Messung hochenergetischer Konversionselektronen von Sm150 nach Neutroneneinfang

In the energy range from 5 MeV to 8 MeV internal conversion electrons emitted by Sm¹⁵⁰ after neutron capture were measured by means of the betaspectrometer at the research reactor at Garching near Munich. 20 lines corresponding to 18 transitions were found.     

Richtungs- und Temperaturabhängigkeit der Lichtimpulse von Anthrazenkristallen bei Anregung mit α-Teilchen

The spectrum of internal conversion electrons emitted by Ag¹¹⁰ after thermal-neutron capture was measured with the beta spectrometer at the research reactor near München. 45 conversion lines corresponding to 34 transitions were found between 0 keV and 300 keV. The multipolarities of 19 transitions were determined. The low-energy gamma radiation was investigated between 10 keV and 600 keV by means of a Ge(Li)-detector. A partial level scheme containing the most intense transitions is proposed.     

Nanoparticles size effects in thermoluminescence of oxyfluoride glass-ceramics containing Sm<Superscript>3+</Superscript>-doped CaF<Subscript>2</Subscript> nanocrystals

Oxyfluoride glass-ceramic in the system SiO₂–Al₂O₃–CaF₂–SmF₃ containing Sm³⁺-doped CaF₂ nanocrystals in the range from 15 to 150 nm size were produced by using the controlled ceramization of the precursor glass. The incorporation of the Sm³⁺-dopant ion in the glass ceramic creates new electron-trapping centers and thermoluminescence (TL) method has been used in order to trace their evolution during glass ceramization. The 370 °C TL peak observed in precursor glass has been assigned to the recombination of the electrons released from the Sm²⁺-traps in the amorphous glass network. In the glass-ceramic sample containing nanocrystals with about 15 nm size the new weak TL peaks at 270, 290, and 310 °C were attributed to the recombination of the electrons released from the Sm²⁺-traps located mainly at the surface of the CaF₂ nanocrystals. In the glass-ceramic sample containing nanocrystals with about 150 nm size, the new TL peaks at 232, 270, and 302 °C size have been assigned to the recombination of the electrons released from the Sm²⁺-traps located inside the CaF₂ nanocrystals.     

Konversionselektronen und Multipolordnungen von Übergängen in Dy165

The spectrum of internal conversion electrons emitted by Dy¹⁶⁵ after thermal neutron capture was measured with the beta spectrometer at the reactor FRM. 225 conversion lines were found between 0 keV and 7 MeV. They correspond to 193 transitions. The multipolarities of most transitions were determined. The result of this measurement is in good agreement with the level scheme proposed bySchult et al. Eighteen additional levels with energies up to 3 MeV are proposed. A new 3/2^?-rotational band with its band head at 1103.30 keV has been disclosed. The level scheme contains 39% of the complete decay of the capture state. The multipolarities of 6 transitions following the beta decay of Dy¹⁶⁵ to Ho¹⁶⁵ are given.     

High power non-linear magnetophotoconductivity in n-GaAs using the UCSB free electron laser

The kinetics of electrons bound to shallow donor impurities in n-GaAs was investigated by saturation spectroscopy using the University of California at Santa Barbara free electron laser. The resonant photothermal conductivity from 1s–2p⁺ transitions was measured at intensities greatly exceeding previous studies. Saturation of bound-to-free photoionization transitions was measured from 0 to 4 Tesla. The 1s–2p⁺ resonant photoconductive signal shows a distinct intensity dependence caused by the competing bound-to-free transitions which saturate differently. Evaluation of the electron recombination kinetics allows us to calculate the transition time of electrons from the 2p⁺ level to the ground state, the recombination time of free electrons, and the thermal ionization probability of the 2p⁺ state.     

Concentration influence on temperature-dependent luminescence properties of samarium substituted strontium tetraborate

The series of divalent samarium substituted strontium tetraborate (Sr_1?xSm_xB₄O₇) polycrystalline samples were prepared by the conventional solid-state reaction. The phase formation of the samples was investigated by X-ray powder diffraction measurements. The luminescence spectra and decay curves of the Sm²⁺ ions were measured. Temperature dependent Sm²⁺ luminescence properties were investigated. The f–d and ⁵D₁–⁷F_J transitions appeared at 350 K and increased with increase in the temperature while the intensity of ⁵D₀–⁷F_J transitions decreased. The emission spectra pointed out that Sm²⁺ occupies of C_2v or lower symmetry site. The photoluminescence decay times of strontium tetraborate doped with different concentrations of Sm²⁺ was investigated as a function of temperature in the range of 100–500 K. However, no obvious concentration quenching was observed.     

Excitation-energy transfer in infrared -stimulable CaS doubly doped with Eu and Sm

The photoluminescence emission (PLE) mapping and infrared-stimulated luminescence (ISL) spectra of CaS:Eu,Sm demonstrated that Eu is formed in Eu²⁺ as a luminescent centre, whereas Sm is formed in Sm³⁺ as an electron-trapping centre by replacing Ca²⁺ in the CaS host lattice. It was found that electron trapping occurred in the photoluminescence excitation (PLX) process. A series of concentrations of Eu with a fixed Sm concentration and a series of concentrations of Sm with a fixed Eu concentration in doubly doped CaS:Eu,Sm were studied by the time-related PLE of Eu²⁺ in the PLX process. According to the electronic energy level(s) of Eu²⁺ and Sm³⁺, excitation-energy transfer is realized by translocation of excited electrons from Eu²⁺ to Sm³⁺, causing simultaneous ionization of Eu²⁺ (leaving Eu³⁺) and capture of excited electrons at Sm³⁺ (forming Sm²⁺). ISL is then produced due to the energy released from recombination of de-trapped electrons from the occupied electron-trapping sites (Sm²⁺) and the previously ionized luminescent centres (Eu³⁺) under infrared irradiation. PACS 78.55.-m; 78.45.+h; 78.55.Et     

The dependence of luminescence on reduction of Sm2+ ions doped in lithium barium borate glasses

Sm³⁺-doped Li₂O–BaO–B₂O₃ glass was prepared by the conventional melt quenching method in air atmosphere. Sm²⁺ ions were obtained by two methods, i.e. heating the as-made glass in a reducing atmosphere and irradiating the sample under X-rays. The two obtained samples were investigated by luminescence spectra and lifetime measurements. It was found that the conversion of Sm³⁺→Sm²⁺ after X-ray irradiation is efficient in this borate glass. Photo-stability of Sm²⁺ ions was evaluated by the photo-bleaching method. Furthermore, thermo-luminescence was also measured. The different defects and the reduction mechanism of Sm²⁺ ions in this borate glass were discussed. This would be helpful to understand the reduction mechanism of Sm²⁺ ions in borate glasses.     

Konversionskoeffizienten von γ-Übergängen in204Pb

Two semiconductor detectors with known efficiencies were employed to measure simultaneously the intensities of the γ-rays and the conversion electrons which are emitted by a mixture of²⁰⁴Bi and^204m Pb in radioactive equilibrium and by pure^204m Pb. Conversion coefficients, conversion ratios and also the relative intensities of many transitions in²⁰⁴Pb were obtained. Informations about transition multipolarities are deduced. Some conversion coefficients and conversion ratios which are measured with good precision are used to check theoretical values.     

Levels in179W studied in the181Ta(p, 3n) reaction by on-line electron and gamma ray spectroscopy

Levels in¹⁷⁹W have been deduced from in-beam gamma and conversion electron studies of the¹⁸¹Ta(p, 3n)¹⁷⁹W reaction. The gamma-ray spectrum was studied with Ge(Li) detectors and a crystal diffraction spectrometer; the conversion electrons were measured with a broad range transport solenoid Si(Li) spectrometer. The multipolarities of some 50 transitions could be determined. Coriolis mixing of the Nilsson orbits withN=6 was calculated.     

Synthesis and photoluminescence properties of Sm-doped CaWO4 nanoparticles

The Sm³⁺-doped CaWO₄ nanoparticles were synthesized by hydrothermal method. The room temperature photoluminescence (PL) spectra of Sm³⁺-doped CaWO₄ nanoparticles doped with different Sm³⁺ concentrations under 405 nm excitation have been investigated. The PL spectra showed four strong emission peaks at 460, 571, 609, and 653 nm. The first emission peak at 460 nm could be due to a structural defect of the lattice, an oxygen-deficient WO₃ complex. The other three emissions at 571, 609, and 653 nm were due to the f-f forbidden transitions of the 4f electrons of Sm³⁺, corresponding to ⁴G_5/2→⁶H_5/2 (571 nm), ⁶H_7/2 (609 nm), and ⁶H_9/2 (653 nm), respectively. In addition, the optimum Sm³⁺ concentration in CaWO₄ nanoparticles for optical emission was determined to be 1.0%. The Sm³⁺⁴G_5/2→⁶H_7/2 (609 nm) emission intensity of Sm³⁺-doped CaWO₄ nanoparticles significantly increased with the increase of Sm³⁺ concentration, and showed a maximum when Sm³⁺ doping content was 1.0%. If Sm³⁺ concentration continued to increase, namely more than 1.0%, the Sm³⁺⁴G_5/2→⁶H_7/2 emission intensity would decrease. The present materials might be a promising phosphor for white-light LED applications.     

Nature of the magnetic excitation spectrum in (Sm,Y)S: CEF effects or an exciton?

The dynamic magnetic susceptibility spectrum in a single-crystal sample of the intermediate-valence compound Sm_0.67Y_0.33S is studied by inelastic neutron scattering with neutron momentum transfer and sample temperatures varying over wide ranges. Two coupled collective modes have been found in the spectrum. Unlike the higher energy mode, whose intensity approximately follows the form factor of Sm²⁺, the lower energy mode exhibits a stronger angular dependence than could be expected from the form factor for the localized f electrons. The total intensity of the inelastic component of the magnetic response decreases with increasing temperature; this is accompanied by the appearance of a broad quasi-elastic signal of a magnetic nature at significantly lower temperatures than follows from the calculated intensities of the transitions within the excited multiplet of the Sm²⁺ ion. An analysis of the observed features allows the suggestion to be made that the fine structure of the magnetic excitation spectrum in (Sm,Y)S is associated with the formation of an exciton-like intermediate-valence state on Sm ions rather than with the crystal-electric-field effects.     

Untersuchung der γ-Strahlung bei Einfang thermischer Neutronen in Sm149 mit der Summen-Koinzidenzmethode

Two-step cascades of neutron captureγ-rays of Sm¹⁴⁹ (n, γ) Sm¹⁵⁰ have been studied by means of the sum-coincidence method. 11 two-step transitions from the capturing state to the 0,33 and 0.77 MeV states were found. Most of them agree with the decay scheme ofGroshev et al., some are new. The relative intensities of the cascades were determined. No two-step transition from the capturing state to the ground state could be observed. Fig. 3 shows the main result.     

Derivation of quantum yields for visible emission transitions of Sm in heavy metal tellurite glass

Under the pumping of violet lighting emitting diode, quantum yields for multichannel transition emissions have been determined in Sm³⁺-doped heavy metal tellurite glass for the first time. For the derivation, the necessary fluorescence spectra were measured and calibrated in an integrating sphere connected to a CCD detector with a 400 μm-core optical fiber. The spectral power distribution of the sample was derived from the measured spectra first, and then the quantum yields of the visible emissions of Sm³⁺ were calculated based on the distribution. The total quantum yield for four emission transitions of Sm³⁺ in visible region is 4.07%. Integrating sphere with a CCD detector is proven to be a reliable and reproducible method to characterize luminescence and laser materials.     

Decay of the 21/2− isomer in211Bi and structure of thevg 9 2/2 πh 9/2 levels

Gamma rays and conversion electrons have been measured in²¹¹Bi populated by the²⁰⁹Bi(t,p) reaction, and the near yrast levels were observed up to 21/2^?. The 21/2^? state is isomeric withT _1/2=70(5) ns. No alpha decaying isomer was found in²¹¹Bi. ObservedM1 transitions reveal mixing of the²¹⁰Pb parent states in the levels of²¹¹Bi. The levels and transitions are well reproduced by the shell model with experimental matrix elements and pure configurations.     

Average multipolarities of quasi-continuum transitions following the (α, 4n) reaction from measured internal conversion coefficients

The quasi-continuum of electromagnetic transitions following the ¹⁶⁰Gd(α,4n)¹⁶⁰Dy reaction exhibits predominant E1 character. This is condluded from conversion electrons observed with a mini-orange spectrometer and corresponding γ-rays, both being selected by coincidences with discrete ground-state band transitions in ¹⁶⁰Dy.     

Tentative level diagram of146Pm below 1.1 MeV

The level scheme of the doubly odd nucleus¹⁴⁶Pm was investigated by means of in-beam spectroscopy. The¹⁴⁶Nd(p, n) reaction in the 3.5–8 MeV proton energy interval on enriched targets has been used to populate the exited states of¹⁴⁶Pm. High resolutionγ-ray spectra using Ge(Li) and hyperpure Ge detectors and conversion electrons with a mini-orange spectrometer were measured. Withγ-exitation functions andnγ-coincidences usingnγ-discriminated NE231 neutron detectors transitions in¹⁴⁶Pm were identified,γγ-coincidences gave information aboutγ-cascades. With these data a level scheme of 38 levels below 1.1 MeV exitation energy has been deduced including 73 transitions. For 12 transitions experimental conversion coefficients have been evaluated, which agree with the expected values forM1/E2-transitions.     

In-beam conversion electrons from 141Pr, 143Pm, 144Pm and 145Pm excited by (α, xn) and (p,n) reactions

Electromagnetic transitions between low-lying states in the odd proton nuclei ₅₉¹⁴¹Pr₈₂, ₆₁¹⁴³Pm₈₂, ₆₁¹⁴⁴Pm₈₃ and ₆₁¹⁴⁵Pm₈₄ with neutron numbers N ≈ 82 were studied by means of in-beam electron-gamma spectroscopy. The triple-focusing electron spectrum selector (TESS) was used to measure in-beam conversion electrons. The TESS, giving very good electron line spectra with small background, was found to be very powerful for in-beam spectroscopy. Accurate values for the internal conversion coefficients (ICC) were obtained by measuring simultaneously both conversion electrons and γ-rays. M2, E3 and some other multipolarities were uniquely assigned from the ICC for the γ-transitions between low-lying states. Properties of these transitions and energy levels are discussed. Analyses of the M2 and E3 transition rates gave, respectively, an isospin-spin (magnetic) core polarization effect and an octupole core polarization effect. The l-forbidden M1 transitions were analyzed in terms of the tensor terms.     

Negative 4ƒ-induced hyperfine field on samarium in paramagnetic Eu(Sm)Al2

The hyperfine field at samarium nuclear site induced by the paramagnetism of 4? electrons has been measured in Eu(Sm)Al₂ using perturbed angular correlation technique and found to have a negative sign which is in striking contrast to the positive sign expected in free Sm³⁺ ion. It amounts to a large negative Knight shift at samarium nuclear site in this alloy.     

Measurements of multipolarities in 227Ra as tests of evidence for stable octupole deformation

Multipolarities of ~30 transitions in ²²⁷Ra have been established by measuring conversion electrons following the β⁻ decay of ²²⁷Fr. For this purpose a “mini-orange”-type electron spectrometer has been constructed. The ²²⁷Fr isotopes were produced by the ISOLDE on-line separator at the CERN Synchro-cyclotron. Internal conversion coefficients were obtained from singles spectra and also from simultaneous γe⁻ and γγ coincidence measurements. The new results support the placement of levels and transitions in the earlier level scheme but require changes in the previously assigned parities for four of the levels. Also, one E0 transition was identified. The results are consistent with previous interpretations for most of the levels that have been used to argue in favour of a small permanent octupole deformation for ²²⁷Ra.