Die Koeffizienten der Inneren Paarbildung bei den γ-Übergängen nach Co60→Ni60 und Pr142→Nd142

The coefficients ε of internal pair formation of the 1.17 and 1.33 MeV transitions in Ni⁶⁰ and of the 1.57 MeV transition in Nd¹⁴² were measured by detecting the annihilation radiation of the positrons. We obtained the values ε=(3.7±0.6)·10^?5 for Ni⁶⁰ and ε=(10.8±1.8)·10^?5 for Nd¹⁴². The results for Ni⁶⁰ are in good agreement with theoretical calculations. The 1.57 MeV transition in Nd¹⁴² is identified as electric quadrupole and the first excited level of Nd¹⁴² is determined to be 2⁺. By further measurements the partial transition from Pr¹⁴² to the first excited level of Nd¹⁴² was found to be (3.7±0.4)% per disintegration. NoK capture of Pr¹⁴² more than 2·10^?4 could be detected.     

Theoretical study of the spin-orbit coupling in the X2Π state of OH

The spin-orbit coupling constant, A(r), as a function of internuclear distance (r) was computed for the X²Π state of OH, using the microscopic spin-orbit Hamiltonian, extended basis sets, and extensive configuration-interaction wavefunctions. Our best theoretical results are in excellent agreement with the “experimental” A(r) functions deduced from an inversion of the observed A_v. Our calculated first-order contributions to A_v, v ≤ 10, obtained by vibrationally averaging our theoretical A(r) function using the X²Π RKR potential, differ from experiment by less than 0.12%. A minimum occurs in the A_v at v = 7 in agreement with experiment, reflecting the local minimum in A(r) near 2.8 bohr. The second-order contributions to A_v are only about 0.1% for v ≤ 10. They arise mainly from the A²Σ⁺ state for the lower vibrational levels, but each of the A²Σ⁺, B²Σ⁺, (1)²Σ^?, (1)⁴Σ^?, and (1)²Δ states contributes significantly for higher vibrational levels. Spin-orbit centrifugal distortion parameters, A_Dv and a_Dv, are reported for v ≤ 6. The theoretical A_Dv are also in excellent agreement with experiment when the “experimental” A(r) function has the same slope at the equilibrium separation as that obtained from the effective spin-rotation constants of OH, OD, and OT.     

Der Zerfall des125m Xe,des127m Xe und des127g Xe

The decay of^125m Xe produced by the reaction¹²²Te(α, n)^125m Xe using a target enriched in¹²²Te (95.4%) and the decay of^127m Xe produced by the reaction¹²⁷J(d, 2n)^127m Xe have been investigated: ^125m Xe decays with a half-life ofT _1/2=(56±3) sec by ayy- cascade withE _γ1=(140.4 ±0.5) keV andE _γ2=(110.5 ±0.5) keV. The experimental conversion coefficients yield multipolarities ofE3 for the 140.4 keV isomeric transition and predominantlyM1 for the 110.5 keV-transition. ^127m Xe decays with a half-life ofT _1/2=(71±2) sec. The decay also proceeds by aγγ-cascade with an isomeric E3 transition ofE _γ1=(172.5±0.3) keV and a predominantlyM1 transition ofE _γ2=(124.6±0.3) keV. In the decay of^127g Xe an additional branching of the electron capture to a level at (618.1±0.3) keV was observed. The relative probability forK-captureP _K618/P_K375=0.40 ±0.07 yields a total transition energyQ _EC=(664 ±4)keV. A spin of 1/2⁺ was assigned to the ground state.     

Der zerfall des J121 (T 1/2=2,12 h)

I¹²¹ was produced by bombarding a target of enriched Te¹²² with deuterons of 25 MeV. Theγ rays associated with the decay of I¹²¹ have been investigated using a Ge(Li) detector and a Ge(Li)-NaI coincidence set up. 58γ transitions ranging from 212.5 to 1841.8 keV have been identified. A decay scheme for the I¹²¹→Te¹²¹ decay which accounts for 50 of the observedγ transitions is proposed.     

Nuclear resonance fluorescence in121Sb

Usingγ quanta from a⁵⁶Co source, resonance fluorescence from a 3,452 keV level in¹²¹Sb was observed. Four deexcitingγ transitions were identified. The profile of theγ emission line, investigated by means of a high speed centrifuge, yields with a novel variety of Doppler shift analysis a lifetime of τ_4,298=(110±50)fs for theγ emitting 4,298 keV level in⁵⁶Fe. The lifetime of the 3,452 keV level was determined to beτ _3,452 =(200±100)fs.     

Zum experimentellen Nachweis von Zweiquantenzerfall beim 0+-0+-Übergang des Zr90

With a scintillation coincidence spectrometer it has been tried to detect double quantum emission in the 0⁺-0⁺ transition of the first excited level of Zr⁹⁰. An effect, probably due to double quantum emission gives 2·10^?3 for this decay mode. This level is reached byβ-decay of Y⁹⁰. From a measurement of the positron annihilation radiation it follows, that (3,4±0,4)·10^?5 pairs deexciting this level are created perβ-decay of Y⁹⁰.     

Low-energy nondipole effects in molecular nitrogen valence-shell photoionization

Observations are reported for the first time of significant nondipole effects in the photoionization of the outer-valence orbitals of diatomic molecules. Measured nondipole angular-distribution parameters for the 3sigma(g), 1pi(u), and 2sigma(u) shells of N2 exhibit spectral variations with incident photon energies from thresholds to approximately 200 eV which are attributed via concomitant calculations to particular final-state symmetry waves arising from (E1)multiply sign in circle(M1,E2) radiation-matter interactions first-order in photon momentum. Comparisons with previously reported K-edge studies in N2 verify linear scaling with photon momentum, accounting in part for the significantly enhanced nondipole behavior observed in inner-shell ionization at correspondingly higher momentum values in this molecule.     

Bounds for the Elastic Properties of Pyrolytic Carbon

The elastic properties of heterogeneous materials without defects depend on both the constitutive properties of the constituents and the microstructural characteristics. In this paper the first-order bounds of aggregates of domains with hexagonal material symmetry are determined in terms of tensorial texture coefficients. The predictive capability of these bounds is compared to higher-order bounds for pyrolytic carbon. (© 2009 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)