Nuclear orientation study of160Tb impurity in yttrium single crystal

The low temperature nuclear orientation of¹⁶⁰Tb impurity in yttrium single crystal has been studied in the temperature range 5–60 mK and in the external magnetic field up to 9 T applied along a- or c-crystal axes. The experimental results are interpreted as a consequence of the interaction of Tb³⁺ ion with crystal field produced by the yttrium neighbours. A possible influence of technology used is also discussed.     

Nuclear orientation study of160Tb impurity in gadolinium single crystal

The low temperature nuclear orientation of¹⁶⁰Tb in gadolinium single crystal has been studied in the temperature range 5–60 mK and in the external magnetic field B_ext ≤9 T, applied both in the a- and c-axis directions. The obtained results indicate the noncollinearity between the Tb magnetic moments and the magnetization of the gadolinium matrix.     

Nuclear orientation of 160Tb in Tb metal

The decay of ¹⁶⁰Tb oriented at low temperatures in Tb metal has been investigated, and angular distributions of 19 γ-rays have been determined. The reduction in anisotropy in polycrystalline metal samples is discussed. Multipole mixing ratios have been determined for many of the γ-rays. A critical discussion is given of the previously reported $\text{M2}\text{E1}$ mixing ratios, and previous nuclear orientation studies are re-analyzed in a consistent manner so that their results can be compared. It is shown that the nuclear orientation and angular correlation results for the 1178 keV transition are consistent only if E3/E1 mixing is present. The El branching ratios and $\text{M2}\text{E1}$ mixing ratios are analyzed on the basis of Coriolis-mixed K = 0, 1 and 2 character for the negative-parity levels of ¹⁶⁰Dy.     

Magnetic behaviour of Tb impurities in Gd andY single crystals: a nuclear orientation study

The low temperature nuclear orientation of¹⁶⁰Tb impurities in Gd andY single crystals has been studied in the temperature range 7–40 mK andin the external magnetic field range 0–7.3 T applied alonga-, b- andc-crystal axes. In the case of Tb in Gd we found a considerable noncollinearity of the Tb magnetic moment with respect to the magnetic external field direction even for highB _ext. In the case of Tb in Y the results cannot be described by a simple model, taking into account the simultaneous influence of the crystal andexternal magnetic fields. Some new proposals for interpretation of the experimental dat are given.     

Magnetostriction in LaAg single crystal with Tb impurities

We have made magnetostriction measurements on a La_0.99Tb_0.01Ag single crystal at low temperature. The shape magnetostriction dominates, and the 〈001〉 and 〈111〉 effects have opposite signs. The volume magnetostriction is positive but small. We analyse the results in a single-ion model, using the crystal-field parameters suggested by Hoenig et al., and we deduce the orbit-lattice coupling parameters V³₂ and V⁵₂. Results are compared with those in other cubic metallic systems containing rare earths.     

The160Tb →160Dy decay

Gamma-ray spectra in the decay of¹⁶⁰Tb were measured with the aid of two coaxial Ge(Li) spectrometers. Absolute intensities and multipolarities were obtained. Three new transitions of 486·5 keV, 1069 keV, and 1102·5 keV were found and introduced into the decay scheme. The level scheme is discussed from the point of view of the generalized model of the nucleus. Experimental data show the 1264·4 keV level to be a two-quasi-particle state of the p p (411–523) type. The beta-transition from the ground state of¹⁶⁰Tb (p 411+n 521) to this two-quasi-particle state with logft=8·00 ± 0·05 is interpreted as -forbidden.The authors are indebted to Prof. K. E. Alexandrov, K. A. Gromov, and E. P. Grigoriev for useful remarks and interest concerning the work.     

Nuclear orientation of the rare-earth system^{160} Tb\underline {Tb} (sc)

We report precision nuclear orientation measurements on a bulk¹⁶⁰TbTb single crystal sample. The results of these experiments allow us to determine the hyperfine parameters for this system, as well as precise multipole mixing ratios for 22 gamma rays from the¹⁶⁰Dy daughter nucleus. Various methods of extracting the mixing ratios will be compared.     

单晶合金激光熔凝过程中晶向对单晶完整性的影响

运用几何模型对单晶合金激光熔凝过程中激光扫描方向与[100]方向夹角ξ变化时熔池内的枝晶生长方向和速度进行了计算,研究了ξ增大时不同晶向区域的分布变化规律.发现随着ξ的增大, 0]区域增大,[010]区域减小,且熔池两边不同部分速度差别增强.根据速度变化规律,构造出了熔池不同部位的过冷区域变化图,说明了可能出现新晶粒的趋势变化,并与实验结果进行了比较,揭示了在晶向不同的交界区域产生新晶粒的内在机理. 关键词： 单晶合金 激光熔凝 晶向 组成过冷     

Nuclear orientation of152,154Tb in gadolinium

The anisotropy in the directional distribution of gamma-rays from the decay of^152,154Tb oriented in a gadolinium matrix at low temperatures, has been measured at the angles of 0 and π/2 with respect to the applied magnetic field direction at temperature of (15±1) mK. Unambiguous values of spin have been deduced for several levels in¹⁵²Gd. Multipole mixing ratios of many gamma-ray transitions occurring in¹⁵²Gd have been found and results are compared with the similar transitions in^150,154,156Gd and they are discussed in terms of the rotational-vibrational model and dynamic deformation theory based on the Strutinsky method. Our results confirm the spin value of 0 for 21·4 h isomer in¹⁵⁴Tb and they establish the spin value of 3 for the 2277·0 and 2336·1 keV levels and the spin value of 4 for the 2416·3 keV level in¹⁵⁴Gd.     

160Tb β-衰变纲图研究

对由160Tb的β-衰变而产生的γ射线利用GeLi和HpGe探测器进行了单谱和γ-γ符合谱的测量. 根据单谱和γ-γ符合谱的测量结果给出了160Tb的β-衰变纲图. 并用绝热对称转动模型对160Dy 中转动带与振动带的耦合参数Zγ值进行了计算,得出从振动带到转动带的γ跃迁几率B(E2)值之比不能通过唯一的Zγ值来描述.     

Characterization of preferential orientation of martensitic variants in a single crystal of NiMnGa

We report the detailed observation of martensitic variants in NiMnGa single crystals. The variants that are twinned with each other in different ways can be clearly identified in our single crystals by optical observation. We also investigated the preferential orientation of the martensitic variants in NiMnGa single crystals. We observed the motion of the variant boundary in response to application of a magnetic field. This observation can be used to explain phenomenologically the magnetic-field-induced strain. In the single crystal with composition Ni₅₂Mn₂₄Ga₂₄, martensite with seven modulated layers (7M) shows preferentially oriented variants. A completely recoverable two-way shape-memory behavior was also observed by measuring the free sample in three different directions during a complete temperature cycle. It was found that the largest strains in the [001] and [010] directions occur in different temperature ranges.     

Nuclear orientation of156Tb in gadolinium matrix

The anisotropy of the angular distribution of gamma-rays from the decay of¹⁵⁶Tb, oriented in a gadolinium matrix at low temperatures, has been measured at the angles of 0 and π/2 with respect to the applied magnetic field direction in the range of temperatures from 14·6 to 68·4 mK. The temperature dependence of anisotropy was measured for the first time. The parameters of hyperfine magnetic dipole and electric quadrupole splittings have been determined and the values of the magnetic dipole moment ¦Μ¹⁵⁶¦=(9·6±1·3)×10^?27 J/T and the electric quadrupole momentQ ¹⁵⁶=(2·9±0·9)×10^?28 m² of the¹⁵⁶Tb ground state have been calculated. Multipole mixing ratios andB(E2) branching ratios of many gamma-ray transitions occurring in¹⁵⁶Gd have been found and the results have been discussed in terms of the rotational-vibration and pairing-plus-quadrupole models.     

Nuclear orientation study of155Tb decay

The angular distribution of gamma-rays following the electron capture decay of¹⁵⁵Tb nuclei oriented in a gadolinium host has been studied at temperatures between 16 and 80 mK. The magnetic dipole hyperfine splitting parameter for¹⁵⁵Tb(Gd) has been deduced and the value of the magnetic dipole moment of¹⁵⁵Tb ground state has been found to be=2.0(2) _N. The multipole mixing ratios have been determined for 9 gamma-transitions in¹⁵⁵Gd.On leave fromthe Department of Physics, University of Jyväskylä, Finland.The authors are indebted to Dr. N. A.Lebedev and to the mass-separator group of Nuclear spectroscopy and radiochemistry department at JINR for preparing the¹⁵⁵Tb activity. The assistance of Ing. M.I.Fominikh and Ing. P.Brada in computer analysis of spectra should be acknowledged. Organisation support of Dr. V. M.Tsupko-Sitnikov and his permanent interest during the course of our work is to be recognized here.     

Low-temperature nuclear orientation of209,210At after recoil-implantation into Be single crystals

The recoil-implantation technique has for the first time been applied to prepare samples of dilute^209,210At in Be single crystals. The quadrupole interaction frequencies _Q=e²qQ/h of²⁰⁹AtBe and²¹⁰AtBe were determined by quadrupole-interaction nuclear orientation at temperatures down to 7 mK to be –208(23) MHz and –138(10) MHz, respectively. The ratio of quadrupole moments Q(²⁰⁹At)/Q(²¹⁰At) was determined to be 1.47(7).We would like to thank Prof. P. Kienle for his kind interest and support of this work and K. Assmus for the irradiations. This work was supported by the BMFT, Bonn, and the KFA, Karlsruhe.     

Zeeman nuclear quadrupole resonance study of a germanium tetrachloride single crystal

Zeeman studies of a single crystal of GeCl₄ have been carried out on a previously described pulsed FT NQR spectrometer. The technique for growing single crystals from liquid samples is described. The Zeeman-split spectrum for each of the resonances at μ₁ = 25.4493, μ₂ = 25.7133, μ₃ = 25.7354, and μ₄ = 25.7457 MHz reveals four quadruplets. The asymmetry parameters found lie in two groups of average values η = 0.035 and η = 0.078, much lower than the previously reported value of η = 0.35 obtained from a polycrystalline sample. The crystal of GeCl₄ is found to be orthorhombic with mmm or D_2h symmetry. From the directions of the field gradient axes the interbond angles have been calculated and show that the GeCl₄ molecule is a slightly distorted tetrahedron.     

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.