The level scheme shows characteristics of a spherical or slightly oblate nucleus. Based on the systematic trends of the level structure in the neighboringN=80 isotones, the level structure in¹⁴⁵Tb below 2 MeV excitation is well eplained by coupling anh _11/2 valence proton to the even-even¹⁴⁴Gd core. Above 2 MeV excitation, most of the yrast levels are interpreted with multi-quasiparticle shell-model configurations.     

Spectroscopy of low-lying positive parity states in 30P from the study of the reaction (3He,d) at 14.0 MeV

The reaction ²⁹Si(³He, d)³⁰P was studied at an incident energy of 14.0 MeV. Spectroscopic strengths for 14 positive parity states up to an excitation of 4.50 MeV have been obtained using DWBA analysis. The incident channel optical-model parameters for the DWBA calculations were extracted from elastic scattering cross sections measured also at 14.0 MeV.     

The structure of25Mg

Gamma-decay modes and spin(-parity) assignments of levels in²⁵Mg have been systematically investigated up to 10 MeV excitation energy by particle-γ-ray angularcorrelation measurements with the²⁴Mg(d, pγ) reaction at 6.5 MeV bombarding energy and with the²²Ne(α,nγ) reaction at 11.8, 12.5, 14.4 and 15.5 MeV bombarding energy. A level scheme has been established which is comprehensive up to 8.3 MeV excitation energy forI≦9/2 and up to 10 MeV for 9/2O d _5/2 — 1s _1/2-O d _3/2 shell and the unifieds-d shell Hamiltonian. The agreement is good to excellent. The first intruder states are located near 6.8 MeV excitation energy. The collective properties of²⁵Mg beyond the well established rotational bands are investigated using both the new experimental information and theB(E2)'s obtained from the shell model. The spectrum of²⁵Mg is completely rotational for the first five to six MeV above the yrast line. Shell modelB (M 1)'s reflect the Nilsson model structure of²⁵Mg in great detail. The prospectiveI ^π=9/2^?, 13/2^?, and 15/2^? members of the established negative-parity,K=1/2 band are found in levels atE _x=7801, 9410, and 8896 keV.     

Response functions of 58Ni, 116Sn AND 208Pb to the excitation of intermediate-energy α-particles

Inelastic scattering of 340 MeV and 480 MeV α-particles has been measured on ⁵⁸Ni, ¹¹⁶Sn and ²⁰⁸Pb up to 60 MeV excitation energy. Consistent background subtraction and multipole analysis has provided the repartition of multipole strength for all three nuclei. The so-obtained response functions show the already known low-energy giant resonances in a detailed way, as well as new giant resonances at high energy.     

On the inelastic excitation of 2− state of 16O by α particles

The excitation of the unnatural parity state (2^?, 8.87 MeV) of ¹⁶O by inelastic scattering of 40 MeV α particle is investigated microscopically. The two step excitation mechanism via the 3^? state at 6.13 MeV is found to reproduce the magnitude of the measured cross section of the 2^- excitation. The α-nucleon interaction used for the 2^- excitation also reproduces the 3^- excitation.     

Spectroscopy of highly excited states in29Si

Particleγ-ray coincidences have been measured in the²⁸Si (d,pγ) reaction at 6.5 and 7 MeV bombarding energy, in the²⁶Mg (α,nγ) reaction at 12, 14 and 15 MeV, and in the²⁷A1 (τ,pγ) reaction at 9 MeV. Theγ-decay has been observed for all bound states of²⁹Si and for 56 unbound states up to 12,960 KeV excitation energy. Particleγ-ray angular correlations were measured in the²⁸Si (d,pγ) reaction at 6.5 MeV and in the²⁶Mg (α,nγ) reaction at 12 MeV. Spin (-parity) assignments or restrictions were obtained for nearly all bound states and some high-spin states above the binding energy. The assignment of mirror levels in²⁹Si and²⁹P has been extended to 8.2 MeV excitation energy. The excitation energies of 41 positive-parity states are reproduced by shell model calculations. The possible existence of aK ^π=5/2⁺ band with prolate deformation is discussed.     

Spectroscopy of A = 16 from 13C(6Li,t)16O

The ¹³C(⁶Li, t)¹⁶O reaction has been studied at 34 MeV. Selective population of narrow states is observed up to 21 MeV excitation in ¹⁶O. This reaction populates strongly both unnatural-and natural-parity states that have little or no ¹²C + α₀ width. The measured angular distributions are compared with Hauser-Feshbach and finite-range DWBA calculations. Reasonable agreement with the DWBA calculations is found for most of the states strongly populated. The widths of the narrow states populated in the 16–20 MeV excitation region are presented. Comparison of the present data with that from medium-energy inelastic scattering and other multiparticle transfer reactions is made.     

Energy levels of 71Ge from 71Ga(p,nγ)71Ge

Energy levels of ⁷¹Ge were populated by the ⁷¹Ga(p, n) reaction at proton energies between 1.72 and 2.96 MeV and their decay studied by both γ-γ and γ-n coincidences. Spins were determined within the framework of the statistical theory from angular distributions of de-excitation γ-rays and from excitation strengths of levels derived from γ-ray intensities and branching. A level and decay scheme for ⁷¹Ge up to an excitation of 1.3 MeV is presented.