Untersuchungen isomerer Übergänge in140Pr und142Pr

The lifetimes of isomeric transitions in¹⁴⁰Pr and¹⁴²Pr have been measured in a pulsed-beam experiment at the Erlangen EN-Tandem accelerator with the aid of the reactions¹⁴⁰Ce (p, nγ)¹⁴⁰Pr and¹³⁹La (α, nγ)¹⁴²Pr. In the energy range 50 keV≦Eγ≦1.5 MeV we found a new delayed transition in¹⁴²Pr and established two previously reported isomers in¹⁴⁰Pr.     

Structure of140Pm from beta decay of140Sm

The structure of¹⁴⁰Pm is investigated through the beta decay of¹⁴⁰Sm, whose half-life is measured to be (14.7 ± 0.2) m. A level structure comprising 41 transitions among 17 excited states is constructed. Using the deduced ft values and measured internal conversion coefficients, spin-parity assignments to several states in¹⁴⁰Pm were made. From beta end-point measurement, the total decay energy is deduced to beQ _EC =3.4±0.3 MeV, which is compared with the predictions of several mass formulae. The systematics of the odd-Z, N=79 isotones are discussed.     

Quasirotational groundstate bands of even-even nuclei with 50≦N,Z≦82

The quasirotational groundstate bands of¹⁴⁰Sm,¹⁴²Sm,¹⁴⁴Gd and¹³⁶Nd have been determined by studying the prompt γ-decay after (α,xn+yp+zα.) reactions using α-particles of up to 104 MeV and targets of¹⁴⁴Sm,¹⁴²Nd,¹⁴¹Pr,¹⁴⁰Ce,¹³⁶Ce and¹³⁹La. The new levels continue the trends of the neighbouring even-even nuclides smoothly. These systematics of the groundstate bands in the region 50<N,Z<82 are not disturbed by expected subshell closure effects.     

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.     

Decay of140Gd to states inN=77140Eu

The structure of¹⁴⁰Eu has been investigated through the decay of¹⁴⁰Gd, which has a measured half-life of 16.2±0.8 s. A decay scheme is constructed, which comprises 22 transitions depopulating 16 excited states.     

The levels of144Pr from the decay of144Ce

The level scheme of¹⁴⁴Pr has been studied from the decay of¹⁴⁴Ce. The intensities and energies of gamma rays have been determined with a X-ray Ge(Li) detector. TheK-shell internal conversion coefficients for γ-rays have been measured with theK X-ray/γ-ray ratio method using NaI(Tl)—X-ray Ge(Li) coincidence techniques.     

States inN=80140Nd populated in the decay of140Pm

The level structure of theN=80,¹⁴⁰Nd has been investigated through the beta decay of^140m Pm and^140g Pm, whose decay half-lives were measured to be 5.95±0.05 min and 9.1±0.5 sec, respectively. Decay schemes for the two isomers have been constructed fromγ-ray measurements. With the help of the beta decayft values and internal conversion electron measurements, spins and parities were deduced for levels in¹⁴⁰Nd. Among the levels a 7^? state at 2222.0 keV and a 5^? state at 2273.3 keV are identified as two-neutron quasiparticle states. The (ie233-01) for^140m Pm and^140g Pm have been deduced as 7^? and 1⁺, respectively. From beta end-point measurements, the decay energies of the two isomers have been determined asQ _EC=6.48±0.07 MeV^140m (Pm) andQ _EC=6.08±0.10 MeV (^140gPm). The results are discussed in the light of nuclear systematics of theN=79 and 80 isotones.     

PAC studies of hyperfine interactions of181Ta in YBa2Cu3O7-δ and of140Ce in La2CuO4 and La1.85Sr0.15CuO4

Results of TDPAC studies of hyperfine interaction in high temperature superconducting ceramics are reported. The γ-ray cascade of 329–487 keV in¹⁴⁰Ce excited in the decay of¹⁴⁰La in La_2-xSr_xCuO₄ samples (x=0 and 0.15), and 133–482 keV cascade in¹⁸¹Ta excited in the decay of¹⁸¹Hf in YBa₂Cu₃O_7-δ samples were used. The procedure of introducing radioactive¹⁸¹Hf into the ceramics is described and indirect evidence for the occupation of Cu sites by the¹⁸¹Hf-¹⁸¹Ta probe is presented.     

β+ decay of unstable praseodymium isotopes: 127Pr, 126Pr and the new isotope 125Pr

The β⁺ decay of ^127,126,125Pr was studied for on-line mass-separated sources. The decay scheme of ¹²⁷Pr reported previously was revised from the results of a more-detailed analysis of the experimental data. The ¹²⁵Pr isotope was newly identified with a half-life of 3.3(7) s and its decay scheme is presented. The γ band in ¹²⁶Ce was identified in the decay of ¹²⁶Pr and its properties are compared with the prediction of the interacting boson model 2.     

DPAC measurements on the Kondo system:140Ce in yttrium

The DPAC technique was applied to investigate the temperature dependence of the hyperfine interaction of¹⁴⁰Ce nuclei in yttrium metal. A weak damping of the anisotropy was observed, which is interpreted as a result of the short spin fluctuation timet _c for the Ce ions.     

Levels of146Ce studied through the decay of high-spin isomer of146La

The decay of 10.0 s high-spin isomer of¹⁴⁶La to levels of¹⁴⁶Ce has been studied using the on-line isotope separator KUR-ISOL. Gamma-ray singles,γ -γ coincidence and conversion-electron spectra have been measured. A level scheme containing 90 levels and 206γ-ray transitions has been constructed for¹⁴⁶Ce, populated in the decay of the high-spin isomer of¹⁴⁶La. Among these, 39 levels are reported for the first time. Spins and parities for some levels are proposed on the basis ofγ-decay mode, logft values and conversion-electron measurements. The band structure of the low-lying levels in¹⁴⁶Ce is discussed.     

Shape of the 935 keV beta transition of143Pr

The beta spectrum shape of the 7/2⁺ → 7/2^? beta transition in the decay of¹⁴³Pr is measured employing a thoroughly tested intermediate image beta ray spectrometer of the Siegbahn-Slatis type and using the source produced by irradiation of highly enriched stable¹⁴²Ce sample. The spectrum exhibits a definite energy dependence and is well fitted with shape factorC(W) = 1 ? (0·057 ± 0·006)W whereW is in m₀c² units for an end point energy of 935 ± 2 keV agreeing well with the results of Hamiltonet al and Spejweskiet al and disagreeing with the results of Persson and Reynolds. The single particle configurations for the low lying levels of¹⁴³Pr could not give quantitative results.     

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.     

(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.     

The γ-decay of excited states of 141Ce observed in the 140Ce(d,pγ) reaction

The reaction ¹⁴⁰Ce(d, pγ)¹⁴¹Ce was studied at 8 MeV bombarding energy. Protons and γ-rays were detected in coincidence. The decay scheme is deduced, and the branching ratios are compared to the results of other experiments and to model calculations.     

Static electric quadrupole interaction of Ce and Pb ions in lead titanate

The static electric quadrupole interaction of¹⁴⁰Ce and²⁰⁴Pb has been studied in polycrystalline PbTiO₃ at the lead site with the time-differential perturbed angular correlation (TDPAC) method. The interaction frequencies areω _Q(2083 keV;¹⁴⁰Ce)=2.11 (17) MHz andω _Q(1274keV;²⁰⁴Pb)=3.60(3) MHz. The results are compared with the electric field gradient calculated in a point charge model. Under the assumption that the covalent contributions for Ce and Pb are equal, one can derive the quadrupole moment of the 1274 keV state of²⁰⁴Pb to be ¦Q¦=0.68 b.     

The Decay of 140La to Levels in 140Ce

The decay of ¹⁴⁰La to levels in ¹⁴⁰Ce has been studied in detail using a GMX-Ge and Hp-Ge coincidence spectrometer. Singles gamma-ray spectra as well as gamma-gamma coincidence were carried out to determine some γ-transitions and to insure others. Energies and relative intensities of 36 γ-transitions in the range from 26 to 3319 keV have been measured. The doubted γ-lines 936.7, 1087.9, 1303.5, 1404.2, 1415.3 and 2533.4 keV were confirmed, while other ones at 798.3, 902.0, 907.0, 1521.8 and 2494.0 keV were not observed. The two γ-lines at 1924 and 2082 keV which were a source of large discrepancies in the previous studies are confirmed in the present work to be sum peaks. Special care was paid in identifying the weak γ-transitions 936.7, 1087.9, 1415.3 and 2533.4 keV.

Es wurde der Zerfall von ¹⁴⁰La in Energienivcaus des ^l40Ce unter Verwendung eines GMX-Ge und Hp-Ge-Koinzidenzspeklrometers untersucht. Es werden einzclne Gammaspektren r und Gamma-Gamma-Koinzidenzen aufgenommen, um einige Gamma-Übergänge zu bestimmen und andere abzusichern. Die Energien und die relativen Intcnsitäten von 36 Gamma-Übergangen im Bereich von 26 … 3319 keV wurden vermessen. Die unsicheren Gamma-Linien 936,7, 1087,9, 1303,5, 1404,2, 1415,3 und 2533,4 keV wurden bestätigt, während die Linien 798,3, 902,0, 907,0, 1521,8 und 2494,0 keV nicht beobachtet werden konnten. Die zwei Gamma-Linien bei 1924 und 2082 keV, die eine Quclle groβer Unstimmigkeiten in früheren Untersuchungen gewesen sind, konnten als Summenpeaks bestätigt werden. Besondere Beachtung wurde der Zuordnung der schwachen Gamma-Übergange bei 936,7, 1087,9, 1415,3 und 2533,4 keV geschenkt.     

Low-lying levels of 140Pr

The doubly odd nucleus ¹⁴⁰Pr has been investigated by means of the ¹⁴¹Pr(d, t)¹⁴⁰Pr and ¹⁴⁰Ce(p, nγ)¹⁴⁰Pr reactions. Twenty-eight levels, up to 1300 keV excitation, were observed in the pickup study. DWBA analysis was used to determine l-values and spectroscopic factors for all but a few which are very weakly populated. Gamma-ray angular distributions, measured at E_p = 4.78 MeV for the five strongest γ-rays, show appreciable nuclear alignment and demonstrate the feasibility of such experiments in this mass region. Taken together, the two studies have permitted the identification of the 12 levels expected from the low-lying ($\text{π2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{ν2}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$), ($\text{π2}\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}\text{ν3}\text{s}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$), ($\text{π1}\text{g}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{ν2}\text{d}{}_{\mathrm{<mtext>3</mtext><mtext>2</mtext>}}{}^{\mathrm{?1}}$) and (π1g_{$\text{7}\text{2}$}ν3s_{$\text{1}\text{2}$}^?1) configurations. Tenta assignments for the strong odd-parity states are suggested on the basis of their spectroscopic factors.     

Total beta-decay energies of heavy fission products

TheQ _β-value of^144,145Ba,^144,145,147La,^145,147,148Ce and¹⁴⁸Pr has been measured using mass-separated sources produced at the on-line mass separator LOHENGRIN. The experimental values are compared with mass formula predictions.