keV Transition Research Articles

Decay of mass-separated183Ptm (43 s)and183Ptg (6.5 min)to183Ir

The decays of ${}^{183}{\mathrm{Pt}}^{m}$ (43 s, ${J}^{\ensuremath{\pi}}={\frac{7}{2}}^{\ensuremath{-}})$ and ${}^{183}{\mathrm{Pt}}^{g}$ (6.5 min, ${J}^{\ensuremath{\pi}}={\frac{1}{2}}^{\ensuremath{-}})$ have been studied with mass-separated sources from the UNISOR facility. Multiscaled spectra of $\ensuremath{\gamma}$ rays, x rays, and conversion electrons, as well as $\ensuremath{\gamma}\ensuremath{\gamma}t,$ $\ensuremath{\gamma}Xt,$ $e\ensuremath{\gamma}t,$ and $\mathrm{eXt}$ coincidences, were obtained. A revision of the low-lying positive-parity states is necessary in order to accommodate a strong 58 keV transition which is previously unreported. Other additions are made to the low-energy part of the ${}^{183}\mathrm{Ir}$ scheme. The systematic features of the neutron-deficient odd-mass Ir isotopes are discussed.

Mössbauer spectroscopy of133Cs following the decay of133Xe atoms implanted in metals

Mossbauer effect measurements for the 81 keV transition in133Cs have been performed with133Xe-implanted sources prepared by means of an electromagnetic isotope separator. The behavior of the isomer shift of133Cs impurities was studied in various metals. Some correlations were found between measured isomer shifts and electronic properties of the host materials, and they show that the host conduction electrons have an important role in the determination of the isomer shift in metals.

Reinvestigation of low-lying levels of231Th

Low-lying excited levels of231Th fed through α-decay of235U were investigated by using α-γ and γ-γ coincidence technique. From the analyses for co-relating energy levels and transition intensities, we found that the most favorable transition from 205.3 keV ([631]7/2) level that is fed by the most dominant α transition from235U is 19.6 keV transition (205.3 keV [631]7/2−→185.7 keV [631]5/2−). We also found that the transition probability of 109.2 keV, 205.3 keV [631]7/2−→96.1 keV [633]9/2+, was corrected to be weak. These findings can explain why the 185.7 keV γ-ray is so strongly observed, 0.57 photons/ga, in the γ-spectrum associated with the α-decay of235U. The decay scheme of231Th levels previously reported has been modified according to the present analysis.

Magnetism under high pressure studied by 57 Fe and 151 Eu nuclear scattering of synchrotron radiation

The nuclear forward scattering (NFS) of synchrotron radiation is especially suited for probing magnetism at very high pressure, here in the Mbar range, by the nuclear resonances of 57Fe and 151Eu. We report on high pressure (h.p.) NFS studies with the 14.4 keV transition of 57Fe on magnetic RFe2 Laves phases of cubic C15 structure (YFe2, GdFe2) and hexagonal C14 structure (ScFe2, TiFe2) at pressures up to 100 GPa (=1 Mbar). We present also h.p. NFS studies performed with the 21.5 keV resonance of 151Eu, probing the magnetism in the CsCl-type h.p. phase of EuTe.

High-pressure studies with nuclear scattering of synchrotron radiation

The nuclear forward scattering (NFS) of synchrotron radiation is especially suited for probing magnetism at high pressure (h.p.), here in the Mbar range, by the nuclear resonances of 57Fe and 151Eu. We report on high-pressure NFS studies with the 14.4 keV transition of 57Fe, presenting at first the pressure induced α–e transformation in iron. Then a systematic study of magnetic RFe2 Laves phases of cubic C15 structure (YFe2, GdFe2) and hexagonal C14 structure (ScFe2, TiFe2) at pressures up to 100 GPa (= 1 Mbar) is given. First, high-pressure NFS studies performed with the 21.5 keV resonance of 151Eu are also presented, probing valence transitions in EuNi2Ge2 and the magnetism in the CsCl-type h.p. phase of EuTe. Finally, we discuss future applications, such as high-pressure studies of phonon densities of states, using the inelastic channel of nuclear scattering of synchrotron radiation.

Pressure-induced valence transition in EuNi 2 Ge 2 studied by 151 Eu nuclear forward scattering of synchrotron radiation

We present the first application of nuclear forward scattering (NFS) of synchrotron radiation by the 21.5 keV transition of 151Eu for a high-pressure study. After introducing to the measurements of isomer shifts by NFS, we present a high-pressure study of the Eu(2+)–Eu(3+) valence transition in EuNi2Ge2 and compare the results with conventional Mossbauer spectroscopy.

Beta-decay half-lives and level ordering of 102m,gRh

Beta-decay half-lives of the ground state and an isomer of 102Rh have been determined 207.3(17) d and 3.742(10) y, respectively, by γ-ray decay curves following each β-decay. It has been found that a state (2 −) which has a shorter half-life (207.3 d) is the ground state from the result that the half-life of the 41.9 keV isomeric γ-transition was equal to 3.742 y. It has also been confirmed that the 41.9 keV transition is certainly an isomeric transition with X– γ coincidence measurement.

The low-energy electron spectrum from the -decay of

The low-energy electron spectrum from the -decay of has been analysed in the region of 2.5-22.5 keV at the 20 eV instrumental resolution using a combined electrostatic spectrometer and a radioactive source prepared by vacuum evaporation. Energies , (?), , , , and have been determined for nuclear transitions in . Relative intensities of some conversion electron lines of these transitions have also been derived. For the 26.3 keV E1 and 43.4 keV transitions, the nuclear structure parameters , and the E2 admixture , respectively, have been obtained. Values of , , and were measured for the dominant , , and Auger transitions in Np, respectively.

Electron-γ angular correlations in134Ba

Electron-\ensuremath{\gamma} directional correlation measurements have been done in ${}^{134}\mathrm{Ba}$ for the first time using an apparatus including cooled Si surface barrier detector for the electrons and HPGe for the \ensuremath{\gamma}'s. Experimental particle parameters for pure intense E2 transitions have been calculated from \ensuremath{\gamma}\ensuremath{\gamma} and electron-\ensuremath{\gamma} results, giving ${b}_{2}(605K)=1.31(28)$ and ${b}_{2}(795K)=1.20(23).$ Some mixed transitions were also analyzed. The $326K$ electron conversion ratio ${\ensuremath{\alpha}}_{326K}=14(6)\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}2}$ was measured. An upper bound for the E0/E2 mixing ratio was estimated to the ${2}^{+\ensuremath{'}}\ensuremath{\rightarrow}{2}^{+}(563$ keV) transition by the $e\ensuremath{\gamma}$ interference E0/E2 method, giving ${q}_{K}^{2}(E0/E2)l~0.06.$

Lifetime measurement of theπg9/2isomer in79As

The lifetime of the 773 keV $\ensuremath{\pi}{g}_{9/2}$ isomer in ${}^{79}\mathrm{As}$ has been measured to be ${T}_{1/2}=0.87(6) \ensuremath{\mu}\mathrm{s}$ by taking coincidences between $\ensuremath{\gamma}$ rays and projectilelike fragments produced in deep-inelastic collisions of ${}^{198}\mathrm{Pt}{+}^{76}\mathrm{Ge}$ (635 MeV). The ${B(M2,9/2}^{+}\ensuremath{\rightarrow}{5/2}^{\ensuremath{-}})$ value for the 542 keV transition in ${}^{79}\mathrm{As}$ is found to be 0.042(3) Weisskopf units (W.u.). An identification method of nuclei produced in deep-inelastic collisions is also described.

Large oblate deformation of69Se proven by measured transition probability

The large oblate deformation of the69Se g9=2 band was proven by the DSA analysis of the 13/2+ →11/2+ 403 keV transition measured via32S(40Ca, 2pn)69Se at 125 MeV beam energy with six escape suppressed EUROBALL Cluster detectors at ±44°. Applying the model of a rigid axial-symmetric rotor the determined lifetime resulted in ∣β2∣ ɛ [0.24,0.85].

Conversion--electron gamma--ray coincidence spectroscopy of superdeformed 135Nd

Three mini-orange conversion–electron spectrometers and four Euroball Ge Cluster detectors have been used for γ–e- coincidence spectroscopy of superdeformed 135Nd. Transitions within the superdeformed band are shown to have the expected E2 multipolarity. The 766.5–keV transition which links the band to a positive-parity state has a conversion coefficient consistent with M1 multipolarity. Consequently, positive parity is deduced for the superdeformed band. No evidence for E0 transitions was found.

Blocking of Octupole Correlations Deduced from the Decay of a Multiparticle Isomer in212At

A high spin isomer with spin ${25}^{\ensuremath{-}}$ and mean lifetime of $220\ensuremath{\mu}\mathrm{s}$ has been observed at an excitation energy of 4772 keV in ${}^{212}\mathrm{At}$. The measured $E3$ decay rate for the 224 keV transition deexciting this level is enhanced but significantly lower than those observed in the neighboring isotopes or predicted using a multiparticle octupole coupling model. The relatively simple configurations involved in this decay and the close relationship to neighboring states allow a clear association to be made between the occupation of a specific single particle orbital and a blocking of the octupole vibrational correlation.

Stopping power of Nd ions in Pb determined from γ-ray lineshape analysis in Coulomb excitation

The stopping power of Nd ions in Pb, in the range from 7 to 35 MeV, has been determined using the γ-ray lineshape analysis of the 696.6 keV transition de-exciting the first 2+ level in 144Nd, populated by Coulomb excitation using a 90 MeV 28Si beam. The data are compared with the most commonly used parameterizations.

Beta decay of 157Dy

The decay of 157Dy(T1/2 = 8.14(4)h) is investigated. Spectra of γ-rays, internal conversion electrons and γ − γ coincidences are measured. The 983.50 and 991.70 keV transitions show E0 admixtures. Our experimental results made it possible to extend substantially the decay scheme. From the coincidence relationships we established four new excited states of 157Tb at 883.32, 895.06, 925.29, 970.38 keV and confirmed the 357.66 keV state. The levels at 1160.71 and 1318.62 keV are introduced from the energy balance. Tentative evidence is given for the existence of five new levels at 252.58, 327.65, 658.36, 793.52 and 922.69 keV. We assign Nilsson’s quantum characteristics to all introduced levels. The structure of the excited states of 157Tb is discussed in terms of current nuclear models.

Evidence of “penetration effects” for the 94 keVK-allowed unhindered transitionin169Tm

From the time differential angular correlation measurement of the 94-63 keV cascade in {sup 169}Tm, a pure {ital M1} character of the 94 keV {gamma} ray is suggested in contrast to the 4{percent} {ital E2} admixture observed in conversion coefficient measurements. Our result indicates {open_quotes}penetration effects{close_quotes} on the internal conversion processes for the 94 keV transition. The observation of penetration effects for a {ital K}-allowed unhindered transition is probably the first. The magnetic moment of the 379 keV state has been remeasured, and the value [{mu}=(3.04{plus_minus}0.14){mu}{ital {sub N}}] is in close agreement with the theoretical prediction (4.5{ital {mu}{sub N}}). {copyright} {ital 1997} {ital The American Physical Society}

Lifetimes of a shears band in 139Sm

Lifetimes have been measured in 139Sm with the DSAM method, using the reaction 62Ni( 81Br,p3n) 139Sm at 350 MeV. In the negative-parity regular dipole band based on the 25 2 − state at 3325 keV values of 0.60(21), 0.40(14) and 0.25(8) ps were found for the 337, 409 and 473 keV transitions, respectively. The deduced B(M1) and B(E2) are in agreement with the predictions of the tilted axis cranking model, allowing a triaxial equilibrium shape for the assumed νh 11 2 ⊗ πh 11 2 2 configuration.

The problem of the anomaly in the beta decay solved

Conversion electron and gamma ray measurements with electrostatic and Si(Li), spectrometers, respectively, revealed the existence of the eV E1 nuclear transition in with the M2 admixture less than . The full intensity of the transition was determined to be almost 100% per decay. Existence of the 7.7 keV transition in solves the problem of the `anomalously fast' first-forbidden EC, transition in decay and introduces substantial changes into the accepted decay scheme of . Energies of the 24.4(2) and 71.95(5) keV transitions in were also improved to and eV, respectively. For the 11.4(1) keV M1 transition in , we improved the transition energy as eV and determined the E2 admixture to be less than 0.6%.

First evidence for the 2+ level in the very neutron-rich nucleus102Sr

Evidence for the 2+ level in102Sr is obtained from theβ-decay of102Rb, mass separated at the ISOLDE facility. The energy of 126 keV and the collectivity of the 2+→0+ transition indicate that102Sr is a strongly deformed rigid rotor. In addition, a sizeable lifetime is measured for the 94 keV transition in102Y.

Study of some nuclear parameters in the decay of 131Ba

The sum peak method has been applied to calculate K-electron capture probabilities to 216, 373, 585, 620 and 1048 keV levels of 131Cs. The relative and absolute intensities of γ-rays have been calculated using a high-resolution HPGe detector. K-conversion coefficients of 123 and 133 keV transitions have been calculated using summing phenomena.