Measurement of partial radiation widths of high energy transitions from keV capture resonances in56Fe and58,60Ni

High energyγ-ray transitions to low-lying states following neutron capture in⁵⁶Fe and^58,60Ni have been investigated for individual resonances in the neutron energy range 7–70keV using a 50cc Ge(Li)-detector. Partial radiation widths fors- and 1>0 wave resonances were determined. For the 1>0 wave resonance in⁵⁸Ni at 47.8 keV a spin of 3/2 was derived. Theγ-ray strength forM1 transitions was found to be (21±17)×10^?9 and (16±7)×10^?9MeV^?3 for⁵⁶Fe and⁵⁸Ni, respectively. The partial radiation widths of the studieds-wave resonances were compared with valence model calculations.     

Thermal neutron capture in isotopes of nickel

The gamma-ray spectra associated with thermal neutron capture in targets of⁵⁸Ni,⁶⁰Ni,⁶²Ni, and⁶⁴Ni have been observed with a high-sensitivity pair-spectrometer. Level schemes for the four product nuclei are discussed, correlation of widths with neutron single-particle states examined, and estimates forM1 andE2γ-ray strength functions obtained.     

Gamma ray energies and 36Cl level scheme from the reaction 35Cl(n, γ)

The γ-ray spectrum emitted after thermal neutron capture in ³⁵Cl has been studied by use of the crystal and pair spectrometers installed at the ILL high flux reactor. We identified about 400 transitions in this reaction 326 of which were placed into the ³⁶C1 level scheme; several new states were found. The level energies up to 3.5 MeV were measured with a precision of 5–20 eV relative to the 412 keV ¹⁹⁸Au standard, those above 3.5 MeV with a precision of ¹⁰ppm. The neutron binding energy was determined to be E_B = 8579.68(9) keV.     

Excited states in neutron deficient even-even thorium isotopes (218≦A≦222)

The nuclei^{218, 220, 222}Th were investigated by conversion electron andγ-ray spectroscopy after compound nucleus reactions of¹⁴N with²⁰⁹Bi and^{16, 18}O with²⁰⁸Pb. The intenseγ-background from fission was suppressed by spectroscopy of conversion electrons andγ-rays in coincidence with the evaporation residues or theirα-decay. Level schemes were determined for²¹⁸Th up toI ^π=10⁺ and for²²⁰Th and²²²Th up toI ^π=15^?. The observed structure of²¹⁸Th may be explained in the spherical shell model with residual interaction by two neutron excitation. ForN≧130 completely different level schemes are observed showing very intense, collective electric dipole transitions (B(E1)?10^?2 W.u.) with energies of typically 200 keV. Interpretation in terms of stable octupole deformations of the ground state as well as in anα-cluster picture are discussed.     

The ground state mass of147Gd from single-neutron-transfer reactions and its impact on derived mass values

Using a¹⁴⁸Gd radioactive target and the (p,d), (d,t), and (³He,α) single neutron pick-up reactions we have measured the¹⁴⁷Gd mass excess as — 75,366(4) keV, which differs by 139(24) keV from the adopted value of the 1983 mass table. From this result, and from recently reported first transfer-reaction mass determinations for¹⁴⁵Eu and¹⁴⁶Eu, we have recalculated the masses of nuclei above¹⁴⁶Gd from a previous shell model analysis of high-spin states.     

Der Zerfall des122Xe (T 1/2=20,l h) und des122J (T 1/2=3,6min)

Theγ spectra emitted in the decay of¹²²Xe and¹²²I have been investigated using Ge(Li) detectors and a Ge(Li)-NaI coincidence apparatus. 14γ transitions with energies between 61.8 and 416.9 keV have been identified in the decay of¹²²Xe, 44 transitions between 564.0 and 3,291.0 keV in the decay of¹²²I. Level schemes having 7 excited levels for¹²²I and 21 excited levels for¹²²Te are proposed.     

Determination of the neutron binding energy of the delayed neutron emitter137Xe

The neutron binding energy of¹³⁷Xe has been deduced to be 4025.2±0.6 keV from a study of the¹³⁶Xe(n, γ)¹³⁷Xe reaction. The importance of a precise value for this quantity is due to the fact that an accurate determination of binding energies of delayed neutron emitters is possible only for⁸⁷Kr and¹³⁷Xe, neighbouring stable isotopes. Nuclear reaction.¹³⁶Xe(n,γ), enriched target; measurede89-01, deduced neutron binding energy, Ge(Li) detector.     

Levels in 156Gd studied in the (n, γ) reaction

Levels up to 2.3 MeV in ¹⁵⁶Gd have been studied using the (n, γ) reaction. Energies and intensities of low-energy γ-rays and electrons emitted after thermal neutron capture have been measured with a curved-crystal spectrometer, Ge(Li) detectors and a magnetic electron spectrometer. High-energy (primary) γ-rays and electrons have been measured with Ge(Li) detectors and a magnetic spectrometer. The high-energy γ-ray spectrum has also been measured in thermal neutron capture in 2 keV resonance neutron capture. The neutron separation energy in ¹⁵⁶Gd was measured as S_n = 8535.8 ± 0.5 keV.About 600 transitions were observed of which ~50% could be placed in a level scheme containing more than 50 levels up to 2.3 MeV excitation energy. 42 of these levels were grouped into 15 excited bands. In addition to the β-band at 1050 keV we observe 0⁺ bands at 1168, 1715 and 1851 keV. Other positive-parity bands are: 1⁺ bands at 1966, 2027 and 2187 keV; 2⁺ bands at 1154 (γ-band) and 1828 keV; and 4⁺ bands at 1511 and 1861 keV. Negative-parity bands are observed at 1243 keV (1^?), 1366 keV (0^?), 1780 keV (2^?) and 2045 keV (4^?). Reduced E2 and E0 transition probabilities have been derived for many transitions. The ground band, the β- and γ-bands and the 0⁺ band at 1168 keV have been included in a phenomenological four-band mixing calculation, which reproduces well the experimental energies and E2 transition probabilities.The lowest three negative-parity (octupole) bands of which the 0^? and the 1^? bands are very strongly mixed, were included in a Coriolis-coupling analysis, which reproduces well the observed energies. The E1 transition probabilities to the ground band are also well reproduced, while those from the higher-lying 0⁺ bands to the octupole bands are not reproduced. Absolute and relative transition probabilities have been compared with predictions of the IBA model and the pairingplus-quadrupole model. Both models reproduce well the E2 transitions from the γ-band, while strong disagreements are found for the E2 transitions from the β-band. The IBA model predicts part of the decay features of the higher lying 2⁺₂, 4⁺₁ and 2^?₁ bands.     

The study of prompt and delayed muon induced fission

The mean life times of negative muons bound to actinide nuclei have been measured by detecting the time difference between a stopped muon and the arrival of fragments from delayed fission after muon capture. The deduced capture ratesΛ _c are 1.392(4)·10⁷/s for²³⁷Np, 1.290(7)·10⁷/s for²⁴²Pu and 1.240(7)·10⁷/s for²⁴⁴Pu. The results are compared with published data for the fission and the neutron decay channels and for the electron decay of the bound muon. Including a former measurement ofΛ _c for²³⁹Pu, an isotopic dependence of the muon capture rates in the Pu isotopes is clearly observed.     

The19F(n, γ)20F reaction

The gamma-ray spectrum emitted following thermal neutron capture in¹⁹F has been studied with curved crystal and Ge(Li) spectrometers. From the 109 transitions assigned to²⁰F, 85 have been placed in a level scheme containing 26 levels. An average gammaray multiplicity of 2.8 gammas per neutron capture was observed. The neutron binding energy was found to be 6601.33(14) keV. The experimental level scheme is compared to rotational model predictions. In addition it is shown that the decay of the capture state is non-statistical and that there is a strong correlation between the strengths of excitation of levels by the (n, γ) and (d, p) reactions. Calculations of the partial cross-sections using the direct capture theory of Lane and Lynn give order of magnitude agreement with experiment.     

Alpha decay studies of neutron-deficient radium isotopes

Neutron-deficient isotopes of radium have been produced in the reactions³⁵Cl+¹⁷⁵Lu,⁴⁰Ar+^170,171Yb, and³⁶Ar+^170,171Yb and separated in-flight with a gas-filled recoil separator. The activities have been identified on the basis of correlated alpha decay chains. The alpha particle energy E_α and the half-life T_1/2 of an isomeric state of the new isotope,^203m Ra, have been determined to be (7615±20) keV and (33 _?10 ⁺²² ) ms, respectively. An assignment of another decay with E_α = (7577±20) keV and T_1/2=(1.1 _?0.5 ^+5.0 ) ms to^203g Ra is made on the basis of one observed three-decay chain. Tentative evidence for the production of the new isotope²⁰²Ra is also given. The values E_α = (7860±60) keV and T_1/2=(0.7 _?0.3 ^+3.3 ) ms were measured. Improved decay data have been obtained for²⁰⁴Ra. The results are E_α = (7484±10) keV and T_1/2=(59 _?9 ⁺¹² ) ms. Earlier findings concerning the decay of two states in²⁰⁵Ra and an isomer in²⁰⁷Ra have been confirmed. Approximate values for cross sections have been determined for²⁰²Ra, produced using the³⁶Ar+¹⁷⁰Yb reaction and for²⁰³Ra,²⁰⁴Ra, and²⁰⁵Ra using the³⁵Cl+¹⁷⁵Lu reaction. The results are 2 nb (²⁰²Ra), 4 nb (²⁰³Ra), 40 nb (²⁰⁴Ra), and 800 nb (²⁰⁵Ra).     

High spin states in205Pb and a precision test of the nuclear shell model for three nucleons

Using the²⁰⁴Hg(α, 3n) reaction withα-particles of about 40 MeV, we have proved by applying nowadays conventionalγ-ray spectroscopy in-beam technique, that there are two isomeric states in²⁰⁵Pb at the excitation energies 5,161.3 and 3,195.5 keV having the half-lives 71±3 and 217±5 ns, respectively. These isomeric states have spins and parities 33/2⁺ and 25/2^? and are mainly due to thei ₁₃ ^2/?3 andi ₁₃ ^2/?2 p ₁ ^2/?1 configurations, respectively. This conclusion is supported by the experimentalg-factors of these states being ?0.159±0.008 and ?0.0676±0.0011, respectively. It is furthermore shown that theE2 effective neutron charge is the same forE2 transitions from the 33/2⁺ state in²⁰⁵Pb and from the 12⁺ state in²⁰⁶Pb as required by the assumption that the²⁰⁸Pb core is responsible for the totalE2 strength of the neutron holes, and that these states are due to thei ₁₃ ^2/?3 andi ₁₃ ^2/?2 configurations. The calculatedB(E3) values ofE3 transitions from isomeric states in²⁰⁵Pb and²⁰⁶Pb agree reasonably well with the experimental values as expected from the assumption that theE3-strength should come from particle coupling to the octupole states of the²⁰⁸Pb core. The energies of the six most well established excited states in²⁰⁵Pb with angular momenta in the region 19/2–33/2 were calculated using empirical single-particle energies, empirical two-particle interactions and angular momentum algebra. The average deviation between experimental and calculated energies is ?3 keV and the root mean square deviation 6 keV as compared to the uncertainty ± 5 keV in the nuclear masses used in the calculation. For the orbits concerned the shell model is thus valid with an extremely high precision. The contribution of effective three-particle interaction in these orbits must consequently be less than about 5 keV.     

Nuclear structure effect on internal conversion ofl-forbidden transitions in139La,141Pr and203Tl

Accurate experimental internal conversion data have been used to study the effect of nuclear penetration in the case of thel-forbidden transitions in¹³⁹La (165.8 keV),¹⁴¹Pr (145.4 keV) and²⁰³Tl (279.2 keV). The nuclear penetration parameterλ and theE2/M 1 mixing ratioδ ² have been deduced by graphical analysis. Following results were obtained:λ=2.8±1.3,δ ² =(8.4 _?8.4 ^+14.0 )·10^?4 for¹³⁹La,λ=1.2±0.6,δ ²=(4.8±0.5)·10^?3 for¹⁴¹Pr, andλ=6.4±1.1,δ ²=1.36±0.12 for²⁰³Tl.     

Triple differential cross section for angle,atomic number and energy (or angular momentum transfer) calculated for the 280MeV40Ar+58Ni (or 365MeV63Cu+197Au) system in a simple model

Highly excited levels of³³S populated by α-particle capture in²⁹Si have been investigated forE _α=1.962 MeV to 4.287 MeV. Excitation curves measured with Ge(Li) and BF₃ detectors are reported. More than fifty resonances can be identified with levels in³³S. (α, γ) angular distributions measured on five strong resonances have yieldedJ ^π values 1/2+, 3/2 +, 5/2?, 5/2?, 5/2? and 3/2+ respectively, for theE _x =10.054, 10.466, 10.523, 10.721, 10.758 and 10.776 MeV levels in³³S. Elastic scattering experiments have been performed and theJ ^π assignments are found to be consistent with thel-values inferred from the elastic scattering data. Decay schemes from the above³³S levels have been proposed. A new level at 9.245 MeV is also suggested and theJ ^π values for the 4.425 and 2.87 MeV states are shown to be consistent with 7/2+ and 3/2+ assignment, respectively. Nuclear Reactions²⁹Si(α, γ) and²⁹Si(α, α),E _α=1.962-4.287 MeV. Measured relative σ(E). DeducedJ ^π andE _γ of³³S levels. New³³S level atE _x =9.245 MeV. Enriched targets.     

The determination of the beta decay energies of105–108In

Theβ ⁺-spectra of the neutron deficient indium nuclei, produced in the reaction^natMo(¹⁶O,pxn), have been measured using a solid state beta detector, and mass separated sources. Values forQ _EC have been determined for^105–108In anc for¹⁰⁵Cd and¹⁰⁶Ag.     

Thermal neutron captureγ-ray spectroscopy of59Ni and61Ni

Theγ-radiation emitted after thermal neutron capture in isotopically enriched⁵⁸Ni and⁶⁰Ni was measured at the ILL high flux reactor by means of Ge/NaI detectors operated in Compton suppression and pair spectrometer mode. The neutron binding energies were determined asB _n (⁵⁹Ni)=8999.15(23) keV and B_n(⁶¹Ni)=7820.07(20) keV; some 95% of the totalγ-ray fluxes through^59,61Ni were assigned. Theγ-ray strength functions of the primary transitions and the level densities are discussed.     

Kernradien von12C,13C,14N und16O aus Elektronenstreuung zwischen 30 und 60 MeV

Elastic electron scattering cross sections of¹²C,¹⁴N and¹⁶O relative to the proton, and of¹³C relative to¹²C have been measured. Using harmonic oscillator wave functions the followingrms charge radiiR _m were deduced by phaseshift calculations: 2.395 (28) fm for¹²C, 2.384 (47) fm for¹³C, 2.492 (33) fm for¹⁵N, 2.666 (33) fm for¹⁶O. The ratioR _m (¹³C)/R _m (¹²C) is 0.995±0.008. The errors given do not include uncertainties from the model dependence of the evaluation which may be of the same magnitude.     

Untersuchung der Anregungen von186Re nach der (n, γ)-Reaktion

Prompt and delayedγ-γ-coincidences were measured after slow neutron capture in¹⁸⁵Re by use of Ge(Li)-detectors. New isomers were found at 99.4 keV (T_1/2=27±7ns) and at ≈330keV (T_1/2=17.4±0.7 ns). The evaluation of coincidence data established 10 rotational bands with band heads below 700 keV. The level scheme is discussed in detail: Nilsson assignments are proposed for the band configurations, and calculations of Coriolis mixing andγ-transition probabilities are presented which reproduce the experimental level energies and transition intensities very satisfactorily.     

810.6–863.6 keV γγ-directional correlation in58Fe

The 810.6–863.6 keV γγ-directional correlation has been measured with an NaI(Tl)-Ge(Li) detector system. The NaI window was set on the 810.6+863.6 keV composite peak. From the (810.6 NaI gate) (863.6 Ge spectrum) data at 90 °, 135 °, and 180 °, we deducedA ₂=+0.51±0.03 andA ₄=+0.09±0.04. These results disagree with the values previously obtained from⁵⁸Co decay (with Nal-NaI detector systems) but agree with the values from γγ(θ) studies following thermal neutron capture by⁵⁷Fe.