Beam-Based Production of 178m2Hf

In this study, the production yield for the reaction ¹⁷⁶Yb(⁹Be, α3n)¹⁷⁸Hf was explored using the FN tandem injected superconducting LINAC at SUNY at Stony Brook at a ⁹Be energy of 65 MeV. By comparing the experimental yield of ¹⁷⁸Hf ground state γ rays with those of ¹⁸⁰W as a function of energy, the cross section for production of the incomplete fusion γ rays in ¹⁷⁸Hf was evaluated. Coincidence measurements were made to get information about the population strength of the high spin states in ¹⁷⁸Hf. From these measurements, the maximum cross section for the reaction ¹⁷⁶Yb(⁹Be, α3n)^178m2Hf is estimated to be no larger than 5 mb. This revised version was published online in August 2006 with corrections to the Cover Date.     

Production, chemical and isotopic separation of the178m2Hf high-spin isomer

The ^178m2Hf with its long-lived (T_1/2=31 y), high-spin I^π = 16⁺, isomeric state, is a challenge for new and exotic nuclear physics studies. The ^178m2Hf isomer has been produced in microweight quantities using the ¹⁷⁶Yb(α,2n) nuclear reaction, by irradiation with a high-intensity beam using the U-200 cyclotron in Dubna. Radiochemistry and mass separation methods have been developed, with the aim to separate and purify the produced Hf material. Thin targets of isomeric hafnium-178 on carbon backings have been prepared and used in experiments with neutron, proton and deuteron beams. This revised version was published online in August 2006 with corrections to the Cover Date.     

The ground-state magnetic moments of odd-mass Hf isotopes

In this paper the Quasiparticle-Phonon Nuclear Model (QPNM), based on QRPA (Quasiparticle Random Phase Approximation) phonons, has been utilized to investigate spin polarization effects on the groundstate magnetic properties such as intrinsic magnetic moment (g _K ) and effective spin gyromagnetic factor (g _s ^eff. ) of odd-mass deformed ^165–179Hf isotopes with K > 1/2. Investigations of the spin polarization effects of the even core on the magnetic moments show that the spin gyromagnetic factors (g _s ) of the nucleons in the nucleus differ noticeably from the corresponding values for free nucleons and that the spin-spin interactions play an important role in the re-normalization of g _s factors of the odd-mass ^165–179Hf isotopes. In addition, some theoretical predictions are presented for the magnetic moments of ¹⁶⁵Hf, ¹⁶⁷Hf, and ¹⁶⁹Hf, whose ground state magnetic moments haven’t been experimentally determined yet.     

Low-temperature nuclear orientation of173Lu,175Hf,178Ta and182m,183,184,186Re in Re

Quadrupole-interaction nuclear-orientation experiments were performed on dilute samples of the Group IIIb and IVb impurities¹⁷³Lu and¹⁷⁵Hf in a (Group VIIb) Re single crystal, the samples being preparedin situ by irradiation of a Re single crystal with 172.5 MeV alpha particles. From the γ-anisotropies at temperatures down to 8mk the quadrupole interaction frequencies Ν_Q=e²qQ/h of¹⁷³LuRe and¹⁷⁵HfRe were determined to be ?1149 (100) and ?540 (43) MHz, respectively. The negative sign in both cases indicates that the direction of the electric field gradient (EFG) at the impurity sites is fixed uniquely by the properties of the host lattice. The absolute magnitudes of these EFG's differ strongly from that of the pure system ReRe; the electronic contribution to the EFG of different impurities in Re decreases with increasing impurity valence, contrary to the expectation. As a byproduct, the quadrupole splittings of¹⁷⁸Ta,^{182m, 183, 184, 186}Re in Re were measured to be ?103(10), ?502(30), ?281(20), ?340(22) and ?73(7) MHz.     

Ground state hyperfine structure and nuclear magnetic dipole moments of177Hf and179Hf

Using the atomic beam magnetic resonance method the experimental hyperfine structure data of the 5d ²6s ^{2 3} F ₂ ground state of¹⁷⁷Hf and¹⁷⁹Hf described in a previous paper [1] have been completed. After applying corrections due to perturbations by other fine structure levels of the configuration 5d ²6s ² we got the following multipole interaction constants: $$\begin{gathered} ^{177} Hf:A = 113.43314 (7) MHz B = 624.3293 (13) MHz \hfill \\ C = 0.27 (18) KHz D = 0.045 (40) KHz \hfill \\ ^{179} Hf: A = - 71.42891 (9) MHz B = 705.5181 (24) MHz \hfill \\ C = - 0.43 (20) MHz D = 0.07 (6) KHz. \hfill \\ \end{gathered} $$ By measuring rf transitions at magnetic fields between 1100 and 1550 Gauss the nuclear ground state magnetic dipole moments were determined. The results are: $$\mu _I (^{177} Hf) = 0.7836 (6) \mu _N , \mu _I (^{179} Hf) = - 0.6329 (13) \mu _N $$ (uncorrected for diamagnetic shielding).     

Iodine magnetic moments measured by on-line nuclear orientation

On-Line measurements of magnetic dipole moments of^117–122I are interpreted using coupling of the odd particles to a deformed core. The results show interesting effects of g_7/2, d_5/2 orbital admixtures in the odd-A isotopes, which are close to spherical. The odd-odd isotopes^{118, 120}I show clear examples of shape co-existence.     

Breakdown of K selection in 178Hf

Coulomb activation of the four quasiparticle Kpi=16+ 178Hf isomer (t1/2=31 y) has led to the measurement of a set of Elamda matrix elements coupling the isomer band to the ground band. The present data combined with earlier 178 Hf Coulomb excitation data have probed the components in the wave functions and revealed the onset and saturation of K mixing in low-K bands, whereas the mixing is negligible in the high-K bands. The implications can be applied to other quadrupole-deformed nuclei.     

Preparation of the 178m2Hf isomer used in the induced gamma decay experiment by X-ray from synchrotron radiation facility

It is widely acknowledged that the ^178m2Hf nuclide is the most suitable substance to study the decay characteristic of the isomer induced by low-energy X-ray. In order to conduct the experiment on the induced gamma emission, the research group has started producing the ^178m2Hf nuclide based on the ¹⁷⁶Yb(??, 2n)^178m2Hf reaction. After the chemical purification is conducted, the sample is prepared and used in Shanghai Synchrotron Radiation Facility. During the production of isomer, the natural metal Yb target is got through magnetron sputtering. Bombarded by ?? particles about 27 MeV, the ^178m2Hf nuclide reaches about 10¹². Yb target prepared in this way is most suitable for the production of ^178m2Hf nuclide in the CS30 cyclotron. There are various nuclides in the irradiated target and the main long-lived nuclides are ¹⁷³Lu, ¹⁷²Lu, ¹⁷⁵Hf, ¹⁷²Hf and ⁶⁵Zn. The chemical separation of ^178m2Hf is studied and its process is monitored by radioactive tracer. The above result shows that decontamination factors of Zn and Lu are 10⁵ and 10³, respectively, and the yield of hafnium is 69%. Under the protection of vacuum filtration technology, the purified ^178m2Hf isomers are entirely transferred to the surface of filter paper, in order to form the sample which satisfies requirements of X-ray triggering the ^178m2Hf isomer decay experiment in Shanghai Synchrotron Radiation Facility in the future.     

Prospect of triggering the <Superscript>178m2</Superscript>Hf isomer and the role of resonance conversion

A mechanism of triggering the 12.7keV E3 transition, based on the new decay mode of the 31y isomer via resonance internal conversion and emission of a 1.4keV X-ray quantum, is considered. Actually, this decay mode was observed previously in the decay of 45- and 46-fold ions of ¹²⁵Te . For the purpose of triggering, the atomic radiative vertex has to be induced by resonance radiation. This mechanism makes triggering by an order of magnitude more efficient than triggering a bare nucleus, and is achieved at a lower combination frequency. An experiment is proposed for the direct observation of the new decay mode. This also offers a new way of resonance scattering of these X-rays. Triggering through higher-lying 2573 and 2805keV states is also considered. The results are extended to the general problem of triggering. The main obstacle for enhancing the efficiency is a high internal conversion rate. For this reason, shape isomers with low multipole order --E1 , M1 , and with a high enough energy of triggering transition are of interest for triggering. The partial ionization of the outer electrons will also help. The same recommendations hold for triggering isomers in laser-produced plasma.     

Gamma Spectroscopy of Hf-178m2 Using Synchrotron X-Rays

Preliminary survey experiments have been performed to examine the triggering of gamma emission from the 31-year Hf-178m2 isomer using intense monochromatic synchrotron radiation from the X15A beamline at the National Synchrotron Light Source at Brookhaven National Laboratory. Initial studies were performed to probe incident photon energies over the L ₁, L ₂, and L ₃ X-ray edges of Hf and the 12–13 keV range. Resonances larger than the experimental minimum detectable level of 10⁻²⁵ cm² keV were not observed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Pressure effect on the magnetic phase diagram of Hf1-xTaxFe2 alloys

Abstract

The lattice constants of Hf_1-xTa_xFe₂ with C14 structure were measured at room temperature under pressure up to 5 GPa. The magnetic phase diagram obtained as a function of pressure was compared with that obtained as a function of Ta concentration x. It is shown that changes in lattice constants by applying pressure and /or by substituting Ta for Hf affect remarkably the magnetic phase stability, which is consistent qualitatively with a recent theoretical prediction based on the local spin density approximation.     

Properties of even ~(168-178)Hf isotopes using IBM-1 and SEF

The properties of the ground and excited-state(γ-and β-bands) of ~(168-178)Hf nuclei have been studied.The ratio r(I +2/I) and Eγ(I→I-2)/I have been calculated as a function of the spin(I) to determine the groundstate evolution. The results indicate that these isotopes have a rotational property SU(3). The energy levels for the ground-state, γ-and β-bands of ~(168-178)Hf have been calculated using the Interacting Boson Model and Semi Empirical Formula(SEF). The parameters of the best fit to the measured data are determined. The behavior of energy and B(E2) ratios in the ground state band are examined.     

Deuteron-induced reaction studies of the nuclear structure of178Hf

The level structure of¹⁷⁸Hf is interpreted on the basis of the population of the states following¹⁷⁸Hf (d, d′),¹⁷⁷Hf (d, p) and¹⁷⁹Hf (d, t) reactions. Evidence for quadrupole and octupole vibrational bands and unmixed and intermixed two-quasiparticle configurations is presented.     

Coulomb excitation paths of high-K isomer bands in 178Hf

Three distinctly different mechanisms are shown to populate the K(pi)=6(+) (t(1/2)=77 ns), 16(+) (31 yr), and 8(-) (4 s) isomer bands of 178Hf by Coulomb excitation. High spin states of the three isomer bands were populated by Coulomb excitation of a hafnium target with a 650 MeV 136Xe beam. Although direct population of high-K bands is highly K-forbidden, isomer bands in 178Hf were populated up to spins 13(+)(K=6), 20(+)(K=16), and 14(-)(K=8) with in-band gamma yields of approximately 10(-4) of the ground state band. The data are consistent with a rapid increase in K mixing with increasing spin in the isomer bands.     

Atomic beam magnetic resonance investigations in the3 F 2 Ground State of177Hf,179Hf and180Hf

The 5d ²6s ^{2 3} F ₂ ground state of¹⁷⁷Hf,¹⁷⁹Hf and¹⁸⁰Hf has been studied using the atomic beam magnetic resonance method. The atomic beam was produced by an universal evaporation technique described in a previous paper. The results are¹⁸⁰Hfg _j (³ F ₂)=0.695812 (10)¹⁷⁷Hf Δv(³ F ₂;F=11/2?F=9/2)=991.7917 (10) MHz Δv(³ F ₂;F=9/2?F=7/2)=477.0081 (10) MHz Δv(³ F ₂;F=7/2?F=5/2)=162.8890 (10) MHz¹⁷⁹HfΔv(³ F ₂;F=13/2?F=11/2)=82.1320 (10) MHz Δv(³ F ₂;F=11/2?F=9/2)=392.8498 (10) MHz. The magnetic dipole and electric quadrupole moments of the¹⁷⁷Hf and¹⁷⁹Hf nuclear ground states as calculated from these hyperfine structure measurements are the following: μ(177)=0.75(8)μ _k , Q(177)=4.34 (65) barns μ(179)=?0.61 (6)μ _k , Q(179)=4.90 (75) barns.     

Lowest-lying spin-1/2 and spin-3/2 baryon magnetic moments in chiral perturbation theory

We review some recent progress in our understanding of the lowest-lying spin-1/2 and spin-3/2 baryon magnetic moments （MMs） in terms of Chiral Perturbation Theory （ChPT）.In particular,we show that at next-to-leading-order ChPT can describe the MMs of the octet baryons quite well.We also make predictions for the decuplet MMs at the same chiral order.Among them,the MMs of the Δ＋＋ and Δ ＋ are found to agree well with data within the experimental uncertainties.     

Lowest-lying spin-1/2 and spin-3/2 baryon magnetic moments in chiral perturbation theory

We review some recent progress in our understanding of the lowest-lying spin-1/2 and spin-3/2 baryon magnetic moments (MMs) in terms of Chiral Perturbation Theory (ChPT).In particular,we show that at next-to-leading-order ChPT can describe the MMs of the octet baryons quite well.We also make predictions for the decuplet MMs at the same chiral order.Among them,the MMs of the Δ++ and Δ + are found to agree well with data within the experimental uncertainties.