On-line nuclear orientation of Au isotopes at KOOL

On-line low temperature nuclear orientation measurements were performed on shortlived¹⁸⁵Au,¹⁸⁶Au,^189mAu,^191mHg implanted in an iron matrix. As decay products¹⁸⁵IrFe and^191mAuFe were studied too. Besides magnetic moment determinations spectroscopic information on spin values of excited levels and mixing ratios of transitions in the daughter nuclei Pt and Au are presented. The results are interpreted in a Nilsson + Coriolis + pairing model.     

On-line nuclear orientation of70As

On-line nuclear orientation was performed on⁷⁰As. Anisotropy data have been obtained at 8.7mK for 29 gamma transitions. Multipole mixing ratios have been extracted for 17 transitions. Our results are in good agreement with existing data for the ten previously measured transitions. Our first time data for the 1496 keV, 2⁺→2⁺ γ-ray suggest the 2536 keV level is a good candidate for a mixed symmetry level.     

On-line nuclear orientation of odd-odd120I

The use of Low Temperature Nuclear Orientation (LTNO) in nuclear structure studies is discussed. LTNO has been employed, together with γ-γ and e-γ spectroscopy, to study the nuclear structure of¹²⁰Te following the beta decay of¹²⁰ I ^g . The strengths and limitations of LTNO as a probe of nuclear structure are discussed with particular reference to this experiment.     

On-line nuclear orientation study of184Au

The¹⁸⁴Au→¹⁸⁴Pt decay, studied on-line with the UNISOR facility at HHIRF, is discussed. Gamma-ray and conversion-electron spectroscopy of¹⁸⁴Pt as well as on-line nuclear orientation measurements of¹⁸⁴Au were done. A new low-lying level scheme of¹⁸⁴Pt is proposed. Two coexisting bands with different deformations and their respective γ-vibrational bands are established. Internal conversion coefficients for interband transitions between states with the same spin are extracted from the spectroscopy measurements. The relative E0 contents of the transitions are determined by combining internal conversion coefficients with E2/M1 mixing ratios deduced from gamma-ray anisotropies measured from oriented nuclei.     

On-line nuclear orientation and relaxation studies of Cs isotopes

The hyperfine field of CsFe has been measured to be (+)40.8(0.7)T, using the technique of on-line low temperature nuclear orientation. The time dependent relaxation of¹²¹Cs^m Fe has also been investigated using a new technique, giving a Korringa constant C_k of 0.059 (15) sK. From this, an effective relaxation time of 3.0 (0.8)s can be deduced for the short lived¹¹⁸Cs^m(T_1/2=17s). This value has then been used to extract the magnetic moment of¹¹⁸Cs^m to be |μ|=5.4 (1.1) nm.     

On-line nuclear orientation of the deformed neutron-deficient Eu,Sm and Pm isotopes

Low-temperature nuclear orientation measurements made on-line at the SERC Daresbury Laboratory on^142m Eu,^141m Sm, and¹⁴¹Pm, with known magnetic dipole moments, have yielded the magnitude of the hyperfine fields of these isotopes in an iron host lattice. Thus measurements for the isotopes^{139, 138}Eu,^139m Sm, and¹³⁸Pm yielded values for the respective magnetic moments. Limits on the thermal relaxation times of Eu and Sm isotopes in Fe were also deduced. The results for¹³⁸Eu appear to contradict the earlier πh_11/2⊗νh_11/2 ground-state configuration assignment.     

On-line orientation of bromine isotopes

Assignments for the principal Nilsson configuration in light β⁺-decaying bromine isotopes were proposed in a contribution to the OLNO-1 conference. These assignments were made on the basis of magnetic moments derived from the temperature dependence of anisotropies in daughter Se isotopes observed in the DOLIS-COLD facility at Daresbury. Anisotropy measurements have since been extended to a lower base temperature in^74m Br and^72g Br decay, leading to more stringent limits on the ground state moment of⁷²Br. The proposed π[312]3/2 configuration for⁷⁵Br has also now been confirmed by a measurement of the sign of its magnetic moment. This was done by observing the β-asymmetry in⁷⁵Br decay using high purity Si detectors mounted within the dilution refrigerator.     

Crystal shape effect on nuclear orientation thermometry at ultra-low temperatures

Absolute temperature measurement (T < 100 mK region) from anisotropy of gamma radiations emitted from oriented⁶⁰Co nuclei in a single crystal of hcp cobalt is found to depend on the shape of the crystal. This dependence is attributed to some closure magnetic domains not oriented along thec-axis of the disc shaped crystal studied. A long rectangular strip of cobalt crystal is found to give correct angular distribution ofγ-radiations and, therefore, suitable for thermometry.     

Magnetization of single-crystal terbium at very low temperatures by nuclear orientation

We report an investigation of the magnetization of high-purity single crystal terbium below 50 mK, using the nuclear orientation of¹⁶⁰Tb, which substitutionally replaces naturally-occurring, monoisotopic¹⁵⁹Tb. The nuclear alignment is determined as a function of applied magnetic field, and can be related to the macroscopic magnetization of the host crystal by a suitable model. In the easy direction (b-axis), a very rapid rise is seen in the first 7 mT of applied field; this is followed by a pleateau region up to 0.1 T, then a slow saturation, completed at ca. 0.4 T. Along an a-axis, a similar rapid increase to about 50% of saturation is observed below 10 mT, followed by a slow, nearly linear increase which agrees with that calculated for domain rotation using the measured crystalline anisotropy constants.     

Nuclear orientation and nuclear structure

The purpose of this paper is to demonstrate how recent experimental results of¹⁵¹Eu and⁵⁷Fe high pressure Mössbauer studies in 4f and 3d metallic magnetic systems can contribute to a deeper understanding of the nature of local moment (4f) and itinerant (3d) magnetism in these systems. Special emphasis is given on the comparison of the experimental results with related theoretical models.     

Relaxation phenomena in nuclear orientation

A survey is given of relaxation phenomena relevant to nuclear orientation at temperatures below 1 K. Relaxation mechanisms, time dependence of the angular distribution of nuclear radiation and experimental methods for relaxation measurements are reviewed. Finally, some open questions related to simultaneous influence of rf fields and relaxation, the existence of a spin temperature and the role of domain walls are discussed shortly.     

Dynamic nuclear polarization and nuclear orientation in terbium vanadate

Dynamic nuclear polarization is a well established technique, which has been used to produce polarized targets for experiments in nuclear physics. This paper suggests new experiments, involving the nuclear magnetic resonance of two isotopes, one stable, the other radioactive, in an antiferromagnet, terbium vanadate. At temperatures well below the Néel point, the line widths should be comparatively small. Resonance may be detected through changes in the rate of gamma-ray emission observed by a nuclear orientation experiment.     

Dynamic nuclear polarization and nuclear orientation in an antiferromagnet

Dynamic nuclear polarization is a well established technique which has been used to produce polarized targets for experiments in nuclear physics. This paper suggests experiments of a similar type but involving the nuclear magnetic resonance of two isotopes, one stable and the other radioactive. The substance is an antiferromagnet, dysprosium phosphate, at temperatures below the Néel point, where line widths are comparatively small. The effect may be detected through changes in the rate of gamma ray emission observed by a nuclear orientation experiment.     

Magnetic moment measurement by nuclear orientation

This review deals with problems concerning ground and long-lived metastable states. The interest of magnetic moments in the knowledge of the nuclear configurations and the couplings is shown. Static, dynamic and transient orientations, and the angular distribution of the emitted radiation by oriented nuclei are discussed.Some problems involved in the extraction of magnetic moment values from low temperature nuclear orientation measurements will be discussed: combined magnetic and electric interactions, intermediate state perturbation, Knight shift, hyperfine anomaly, and thermal reorientation. Methods allowing to find the sign of the magnetic moment are also outlined.     

Applications of low temperature nuclear orientation

The techniques of low temperature nuclear orientation (LTNO) and nuclear magnetic resonance on oriented nuclei (NMRON) are versatile tools used across a range of applications. Such applications include nuclear moment and hyperfine field measurements and testing of nuclear decay models, as well as condensed matter studies, particularly applied to magnetism. Following the tradition of such presentations, the techniques LTNO and NMRON, are briefly outlined along with the principal applications with a focus on some recent works.     

Magnetic structure determined by nuclear orientation

Conclusion In conclusion we suggest that nuclear orientation is a useful technique for determining nuclear spin structures. For a known hyperfine interaction atomic magnetic structures may also be deduced. Measurements on antiferromagnets and the rare earth magnet holmium demonstrate the method, although in the latter case the turn angle cannot be determined because of the limitation of L2 radiation. These experiments show that nuclear orientation can at least complement neutron diffraction and at best furnish information about magnetic structure when the latter technique is not applicable. We intend to study other rare earth magnets and more complicated antiferromagnetic structures.