Study of theβ +/EC decay of the neutron deficient nuclei76,78Sr and79Y

The +/EC decay of the neutron deficient nuclei^76,78Sr and⁷⁹Y was studied employing mass separated molecular beams of SrF⁺ and YF₂ ⁺ from the ISOLDE mass separator. The halflives of^76,78Sr and⁷⁹Y were measured as t_1/2=8.9(3)s, 159(8)s and 14.4(15)s, respectively, and decay schemes were established for⁷⁶Sr and⁷⁹Y. In the⁷⁸Sr decay 10 new -ray transitions were identified.     

Experimental beta-decay energies of very neutron-rich isobars with mass numbers A=101 and A=102

TheQ -values of¹⁰¹Rb,^101,102Sr and^101,102Y have been measured for the first time at the mass separator ISOLDE by means of-coincidence techniques with a plastic scintillation detector telescope and a large Ge(HP)-detector. For some of these nuclei, also new details of their decay schemes could be derived from the measured-decay properties. The experimental results are discussed, as far as the systematics of two-neutron separation energies derived from them is concerned. In addition, the nuclear masses deduced from theseQ -values are compared with the predictions of recent mass calculations.Dedicated to Prof. Dr. Peter Armbruster on the occasion of his 60th birthday     

Half-lives andQ β measurements for new nuclei of89Tc and89mTc

Neutron deficient isotopes of⁸⁹Tc and^89mTc have been produced through the⁶⁰Ni(³²S,p 2n)⁸⁹Tc at 95 MeV and the⁵⁸Ni(³⁵Cl, 2p 2n)⁸⁹Tc reaction at 135 MeV. A rotating catcher foil system was used to collect the activities and transfer them to a measuring position for- spectroscopy. The half-lives of⁸⁹Tc and^89mTc were measured to be 12.8±0.9 s and 12.9±0.8 s, respectively. The total decay energy, Q_EC, for⁸⁹Tc was determined to be 7.51±0.21 MeV.The authors would like to express their thanks to technical staff of the Tandem Accelerator Center at the University of Tsukuba for their operation of the accelerator and assistance during the experiment. This work is partly supported by a Grant-in-Aid from the Japanese Ministry of Education, Grant No. 01790180.     

Non-collective oblate states in121Te

Two new neutron-deficient isotopes,²¹³Pa and²¹⁴Pa were produced in complete fusion reactions of⁵¹V-ions with¹⁷⁰Er targets at (5.2–5.6) AMeV. The assignment was based on delayed evaporation residue - - time and position coincidences. The- decay energies of^213,214Pa were measured to be E=(8236±20) keV and E=(8116±20) keV, respectively. The half-lives of^213,214Pa were determined to be T_1/2=(5.3 _–1.6 ^+4.0 ms and T_1/2=(17 ±3) ms, respectively.This article was processed by the author using the LAT_EX style filecljour2 from Springer-Verlag.     

The magnetic hyperfine field at Hg impurities in ferromagnetic Gd

The magnetic hyperfine field at dilute Hg impurities in Gd has been investigated by the conversion electron (e ^–)--time differential perturbed angular correlation (TDPAC) technique. The radioactivities^197m Hg and¹⁹⁹Tl were implanted into Gd foils by means of an isotope separator. TDPAC measurements were performed with the 165 keV-L-conversion electron—134 keV--cascade of¹⁹⁷Hg at different temperatures and with the 334 keV--158 keV-K-conversion electron cascade of¹⁹⁹Hg at 200 K.The regular site occupation probabilities were found to be 15(3)% for an annealed^197m HgGd sample and 29(5)% in unannealed¹⁹⁹TlGd samples.From the magnetic hyperfine interaction frequencies measured for the regular sites at 200 K the magnetic hyperfine fields |H _hf(¹⁹⁷HgGd; 200 K)|=256(13) kG and |H _hf(¹⁹⁹HgGd; 200 K)|=267(7) kG were deduced.On leave from the University of Lisboa, Portugal     

ISOLTRAP: A tandem penning trap mass spectrometer for radioactive isotopes

The masses of over sixty short-lived Rb, Sr, Cs, Ba, Fr and Ra isotopes have been measured at the on-line mass separator ISOLDE at CERN/Geneva by determination of their cyclotron frequency in the tandem Penning trap system ISOLTRAP. Resolving powers exceedingm/m(FWHM)=10⁶ and accuracies of typically m/m=10^–7 could be achieved. ISOLTRAP can also act as an isomer separator, as proven for the cases of⁸⁴Rb and⁷⁸Rb.     

Decay of the new isotope127Pr

A new isotope,¹²⁷Pr, has been identified and its decay has been studied using on-line isotope separation of⁹⁴Mo (³⁶Ar,p2n) reaction products. The half-life of the isotope was determined to be 7.7(6) s, and a /X-ray spectrum has been obtained. A partial level scheme is proposed for¹²⁷Ce on the basis of-singles,-gated and-coincidence data.The authors would like to thank the TIARA cyclotron crew for their cooperation in generating an intense³⁶Ar beam as well as in operating the cyclotron. This work was partly supported by the JAERI-University Collaborative Research Project.     

Contactless density measurement of high-temperature BiFeO<Subscript>3</Subscript> and BaTiO<Subscript>3</Subscript>

The density of liquid and undercooled BiFeO₃ and high-temperature solid, liquid, and undercooled BaTiO₃ was measured with an electrostatic levitation furnace. The density was obtained with an ultraviolet-based imaging technique that allowed excellent sample contrast throughout all phases of processing, including at elevated temperatures. Over the 1250- to 1490-K temperature range, the density of liquid BiFeO₃ can be expressed as _L(T)=6.70×10³–1.31(T-T_m)(kgm^-3) (±2 per cent) with T_m=1423 K, yielding a volume coefficient of thermal expansion _L(T)=1.9×10^-4 K^-1. For BaTiO₃, the density of the solid can be expressed as _S(T)=5.04×10³–0.21(T-T_m) (T_m=1893 K) over the 1220- to 1893-K range, yielding a volume coefficient of thermal expansion _S(T)=4.2×10^-5 K^-1, whereas that of the liquid can be expressed as _L(T)=4.04×10³-0.34(T-T_m) over the 1300- to 2025-K range with _L(T)=8.4×10^-5 K^-1. PACS 77.84.-s; 81.05.Je; 81.20.n     

Detection on NMR via the anisotropy of X-rays (X-NMR-ON)

Nuclear magnetic resonance on oriented nuclei has been detected for the first time via the destruction of the anisotropy of characteristic L_x-rays. The new method can be applied to isomeric states which decay only via highly converted transitions, for which the standard NMR-ON technique — detection of NMR via the anisotropy of -rays — is not applicable. The X-NMR-ON technique has been used to measure the magnetic hyperfine splitting of^193mpt (I=1322⁺; E=149.8 keV; T_1/2= 4.3 d) to be ¦ g _NB_HF/h¦=111.3 (3) MHz. with the known hyperfine field of –1280(27) kG the magnetic moment of^193mpt is deduced to be ¦¦=0.7417(14) _N. This magnetic moment differs strongly from the known magnetic moments of the 13/2⁺ isomeric states in Hg and Pb and^195mPt.     

A test of special relativity with stored lithium ions

Laser spectroscopy at the heavy ion storage ring TSR in Heidelberg allows for precision experiments testing the limits of the special theory of relativity. With an optical-type three-level system of⁷Li⁺ the Doppler shift has been measured by saturation spectroscopy as a test of the time dilatation factor = (1 – ²)^–1/2 at an ion velocity of = 6.4% c. A precision of/ < 9 × 10^–9 has been obtained, which sets a second-order limit of 1.1 × 10^–6 for any deviation from the time dilatation factor. The fourth-order limit of this deviation is set below 2.7 × 10^–4 by the present experiment. These limits are given at a 1 confidence level.     

57Fe Mössbauer investigations of manganese-containing spinels

Cation distributions and related order-disorder phenomena in the naturally occurring Mn-spinels: iwakiite, galaxite and franklinite, have been investigated by means of⁵⁷Fe Mössbauer spectroscopy. Previous measurements on an iwakiite sample indicated the existence of Mn-rich and Mn-poor regions. This interpretation has been confirmed in this investigation by further measurements on annealed iwakiite samples. The⁵⁷Fe Mössbauer spectrum of galaxite from Bald Knob, NC, is a well-resolved quadrupole doublet and indicates the presence of a single crystallographic Fe³⁺ species. A galaxite sample from Thailand exhibited a complex spectrum of Fe²⁺ and Fe³⁺ quadrupole doublets: This sample has been misidentified and should be regarded as a member of the (Mg, Fe)(Al, Fe)₂O₄ series. The⁵⁷Fe hyperfine parameters of a rare franklinite from Längban, Sweden, are very close to those for synthetic zinc ferrite, confirming electron microprobe results of an unusually high zinc content.     

Precision PAC measurements in Er2O3 and Ho2O3 single crystals and structure refinement

The structure of C-form Ho₂O₃ and Er₂O₃ single crystals and powder samples was investigated by the electric quadrupole hyperfine interaction of¹¹¹In(EC)¹¹¹Cd probe ions using the perturbed - angular correlation method (PAC). The resulting set of refined atomic coordinates is compared to X-ray data and used to calculate the orientations of the electric field gradients (EFG) which are reproduced by the PAC measurements in single crystals. The temperature dependence of the coordinates was measured for both substances.     

New investigation of83Zr and85Zr beta decay

The decay of on-line mass separated⁸³Zr and⁸⁵Zr sources has been studied by singles and coincident X-ray and-ray and conversion electron measurements. The previous level scheme of⁸³Y is confirmed and 5 new levels have been added up to 2.74 MeV excitation. A decay scheme of^85gZr with 40 levels up to 2.66 MeV in⁸⁵Y is deduced. The experimental observation below 2 MeV excitation in⁸⁵Y agrees qualitatively with the predictions of the interacting boson-fermion model.     

New neutron-rich nuclide185Hf

The unreported hafnium isotope¹⁸⁵Hf has been identified for the first time. Sources of¹⁸⁵Hf prepared by 14-MeV neutron irradiation of tungsten followed by radiochemical separation have been studied. The new activity was identified by following the time variation of the rays. The half-life of¹⁸⁵Hf has been determined to be 3.5±0.6 min. In addition, a new 164.5±0.5keV ray was found and assigned to¹⁸⁵Hf based on the measurements of transition energy and half-life.This work was supported by Academia Sinica     

Revision of the decay data of166–170Re,including new isomers167m,169mRe

The neutron-deficient rhenium isotopes^166–170Re were investigated using reactions of³²S with monoisotopic¹⁴¹Pr targets. Gamma-rays following the-decays of^166–169Re were measured for the first time. Four new-rays with energies of 4.70,4.83, 4.87, and 5.02 MeV were detected in addition to the known 5.50, 5.26, and 5.06 MeV-rays. Alpha-decaying isomer pairs were discovered in¹⁶⁷Re and¹⁶⁹Re. The measured half-lives are 2.3(2)s for¹⁶⁶Re, 3.4(4)s and 6.2(5)s for¹⁶⁷Re, 4.4(1)s for¹⁶⁸Re, 8.1(5)s and 16.3(8)s for¹⁶⁹Re, and 9.2(2)s for¹⁷⁰Re. The nuclear structure is discussed in terms of single-particle states.This work has been funded by the German Federal Minister for Research and Technology (BMFT) under contract number 06GÖ105     

Search for superconducting effect on the decay of99m Tc

An experimental investigation of the influence of superconductivity on the decay rate of^99m Tc, _T, has been performed by means of a differential method. The^99m Tc samples containing⁹⁹Tc as a carrier were prepared by electrodeposition on a copper plated tungsten wire. For production of metallic technetium the samples were reduced in pure hydrogen gas at 800~1000°C. X-ray analysis of the samples showed they were surely metallic with anhcp structure. The lattice constants observed area=2.741 Å andc=4.398 Å. The transition temperature was found to be 7.5±0.2K. Comparison of two sources, normal (room temperature) and superconducting (4.2 K), did not show an appreciable effect of superconductivity on the decay rate of^99m Tc exceeding the limit of uncertainty of our experiment:/ _T=(1.1±2.7) × 10^–4.     

The limit of stability of proton-rich thallium isotopes: a search for the decay of177Tl

The fusion reaction⁷⁴Se+¹⁰⁶Cd¹⁸⁰Pb^* at a compound nucleus excitation energy E_x 40 MeV, has been used in a search for the decay of the unknown nucleus¹⁷⁷Tl. Evaporation residues were velocity and mass analysed prior to implantation into a position sensitive silicon surface barrier detector. No evidence was discovered for the proton or alpha-decay of¹⁷⁷Tl for a cross-section > 10 _– ⁵⁺¹⁰ nb. This indicates either that¹⁷⁷Tl decays too rapidly (t_1/2 < 1=">s) by proton emission for the decay to be detected, or that¹⁷⁷Tl is produced with a cross-section less than the limit established in the present experiment. The following nuclear decay half-lives were measured with improved accuracy;¹⁷⁷Hg (t_1/2 = 130±5 ms),¹⁷⁸Hg (t_1/2=250±25 ms) and¹⁷⁷Au (t_1/2=1180±70 ms). The experiment also provided the first direct confirmation of the correct mass assignment of the alpha-decay, E=6.26 MeV, to the decay of¹⁷⁶Au. Two additional halflife measurements of proton-rich Osmium isotopes are also presented from a previous similar experiment;¹⁶⁵Os (t_1/2=73±8 ms) and¹⁶⁶Os (t_1/2 = 194±17 ms).     

The deformedN=60 nucleus 41 101 Nb

The ^– decay of¹⁰¹Zr has been investigated at the fission-product separators JOSEF and LOHENGRIN. The half-life of¹⁰¹Zr has been determined to 2.5(1) s and a level scheme for¹⁰¹Nb has been established from ray singles as well as X/3- and — coincidence measurements. Conversion coefficients for transitions in¹⁰¹Nb and level half-lives between 10 ps and 2 ns have been determined. Three rotational bands are identified among the low-lying levels with band heads at 0 keV, 206 keV and 208 keV. The bands are probably based on the Nilsson configurations [422 5/2⁺], [301 3/2^–] and [303 5/2^–], respectively. The deformation has been determined to _q=0.40(4) and 0.41(8) for the ground state band and the band based on the 206 keV level from the half-lives of the first and second excited members of these bands. This shows that the rapid onset of deformation at N=60 which is typical for the A=100 region of neutron-rich nuclei, takes also place in the Nb isotopes. Nilsson model calculations describe the experimental data well, especially the several determined transition probabilities including those for E1 transitions from the 206 and 208 keV band heads to the ground state.Dedicated to Prof. Dr. P. Armbruster on the occasion of his 60th birthday     

Stimulated emission and excited state absorption in neodymium-doped CaNb2O6 single crystal fibers grown by the LHPG technique

This work presents the structural and spectroscopic characterization of undoped and neodymium doped CaNb²O⁶ single crystal fibers grown by the low cost and versatile Laser Heated Pedestal Growth technique. To evaluate the potentialities of doped fibers, polarized absorption (^{GSA,max 809nm} = 5.85×10^–20cm² with FWHM = 18 nm), luminescence and lifetime (^exp = 145 s) measurements were taken, and radiative properties were also assessed by the Judd–Ofelt approach. The gain (^SE–^ESA) spectrum was measured using the pump-probe technique and stimulated emission was observed at 1.064 m with (^{SE, max 1.064 m} = 7.2× 10^–20 cm² and FWHM = 12 nm). The results are comparable to those of other well known niobate bulk laser crystals, but the easier, cheaper and faster growth of compact CaNb²O⁶:Nd³⁺ single crystal fibers makes them more attractive media for compact optical devices, such as diode laser pumped miniature lasers in the near infrared region.This revised version was published online in March 2005. In the previous version, the published online date was missing     

High resolution study of24Mg(p,d)23Mg for the Ne-E problem

Nuclear levels of²³Mg near and above the proton threshold were investigated with high resolution. A new level has been identified at 7.643 MeV (66 keV above the proton threshold) with a possible J=(3/2, 5/2)⁺. Some other spin-parity and excitation-energy assignments are also made. These results enable the reaction rate estimate of²²Na(p,)²³Mg with much smaller uncertainties, which is critical for the Ne-E problem in nuclear astrophysics.