The reaction 26Mg(d, τ)25Na and the structure of 25Na

The nuclear structure of the nucleus ²⁵Na has been studied with the (d, τ) proton pick-up reaction on ²⁶Mg at a bombarding energy of 29 MeV with an energy resolution of 25 to 30 keV FWHM. Excited states in ²⁵Na have been measured up to excitation energies of 8 MeV. The experimental angular distributions show good agreement with the predictions from the standard distorted-wave Born-approximation theory (code DWUCK; non-local and finite range). However, the agreement is improved considerably if the procedure of Kunz, Rost and Johnson is applied which accounts approximately for strong couplings to inelastic channels in the initial and final (strongly deformed) nuclei. The influence of this treatment on the evaluation of spectroscopic factors has been investigated and was found to be particularly pronounced for l = 0 transitions. The measured spectroscopic factors are compared to those from other experimental work and from shell-model and Nilsson-model calculations.     

A study of the 51V(6Li,d)55Mn reaction

Alpha particle spectroscopic strengths extracted for transitions to low-lying levels in ⁵⁵Mn observed in a study of the ⁵¹V(⁶Li, d) reaction at 32 MeV are compared with the results of shell-model calculations. These reproduce well the relative strengths of the levels.     

Radiative decays of unbound levels in 20Ne

Nine levels in the range 8.7 to 12.5 MeV in ²⁰Ne have been investigated with the ¹⁶O(α, γ)²⁰Ne and ¹⁶O(α, α')¹⁶O¹(6.13 MeV) reactions using a differentially pumped windowless gas target. Three of the levels have not been observed previously in these reactions, and new information has been obtained for most of the others. In particular, the 11.27 MeV 1^? level is shown to have T = 1, a result of relevance to a proposed parity violation experiment, and the analogue of the 1.97 MeV (3^?T = 1) level in ²⁰F is shown to lie at 12.25 MeV in ²⁰Ne rather than at 12.39 MeV as proposed previously. In addition, the 12.25 MeV level has a width Γ < 1 keV, in contrast to the value Γ ～ 5 keV reported in other work. The electromagnetic transition rates for positive parity T = 1 states in ²⁰Ne are compared with shell-model calculations.     

Four-nucleon transfer with the 32S(16O, 12C)36Ar reaction

Angular distributions have been measured for the ³²S(¹⁶O,¹²C)³⁶Ar reaction at 45.5 MeV leading to excited states between E_x, = 0 and 8 MeV. Experimental cross sections are compared with exact finite-range DWBA calculations in combination with extensive shell-model calculations, which include sd- and fp-shell configurations. Transitions to low-energy positive-parity states and bound negative-parity states are well reproduced. The calculations, however, fail to describe some high-energy positive-parity states. Calculations with a complete cluster expansion for the four transferred nucleons give about 50% larger cross sections, but can not explain the observed discrepancies. Possible interference of reaction processes other than direct α-transfer and special structure effects are discussed.     

Lifetimes of levels in 25Na and 26, 27Mg excited via the 26Mg bombardment of 3H

Lifetimes have been measured for nine levels in ²⁵Na, the first two excited states of ²⁷Mg, and the First excited state of ²⁶Mg by bombarding a Ti³H target with 40 MeV ²⁶Mg ions. Mean lifetimes were determined by fitting the Doppler-broadened γ-ray lineshapes with lineshapes calculated using experimentally-measured stopping powers. The ²⁵Na results are compared to predictions of recent shell-model calculations.     

The reaction 16O(6Li,d)20Ne at 75 MeV

The angular distributions of the reaction ¹⁶O(⁶Li, d)²⁰Ne at 75 MeV for transitions to members of the ground state band are well fitted by exact finite-range DWBA calculations assuming a direct α-cluster transfer and yield spectroscopic factors in good agreement with shell-model predictions.     

Investigation of states in 30P via the 30Si(3He,t)30P reaction at 30 MeV

The ³⁰Si(³⁰He, t)³⁰P reaction has been measured for about 100 levels in ³⁰P with E_x < 8.8 MeV. Little selectivity in the population of states has been observed. For 75 levels angular distributions have been analysed using a “fingerprint method” by determining the L-value from a comparison in shape with transitions to states with known J^π. For possible mixed L-transitions a dominance of the higher L-value is observed for almost all cases. Coulomb displacement energy calculations utilizing shell-model wave functions have been used to identify T = 1 states.     

High-spin states in 208Rn

The yrast decay scheme of ²⁰⁸Rn has been investigated up to spin $\text{≈ 20}\text{h}\text{?}$ and an excitation energy of ≈ 6 MeV. Several different γ-ray spectroscopic techniques were used to determine the properties of excited states and transitions in the nucleus. Significant changes to the previously established level scheme are proposed, based on the existence of an unobserved 3.1 keV transition. Simple empirical shell-model calculations of level energies aided in the assignment of shell-model configurations to excited states and the decay scheme is discussed in terms of these configurations. The energy level systematics for the even radon isotopes, from A = 206 to 212 are discussed, as are core polarization effects in the even radon isotopes (A = 204 to 210) and polonium isotopes (A = 202–208).     

Investigation of the reaction 35Cl(τ, α)34Cl at Eτ = 15 MeV

The ³⁵Cl(τ, α)³⁴C reaction has been used to study the properties of ³⁴Cl levels up to an excitation energy of 5 MeV. Angular distributions of 37 levels were measured with a split-pole magnetic spectrograph, at a bombarding energy of 15 MeV. New levels have been found at 3847, 3964, 4206, 4321 and 4715 keV, all ± 10 keV. There is a strongly excited multiplet at E_x = 5.0 MeV with components at 4939 ± 11, 4958 ± 11, 4971 ± 11, 4998 ± 12 and 5010 ± 13 keV. A DWBA analysis of the α-particle angular distributions yielded l_n values and spectroscopic factors. New spin and parity assignments were obtained. The T = 1 character of the levels at E_x = 4.21 and 4.72 MeV has been determined. Experimental spectroscopic factors are compared with results from recent many-particle shell-model calculations.     

High-spin states in 58Ni

High-spin states of ⁵⁸Ni were investigated via the study of in-beam γ-ray induced by the compound reaction ⁴⁸Ti(¹²C, 2n)⁵⁸Ni between 26 and 48 MeV. The energies and decay modes of these levels were determined from the analysis of γ-γ coincidence measurements at 35 MeV. The most intense lines in the ⁵⁸Ni γ-ray spectrum correspond to a cascade to the ground state, through levels at 1.454, 2.459, 3.619 and 4.381 MeV, also fed in other reactions, and by two previously unknown levels at 5.125 and 5.662 MeV; the spin assignments based on the present study are (apart from the ground state) 2, 4, 4, 5, 6 and 7 respectively for these levels. The first three were already known and the last three are new. The mixing ratios for the transitions between these levels are also determined. We observe also the same cascade in the reaction ⁵⁶Fe(α, 2n)⁵⁸Ni at an incident energy 18–24 MeV. Comparisons with other reactions, previous studies and recent shell-model calculations are presented.     

High resolution investigation of 91Mo and 92Mo via (p,d) and (p,t) reactions on 90Mo

The (p, d) and (p, t) reactions on ⁹²Mo have been studied at a proton energy of 28.0 MeV. Using an Enge split-pole spectrograph, resolutions of 11–15 keV for the detected deuterons and tritons were obtained. A total of 87 levels up to 4.9 MeV in ⁹¹Mo and 25 levels up to 4.0 MeV in ⁹⁰Mo were found, several of which were previously unknown. By comparing the measured angular distributions with DWBA calculations l-values and spectroscopic factors were determined. The results are compared with data from previous experiments on ⁹¹Mo and ⁹⁰Mo, with experiments on other N = 49 and 48 nuclei, and with theoretical calculations.     

High-spin states in 92Tc

High-spin states in ⁹²Tc have been studied using the 33 MeV ⁹²Mo(³He, p2nγ)⁹²Tc reaction. Levels up to J = (13) are identified. The results are compared with various shell-model calculations.     

The structure of 26Mg investigated with the (d,p) reaction

Angular distributions have been measured for the ²⁵Mg(d, p)²⁶Mg reaction at 13 MeV leading to excited states between E_x = 0 and 8 MeV. Experimental cross sections are compared with DWBA calculations and extended shell-model calculations in the full sd shell. Spin and parity restrictions are obtained for several levels in the region E_x = 6?;8 MeV. Spectroseopic factors for transitions to the lowest four positive-parity states of each spin are well reproduced by the shell-model calculations; however, in mixed configurations the largest component is systematically underestimated by the shell model. Only 60% of the strength for $\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ transfer is observed.     

High-resolution measurements of beta-delayed protons from 37Ca and 41Ti

Protons with energies from 870 keV to 5.4 MeV have been observed following bombardment of a ⁴⁰Ca target with ³He at beam energies of 29.5, 36.5 and 60 MeV, as well as from 40 MeV ³He bombardment of an ³⁶Ar gas target. These data, and those resulting from 20 MeV proton bombardment of ⁴⁰Ca, permit accurate identification of proton unbound levels in ⁴¹Sc, ³⁷K, and ⁴⁰Ca fed by allowed beta decay from ⁴¹Ti, ³⁷Ca or ⁴⁰Sc, respectively. Absolute ft values have been determined for beta decay to these levels. The half-life of ⁴¹Ti has been remeasured to be 80±2 ms and the log ft for its superallowed decay branch has been found to be 3.35±0.02, indicating an isospin purity for the lowest $\text{T =}\text{3}\text{2}\text{state in}{}^{41}\text{Sc of}\text{≈ 91 \%}$. The $\text{ft}\text{values for}{}^{37}\text{Ca}\text{β}{}^{\mathrm{+}}$ decay are compared to shell-model calculations for beta-decay in A = 37 nuclei.     

High-spin states in 34CI

High-spin yrast states in ³⁴Cl have been studied with the reactions ³¹P(α, nγ)³⁴Cl at E_α = 11.7?16.3 MeV and ²⁴Mg(¹²C, pnγ)³⁴Cl at E(¹²C) = 32–35 MeV. Ambiguities in the ³⁴Cl level scheme for levels at E_x = 4.82 and 5.32 MeV have been resolved through combination of threshold measurements with the ³¹P + α reaction and gamma-gamma coincidence and E_γ-measurements with the ²⁴Mg + ¹²C reaction. Gamma-gamma coincidence and in-beam γ-γ angular correlation experiments have been performed employing a Compton-suppression spectrometer with a solid angle of 120 msr.Unambiguous spin-parity assignments of J^π = 6^?, 5⁺ and 7⁺ to the ³⁴Cl levels at E_x = 4.74, 4.82 and 5.32 MeV, respectively, are obtained.Previously unreported levels of high spin are found at E_x = 7.25 and 7.80 MeV with J^π = (9⁺) and (8⁺); τ_m = 200 ± 70 fs and 100 ± 70 fs, respectively. Excitation energies, mean lives, branching ratios and multipole mixing ratios are reported. The experimental results are compared with large-scale shell-model calculations. The high-spin yrast levels can be characterized by a rather simple shell-model structure.     

The (3He,n) reaction on 16O and 18O

The (³He, n) reaction on ¹⁶O and ¹⁸O has been used to study low-spin states in ¹⁸Ne and ²⁰Ne up to E_x ≈ 8 and 20 MeV, respectively. The measured neutron angular distributions have been analysed using DWBA. By a comparison with shell-model calculations in the (s, d) shell it is found that most of the two-proton transfer strength can be explained within that shell. Important contributions, however, from the (f, p) shell in low-lying negative parity states are also present.     

On the mechanism of the 27Al(α, d)29Si reaction

The ²⁷Al(α, d)²⁷Si reaction has been studied at three bombarding energies: 26.2, 26.45 and 26.7 MeV. The energy-averaged angular distributions for states populated in ²⁹Si have been compared with the microscopic and macroscopic DWBA calculations and Hauser-Feshbach theory. Spectroscopic amplitudes were calculated using the available shell-model wave functions.     

A study of the 99Tc(p,d)98Tc reaction

The energy levels of ⁹⁸Tc were studied with the ⁹⁹Tc(p, d)⁹⁸Tc reaction at a bombarding energy of 22.9 MeV and 15 keV resolution (FWHM). The Q-value for this reaction was found to be ?6.755 ± 0.009 MeV and the ⁹⁸Tc mass excess was calculated to be ?86.421 ± 0.011 MeV. This reaction provided the excitation energies for 49 neutron hole states below 1.5 MeV excitation. Comparison of experimental angular distributions with DWBA calculations permitted assignment of lf-values and the extraction of spectroscopic factors for 44 of these levels. Extensive configuration mixing is observed except in the low-lying multiplet. Effective proton-particle, neutron-hole interaction matrix elements were obtained from the low-lying positive-parity multiplet of ⁹⁸Tc.     

Level structure of 72As studied with the (α, xnp) reaction

States of ⁷²As, excited through the ⁷⁰Ge(α, np) and ⁷²Ge(α, 3np) reactions at E_α = 30 to 55 MeV, were studied. Excitation functions, γ-ray angular distributions, γ-γ coincidences and γ-time distributions with respect to the beam bursts, were determined. Five excited states are identified with levels previously observed with the (p, n) reaction. In addition seven new levels and their decay pattern are incorporated into a level scheme. A half-life of 17 ± 3 nsec was determined for the 309.8 keV state, and evidence for the existence of a long-lived state (>100 nsec) was obtained. A simple scheme based on simple particle shell-model configurations accounts for the gross properties of the low lying levels. While definite spin and parity assignment for the upper excited states require further measurements, tentative spin values up to 7 are obtained.     

Collective and shell-model excitations in 9745Rh52

⁹⁷Rh has been studied by deexcitation of the compound nucleus formed through the reactions ⁹⁶Ru(³He,pn) at 20 MeV and ⁹⁶Ru(²H,n) at 9 MeV. Direct γ-spectra, multidimensional γγ coincidences and angular distribution measurements lead to a proposed level scheme. These levels are compared to calculations based on the interacting boson-fermion approximation IBFA model in which the odd particle moves in the $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ orbital. Evidence for the observation of shell-model states outside the sd boson configuration space in ⁹⁷Rh is obtained.