The slowing down of atoms with energies ofE<10 eV in crystals

The line shape of the 773 keV emission line emitted by¹⁸⁷Re depends on the slowing down of the recoil the atom receives in the precedingβ transition. Using the nuclear resonance fluorescence method the line profile was studied for sources where the radioactive atoms are embedded in single crystals of W and WSe₂ and in polycrystalline samples of Nb. The experimental results for W and Nb are in complete agreement with predictions by a theory in which the slowing down is calculated starting from a Born-v. Karman lattice model. The temperature dependence of the line shape yields the phonon lifetimes in W and Nb (W) to beτ(300 K)=(2.4±0.3)ps andτ(300 K)=(1.7±0.2) ps, respectively. Measurements for the slowing down of the recoiling atoms perpendicularly to and along the hexagonal axis of WSe₂ yielded an anisotropy in qualitative agreement with expected values.     

Mößbauereffekt anFe 57 nach Neutroneneinfang in Fe56

Mößbauer effect measurements with the 14.4 keV gamma rays of Fe⁵⁷ following thermal neutron capture in Fe⁵⁶ are reported. During the transition from the capture level at 7.6 MeV to the first excited state at 14.4 keV recoil energies up to 549 eV are imparted to the Fe⁵⁷ nuclei. Thus the Mößbauer gamma rays are emitted by nuclei displaced from their normal lattice positions. The measurements have been performed in order to get informations about the final position of the recoiled nuclei in metallic iron and in ordered Fe-Al alloys. Mößbauer spectra of recoil atoms in metallic iron did not show any significant deviation from the spectra of atoms on normal lattice positions. In ordered FeAl alloys of CsCl structure changes in the isomer shift due to recoil effects have been found. In a Fe₃Al alloy of DO₃ type order additional changes in the internal magnetic field have been observed. All results are discussed in terms of possible final positions for the primary recoiled iron atoms in the lattice.     

The real part of the nucleon-nucleus optical potential

The nucleus²⁴Na has been investigated by studying the gamma-rays emitted following thermal neutron capture in²³Na, with curved crystal and Ge(Li) spectrometers. Of the 277 transitions assigned to²⁴Na, 216 were placed in the²⁴Na level scheme containing 45 levels, of which six (1,961, 1,977, 3,866, 5,810, 5,918, and 6,222 keV) are reported for the first time. An average gamma-ray multiplicity of 3.3 gammas per neutron capture was observed. The neutron binding energy was determined to be 6,959.73 (14) keV. The resulting level scheme is compared to shell and rotational model predictions.     

Measurement of the lifetime of the first excited state in17O and17F

A new version of the “recoil distance method”, making use of a gas target, has been used to determine the lifetime of the 871 keV level in¹⁷O and of the 495 keV level in¹⁷F. The measured values of the lifetimes are (2.32±0.08) · 10^?10 sec and (3.96±0.10) · 10^?10 sec for¹⁷O and¹⁷F, respectively.     

Messung der rückstoßfreien Resonanz-Absorption am 6,2 keV-Niveau in181Ta

A strong recoilless resonance absorption was observed for the extraordinarily narrow 6.2 keV level (T _1/2=6.8 μs) of¹⁸¹Ta. Using sources of¹⁸¹W in W-metal and Ta-metal absorbers, a linewidth of about 9 times the natural width was obtained, with an enormous isomer shift of +(0.85±0.02) mm/sec, which is equivalent to a shift by 260 times the natural linewidth. Recoilless resonance spectra of cold worked and of oxygen doped absorbers showed a high sensitivity of the linewidth against lattice imperfections due to inhomogeneous quadrupole interactions and isomer shifts. Measurements of the residual resistivity ratio and of the lattice constant of the impurity doped absorbers yielded a linear correlation between linewidth and isomer shift.     

Gamma-gamma angular correlations in105Rh

Gamma-gamma angular correlation measurements have been performed on the cascades 393-263 keV, 413-263 keV, and 316–469 keV emitted in¹⁰⁵Rh after theΒ-decay of¹⁰⁵Ru. From the measured angular correlation coefficients the spins of the states at 469 keV, 785 keV, and 806 keV and the multipolarities of the involved gamma-rays are determined.     

Angular distribution measurements of gamma-rays from the22Ne(p, γ)23Na reaction

Angular distribution measurements of gamma-rays from the²²Ne(p, γ)²³Na reaction on theE _p =897, 1006, 1091 and 1278 keV resonances have been made. Spin and parity assignments for several bound states are presented together with multipole mixing ratios for transitions from resonance and bound states. The level at 6617 keV (7/2⁺) is proposed to be a member of the rotational band based on the Nilsson orbit 5(K ^π=5/2⁺).     

Ion induced secondary electron emission from single crystal surfaces

Yields of ion impact induced electrons from very pure Ni(110) and Ni(111) surfaces have been measured. In several tilt planes the angle of incidence of a 5 keV H⁺, H⁺₂ or H⁺₃ ion beam is varied from perpendicular to grazing incidence. Below = 75° the yield increases as sec but shows characteristic depressions when the beam is incident along crystallographically low indexed lattice directions. This is explained by kinetic electron emission with respect to the projectile transparency of the crystal lattice.     

对40Ca9.5—10.5MeV能区内几组核能级宽度的测量

本文介绍了用γ共振吸收法测量⁴⁰Ca 9603.9keV,10321.0keV两组能级和9864.6,9868.8keV一组双重态能级的能级宽度,选用³⁹K(p,γ)反应所放出的γ射线激发相应的⁴⁰Ca吸收核能级。对于9603.9keV,10321.0keV的能级宽度,这里给出了比较精确的结果,相应的能级宽度分别为Γ=188±47eV,Γ=91±15eV。对于9864.6,9868.8keV能级,结果为Γ=100±24eV,Γ=899±214eV,由于⁴⁰Ca 9864.6,9868.8keV两能级靠得很近,因此这里用γ共振吸收法测量它们的能级宽度与以往有所不同,将同时有两组γ射线用来激发同样两个能级而发生交叉激发。我们对相应的实验处理方法作了推广。此外,用(p,γ)共振产额法测量了⁴⁰Ca 9603.9keV,10321.0keV能级宽度,得到了与γ共振吸收法一致的结果。本文还对⁴⁰Ca 9603.9keV,10321.0keV能级的(p,γ)共振强度S_pγ、同位旋T等进行了讨论。 关键词：     

Study of the133Cs(γ,n)132Cs reaction

The photoneutron spectrum from the¹³³Cs(γ, n)¹³²Cs reaction induced by 9.720 MeV neutron capture gamma-rays has been studied with a³He-spectrometer. The energies and relative intensities of the emitted neutrons were determined. AQ-value of 8,986 +/?2 keV is suggested. The data reveal the existence of seventeen excited states in¹³²Cs in the region up to 551 keV.     

Richtungskorrelation für Kernresonanzfluoreszenz und Lebensdauer des 412 keV-Niveaus von198Hg

Using the method of thermal Doppler-broadening of the emission line, the effective differential cross sections for nuclear resonance scattering for 412 keV photons by¹⁹⁸Hg has been measured for well defined scattering angles of 120° and 160°. The results indicate a partial mean lifetime for this energy level of τ_γ=(5·12±0·23)·10^?11 sec. This result differs appreciably from the values reported by other workers. Possible reasons for these discrepancies are discussed. The ratio of the differential cross sections for resonance scattering at angles of 120° and 160° is consistent with a 0-2-0 transition.     

Giant dipole resonance in55Mn* studied with the BGO detector

High-energy gamma-rays emitted in the decay of the giant dipole resonance built on excited states of⁵⁵Mn nucleus were measured with a bismuth germanate detector. Resonance parameters were extracted from the fits to the experimental spectra. Two new high-energy calibration points originating from slow-neutron capture in germanium isotopes of bismuth germanate crystal are proposed for large-volume BGO detectors.     

Kaonic atoms measurements at the DAΦNE accelerator

Radioactive ⁵⁷Mn⁺(T _1/2?= 1.5 min) ions have been implanted at the ISOLDE facility at CERN with 60 keV energy to fluences <10¹²/cm² into p-type Si_1???x Ge _x (x < 0.1) single crystals held at 300–600 K. The implantation and annealing processes result in the majority of the implanted Mn ions occupying substitutional lattice sites. In the subsequent ⁵⁷Mn nuclear β ^???-decay to the 14.4 keV Mössbauer state of ⁵⁷Fe (T _1/2?= 100 ns), an average recoil energy of 40 eV is imparted to the ⁵⁷Fe daughter atoms which results in a large fraction being expelled into tetrahedral interstitial sites and the creation of a vacancy. The remainder occupies substitutional sites. This technique of recoil production of ^57m Fe_I thus allows for the study of the diffusion characteristics of interstitial Fe. From the temperature dependent line broadening, the activation energies have been determined and decrease with increasing Ge concentration which contributes significantly to the increase of the jump frequency. A similar result has been obtained in n-type SiGe but there the values for the activation energies were much higher.     

Residence sites for19F ions implanted into diamond

¹⁹F has been used to probe the structure of the diamond lattice. The measurements were performed via the time differential perturbed angular distribution (TDPAD) technique applied to the 197 keV state (τ=128 ns,Q=0.10 b) of¹⁹F. The nuclei were excited and recoil implanted into an oriented diamond using a (p,p′γ) reaction initiated by a pulsed 4 MeV proton beam. Model functions simulating a variety of residence sites for the probe ions in a single crystal were developed for the analysis of the data. The data implies the formation of two molecular types, or sites within the lattice, with possibly a third radiation damage component.     

Gamma-rays from the24Mg(p,γ)25Al reaction for proton energiesE p=800 keV toE p=1,830 keV

The yield curve and resonance strengths of resonances in the²⁴Mg(p, γ)²⁵Al reaction for the proton energy rangeE _p=800 keV toE _p=1,830 keV, have been determined and the existence of a resonance atE _p=1.184 MeV confirmed. Single energy spectra as well as decay schemes and branching ratios are given for these resonances. An upper level of 2.0×10^?15 sec for the lifetime of the 3.079 MeV level in²⁵Al results from a Doppler shift attenuation measurement carried out on the 2.624 MeV gamma line originating in the 3.070 MeV→0.455 MeV transition in²⁵Al.     

Satellite line structure in NMR-ON on206BiFe and182ReFe

Nuclear magnetic resonance on oriented²⁰⁶BiFe and¹⁸²ReFe has been measured using recoil implanted samples. Clearly resolved satellite structures were found for both systems. By annealing at an appropriate temperature, the resonance width was reduced. The satellite line structure for¹⁸²ReFe was studied with various annealing temperatures. The ratio of the resonance strength changed with the annealing temperature. The resonances for¹⁸²ReFe were also measured in external magnetic fields of 0.1, 0.2 and 0.4 T. The resonance frequencies for the satellite structure at an external magnetic field of 0.2 T were determined:v ₁=691.7(3),v ₂=684.4(2),v ₃=687.2(2) MHz for²⁰⁶BiFe;v ₁=231.15(5),v ₂=230.20(5) for¹⁸²ReFe. The origin of the satellite structure is discussed. The effective relaxation time of¹⁸²ReFe at 8 mK and external magnetic field of 0.2 T was determined to be 18.6(6) s using a single-exponential fit.     

Gamma-ray emission from 134Ce and levels in 134La

The decay of ¹³⁴Ce to doubly odd ¹³⁴La has been studied using Ge(Li) and Si(Li) photon detectors. Samples of the ¹³⁴Ce(75.9 h)- ¹³⁴La(6.67 min) have been produced by ≈ 800 MeV proton bombardment of Pr foils in LAMPF, followed by chemical and mass separation. To increase the sensitivity (by up to a factor ≈ 50) for detection of ¹³⁴Ce γ-rays in the presence of the interfering ¹³⁴La activity, the ¹³⁴Ce-¹³⁴La samples were loaded onto a HDEHP column and the ¹³⁴La eluted off continuously. Gamma-ray singles and γ-γ coincidence measurements were made using the ¹³⁴Ce activity remaining on the column as the source. Some 32 γ-rays, ranging in energy up to 355 keV, are observed to be associated with this decay. Approximately 30 of these have been fitted into a level scheme for ¹³⁴La with excited states at energies of 31, 54, 93, 136 or 148, 162, 187, 150 or 205, 252, 294 and 355 keV. Only limits can be set for the spin and parity values of each of these states. The observation of γ-rays with energies up to 355 keV indicates that the previously reported values of ≈ 0.1 MeV for the ¹³⁴Ce electron-capture decay energy, inferred from the K-electron capture probability, are incorrect.     

Search for hyperdeformed structures populated in the <Superscript>37</Superscript>Cl+<Superscript>120</Superscript>Sn reaction by using EUROBALL III

The ridge structure with ΔE_γ=±30 keV, observed in the past in coincidence with protons emitted in the reaction 187 MeV ³⁷Cl +¹²⁰Sn and attributed to an hyperdeformed nuclear shape in ¹⁵²Dy, has been studied in a new experiment performed with the EUROBALL III array. The ridge is now observed in coincidence with transitions in the yrast superdeformed band of ¹⁵²Dy but no discrete rotational bands have been identified. Received: 7 February 2000