Electric quadrupole interaction of Ce isomers in tin

The quadrupole coupling constants for 10⁺ Ce isomers have been measured in a polycrystalline Sn host. The quadrupole moment ratios are Q[¹³⁸Ce(10⁺)]: Q[¹³⁶Ce(10⁺)]: Q[¹³⁴Ce(10⁺)]=11.45(14)1.71(16). The temperature dependence of the EFG was measured in the range 160–468 K.Incumbent of the Arye Dissentshik Career Development Chair.We thank Dr. A. Abbas for submitting to us the seniority scheme wave functions prior to publication.     

(EC +β +) decay of130Ce

The nuclide¹³⁰Ce was produced by a (¹⁶O, 4n) reaction on an enriched¹¹⁸Sn target. Reaction products were transported to a shielded location by using a heliumjet tape transport system. A 22.9 min activity in chemically separated cerium sample was identified as¹³⁰Ce. The (EC+β ⁺) decay scheme of¹³⁰Ce was proposed for the first time. This scheme includes 108γ-lines, 107γ-lines among them being new. More than 13 1⁺ low-lying states of¹³⁰La are populated in the decay of¹³⁰Ce. Two new isomers with half-life of 77±10 ns and 17±5 ns were observed by means of delayedγ-γ coincidence measurements.     

On the parity of the yrast 8+ level in138Ce and an anomaly in theB(E2) values

On the basis of conversion electron andγ-angular distribution measurements new spin and parity assignments in¹³⁸Ce have been made. They lead together with the already known lifetime of the 10⁺ yrast state whose parity was unclear to an extremely low transition probability of the 10⁺→8⁺ transition. A comparison with neighbouring even isotopes is made.     

Excited levels of 148Ce

Available experimental data on excited levels of the ¹⁴⁸Ce nucleus are analyzed. With the aid of model concepts and systematics that cover neighboring nuclei, the spectrum of ¹⁴⁸Ce is supplemented with a K ^π = 2^? rotational band that has a bandhead at 1368.98 keV, which extends up to the 16^? state at 3897.9 keV, and which is new. Three states at E = 1422.85, 1786.57, and 2198.6 keV of spin-parity 5⁺, 7⁺, and 9⁺, respectively, are included in the gamma-vibrational band featuring the known 2⁺ and 3⁺ levels at 989.90 and 1116.63 keV, respectively. A significant difference in the behavior of the moments of inertia in positive-and negative-parity bands is highlighted.     

New sonochemiluminescence involving solvated electron in Ce(III)/Ce(IV) solutions

The moving single-bubble sonoluminescence of Ce³⁺ in water and ethylene glycol solutions of CeCl₃ and (NH₄)₂Ce(NO₃)₆ was studied. As found, a significant part of intensity of the luminescence (100% with cerium concentration less than 10^–4 M) is due to the sonochemiluminescence. A key reaction of sonochemiluminescence is the Ce⁴⁺ reduction by a solvated (or hydrated in water) electron: Ce⁴⁺ + e_s (e_aq) → *Ce³⁺. Solvated electrons are formed in a solution via electrons ejection from a low-temperature plasma periodically generated in deformable moving bubble at acoustic vibrations. Reactions of heterolytic dissociation of solvents make up the source of electrons in the plasma. In aqueous CeCl₃ solutions, the Ce⁴⁺ ion is formed at the oxidation of Ce³⁺ by OH radical. The latter species originates from homolytic dissociation of water in the plasma of the bubble, also penetrating from the moving bubble into the solution. The sonochemiluminescence in cerium trichloride solutions are quenched by the Br⁻ (acceptor of OH) and H⁺ ions (acceptor of e_aq). In water and ethylene glycol solutions of (NH₄)₂Ce(NO₃)₆, the sonochemiluminescence also quenched by the H⁺ ion. The sonochemiluminescence in CeCl₃ solutions is registered at [Ce³⁺] ≥ 10^–5 M. Then the sonochemiluminescence intensity increases with the cerium ion concentration and reaches the saturation plateau at 10^–2 M. It was shown that sonophotoluminescence (re-emission of light of bubble plasma emitters by cerium ions) also contributes to the luminescence of Ce³⁺ in solutions with [Ce³⁺] ≥ 10^–4 M. If the cerium concentration is more than 10^–2 M, a third source contributes to luminescence, viz., the collisional excitation of Ce³⁺ ions penetrating into the moving bubble.     

Investigation of the Magnetic Hyperfine Field at 140Ce on Gd Sites in GdCo2 Compound

Perturbed angular correlation experiments on ¹⁴⁰La–¹⁴⁰Ce probes substituting for the Gd positions on GdCo2 demonstrate that the magnetic hyperfine field (MHF) on Ce atoms follows an expected Brillouin function but with a substantially reduced saturation value as compared with the MHF acting on free Ce⁺³ ions. The results were interpreted with the aid of first principles electronic structure calculations showing that the reduced value of the MHF is a consequence of a small orbital contribution to the MHF which was attributed to the de-localization of the Ce 4f electronic state.     

Integrated chemical process for exothermic wave synthesis of high luminance YAG:Ce phosphors

In this paper, high-luminance yellow-emitting Y₃Al₅O₁₂:Ce³⁺ phosphor (YAG:Ce) microparticles were prepared in a solid flame using a 1.425Y₂O₃+2.5Al₂O₃+0.15CeO₂+k(KClO₃+urea)+mNH₄F precursor mixture (here k is the number of moles of the KClO₃+urea red-ox mixture, and m is the number of moles of NH₄F). The self-sustaining combustion process for the entire reaction sample was provided by the heat generated from the KClO₃+urea mixture. Parametric studies demonstrated that the maximum temperature in the combustion wave varied from 885 to 1200 °C for k=2.0-3.0 mole and m=0-1.5 mole. X-ray analysis results showed that the product obtained in the solid flame consisted of Y₃Al₅O₁₂:Ce³⁺ and KCl phases. Therefore, after dissolving potassium chloride in distillated water, pure-phase YAG:Ce phosphor powder was obtained. The as-prepared YAG:Ce phosphor particles had diameters of 10-25 μm and good dispersity and exhibited luminescence properties comparable to those of YAG:Ce phosphor powders prepared by conventional high-temperature processing.     

High-spin levels in137,139Ce and139,141Nd evidence for hole-core coupling

Excited states of the¹³⁷Ce,¹³⁹Ce,¹³⁹Nd and¹⁴¹Nd nuclei have been studied using the¹³⁸Ba(α, 5nγ)¹³⁷Ce,¹³⁸Ba(³He, 4nγ)¹³⁷Ce,¹³⁸Ba(α, 3nγ)¹³⁹Ce,¹⁴⁰Ce(α, 5nγ)¹³⁹Nd,¹⁴⁰Ce(³He,4nγ)¹³⁹Nd,¹⁴⁰Ce(α, 3nγ)¹⁴¹Nd and¹⁴²Ce(α, 5nγ)¹⁴¹Nd reactions. Singlesγ-ray spectra,γ —γ coincidence spectra, angular distributions and time distributions ofγ-rays with respect to beam pulses have been measured. Gamma transitions between excited states with spin values up to 21/2, 23/2 or 25/2 have been observed. Isomeric states with T_1/2=70 ns have been observed in¹³⁹Ce at 2631.5 keV (19/2) and in¹⁴¹Nd probably at 2952.0 keV (19/2). The level structure observed in the nuclei studied can be explained if the neutron-holes are coupled to the doubly even core excitations. The coupling of theh _11/2 neutron-hole with the 2⁺, 4⁺ and 3^? collective excitations are calculated in terms of the weak and intermediate coupling models. The intermediate coupling results seem to be in better agreement with the experimental data. The energies of theree-particle states, being the result of the coupling of theh _11/2 neutron-hole with the two-proton excitations in the core, are well reproduced in the calculations when empirical values of the two-body interaction matrix elements were used.     

稀土元素Ce热引入Si单晶中及Ce在Si中的扩散系数

利用真空淀积和真空热处理(1050℃,20h)向Si单晶中引入了稀土元素Ce,热处理过程中Ce首先与Si形成合金,然后向Si中扩散,于是在Si中形成Ce的扩散层。用二次离子质谱(SIMS)技术测定了Ce的纵向相对浓度分布,并据此分析了Ce在Si中的扩散系数。并在77—450K范围内测量了扩散层的平均电导率。 关键词：     

Decay of 129Ce to low-lying positive-parity states in 129La

Low-lying levels of the ¹²⁹La isotope have been investigated through the β⁺/EC decay of ¹²⁹Ce. The radioactive nuclei were produced in the ⁹⁴Mo+⁴⁰Ca reaction at a bombarding energy of 255 MeV and transported with a He-jet system. On-line mass separation was used to select the ¹²⁹Ce beta-decay γ-γ-t, X- γ- t, e^?-γ -t coincidence measurements as well as time multi-analysis were performed. Internal conversion electrons were recorded with a magnetic selector and multipolarities deduced. The level scheme of ¹²⁹La is discussed and compared with the calculations made in the frame of the neutron-proton Interacting Boson-Fermion Model (IBFM-2).     

Cerium isotope effects in Ce(III) malate and lactate complex formation studied by long-distance displacement chromatography

Isotope effects of cerium were observed in malate and lactate complex formations during the long-distance displacement chromatographic processes at 313 K. Heavier isotopes were found fractionated in the frontal edges of the Ce adsorption bands in both the systems, registering a preference of the heavier isotopes for the Ce(III) complexes in the solution phase over the simply hydrated Ce(III) ions in the resin phase. The fractionation coefficients ? for the ¹³⁶Ce/¹⁴⁰Ce, ¹³⁸Ce/¹⁴⁰Ce and ¹⁴²Ce/¹⁴⁰Ce isotopic pairs were 7.1 × 10^?6, 5.2 × 10^?6 and ?2.1 × 10^?6 for the malate system, and 4.8 × 10^?6, 4.5 × 10^?6 and?2.6×10^?6 for the lactate system, respectively. They all show the mass-dependent law if the deviation of ? for the ¹³⁸Ce/¹⁴⁰Ce pair was considered merely due to the isobaric interference in Ce isotopic ratio measurements, suggesting the molecular vibration, rather than the nuclear field shift, mainly contributes to the Ce isotope effects in the complex formation systems. The absolute values of ? between the two systems are comparable, suggesting no instinct difference in structural properties between Ce malate and lactate complexes involved.     

L X-ray-gamma angular correlations following the decay of139Ce

A reinvestigation of theL X-ray-gamma angular correlations following the decay of¹³⁹Ce is made by using a Si(Li) semiconductor detector asL X-ray detector. Coincidence measurements at five different angles were made between the 166-keV gamma ray and theL X-ray spectrum. The data were handled in two different ways: (i) the counts under theL _l +L _α+L _β+L _γ peaks were taken; (ii) the counts under theL _l +L _α+L _β peaks were only considered. Chance coincidences as well as coincidences background were taken into account. The results indicate that no anisotropy is to be found within a margin of error of 6×10^?3.     

K-capture probability in the decay of139Ce(137.5d)

The K-capture probability (P _K) in the decay of¹³⁹Ce (137.5d) has been determined from the analysis of the K x-ray gamma ray sum-peak observed with a Ge (Li) x-ray detector. Furthermore,P _K is estimated independently from the measurement of the K x-ray intensity in the decay, using the known conversion coefficients of the 165.8 keV transition. Using the weighted average ofP _K measured as above, the mass difference between¹³⁹Ce and¹³⁹La is found to be 273 _?13 ⁺²¹ keV.     

The magnetic moment of the 10+ isomer in140Ce andE1 transitions inN=82 isotones caused by outer subshell configurations

Using the reaction¹³⁸Ba(α,2n)¹⁴⁰Ce the magnetic moment of the 10 ₁ ⁺ isomer atE _x =3714.7 keV in theN=82 nucleus¹⁴⁰Ce has been determined by means of the TDPAD method toμ=+10.3(4)μ _N . Measuredg-factors in¹⁴⁰Ce are compared to calculations within the shell model with configuration mixing. For the 10 ₁ ⁺ isomer in¹⁴⁰Ce the four proton configuration π(1g ₇ ^2/2 ,2d ₅ ^2/2 ) has been found to be dominant. From theg-factor measurement strong contributions of multiparticle excitations to thegp2d _3/2,π3s ₁ ² or π1h ₁₁ ² shells and admixtures of neutron excitations to the wave function of the 10 ₁ ⁺ state could be excluded. The strongE1γ-branch of the deexcitation of the 10 ₁ ⁺ isomer in¹⁴⁰Ce can be explained by means of small admixtures of configurations which contain the outer subshell excitationsπ2f _7/2 andπ1h _9/2. On this basisE1 transitions experimentally observed in theN=82 nuclei¹⁴⁰Ce,¹⁴¹Pr and¹⁴⁵Eu may be understood.     

Beta decays of 128Ce and 128La

Low-lying states in ₅₇ ¹²⁸ La and ₅₆ ¹²⁸ Ba have been investigated by γ-ray spectroscopy after the β decays of ₅₈ ¹²⁸ Ce and ₅₇ ¹²⁸ La. For the EC+β⁺ decay of ¹²⁸Ce, a new halflife has been determined to be 4.1 ± 0.3 min. In ¹²⁸La a new β-unstable isomeric state with a halflife shorter than 2 min is suggested in addition to a previously known isomeric state with the halflife of 5.2 min. A tentative level scheme of ¹²⁸La at low excitation energies has been constructed from the γ?γ coincidence measurement after the β decay of ¹²⁸Ce. The γ?γ angular correlation for γ rays from ¹²⁸Ba after the β decay of ¹²⁸La suggests that the spin-parity assignment of I ^π = 4^? or 5⁺ is preferable for the 2424.9 keV level which is populated via the β decay of the 5.2-min isomeric state with a log ft value of 5.6. For the 2877.1 keV level observed with log ft = 5.8, a preferable spin-parity assignment is 5^? or 6⁺. On the basis of these decay properties and low-lying excited states in neighboring odd mass nuclei, the spins and parities of isomeric states in ¹²⁸La are proposed to be (1⁺ or 2⁺) for the low-spin state, while (5± or 6⁺) for the high-spin state, within the limit of zero order approximation to the proton-neutron couplings.     

Exotic clustering in Ce and Nd isotopes

We propose exotic binary cluster models for the intermediate mass nuclei ^146,148,150Ce and ^{148,150,152,154}Nd. The optimum choice of cluster and core is determined by joint consideration of the penetrability for exotic cluster emission, the deviations of cluster and core binding energies from underlying liquid drop values and the Q-values for breakup. It is noticeable that the core neutron number selected in this way is at or near the N = 82 shell closure. We use a standard form of the cluster-core potential to calculate the energies and wave functions of states in the ground 0⁺, 2⁺, 4⁺, … and lowest lying negative parity 1⁻, 3⁻, 5⁻, … bands. The theoretical spectra and electromagnetic properties are compared with measurements, and their general trends are reproduced satisfactorily.     

Identification of152Ce

Although the¹⁵²Ce isotope, the heaviest one of cerium, was once reported as identified, it was pointed out later on that the assignment should be corrected and¹⁵²Ce is still unknown. The search for¹⁵²Ce has been carried out again in the present report. From γ-ray spectra of mass separated fission products produced by KUR-ISOL, the Pr-K X-rays and two γ-rays are assigned to be generated by the ß-decay of¹⁵²Ce. The half-life is determined to be 1.4(2) s, which is a little shorter than theoretical predictions, 2.2 s and 2.1 s.     

The magnetic hyperfine field at140Ce in nickel

The hyperfine interaction of¹⁴⁰Ce in nickel has been investigated by the time-differential perturbed-angular-correlation technique (TDPAC). The probe was produced by isotope separator implantation of the fission product¹⁴⁰Xe, the ^- decay chain of which finally populates excited states of¹⁴⁰Ce.Different spin rotation spectra were observed before and after an 8 h annealing at 415°C. The analysis of the spectra led to the conclusion that the Ce ions were in the diamagnetic 4⁺ state. The dominant contributions to the hyperfine interaction are two different magnetic hyperfine fields: |H _hf ¹|=385±7 kOe and |H _hf ²|=276±12 kOe.H _hf ¹ disappears after annealing. The fraction of nuclei which observeH _hf ² is increased by the annealing procedure from 16% to 75%. It is assumed thatH _hf ¹ is the hyperfine field of CeNi in an unperturbed substitutional site andH _hf ² is attributed to Ce ions which have trapped a single vacancy.     

Radiative lifetimes in Ce I and Ce II

New radiative lifetime measurements based on time-resolved laser-induced fluorescence techniques are reported for 18 even-parity levels belonging to the 4f5d^26p and 4f ²5d ² configurations of Ce I and 6 even-parity levels belonging to the 5d^26s, 4f5d6p, and 4f6s6p configurations of Ce II. Free neutral and singly ionized cerium atoms were produced by laser ablation. The Ce I and Ce II levels range in energy from 26 545 to 29 102 cm^-1, and 42 573 to 48 152 cm^-1, respectively. Received 25 September 2002 Published online 4 March 2003     

Magnetic moment of the 19/2+ isomer in135Ce

Employing the time-integral PAC technique with an external magnetic field, the g-factor of the 19/2⁺ state at 2,125.6 keV in¹³⁵Ce was determined to be g=?0.07(1). This value favours a predominant (h ₁₁ ^2/?2 s ₁ ^2/?1 ) neutron configuration for this level. Its meanlife has been redetermined with improved precision to be τ=11.8(5) ns.