Elastische Elektronenstreuung an14N,15N,16O und18O bei kleiner Impulsübertragung

Elastic electron scattering cross sections of¹⁴N and¹⁶O have been measured relative to the proton and of¹⁵N and¹⁸O relative to the lighter isotope (¹⁴N,¹⁶O resp.) using gas targets. The momentum transfer ranged from 0.22 to 0.48 fm^?1. The data were analyzed by phase shift calculations assuming harmonic oscillator shell model charge distributions. The following rms charge radii have been deduced: R_m(¹⁴N)=2.540±0.020 fm R_m(¹⁵N)=2.580±0.026 fm R_m(¹⁶O)=2.718±0.021 fm R_m(¹⁸O)=2.789±0.027 fm. The errors include statistical and systematic uncertainties and an estimate of effects due to the choice of the model. The radius differences of the isotopes are smaller than the values predicted by anA ^1/3 relation     

Nuclear charge radii of Al and Si from elastic electron scattering between 25 and 60 MeV

Elastic electron scattering cross sections of²⁷Al and Si (natural isotopic mixture) have been measured relative to carbon. The rms charge radiiR _m , deduced with partial wave calculations, are (3.01±0.05) fm for²⁷Al and (3.06±0.05) fm for Si, in good agreement with results from muonic X-ray energies. The values given are those for a Fermi charge distribution with skin thickness 2.5 fm; harmonic oscillator shell model distributions yield radii smaller by 0.03 fm. The ratioR _m (²⁷Al)/R_m(Si) is 0.984±0.016.     

Isotope-selective infrared multiphoton dissociation of CF3Br in a supersonic free jet

The carbon-isotope selectivity in the multiphoton dissociation of CF₃Br is studied in the collisional region of supersonic free jet. The isotopic abundance of¹²C and¹³C in C₂F₆ formed by recombination of the dissociation products is measured with a quadrupole mass spectrometer. An enrichmet factor of 9.4 is obtained for¹²C with the 9R(30)CO₂ laser line while the factor of 6.9 is obtained for¹³C with the 9P(16) line.     

Messung der Kernradiusdifferenzen von46Ti,48Ti und50Ti durch elastische Elektronenstreuung

Ratios of differential cross sections for elastic electron scattering from⁴⁶Ti,⁴⁸Ti and⁵⁰Ti have been measured at 29 MeV and 58 MeV. A partial wave analysis, carried out for static Fermi-type nuclear charge distributions, yields differences of the r.m.s. radiiR _m ofR _m ⁴⁸ ?R _m ⁴⁶ =(?0,00₅±0,02₇) fm andR _m ⁵⁰ ?R _m ⁴⁶ =(0,00₃±0,02₁) fm, if the skin thickness parameterz of the charge density is assumed to be constant. If allowance is made for a change inz ofΔz/z=±5% and ±10%, then the errors increase by ±0,01₃ fm and ±0,02₈ fm, respectively. This indicates a relatively small change in nuclear r.m.s. radii below the magic neutron number N=28.     

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.     

Nuclear charge radii of Sc,V, Fe,Co, Ni,Cu and Zn from elastic electron scattering at 60 MeV

Elastic electron scattering cross sections have been measured at 60 MeV for scattering angles between 45 and 153 degrees relative to⁴⁶Ti (for⁴⁵Sc),⁵⁰Ti (for⁵¹V) and¹²C (for the other nuclei). The following rms radii (in fm) have been deduced with a Fermi-type charge distribution (skin thickness 2.5 fm):⁴⁵Sc: 3.52(9);⁵¹V:3.62 (9); Fe: 3.71 (11);⁵⁹Co: 3.77 (5); Ni: 3.78 (8); Cu: 3.85 (5); Zn: 3.90 (5). The present uncertainty of the rms radius of¹²C increases the errors given by 0.01 fm. The rms radius differences 0.04 (5) fm for⁴⁶Ti-⁴⁵Sc and 0.06 (5) for⁵¹V-⁵⁰Ti were measured directly.     

Nonstatistical structures in the excitation functions of20Ne(16O,12C)24Mg and20Ne(16O,20Ne)16O reactions

The data on the excitation functions of²⁰Ne(¹⁶O,¹²C)²⁴Mg,²⁰Ne(¹⁶O,¹²C)²⁴Mg^*(1.37, 2⁺),²⁰Ne(¹⁶O,¹²C)²⁴Mg^*(4.12, 4⁺+4.24, 2⁺) +²⁰Ne(¹⁶O,¹²C^*(4.44, 2⁺))²⁴Mg,²⁰Ne(¹⁶O,¹²C)²⁴Mg^*(6.01, 4⁺+6.43, 0⁺),²⁰Ne(¹⁶O,²⁰Ne)¹⁶O,²⁰Ne(¹⁶O,²⁰Ne^*(1.63, 2⁺))¹⁶O, and²⁰Ne(¹⁶O,²⁰Ne^*(4.25, 4⁺))¹⁶O reactions atθ _lab=13° fromE _c.m.=22.8 to 38.6 MeV have been subjected to a statistical analysis comprising of the calculations of the distribution of cross sections, deviation functions, cross-correlation functions, summed excitation functions, cross-channel correlation coefficients and coherence widths. The analysis confirms the existence of nonstatistical structures atE _c.m.=24.6, 27.8, 31.7 and 35.5 MeV, and identifies a new structure of the same nature atE _c.m. =25.6 MeV.     

Line Shift Investigations for Different Isotopomers of Carbon Monoxide

Line shift coefficients for five lines of five different isotopomers in the fundamental band of CO in the spectral region near 2058 cm⁻¹were measured using a three channel lead salt diode laser spectrometer. The study includes the linesP(3) of¹³C¹⁷O,R(3) of¹³C¹⁸O,P(9) of¹²C¹⁸O,P(10) of¹³C¹⁶O, andP(21) of¹²C¹⁶O, and covers collisions with N₂, O₂, H₂, D₂, He, Ne, Ar, Kr, and Xe. Line shifts of the isotopomers¹³C¹⁶O,¹²C¹⁸O,¹³C¹⁸O, and¹³C¹⁷O were determined for the first time. Within the experimental uncertainty no significant dependence of the shift effect on the isotopomer was found. TheR-branch line under study shows a smaller line shift coefficient than aP-branch line with a similar rotational quantum number. With increasing mass of the noble gas perturber the absolute size of the shift coefficient increases. Moreover self- and nitrogen-broadening coefficients for the isotopomer lines were determined. Compared to previous measurements no significant deviations between different isotopomers were observed.     

Cross sections of the reactions16O(γ,x)13 N and16O (γ,x)11 C,and Yield of12C (γ, t) up to 55 MeV

Yield curves of the reactions¹⁶O (γ, x)¹¹C,¹⁶O (γ, x)¹³N and¹²C(γ, t) have been measured relative to¹²C(γ, n)¹¹C with bremsstrahlung. The cross section σ[¹⁶O(γ, x)¹¹C] has a shape similar to σ[¹⁶O(γ, t)] and shows a broad maximum near 38 MeV. Differences between σ[¹⁶O(γ, x)¹³ N] and σ[¹⁶O(γ, t)] point to a reaction mechanism via quadrupole absorption in¹⁶O. The yield of¹²C(γ, t) exceeds the¹⁶O(γ,t) yield by a factor of two.     

Nuclear Rms charge radii from relative electron scattering measurements at low energies

The nuclear rms charge radii measured by low energy electron scattering at Darmstadt are summarized. Improvements in the experimental equipment and method permitted a redetermination of the¹²C radius which yieldedR _m (¹²C)=2.462 ± 0.022fm. This value has been used to recalibrate the radii measured relative to¹²C.     

Measurement of spin-alignment of excited12C2+ nuclei in interactions of16O with12C usingγ-decay in flight

Measuring energy spectra of nuclei afterγ-decay of excited states in flight the spin alignment of¹²C₂₊ states has been measured. Inelastic scattering,¹⁶O(¹⁶C,¹²C₂₊)¹⁶O and the reaction¹²C(¹⁶O,¹²C₂₊)¹⁶O leading to¹²C₂₊ (4.43 MeV) state have been studied. Characteristic line shapes of the¹²C₂₊ peak were observed using a Q3D magnetic spectrometer. The magnetic substate (m-states) population has been deduced from the spectra as function of reaction angle. A comparison of the measuredm-state population with reaction models shows that the first reaction is consistent with inelastic scattering although discrepancies remain. Discrepancies are also obtained if the reaction¹²C(¹⁶O,¹²C₂₊)¹⁶O is interpreted using a FRDWBA transfer calculation. At least 1/3 of the cross section can be attributed toα-transfer. A calculation which couples transfer and inelastic scattering channels seems to be necessary.     

The 12C(α, γ)16O reaction and stellar helium burning

The cross section for the reaction ¹²C(α, γ)¹⁶O has been measured for a range of c.m. energies extending from 1.41 MeV to 2.94 MeV, by using ¹²C targets of high isotopic purity, large NaI(T1) crystals, and the time-of-flight technique for the suppression of prompt neutron background and time-independent background. Gamma-ray angular distributions were measured at c.m. energies of 2.18, 2.42, 2.56 and 2.83 MeV. By means of theoretical fits, which include the coherent effects of the 1^? states of ¹⁶O at 7.12 MeV, 9.60 MeV, and those at higher energies, the electric-dipole portion of the cross section at astrophysically relevant energies has been determined. A three-level R-matrix parametrization of the data yields an S-factor at E_c.m. = 0.3 MeV, S(0.3 MeV) = 0.14^+0.14_?0.12 MeV · b. A “hybrid” R-matrix optical-m parameterization yields S(0.3 MeV) = 0.08^+0.05_?0.04 MeV · b. This S-factor is of crucial importance in determining the abundances of ¹²C and ¹⁶O at the end of helium burning in stars.     

Elasticp+12C scattering between 0.3 and 2 MeV

Absolute differential cross-sections ofp+¹²C elastic scattering have been measured atθ _cm=89.1°, 118.7°, 146.9° for bombarding energies between 0.3 and 2.0 MeV. Revised level parameters of the first three excited states in¹³N have been extracted with aR-matrix analysis. It is shown that the influence of the bound ground-state of¹³N has an appreciable effect on low-energy scattering. Recent predictions concerning Mott-Schwinger polarization are also discussed.     

Comparison of one and two-neutron transfer near the coulomb barrier for the27Al(18O,16O)29Al,27Al(180,17O)28Al and27Al(13C,12C)28Al reactions

Total reaction cross sections for the transfer reactions²⁷Al(¹⁸O,¹⁶O)²⁹Al,²⁷Al(¹⁸O,¹⁷O)²⁸Al and²⁷Al(¹³C,¹²C)²⁸Al are reported for center-of-mass energies between 13 and 20 MeV for¹⁸O projectiles and between 11 and 17.5 MeV for¹³C projectiles. The reaction products,²⁹Al and²⁸Al, beta decay to²⁹Si and²⁸Si, respectively, and the subsequentγ decays of²⁹Si and²⁸Si were measured. Due to the relatively long beta decay half lives, data were taken in a beam-off mode, resulting in very clean spectra. Total cross sections were calculated and compared with a theoretical model for barrier penetration proposed by C.Y. Wong. Differences between¹⁸O induced one and two-neutron total transfer reaction cross sections are discussed.     

High-velocity DSA measurements in the 1–20 ps lifetime region: Comparison between DSA and RD

Mean lives in the range 1–20 ps of low-lying states of ¹³C, ¹⁶N, ²⁰O and ³⁶Cl have been measured with the Doppler-shift attenuation method by heavy-ion bombardment of ²H and ³H targets. The recoils are slowed down in Mg, Al, Cu, Ag and Au. The γ-ray patterns are observed with a large Ge(Li) detector at 0° in coincidence with protons; for ¹³C the patterns are measured in singles with a Compton-suppression spectrometer. Analysis of the γ-ray patterns with ⁴He-scaled stopping power data of Northcliffe and Schilling yields the following results: ¹³C, τ_m(3.85 MeV) = 12.6 ± 0.3ps; ¹⁶N, τ_m(0.40 MeV) = 5.1 ± 0.3 ps; ²⁰O, τ_m(1.67 MeV) = 9.8 ± 0.7 ps; ³⁶Cl, τ_m(0.79 MeV) = 19.9 ± 1.7 ps, τ_m(1.16 MeV) = 9.2 ± 0.6 ps and τ_m(1.60 MeV) = 0.94 ± 0.06 ps. A comparison with results obtained with the recoil-distance method shows agreement to about 10 %, with a slight tendency to somewhat longer lifetimes for the recoil-distance technique. The above stopping power is also used to reanalyze our previously published measurements. The new mean lives differ less than 4.5 % from the previous results.     

Heterodyne measurements of 12C18O, 13C16O,and 13C18 O laser frequencies; mass dependence of Dunham coefficients

Difference frequencies between rare isotope CO lasers and a ¹²C¹⁶O laser have been measured by optical heterodyne techniques. These data for ¹²C¹⁸O, ¹³C¹⁶O, and ¹³C¹⁸O have been used together with the 15 previously reported Dunham coefficients Y_kl for ¹²C¹⁶O to determine a set of mass independent parameters Δ_kl and U_kl defined by Y_kl = μ^-(k/2+l)[1+m_e(Δ^C_kl/M_C + Δ^O_kl/M_O)] U_kl. The 01, 1 0, and 20 correction terms were found to be statistically significant. Line frequencies calculated from the resulting 15 Dunham coefficients for the rare isotopes are accurate to a few MHz in the measured laser bands.     

Atomic beam magnetic resonance investigations in the 2p 2 3 P ground multiplet of the stable carbon isotopes12C and13C

The hyperfine structure seperations Δv andg _J -factors have been measured in the 2p ^{2 3} P states of¹³C(I=1/2) and¹²C(I=0), respectively, using the atomic beam magnetic resonance method. The results are Δv(³ P ₁,¹³C)=4.200 (25) MHz, Δv(³ P ₂,¹³C)=372.593 (25) MHz,g _J (³ P ₁,¹²C)=1.501052 (13), andg _J (³ P ₂,¹²C)=1.501039 (15). After applying corrections due to perturbations by neighbouring fine structure levels one deduces the constants of the magnetic dipole interactionA(³ P ₁,¹³C)=+2.838 (17) MHz, A(³ P ₂,¹³C)=+149.055 (10) MHz. No signs of theA-factors were determined by the experiment; they follow from the known positive sign of the nuclear magnetic moment μ _I of¹³C. CombiningA(³ P ₂,¹³C) with the results of other measurements on¹¹C, yields μ _I (¹¹C)=?0.964 (1) nm.     

N2Broadening in theCO 2–0 Band around 4167 cm

N₂broadening coefficients have been measured for 65 lines of the¹³C¹⁶O 2–0 band using a Fourier transform spectrometer. These lines are located in the spectral range 4011–4252 cm⁻¹. The spectra were recorded with 99% isotopically pure¹³CO in a White-type cell at a resolution of 0.005 cm⁻¹. Voigt profiles convolved with the FTS apparatus function were fitted to the experimental lineshapes using a nonlinear least-squares fit technique. From the fits the Lorentzian HWHM was determined as function of N₂pressure. Pressure broadening coefficients formbetween −33 and +34 were obtained with uncertainties of 5.8%. The results are compared to earlier published N₂broadening coefficients and our measurements in the 2–0 band of¹²C¹⁶O. To our knowledge this is the first investigation of¹³CO pressure broadening.