Hyperfine interactions of light Ir,Re isotopes in iron

The technique of On-line Nuclear Orientation has been applied to light Ir and Re isotopes. Using both¹⁹²IrFe and⁵⁴MnNi thermometers, orientation as a function of temperature was measured over the range 10–100 mK. Pulsed implantation methods were used to obtain spectra with gamma transitions well identified and clear of contaminant activities. Magnetic moment/oriented state spin combinations were obtained for^180,182,183Ir and for^180,179Re. The results are briefly discussed.     

An Overview of 166Er, 169Tm and 170Yb Mössbauer Spectroscopy

The hyperfine splittings of the nuclear energy levels in rare-earth (R) isotopes are sensitive measures of the complex interplay between magnetic exchange and electrostatic crystal-field interactions operating at the atomic level. Mössbauer spectroscopy has been used to great effect in the on-going investigation of these fundamental interactions in R compounds and in this paper we present an overview of ¹⁶⁶Er, ¹⁶⁹Tm and ¹⁷⁰Yb Mössbauer spectroscopy. In particular, we derive expressions for the nuclear energy level splittings incorporating both magnetic and electric quadrupole interactions, using second-order perturbation theory. Such expressions provide a useful means of fitting experimental spectra and also yield criteria for determining whether or not a proposed set of energy level values is physical or not. We also present a number of useful rules of thumb for the analysis of ¹⁶⁶Er, ¹⁶⁹Tm and ¹⁷⁰Yb Mössbauer spectra and, as such, this paper is in effect a Resource Letter.     

Nuclear orientation of154EuFe,166TmGd and169YbFe and169YbGd

Nuclear orientation measurements at low temperatures have been carried out on radioactive isotopes of¹⁵⁴Eu and¹⁶⁹Yb in Fe and of¹⁶⁶Tm and¹⁶⁹Yb in Gd. Gamma-rays from¹⁶⁹YbGd, obtained by the decay of implanted and melted sample of¹⁶⁹IuGd, were observed to have smaller anisotropies of opposite signs compared with those from¹⁶⁹YbFe. This may indicate that for Yb polarized in Gd electric quadrupole interaction is comparable with magnetic dipole one. Mixing ratios of the transitions in¹⁵⁴Gd,¹⁶⁶Er and¹⁶⁹Tm have been made for two levels in¹⁶⁶Er. Our analysis showed that the 3^– to 3⁺ beta decay to the 1128 keV level in¹⁵⁴Gd has 65(20)% j=0.     

The decay of the isotopes176Ir and177Ir

^176,177Ir were produced by irradiation of¹⁴¹Pr with⁴⁰Ar. β-delayed γ-rays of^176,177Ir were observed for the first time. From γγ-coincidence data decay schemes could be constructed. A new half-life of¹⁷⁷Ir was obtained yielding t_1/2=30 (2) s. α-branching ratios of 3.1(6) % for¹⁷⁶Ir and 0.06(1)% for¹⁷⁷Ir were measured.     

The decay of the isotopes179Ir and180Ir

The probability for non-radiative (n.r.) excitations in muonic²⁰⁹Bi was determined from a ( ^–,)-measurement by comparing the intensities of muonic X-ray transitions in single and coincidence spectra. The values of P_n.r(3p1s)=(17.9±2.0)% and P_n.r.(3d1s)=(3.0±2.2)% were measured for the first time. The strength of the n.r. decay of the 2p-level was found to be (4.2±2.2)%. The n.r. transition probabilities of two subcomplexes of the (2p1s)-transition leading to different mean excitation energies are (3.2±1.8)% and (5.0±2.0)%, respectively.We are indebted to the following institutes or organizations for financial support: Bundesministerium ffir Forschung und Technologic der Bundesrepubfik Deutschland contract number 06 BN 271 (HP, PD, HH, FR, CR), Foundation for Fundamental Research on Matter (FOM) and the Netherlands Organization of the Advancement of Pure Research (NWO) (JK, CTAMdL, WL, AT) and the Schweizer Nationalfonds (LS).     

Isomeric ratios in reactions induced by gamma rays and fast neutrons in the isotopes of Re,Ir, and Au

Isomeric ratios were measured in the (γ, n) and (n, 2n) reactions leading to the formation of ¹⁸⁴Re, ¹⁹⁰Ir, and ¹⁹⁶Au odd-odd nuclides. The measurements were performed by the activation method implemented for Re, Ir, and Au samples of natural isotopic composition that were irradiated with 14.7-MeV neutrons and bremsstrahlung photons of endpoint energy 22 MeV. Isomeric-and ground-state nuclei formed in these reactions were identified by their x-or γ-ray spectra and by their half-lives. The isomeric ratios were calculated on the basis of the statistical model, and the results were compared with experimental data, where by it was possible to determine parameters that characterize the dependence of the level density on the excitation energy and angular momentum. The effect of the nuclear structure on these parameters is discussed.     

Evidence for hexadecapole vibrations in A ≈ 170 deformed nuclei; New results for 168Yb

Dominating proton structure has been identified in the K^π=3⁺ band of ¹⁶⁸Yb, contrasting with neutron structure in the corresponding band of ¹⁷²Yb. A region of low-lying K^π=3⁺ bands is now established, with N=98?104, Z=68?72. For all stable nuclei in this region, the I^πK=4⁺3 state is excited by inelastic deutron scattering.     

The radioactive decay of 170Re

A new, highly neutron deficient isotope, ¹⁷⁰Re, $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{= 8.0±0.5}\text{s}$, has been produced via the ¹⁵⁹Tb(²⁰Ne, 9n) reaction at beam energies of 180 MeV. The helium-jet transport technique was used to study the decay. Results from singles and coincidence γ-ray spectroscopy are reported.     

The conversion electron spectra of Lu169 and Lu170

The isotopes Lu¹⁶⁹ and Lu¹⁷⁰, obtained in the fraction of radioactive Lu isotopes by bombarding a Ta target with fast protons, were measured on a double focusing -ray spectrometer. The gamma transitions are given together with the relative intensities of the conversion lines. The multipolarity of the transition is determined for some gamma transitions from the internal conversion coefficient ratios of theK andL shells.

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Lu¹⁶⁹ Lu¹⁷⁰

Lu¹⁶⁹ Lu¹⁷⁰, . - . - K L .

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We should like to thank V. Kopiva and M. Buriánek for help during the measurements.     

Beta-decays of172–175Ir neutron-deficient isotopes

Theβ-decays of^172–175Ir have been studied using a Hejet system through³²S induced reactions,β half-lives have been measured and compared with those given fromα decays. The level schemes of osmium nuclei are deduced and for¹⁷²Os and¹⁷⁴Os, the 2₂ ⁺ level is possibly located. The observedβ-decay half-lives clearly indicate an isomerism phenomenon occuring in light Ir isotopes.     

Evidence for new isotopes of element 107: 266Bh and 267Bh

New neutron rich isotopes 267107Bh and 266107Bh were produced in bombardments of a 249Bk target with 117-MeV and 123-MeV 22Ne ions at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. Identification was made by observation of correlated alpha-particle decays between the Bh isotopes and their Db and Lr daughters using a rotating wheel system. 267Bh was produced with a cross section of approximately 70 pb and decays with a 17(+14)(-6) s half life by emission of alpha particles with an average energy of 8.83+/-0.03 MeV. One atom of 266Bh was observed, decaying within 1 s by emission of a 9.29-MeV alpha particle.     

Investigation of neutron-deficient tungsten isotopes168−174W

The decays of^168?174W were observed in the reactions of³⁶Ar and⁴⁰Ar beams with enriched targets of¹³⁶BaF₂ and¹³⁸BaF₂. The measured half-lives are 53(2) s, 76(6) s, 2.42(4) min, 2.38(4) min, 6.6(9) min, 6.3(4) min, and 35.3 (5) min, respectively. Decay schemes were derived from theγ ^? and X-ray coincidence data. Spin assignments of ground- and excited states are discussed within experimental level systematics and compared with the results of microscopic-macroscopic model calculations. Excitation energies of modeled one-quasiparticle states were found in reasonable agreement with the experimental data. Allowed unhindered beta decay from the 5/2^? [523] to the 7/2^? [523] configuration was identified in¹⁷¹W and this transition is also proposed for the decays of the even-even isotopes^{168, 170}W.     

The COMPLIS experiment on neutron deficient Au, Pt and Ir isotopes

The COMPLIS (COllaboration for spectroscopic Measurements using a Pulsed Laser Ion Source) experiment is carried out at the ISOLDE Booster facility at CERN. The aim is to measure the hyperfine structure and the isotope shift of a series of radioactive laser desorbed atoms by multiple step laser ionization. This technique is especially suitable for refractory elements not directly available as beams from the isotope separator. By collecting a primary radioactive beam, it is possible to delay the laser desorption as long as necessary to obtain the particular daughter of interest. Laser spectroscopy measurements have been carried out on very neutron deficient gold, platinum and iridium isotopes. Magnetic moments μ_I, spectroscopic quadrupole moments and changes of the nuclear mean square charge radius along each isotopes series have been extracted. From some results, a detailed comparison with the predictions of the models is presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Identification of a new isotope,168Dy

A previously unreported nuclide,¹⁶⁸Dy, has been identified and found to have a half-life of 8.5+-0.5 min. The activity was produced in the spontaneous fission of²⁵²Cf and transported via a He jet system to a rapid radiochemical separative facility where the Dy fraction was removed from the mixed fission products. The assignment of this activity to¹⁶⁸Dy decay was based on the presence of five γ rays in the chemically separated Dy fraction which were associated with the decay of an 8.5-min activity and on the observation of the grow-in and subsequent decay of the daughter, 2.98-min¹⁶⁸Ho, with approximately an 8-min half-life. The γ-ray emission probabilities have been determined.     

双奇核~(170)Re高自旋转动带分析(英文)

通过重离子熔合蒸发反应142Nd(32S,1p3nγ)170Re布居了缺中子双奇核170Re的高自旋激发态,识别出了该核的一条转动带并建议了其组态为πh1/2 νi13/2。基于对同中子素能级系统性、旋称反转系统性、带内B(M1)/B(E2)、准粒子Routhians、动力学转动惯量和Total Routhian Surface(TRS)等带结构特征的详细分析和讨论,进一步确认了对A=170核区目前最缺中子双奇核高自旋转动带组态、宇称和自旋值的指定。     

双奇核170Re高自旋态实验研究

在166MeV的束流能量下,利用重离子熔合蒸发反应142Nd(32S, 1p3nγ) 170Re布居了170Re的高自旋激发态. 用12套带BGO反康普顿抑制的高纯锗探测器阵列进行了在束X-γ和γ-γ符合测量. 基于对实验测量结果及周围邻近核已知信息的综合分析,首次建立了双奇核170Re的转动带能级纲图. 根据实验提取出的准粒子顺排、旋称劈裂等结构特征和Re双奇核同位素带结构系统学知识的比较分析,指出该带的准粒子组态是πh11/2(○×)υi13/2.     

166Er and 170Yb Mössbauer Studies of Magnetic Order and Valence

We present three case studies of magnetic ordering in Er and Yb intermetallic compounds (ErFe₆Sn₆, Er₃Ge₄ and YbMn₂Si_2?x Ge _x ). Mössbauer measurements of electric field gradients and hyperfine fields at the rare-earth sites provide direct, local information which yields insight beyond that which could be obtained using neutron diffraction. We argue that such Mössbauer work is an ideal complement to bulk studies.