Half-life and configuration of the 1/2+ intruder state in203Bi

The decay properties of theJ ^π=1/2⁺,E _exc=1,098 keV state in²⁰³Bi were studied. The state was populated via the²⁰⁴Pb(p, 2n) reaction and the activity was studied with the ion guide isotope separator on-line system IGISOL. The half-life of the 1/2⁺ state was measured to beT _1/2=303 ±5 ms. From this value the partial half-lives of the three depopulating branches 1/2⁺ →7/2^? (E3), 1/2⁺→5/2^? (E3 +M2) and 1/2⁺→9/2 _g.s. ^? (M4) were deduced. Since all the transitions are configuration forbidden in first order, a detailed study of second-order shell-model configuration mixing could be performed.     

Half-life of the 89.83 keV level in152Eu

The half-life of the 89.83 keV level in¹⁵²Eu was measured in the¹⁵¹Eu(n, γ)¹⁵²Eu reaction to be 381±19 nsec. This results in the determination of the absolute transition probabilities of the 89.83 keVE1+M2 transition to the ground state, yielding hindrance factors relative to the Weisskopf estimateF _W(E1)=(2.3 ± 0.4) × 10⁶ andF _W=0.20±0.08.     

Half-life measurements of intrinsic states in deformed odd-mass nuclei

The half-lives of the following intrinsic states in deformed odd-mass nuclei has been measured by delayed coincidences with a time-to-amplitude converter:

1. 5/2 5/2⁺[642] at 86.5 keV in¹⁵⁵Gd:T _1/2=6.7±0.3 ns, which results in the determination of theE1,ΔK=1 transition probability to the ground state 3/2 3/2^?[521] and first rotational state 5/2 3/2^?[521], yielding hindrance factors ofF _N ≈5.5 and ≈1.8 (F _W =3.1×10⁴ and 2.3×10⁴) respectively.
2. (3) 5/2 5/2^?[512] at 191.4 keV in¹⁶⁹Yb:T _1/2=3.35±0.15 ns and at 122.39 keV in¹⁷¹Yb:T _1/2=265±20 ns which results in the determination of the transition probabilities of theE1,ΔK=1 transitions to the ground states 7/2 7/2⁺[633], of theK-forbiddenM1 transitions to the 5/2 and 3/2 1/2^?[521] and of theE2 transitions to the 5/2, 3/2 and 1/2 1/2^?[521] states in both nuclei.

TheE1 transition probabilities are compared to the transitions between the same Nilsson states in¹⁷³Yb and¹⁷⁵Hf discussing the influence of the position of the Fermi surface — obtained from recent stripping and pick-up reactions — on these transition probabilities. Additional information on the decay scheme of¹⁷¹Lu→¹⁷¹Yb is obtained by delayed coincidence measurements. For testing the used time-to-amplitude converter the well known half-lives of the 482 keV level in¹⁸¹Ta (T _1/2=10.4±0.3 ns) and of the 279 keV level in²⁰³Tl (T _1/2=0.285 ±0.015 ns) were measured, in good agreement with other measurements.     

Pion photoproduction on197Au to ground and isomeric states in197Hg

The lifetime of the 331.3 keV 0 ₂ ⁺ state in¹⁰⁰Zr has been measured at the gas-filled recoil separator for fission products JOSEF. By observing the delayed coincidences between theβ-particles populating the level and theE0 conversion electrons from its decay into the ground state, a half-life of 3.37±0.30 ns has been obtained. From the measured lifetime and the relative intensities of the 0 ₂ ⁺ →0 ₁ ⁺ and 0 ₂ ⁺ →2 ₁ ⁺ transitions, values of 0.493±0.015 for theE0 strength parameterρ, and of 16 single particle units forB(E2,2 ₁ ⁺ → 0 ₂ ⁺ ) have been deduced. The enhanced nature of theE0 transitions suggests mixing of the 0 ₁ ⁺ and 0 ₂ ⁺ states which may be estimated by comparing the experimentalB(E2) values for the 2 ₁ ⁺ →0 ₁ ⁺ and 2 ₁ ⁺ →0 ₂ ⁺ transitions with the predictions of the asymmetric VMI model.     

A measurement of the electromagnetic form factor of the eta meson and of the branching ratio for the eta Dalitz decay

In an optical spark chamber experiment we have obtained a sample of 80 eta Dalitz decays (η → e⁺e^?γ) and have measured the eta electromagnetic form factor to be F(X) = 1.0?(0.22 ±0.45)X, where X=M_ee²/M_η², and the branching ratio (η→e⁺e^?γ/(η→π⁺π^?π⁰)= (0.0082 ± 0.0020).     

OnE0 transitions in the decay of152Eu m (9.3 h)

The conversion electron spectrum of the decay of¹⁵²Eu ^m (9.3 h) has been specially investigated forE0 transitions with the aid of a magnetic spectrometer and coincidence techniques. Besides the knownE0 transitions of 685 keV in¹⁵²Sm and 615 keV in¹⁵²Gd two further pureE0 transitions of 432 keV and 1048 keV have been observed. It is shown that theseE0 transitions are identical with those observed previously in the decay of¹⁵²Tb. NoE0 transitions could be found from a 0⁺ state of 1083 keV in¹⁵²Sm. The measured intensities together with the gamma spectrum measured by Barretteet al. give a consistent decay scheme of¹⁵²Eu ^m . Furthermore the half-life of the 0⁺ level at 615 keV in¹⁵²Gd was measured using the method of “delayed coincidences”. The result was (0.2≦t _1/2≦2.1)×10^?10 s. From this theE0 transition probability for the level was derived as (0.3≦W _K (E0)≦3.7)× 10⁹ s^?1 and theρ-value as 0.10≦¦ρ¦≦0.36. The results are discussed within the framework of the collective model.     

Seniority isomerism in theN]=82 isotone152Yb; Favouredβ transitionsπh 11/2→vh 9/2

The reaction⁵⁸Ni→⁹⁶Ru has been investigated withγ spectroscopic methods and pulsed-beam techniques. A level scheme of the magic nucleus¹⁵²Yb has been established. The half-life of the isomeric 10⁺ state was found to be 39±5 μs. The result is discussed in the frame-work of the seniority scheme. Theory and experiment show excellent agreement for the half-lives of the 10⁺ states in theN=82 isotones¹⁴⁸Dy,¹⁵⁰Er and [¹⁵²Yb. A level scheme of¹⁵¹Tm, consisting of ten excited states, has been established.β-decay schemes of [¹⁵²Yb (3.2±0.3 s),¹⁵²Tm^(m) (8.0±1.0 s) and¹⁵¹Tm (3.8±0.8 s) have been derived. The logft value of theβ transition¹⁵²Yb (0⁰)→¹⁵²Tm (1⁺) has been determined to be about 3.4. It was found that theft values of the favouredβ transitions 0⁺→1⁺ in theβ decays of [¹⁴⁸Dy,¹⁵⁰Er and¹⁵²Yb are almost inversely proportional to the numbers of protons out of theh _11/2 subshell.     

The odd-parity level at 687.59 keV in236U

The spin-parity of the 687.59 keV level in²³⁶U populated in the decay of²³⁶Np is determined to be 2^? in disagreement with recent 1^? assignments from reaction data, but in accordance with previous radioactive²³⁶Np decay studies. The 687 keV ground state transition is shown to have a pureM2 character. The 642 keV 2^?→2⁺ transition hasE1:M2:E3 mixing ratios of 64∶30∶6. The half-life of the 2^? state is 3.78 ± 0.09 ns. The hindrance factor of the E1-part fits an E1 transition withΔK=2, theM2-part has the same transition rate as the M2 transitions in the neighbouring²³⁷Np nucleus and the E3-part is enhanced by two orders of magnitude relative to the Weisskopf estimate. The data are compared to analogous transitions in the rare earth region.     

Experimental evidence for anomalous L/M conversion ratio of the 2+→0+ transitions in some deformed even-even nuclei

TheL-subshell andM conversion coefficients ratios of the 2⁺→0⁺ transitions in some deformed even-even nuclei have been determined using a high resolution iron free double focusing beta-ray spectrometer. All possible uncertainties in these measurements have been minimized and properly evaluated. TheL ₁+L ₁₁/L ₁₁₁ ratios for the 2⁺→0⁺ E2 transitions in Dy¹⁶⁰, Er¹⁶⁶, Yb¹⁷⁰, Hd¹⁷⁶ and W¹⁸² are found to be in agreement with the theoretical ones within an experimental error of about 4%. However, large deviations from the theory of about two order of magnitude are observed forL/M conversion ratios. The deviations indicate the possibility of considerable approximation in the theoretical calculation of theM-internal conversion coefficients.     

Directional correlations in the decay of 1200y 166Ho

γγ-directional correlations have been measured between the ground state band transitions 6→4, 4→2 and 2→0 and the γ-rays depopulating the levels of the gamma vibrational band and the negative parity states of¹⁶⁶Er. Thereby angular momenta could be assigned to the latter states andM2/E1 multipole mixtures determined for the depopulating γ-transitions. TheE2/M1 mixing ratios were obtained for a series ofI _γ→I _g transitions up toI _γ=8⁺. These are used to investigate the angular momentum dependence of theE2/M1 admixtures.     

Messungen zu den Vibrations- und Zweiquasiteilchenzuständen in172Yb

The Coster-Kronig and Auger spectrum of theL ₁ shell of gaseous argon has been investigated with an electrostatical spectrometer. The ionization in theL ₁ shell of argon was caused by electron impact. Absolute energies and relative intensities of all the Coster-Kronig and Auger transitions have been determined. The relative intensities of transitions within the groupsL ₁ L _{2, 3} M ₁,L ₁ L _{2, 3} M _{2, 3} andL ₁ MM agree fairly well with the theoretical values, calculated byRubenstein for extreme Russel-Saunders coupling, if intermediate coupling theory is used properly. Via the widthγ(L ₁) of theL ₁ level of argon, found in this experiment to be (1.84±0.2) eV, the following absolute group transition probabilities were determined (in units of 10¹⁴ sec^?1):W(L₁ L _{2, 3} M ₁)=(5.5±1.0),W(L₁ L _{2, 3} M _{2, 3})=(20.8±2.8),W(L₁ MM)=(1.44±0.16). The theoretical values are 21.0, 20.4 and 1.27. The possible reason for the large discrepancy between the experimental and theoretical value ofW(L₁ L _{2, 3} M ₁) is the use of the incorrect value of 287 eV for the binding energyE(L₁) byRubenstein. From the energies of theL ₁ MM transitions this value has been determined to beE(L₁)=(326.5±0.5) eV. This is the first direct measurement ofE(L₁) of argon.     

Gyromagnetic ratios of the 4+ and 6+ rotational states of184W

The nuclear Larmor precession has been observed for the 2⁺, 4⁺ and 6⁺ rotational states of¹⁸⁴W in the hyperfine field of WFe by application of the TDPAC and the IPAC techniques. A carrier free radioactive source of^184m Re alloyed with high purity iron was used for all three measurements. From the Larmor precession observed in the 2⁺ state by TDPACω _L = 944(15) MHz and the knowng-factor the hyperfine fieldB _{300 K} ^hf (WFe)=?69.6(27)T was derived. The deviation from the result of a spin echo experiment with¹⁸³WFe extrapolated to room temperature may be caused by the Bohr-Weisskopf effect (hyperfine anomaly). IPAC measurements with the same sample polarized in an external magnetic field of 1.6T gave for the 4⁺ and 6⁺ rotational states: ω _L τ(4⁺)=0.0609(22) andω _L τ(6⁺)=0.00735(102). By use of experimentalB(E2)-values theg _R -factors were derived asg _R (4⁺)=+0.276(26) andg _R (6⁺)=+0.281(45). The directional correlation of the 537?384 keVγ-γ cascade has been analysed in terms of anE1/M2/E3 mixture for theK-forbidden 537keV transition. We obtained the mixing ratiosδ(M2/E1)=±0.086(16),δ(E3/E1)=?0.028(5) with the sign convention of Krane and Steffen.     

A retarded intramultipletM1 transition in214Bi

The half-life of the 53.2 keV level in²¹⁴Bi has been measured asT _1/2=0.52±0.15 ns, furtherT _1/2(295.2 keV and 351.9 keV levels)≦0.10 ns was estimated. TheB(M1,2^?→1^?) transition rates within theπh _9/2 vg _9/2 multiplet in^210,212,214Bi are found to decrease rapidly with increasing neutron number, reaching in²¹⁴Bi a value as low as those typical for intraband M1 transitions in deformed odd-odd nuclei.     

Renormalization scheme dependence of electroweak radiative corrections

We compare two renormalization schemes of the electroweak standard model: the on-shell scheme withe, M _W ,M _Z ,M _H , and the fermion masses {m _f } as free parameters, and an intermediate scheme where theW boson self energy is renormalized atq ²=0 instead ofq ²=M _W ². TheM _W ?M _Z interdependence, and the differentiale ⁺ e ^?→μ ⁺ μ ^? cross section including polarized beams are calculated in both schemes to one-loop order. We find striking differences between the forward-backward asymmetries and the polarization asymmetries near theZ resonance after inclusion of weak and QED corrections.     

On the octupole excitation in236U

Measurements of theK,L _I,L _II andM _I conversion lines of the 687.7 keV transition in²³⁶U are evaluated within the electron penetration formalism. The spin-parity assignment of the octupole bandhead is found to be 1^? in accordance with reaction data, and an assignment of 2^? to the 687.7 keV state is ruled out. The penetration matrix element ∥η∥ has the value of 13.5 for theK-shell and increases slightly for higher main shells. An estimate of the anomalous amplitudes is compared with values reported for transitions in the odd even actinide nuclei. Furthermore electron conversion data for the 1^?→2⁺ and 1^?→4⁺ transitions are given. Radioactivity²³⁶U from²³⁵U(n,e ^?); measured: conversion electron decay; deduced: conversion coefficients fromK, L andM shells; evaluated: dynamic matrix elements.     

Estimation of the QED coupling constant α at\sqrt s = M_Z

LEP measurements of theZ ⁰ parameters have been used to estimate the value of QED coupling constant at theZ ⁰ mass. The estimated value α _eff ^-1 (M _Z )=128.2±0.9 _-0.4 ^+0.0 (M _top) is in good agreement with the expectation of 128.0 _?0.4 ^+0.2 from the Standard Model.     

Production ofW-bosons in high energye + e − ande − p collisions

We study the processe ⁺ e ^?→W+hadrons from theZ ⁰-pole to the threshold region forW-pair production, keeping the widths of theZ ⁰ andW finite. Already slightly below threshold the cross section is strongly depressed. Also the total cross section at theZ ⁰-peak is very small. We present a simple model to account for this. We also give exact results to lowest order for the weak Compton processese ⁺ e ^?→e ⁺ W ^? v _e ande ^? p→pW ^? v _e and compare them with results obtained with the equivalent photon approximation.     

An interpretation of the energy-momentum tensor of the dirac field with anomalous magnetic moment

The ground state radiative widths of the 1.56 MeV (3/2⁺) and the 1.35 MeV (5/2^?) levels in¹⁹F were determined by inelastic electron scattering. The measured cross sections have been analysed using DWBA calculations. The resultsΓ _y ⁰ (5/2^?→1/2^?,E3)=(8.1±1.7)·10^?10eV andΓ _y ⁰ (3/2⁺→1/2⁺,E2=(1.76±0.15)·10^?4eV are in agreement with, but more accurate than, former measurements.     

Multiplicities of charged particles prior to fission

Electric monopole transitions between the 0 ₂ ⁺ , 0 ₁ ⁺ and 2 ₂ ⁺ , 2 ₁ ⁺ levels in⁷⁶Se, populated in the decay of⁷⁶Br, were investigated by means of conversion electrons and gammaray spectroscopy. TheK-electron intensity ratios ofE0 andE2 transitions connecting the 0 ₂ ⁺ level to the 0 ₁ ⁺ and 2 ₁ ⁺ levels and of theE0 andE2 components in the 2 ₂ ⁺ →2 ₁ ⁺ transition were determined. The ratioX(E0/E2) of theE0 toE2 reduced transition probabilities and, from the available lifetimes, theE0 strength parameters ρ(E0) were deduced for the two transitions. The results are compared with the predictions of current models.     

The 0 1 + →0+ electric monopole transition in112Cd

The low-lying levels of¹¹²Cd have been populated in the decay of¹¹²In (T _1/2=14 ^m ) produced through the¹¹²Cd (p, n)¹¹²In reaction atE _p=6.5–7 MeV. The intensity ratio of theE0 toE2K-conversion electrons from the 0 ₁ ⁺ level to the ground (0⁺) and to the first (2⁺) excited state in¹¹²Cd has been measured and the ratioX(E0/E2) =B(E0;0 ₁ ⁺ →0⁺)/B(E2;0 ₁ ⁺ →2⁺) has been determined. The result is compared with the predictions of current macroscopic models.