Spectroscopy of intermediate 16F states with the reaction 14N(3He,np)15O

Excited states of ¹⁶F have been investigated with the reaction ¹⁴N(³He, np)¹⁵O at E = 10.5 and 12 MeV in kinematically complete experiments. Proton groups corresponding to the decays of intermediate ¹⁶F states were observed at various angles with counter telescopes in time coincidence with the associated neutrons detected at θ_n^lab = 0° with a time-of-flight spectrometer. Excitation energies and decay widths Γ_p0 of these states have been extracted from the proton spectra. Lower limits for the orbital angular momentum in the decay channel and for the spin of the states have been deduced from the obtained angular correlations. By comparison with the reaction ¹⁴N(³He, pp)¹⁵N measured at E = 13 MeV, pairs of $\text{T = 1}{}^{16}\text{F}$ parent/¹⁶O analog states have been identified. J^π assignments and shell-model configurations are discussed on the basis of the selectivity of the reactions measured.     

Low-lying states of the 16F nucleus

Low-lying proton-emitting states of ¹⁶F have been investigated through the sequential particle decay reactions ¹⁴N(³He, n)¹⁶F(p)¹⁵O. Excitation energies were determined by measuring outgoing proton energies. Estimations of proton decay widths and spin limitations were made from proton spectra and angular correlation data which were obtained by detecting the protons in time coincidence with the associated neutrons at θ_n = 0°. To date, the ground-state spin of ¹⁶F has been considered to be J = 0; however, the present work suggests J = 1 to be preferable.     

Rotational structure of 16O2, 16O17O,and 16O18O (X3Σg−) from laser magnetic resonance spectra

Improved values of the rotational constants B and D of ¹⁶O¹⁷O(v = 0) and D of ¹⁶O₂(v = 1) were obtained from an analysis of the laser magnetic resonance spectra at 765 and 4252 GHz.     

Phase-shift analysis of 16O + 16O elastic scattering data

A phase-shift analysis of precisely measured elastic ¹⁶O + ¹⁶O data has been carried out in order to establish the existence of molecular resonances between E_c.m = 15.5 and 18 MeV and to investigate the possible structure of these resonances.     

Doubly radiative thermal neutron capture in 2H and 16O: Experiment and theory

Measurements and calculations are presented for the cross sections for two-photon emission following thermal neutron capture in ²H and ¹⁶O. Upper limits for σ_2γ were measured in both cases. For ²H, σ_2λ = 8 ± 15 μb, for γ-rays in the energy region 700 < E_γ < 5550 keV. A detailed threeparticle calculation gives σ_2γ^tot = 26 nb. For ¹⁶O, the experimental result is σ_2γ = 3 ± 19 μb for 1200 < E_γ < 2943 keV. A single-particle, direct-capture calculation for ¹⁶O gives σ_2γ^tot = 41 nb. Contributions from excitation of the giant dipole state of the core change this result by ± 16 %. In a separate measurement the total cross section for ¹⁶O(n, γ)¹⁷O was measured to be 202 ± 28 μb. Branching ratios of (82 ± 3)% and (18 ± 3)% were determined for decays to the 3055 and 871 keV levels of ¹⁷O, respectively.     

Rotational spectra of 16O3 and of the five 18O isotopic species

The pure rotational spectrum of all of the isotopic species (with ¹⁸O in place of ¹⁶O) of the molecule of ozone has been studied in the range of 18 to 382 GHz. The Watson Hamiltonian developed up to terms in P⁶ is used. For each substituted form, the Watson molecular parameters, measured frequencies, calculated frequencies, and associated uncertainties are given. By using the distortion parameters, the Coriolis coupling constant and the force constants are calculated. The equilibrium structure is obtained from the particular isotopic substitution ¹⁶O₃ ? ¹⁸O₃.     

Direct lifetime measurement of the 6.05 MeV 0+ level in 16O

The reaction ¹⁹F(p, α)¹⁶O¹ was used to populate levels in ¹⁶O. Delayed coincidence measurements of α-π and α-γ gave a value of 96±7 ps for the mean life of the 6.05 MeV 0⁺ level in ¹⁶O.     

16O, 24, 26Mg, 28Si, 32S, 40Ca(α, 12C) and multi-α-cluster transfer reactions

The (α, ¹²C) reaction has been studied on a variety of nuclei, A = 16 to 40, at E_α = 90.3 MeV. The data indicate a rapid fall-off of cross sections with increasing target mass, approximately as A_t^{?5 ± 1}. This and other systematics are used to estimate cross sections for multi-α-cluster transfer reactions in heavy nuclei and suggest σ_T < 10^?34 cm² consistent with present experimental limits. The data for ²⁴Mg(α, ¹²C)¹⁶O has been studied in more detail and indicates a selective population of final states including ¹⁶O g.s., with oscillatory angular distributions in some instances. Finite-range distorted-wave Born approximation calculations for direct ⁸Be pickup have been performed utilizing cluster overlap amplitudes obtained with zero-order SU(3) wave functions. The calculations are in qualitative, and often quantitative, agreement with shapes and absolute magnitudes of the measured angular distributions although the cross sections for certain α-cluster states (2⁺, E_x ≈ 7 MeV; 4⁺, E_x ≈ 10.3 MeV) are greatly overestimated with this model. Other more complicated mechanisms, such as successive α-transfer, cannot be excluded. The systematics of the calculated ⁸Be cluster overlaps and the calculated and measured (α, ¹²C) cross sections are investigated, and implications for multi-α-cluster transfer reactions are discussed.     

Nuclear matter distributions for 16,17,18O from a microscopic analysis of elastic proton scattering

An analysis of 65 MeV elastic proton scattering by ^16,17,18O has been made in terms of a reformulated optical model. Matter distributions for ¹⁷O and ¹⁸O have been obtained relative to ¹⁶O. The results for the rms matter radii are R₁₇?R₁₆ = 0.04±0.03 fm and R₁₈?R₁₆ = 0.35± 0.07 fm.     

A re-investigation of 19O(β−)19F

Gamma rays observed in¹⁹O(β^?)¹⁹F have been studied with Ge(Li) spectroscopy utilizing activity created via the ¹⁸O(d, p) ¹⁹O reaction. Precision measurements of γ-ray energies and intensities, in conjunction with previous work, define the following excitation energies (in keV) and β-branching ratios (in %) for states of ¹⁹F: 109.894(5), 0.055(13/38); 197.143(4), 45.4(1.5); 1345.67(13), 0.017(2); 1554.038(9), 54.4(1.2); 2779.849(34), < 0.002; 3908.17(20), 0.0081(5); 4377.700(42), 0.0984(30). The corresponding values of logft are 8.34(30/10); 5.384(14); 8.25(5); 4.625(10); > 8.17; 6.133(27); and 3.859(17), respectively. The β-branches to the 1346 and 3908 keV states had not been observed previously. The β-branch for the 4378 keV state is in significantly better accord with theoretical expectations than the previous value of 0.160(12) %.     

Formation and deexcitation of the 32S compound nucleus via the 20Ne+12C and 16O+16O entrance channels

Reaction-product cross sections following ²⁰Ne+¹²C and ¹⁶O + ¹⁶O collisions at several incident energies have been measured with a E-ΔE counter telescope. They are compared to statistical model predictions. Fair agreement is obtained for the high-Z evaporation residue cross sections, but a strong discrepancy is observed for the lower-Z reaction products. Possible explanations are discussed. It is shown that the compound nucleus formation does not depend on the structure of the colliding ions in the entrance channel and also that it is not limited by the ³²S yrast line.     

Vibration-rotation bands of 15N216O14N218O

The infrared spectrum of 64 bands of the isotopic species ¹⁵N₂¹⁶O of nitrous oxide and of 37 bands of ¹⁴N₂¹⁸O have been analyzed. The studied spectral range extends from 1750 to 6000 cm^?1 for ¹⁵N₂¹⁶O and from 1750 to 3100 cm^?1 for ¹⁴N₂¹⁸O. The effective rotational constants are given for 44 levels of ¹⁵N₂¹⁶O comprising 21Σ, 12Π, 7Δ, 4Φ levels and also for 29 levels of ¹⁴N₂¹⁸O comprising 13Σ, 7Π, 6Δ, 3Φ levels. Thirty-one levels (20Σ, 11Π) of the following isotopic species have also been studied: ¹⁵N₂¹⁷O, ¹⁵N₂¹⁸O, ¹⁴N¹⁵N¹⁸O, ¹⁵N¹⁴N¹⁸O, ¹⁴N₂¹⁷O. In ¹⁵N₂¹⁶O a local Coriolis resonance affects the 10⁰1 level. The “forbidden” Δ-Σ transition 12^2c0-00⁰0 is observed in the spectrum of ¹⁵N₂¹⁶O. The equilibrium values for the internuclear distances have been calculated.     

12C(6Li,d)16O and16O(6Li,d)20Ne at E(6Li) = 42 MeV

Spectra up to 25 MeV excitation in ¹⁶O have been obtained from ¹²C(⁶Li, d) at 42 MeV bombarding energy. Angular distributions have been measured for ten states, including two J^π = 1^? states of astrophysical interest, and appear to be mostly direct α-transfer. In addition, data for ¹⁶(⁶Li, d)²⁰Ne(g.s.) and ²⁰Ne¹(2⁺) have been obtained. Excitation energies and widths have been extracted for states in ¹⁶O, including several states at E_x > 15 MeV. Alpha spectroscopic factors, S_α, and reduced α-widths, γ²_α and θ²_α have been deduced for levels in ¹⁶O and ²⁰Ne and compared with theoretical predictions. The J^π = 1^? levels in ¹⁶O at 7.12 and 9.6 MeV excitation appear to have comparable S_α and γ²_α values, viz. $\text{γ}{}^2{}_{\mathrm{\alpha }}\text{(7.12 MeV)}\text{γ}{}^2{}_{\mathrm{\alpha }}\text{(9.6}\text{MeV}\text{) = 0.6}{}^{\mathrm{+1.7}}{}_{\mathrm{?0.3}}$. Both states have apparent S_α and γ²_α values smaller than that for the J^π = 2⁺ “α-cluster” state at 6.9 MeV however. Furthermore, the observed line shape for the J^α = 1^?, 9.6 MeV level indicates Γ_c.m. = 400 ± 50 keV, which is substantially less than the accepted width for this level Γ_c.m. = 510±60 keV). The possible implications of these results for stellar helium burning calculations are discussed.     

Proton polarization in 16O(p,p0)16O and states in 17F1 (II)

The proton polarization in ¹⁶O(p, p₀)¹⁶O has been measured for laboratory proton energies between 10.0 and 16.0 MeV. Measurements were made for 18 or more angles at 60 energies. In addition, excitation functions of polarization were measured at 6 angles in 50 keV steps from 12.8 to 16.0 MeV. Both optical-model and phase-shift analyses were performed using published cross-section data in conjunction with the polarization data. The energy dependence of the complex phase shifts yielded spin, parity, and width assignments for 10 levels in ¹⁷F and possible assignments for 10 additional levels. A review of the energy levels of ¹⁷F below 16 MeV is given.     

7 MeV dipole ground state transitions in 207Pb, 208Pb and 209Bi

The Doppler-broadened 7.117 MeV line from the ¹⁹F(p, αγ)¹⁶O reaction has been used to resonantly excite levels in ²⁰⁸Pb at 7071±2 and 7091±2 keV, in ²⁰⁷Pb at 7186±5 and 7206±5 keV and in ²⁰⁹Bi at 7179±5 and 7202±5 keV. On the basis of angular distribution measurements the 7071 and 7091 keV levels of ²⁰⁸Pb are assigned spins of 1 and assuming 100% ground state branching the widths are calculated to be 31±3 and 17±2 eV respectively. It is suggested that the states in ²⁰⁷Pb and ²⁰⁹Bi arise from the weak coupling of a $\text{P}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ neutron hole and an $\text{h}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ proton respectively to one or the other of the ²⁰⁸Pb levels. The widths obtained in terms of _gΓ_o²/Γ are 15±4 and 25±5 eV for the 7186 and 7206 keV levels of ²⁰⁷Pb and 24±5 and 30±5 for the levels of ²⁰⁹Bi respectively. These values are consistent with the weak-coupling suggestion.     

Microscopic analysis of the 12C(α, γ)16O reaction

Electric transition probabilities in the ¹⁶O spectrum, and the ¹²C(α, γ_o,3¹⁶O capture cross sections are calculated with antisymmetric wave functions by the generator coordinate method. The influence of bound states on radiative capture is shown to be automatically included in the model. The reduced α-widths of the ¹⁶O bound states are discussed, and compared with previous theoretical and experimental estimates. The microscopic E2 capture cross sections to the O⁺₁ and 2₁⁺ states yield an astrophysical S-factor of 0.09 MeV · b at 0.3 MeV. An attempt to treat the El multipolarity by relaxing the long-wavelength approximation leads to a large underestimation of the γ-widths. Adopting the experimental γ- width and the theoretical reduced α-width of the 1₁^? state provides s_E1 = 0.30 MeV · b at 0.3 MeV.     

Scattering and reactions of 14C + 14C and 14C + 14C

We have studied elastic scattering, inelastic scattering and several transfer channels of the systems ¹⁴C + ¹⁴C and ¹⁴C + ¹²C over a wide range of energies up to E_c.m. = 35 eMeV and 32 MeV, respectively. The reaction channels were identified by means of kinematic coincidences between solid-state detectors, γγ coincidences were measured to determine cross sections for mutual inelastic scattering of ¹⁴C + ¹⁴C.Pronounced regular gross structures, similar to those found for ¹⁶O + ¹⁶O, are observed in the elastic excitation function of ¹⁴C + ¹⁴C at θ_c.m. = 90°, The angular distributions measured at the energies of the maxima and an optical-model analysis suggest that one or a few surface partial waves dominate the scattering behaviour. Correlated structure of narrower width is found in the inelastic channels and, to a lesser degree, in the transfer channels which appear with rather small cross sections.In ¹⁴C + ¹²C elastic scattering the gross structures are strongly fragmented, in contrast to ¹⁴C + ¹⁴C but similar to ¹²C + ¹²C. While the ¹²C(2⁺) excitation is very weak, the observed strengths of the ¹⁴C(3^?) excitation and of neutron transfer point to a substantial role of these channels as coupling partners to the elastic configuration and to their influence on the elastic scattering behaviour. A correlated intermediate structure is observed near 23.5 MeV, where a dominance of l = 18 is suggested by the elastic scattering angular distribution. This unexpectedly high l-value exceeds l_graz at this energy by at least two units of ?.     

15N16O的激光磁共振谱与同位素分子15N17O和15N18O的光谱分析

采用内腔式饱和吸收技术获得Lamb凹陷,使CO激光磁共振谱仪的灵敏度及分辨率大大提高.利用该技术对自然丰度下¹⁵N¹⁶O的X²Π(υ=1)←X²Π(υ=0)塞曼跃迁进行测量,实现了包括Λ双分裂在内的各种精细结构的谱分辨.结合已发表的¹⁵NO同位素分子光谱实验数据进行分析计算,拟合得到迄今最完备、最精确的各相关同位素分子¹⁵N^mO(m=16—18)的结构参 关键词：