Resonance strengths,branching ratios and mean lifetimes of nuclear energy levels in23Na

The gamma decay of the²²Ne(p, y)²³Na resonances in the proton energy rangeE _p=1.0→2.0 MeV has been investigated with a 20cm³ Ge(Li) detector. Implanted targets were used. The absolute strengths of the strongest resonances were determined and the branching ratios of twenty resonance levels and several bound states are reported. Mean lifetimes of the levels atE _x=2.078 MeV (18.7±3.5 fs), 2.393 MeV (580 _?190 ⁺³⁷⁰ fs), 2.641 MeV (88 _?14 ⁺²⁰ fs), 2.985 MeV (4.0 _?1.0 ^+1.3 fs), 3.679 MeV (24 _?4 ⁺⁵ fs), 3.915 MeV (7.4 _?2.0 ^+2.5 fs) and 4.775 MeV (<2.0 fs) were obtained from measurements of the gamma ray Doppler shifts.     

DSA lifetime measurements in21Ne at high recoil velocity

States in²¹Ne up to 5 MeV excitation energy have been populated using the inverted reaction²H(²⁰Ne,pγ). The Doppler shift attenuation (DSA) analysis of thepγ coincidence spectra taken in a Ge(Li) detector at 45° and 135° and an annular silicon surface barrier detector near 0° yielded the lifetimes of 8 states in²¹Ne. Due to the large recoil ofπ _i/c～ 4% three new lifetimes were determined for the short lived levels at 2.80, 4.68 and 4.73 MeV, namely 10±4 fs, 16±4 fs and 10±4 fs, respectively. The results are compared with rotational and shell model calculations.     

Studies of neonL-shell excitation by impact of highly ionized heavy ions

Passage of foil-excited 1.4 MeV/A S and 1.1 MeV/A Cl ions of neon charge state ～ 12⁺ through neon gas targets at pressure ～100 mTorr has been found to be accompanied by copious production of Ne II–VIII excited states. Comparable excitation cross-sections ～10^?18 cm² are found for a large number of levels belonging to all of these charge states and corresponding to principal quantum numbersn=2, 3, 4. Vacancy distributions very similar to those found in beam-foil excitation of ～1MeV neon beams are found. Because the Ne recoil velocities are small compared to the fast beam velocities characteristic of the beam-foil source, it is possible to reduce both Doppler shifts and spreads by 3–4 order of magnitude for equivalent collimation. It has also been found that there is an excitation cross-section change of a factor ～5 for a corresponding projectile charge state change from 6⁺ to 12⁺, that efforts to classifyK x-ray satellite spectra byLshell vacancy labels (KL ⁰,KL ¹,...) are probably inaccurate due to extensive population ofn≧3 spectator levels, that both the recoil ion and beam-foil spectra exhibit few lines withn≧4, and that for the allowed transitions studied here, collisional excited states quenching effects due to the ～100mTorr target gas pressures used are negligible.     

Investigations of Properties of <Superscript>89</Superscript>Y Levels with Reactor Fast Neutrons

By employing a beam of reactor fast neutrons, the spectrum of gamma rays up to an energy of 4.6MeV and their angular distributions with respect to the neutron-beamaxis aremeasured in the reaction ⁸⁹Y(n, n'γ). The multipolarities and multipole-mixture parameters for 34 gamma transitions and the spin–parities J^π of states excited in this reaction are determined. The lifetimes of the lowest 32 levels of 89Y were measured by the Doppler shift attenuation method, and the reduced probabilities for the respective gamma transitions were calculated. Levels of the K^π = +5/2⁺ and K^π = ?7/2⁺ bands associated with, respectively, prolate and oblate deformation shapes are found in ⁸⁹Y at low excitation energies.     

Experimental study of the isomeric states101mRu,103mRu and101mTc

In natural Ruthenium isomeric states were produced by photonuclear reactions with LINAC Bremsstrahlung of 26 MeV. They were identified as: 526.6±0.7 keVT _1/2=22.5±0.5 μsec in¹⁰¹Ru 192.0±0.2 keVT _1/2=760±50 μsec in¹⁰¹Tc 210.9±0.2 keVT _1/2=1560±50 μsec in¹⁰³Ru The experimental techniques are described.     

The gamma-decay of34Ar

States in³⁴Ar up to 5.5 MeV excitation energy, populated by the³²S(³He,nγ) reaction at 8–12 MeV bombarding energy, have been investigated with the Doppler shift attenuation method,nγ angular correlation andnγγ triple coincidence measurements. For the states at 2.09, 3.29 and 4.52 MeV the lifetimes 200±60 fs, 130±60 fs and 260±80 fs have been found, respectively. Thenγ correlations yielded the spin assignmentsJ ^μ=(2⁺) for the level at 4.13 MeV andJ ^μ=3^? for the 4.52 MeV state, and the mixing ratiosδ(3.29→2.09)=?0.12±0.05 andδ(4.13→3.29)=?0.52±0.15. The results are compared with shell model calculations and predictions from the weak coupling unified model.     

6Li electromagnetic form factors and phenomenological cluster models

The longitudinal form factors of the ground and 2.18 MeV (3⁺, T = 0) states, and the transverse form factors of the 3.56 MeV (0⁺, T = 1) and 5.37 MeV (2⁺, T = 1) states of ⁶Li are compared with the predictions based on fully antisymmetrized α-d and t-τ cluster models. The longitudinal form factors are adequately described by the α-d model, but the transverse form factors seem to be more consistent with a t-τ model which is close to the shell-model limit. Estimates are made for the ground state t and α spectroscopic factors. The 3.56 MeV M1 transition current density is calculated for both models and compared with experiment.     

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.     

Unelastische Elektronenstreuung an14N für Anregungsenergien zwischen 8,5 und 11,5 MeV

¹⁴N was investigated by inelastic scattering of 35... 58 MeV electrons (scattering angles 117 to 165°). For theM1-transitions to the 2⁺,T=1 levels at 9.17 and 10.43 MeV, ground state radiation widths of (7.7±0.9) eV, and (12.1±1.5) eV, respectively, were obtained. The ratio of these two widths is 1.57±0.07. The 3^?,T=1 level at 8.90 MeV is excited by anM2-transition withΓ _γ ⁰ =(6.6±2.2) · 10^?3 eV. An excitation of a level at (11.01±0.07) MeV is observed.     

Precise excitation energy and γ-ray decay of the lowest T = 2 state in 40K

The excitation energy of the lowest T = 2 state in ⁴⁰K has been determined as E_x = 4384.0 ± 0.3 keV from n-γ and γ-γ coincidence experiments. The state was populated with the ⁴Ar(p,n)⁴⁰K reaction at E_p = 8.30 MeV. Gamma-gamma angular correlation measurements yield unambiguous spin assignments J = 0 and 1 for the 1.64 and 2.290 MeV states, respectively. The excitation energy of the T = 2, J^π = 0⁺ state leads to a calculated mass excess of ?9120 ± 150 keV for ⁴⁰Ti.     

Two-particle,two-hole Jπ=0+ states in 40Ca

Excited J^π=0⁺ states in ⁴⁰Ca have been identified by the observation of L=0 angular distributions in the ³⁸Ar(τ, n) ⁴⁰Ca reaction. Strong transitions are observed to the ground state, the known 2p–2h at 9.38 (T=1) and 11.98 MeV (T=2), and to states at 8.28 and 10.65 MeV. The strongest excited-state transition is to the 8.28 MeV state, which we identify as the 2p–2h T=0 state. The J^π=0⁺ state at 7.30 MeV which has been suggested as the 2p–2h T=0 state is not observed.     

Lifetimes of low-lying levels in 18F

Mean lifetimes of levels in ¹⁸F have been measured using the Doppler-shift attenuation method and the inverse reaction ³He(¹⁶O, p)¹⁸F. Targets of ³He implanted into Al, Nb, and Au foils were employed in the measurements. The Doppler-broadened lineshapes observed at 0° to the beam were analyzed to obtain the following lifetime values: 0.971 ± 0.030, 0.605 ± 0.029 and 0.435 ± 0.041 ps for the 1.70(1⁺), 2.52(2⁺) and 3.36(3⁺)MeV members of the K^π = 1⁺ rotational band, 5.12 ± 0.56, 0.403 ± 0.018 and 1.91 ± 0.17 ps for the 2.10(2^?), 3.13(1^?) and 3.79(3^?) MeV members of the K^π = 0^? bands, and 〈1.2, 2.7^+4.1_?2.7 and 20 ± 2 fs for the 3.06(2⁺, T = 1), 3.72(1⁺) and 3.84(2⁺) MeV states, respectively.     

Messung der Zirkularpolarisation der 478 keV-Gammaquanten aus der Reaktion Li6(d,p)Li7 mit 2 MeV-Deuteronen

The circular polarizationP _γ of 478 keVγ quanta from the reaction Li⁶(d, pγ) Li⁷ with 2 MeV deuterons was measured by forward Compton scattering from magnetized iron. The protons were observed at 25° lab angle. The fast neutron background in theγ detector was suppressed by pulse shape discrimination. The resultP _γ=+ 0.022 ± 0.17 with the Basel sign convention confines the ratio of the reduced widthsΘ _± for the capture of the neutron withj=1±1/2 to the regions ?2.36≦Θ ₊/Θ _?≦?0.74 or ?0.06≦Θ ₊/Θ _?≦+0.61.     

Electron scattering studies of magnetic isovector transitions in 12C at high momentum transfer

The inelastic electron scattering cross sections for the M1 transition to the 15.11 MeV (1⁺, T = 1) level and for the M2 transition to the 16.58 MeV (2^?, T = 1) level in ¹²C have been measured in the momentum transfer region q = 0.4–3.0 fm^?1, with emphasis on precise data at high momentum transfers. Additionally, a broad state near 15.4 MeV excitation has been observed and its excitation energy and natural width have been established as 15.44 ± 0.04 MeV and 1.5 ± 0.2 MeV, respectively. The Fourier-Bessel technique for determining the Mλ transition current density has been applied to the M1 and M2 transitions. Particular attention has been paid to the Coulomb corrections required to deduce the PWBA form factors. The M1 radiative width is Γ_γ0 = 38.5 ± 0.8 eV.     

Quantum numbers of26Al levels above 6 MeV excitation energy

Measurements of resonance strengths and ofγ-ray angular distributions or anisotropies have been performed on selected resonances of the²⁵Mg(p, γ) reaction in the rangeE _p=2–4 MeV,E _x=8.2?10.1 MeV with an emphasis on high-spin andT=1 analog resonances. EightT=1 states are identified, among them high-spin states at 8747 keV (I=6), 9286 KeV (I=5), and 9986 keV (I ^π = 7⁺, 6⁺). Shell model calculations in thes-d basis space reproduce the branching ratios of these states and clarify the nature of final states. New high-spinT=0 states are observed at 9720 keV (I ^π = 7⁺), 8602 keV (I = 6), and 6695 keV (I ^π = 7⁺). TheI ^π assignments to severalE _x = 6–8 MeV states are revised and the role of two-particle excitations into thef-p shell is elucidated. A revised spectrum of 73 positive-parity,T = 0 states is compared to the predictions of shell-model calculations in thes-d basis space using the universals-d shell Hamiltonian.     

The ground stateM1 strength in40Ca

The M1 gamma decay strengths of the ground state transitions of the 1⁺,T=1 states of⁴⁰Ca at 9.86 MeV and 10.32 MeV have been measured using the reaction³⁹K(p,γ)⁴⁰Ca. The measured ground state gamma decay widths of these levels are 1.06±0.15 eV and 5.8±0.8 eV respectively. These relatively large M1 strengths can be explained by a shell model calculation incorporating excited core configurations.     

Evidence for the coexistence of spherical and deformed states in38Ar

The³⁸Ar levels at E_x=5350, 7289 and 9341 keV have been investigated using the³⁵Cl(α,pγ) reaction at E_α=l4 and 14.5 MeV. From particle-γ-ray angular correlations the spin assignments J(5350)=4, J(7289)=6,4 and J(9341)=8,6,4 have been obtained. Life-time measurements using the Doppler-shift attenuation method yielded τ(9341)=106±25 fs and τ(7289)=77±30 fs, while the lifetime τ(5350)=200±50 fs was known previously. All levels have positive parity and decay by enhanced E2 transitions. Hence we propose that they are the J^π=4⁺, 6⁺ and 8⁺ members, respectively, of a K^π=0⁺ rotational band which has the E_x=3377keV, J^π=0⁺ and the 3937 keV, J^π=2⁺ levels as further members. The enhancement of inband E2 transitions is 30 _?6 ⁺¹⁰ W.u. (4→2), 35 _?14 ⁺³⁰ W.u. (6→4) and 20–36 W.u. (8 → 6), respectively, yielding an average intrinsic quadrupole moment Q₀=850 _?125 ⁺²⁰⁰ mb. The moment of inertia is given by h²2θ=92 keV. The present data are in good agreement with the predictions of a deformed state in³⁸Ar that coexists with the spherical states.     

Three-particle correlations from208Pb+6Li

Three-particle correlations in the reaction²⁰⁸Pb+⁶Li were studied near the Coulomb threshold between \(E_{6_{Li} } = 24\) and 30 MeV. Three reaction mechanisms contribute predominantly to the observed coincidences of the charged particles: 1. Coulomb excitation of the 2.184 MeV,J=3⁺ state of⁶Li, followed by the decay intoα+d, 2. Deuteron pick-up of the⁶Li to the ground state of⁸Be and sequential decay into twoα-particles and 3. Neutron-transfer to the ground state and the first excited states of²⁰⁹Pb:²⁰⁸Pb(⁶Li,αp). The last two reaction mechanisms explain the previously measured large contributions to theα-channel relative to thed-channel.     

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.