132Cs gamma radiation

The decay of¹³²Cs was studied by means of Ge(Li) detectors and a magnetic beta-ray spectrometer. The energies and intensities of the transitions in¹³²Xe and¹³²Ba were determined. Of the decay schemes proposed hitherto, that of Johnson et al. [Phys. Rev.138 (1965), B 520] was confirmed.     

Experiment and dynamic simulations of radiation damping of laser-polarized liquid<Superscript>129</Superscript>Xe at low magnetic field in a flow system

Radiation damping is generally observed when a sample with high spin concentration and high gyromagnetic ratio is placed in a high magnetic field. However, we firstly observed liquid-state¹²⁹Xe radiation damping with laser-enhanced nuclear polarization at low magnetic field in a flow system in which the polarization enhancement factor for the liquid-state¹²⁹Xe was estimated to be 5000, and, furthermore, theoretically simulated the envelopes of the¹²⁹Xe free induction decay and spectral lineshape in the presence of both relaxation and radiation damping with different pulse flip angles and ratios ofT ₂ ^* /T _rd. The radiation damping time constantT _rd of 5 ms was derived on the basis of the simulations. The reasons of depolarization and the further possible improvements were also discussed.     

Messungen der Geschwindigkeitsabhängigkeit totaler Streuquerschnitte für Atom-Atom-Stöße im Energiebereich zwischen 6 und 1000 eV

The velocity dependence of the total scattering cross sectionQ(v) for fast Cs, K, and Na beams scattered by Xe, Kr, and Ar has been measured for energies of 6 to 1000 eV. In all cases, the transition region between thev ^?2/5-dependence ofQ(v) (where the cross section is predominantly influenced by the attractive part of the potential) and the high energy behaviour (where the cross section is determined by the repulsive part of the potential) is observed. Values for the product?r _m of the potential well depth? and the equilibrium distancer _m are determined by comparing the measurements with calculations for a five parameter potential model.     

Über die Berechnung der Photoerzeugung von π0 aus Streudaten

The cross section forπ ⁰-production is calculated from the results of the dispersion relation approach ofChew, Goldberger, Low andNambu and compared with the experimental data. The predictions are made using the measured values of all scattering phase shifts. A fit of the theoretical result toσ(90?) between 260 and 370 MeV givesf ²=0,082. There is no systematic deviation from the predictions forσ (90?) up toE _γ =450 MeV. The general behavior of the asymmetry coefficientB is correct. A quantitative comparison which would show the contribution of the unknown electric dipole termN ⁽⁺⁾ ofChew et al. is only reasonable after the calculation ofB and the measurements have been improved.C/A depends strongly on the small phases up to 240 MeV. The effects of the small phases are pretty large forσ(l50?) but there is no discrepancy similar to the results forπ ⁺-production above 290 MeV. The formula for the cross section does not reduce to the results of the phenomenological theories ofBrueckner-Watson, Sachs et al. andFeld, if the simplifications made by these authors are taken into account. The origin of the differences is discussed.     

Spins und γ-Multipolordnungen beim Zerfall Fe59→Co59

In the decay of Fe⁵⁹ the following quantities have been measured:γ-ray intensities, conversion coefficients andβ-(circularly polarizedγ) correlations. The conversion coefficients were found to be: for the 1.10 MeVγ-transition, α_tot.=(1.36±0.10)·10^?4 and for the 1.29 MeVγ-transition, α_tot.=(1.07±0.08)·10^?4. The asymmetry parameterA of the correlationβ(0.27 MeV)?γ(1.29 MeV) were measured to beA= ?0.17±0.10, and forβ(0.46 MeV)?γ(1.10 MeV),A=?0.13±0.04. From these data and publishedγ?γ angular correlation measurements the following spins of Co⁵⁹ levels could be deduced: 1.10 MeV,I=5/2^?; 1.29 MeV,I=5/2^?; and 1.43 MeV,I=3/2^?. The two strongβ-ray groups are pure Gamow-Teller transitions (ΔI=1). The multipolarities of all fiveγ-rays are given.     

Zerfallsschema und Matrixelemente für denβ-Übergang Ag110m→Cd110

Theβ decay Ag^110m→Cd¹¹⁰ has been investigated with a double lens spectrometer and aβ-γ circular-polarization correlation setup. The shape of the 6⁺→6⁺ β spectrum withE ₀=529 keV was found to be allowed, in disagreement with earlier work. The constantA of theβ-γ circular-polarization correlation was measured to beA=0·07±0·02. This implies a ratioX of Fermi to Gamow-Teller contribution to the decay ofX ₁=?0·02±0·03 orX ₂=?10·3 _?4·1 ^+2·3 . Qualitative shell model considerations favor the valueX ₁. Additional information is given for the disintegration schemes of Ag^110m and Ag¹¹⁰.     

Zerfallsschemata, β-Matrixelemente und γ-Multipolordnungen für die Übergänge Co56→Fe56 und J131→Xe131

In the decay of Co⁵⁶ the following quantities have been measured:γ-ray intensities,β-γ directional correlation, andβ-(circularly polarizedγ) correlation. The directional correlation anisotropy was found to be, forβ energies above 300 keV,A ₂=0.5±0.4 per cent, corresponding to small or vanishing twice forbidden contributions to the allowed decay. The asymmetry parameterA of theβ-(circularly polarizedγ) correlation was measured to beA=?0.01±0.05 which implies a ratiox between Fermi and Gamow-Teller contributions to the decay ofx=?0.10±0.07, in agreement with the isospin selection rule. In the decay of J¹³¹ the following quantities have been measured: shape of the 606 keVβ-ray group,γ-ray intensities, conversion coefficients, andβ-(circularly polarizedγ) correlations. The measuredK/L ratio of the 364 keVγ-transition,K/L=6.0±0.2, is compatible with the conversion tables of Sliv and Band only. The multipolarities of theγ rays of 364, 637, and 723 keV were deduced. The 606 keVβ-364 keVγ cascade was used as a new calibration standard for analysers of circularly polarizedγ-rays.     

Resonanzstreuung am 202,8 keV-Niveau im J127

Using a gaseous Xe¹²⁷ source as exciting radiation resonance fluorescence from the 202.8 keV level in I¹²⁷ has been observed. The detection of the weak resonance effect in the presence of a strong 375 keV radiation was possible because of the high energy resolution of a Li-drifted Germanium detector. Assuming a transition energy ofQ _ECO =543 keV for the Xe¹²⁷-I¹²⁷decay the mean lifetime of the 202.8 keV level was determined to be τ=(0.56±0.09)nsec.     

Unique second-forbidden β transitions: Decay of <Superscript>137</Superscript>Cs

The intensity of the 283.4-keV γ line in the decay of ¹³⁷Cs has been measured. The value obtained is used to determine the probability of the unique second-forbidden β transition of the 7/2⁺ → 1/2⁺ type: (8.7 ± 2.0) × 10^?4% of the number of decays; this value corresponds to log f ₂ ^un t = 16.45 ± 0.12. The intensity of the possible E5 transition at 378.3 keV is estimated to be < 0.9 × 10^?4%. The technique for determining the values of log f ₂ ^un t in calculations of the tensor matrix elements in the Cartesian and spherical coordinate systems is discussed. The possible intensity of the unique second-forbidden β transition between the ground states of ¹²⁹I and ¹²⁹Xe is estimated to be I _β ≈ 0.1% of the number of decays of ¹²⁹I.     

Photoionization of the Xe atom and Xe@C<Subscript>60</Subscript> molecule

Photoionization of the Xe atom and Xe@C₆₀ molecule have been studied usingthe random phase approximation with exchange (RPAE) method. The Xe atom was described byrelaxed orbitals including overlap integrals. The C₆₀ fullerene has beenrepresented by an attractive short range spherical well with potentialV(r), given byV(r) =  ?V ₀ forr _i  < r < r _o ,otherwise V(r) = 0 wherer _i andr _o are respectively, the inner and outerradii of the spherical shell. The time independent Schrödinger equation was solved usingboth regular and irregular solutions and the continuous boundary conditions atr _i andr _o . The results demonstrate improvementto previous calculations for both the Xe atom and Xe@C₆₀ molecule and comparevery well with the recent experimental data.     

Two-Neutron Alignment in <Superscript>127</Superscript>Xe

High spin states in ¹²⁷Xe have been investigated via ⁹Be induced fusion-evaporation reaction at 48 MeV. Spin and parity of excited states up to \( \sim \frac {47}{2} \hbar \) have been confirmed from angular correlation and linear polarization results. Rotational alignment of the second pair of h _11/2 neutrons has been observed at \(\hbar \omega \sim \) 0.44 MeV; beyond that, the band is associated with ν[h _11/2]³ configuration. The alignment phenomena has been discussed in comparison with the neighboring ^125,129Xe.     

Doppelkonversion

An excited nuclear state can decay by three different modes of double quantum emission, namely doubleγ-emission,γ-electron emission and double conversion electron emission. The emission of twoγ-quanta has been considered in an earlier paper¹. The purpose of the present work is to treat all three processes together in a systematic manner. It is shown that the connection between the transition rates forγ-electron emissionT _γc and doubleγ-quantum emissionT _γγ is more complicated than in the case of single quantum processes. However,T _γc can still be expressed in terms of the usual conversion coefficients. This is also true for the transition rate T_cc for the emission of twoK-shell electrons, although only approximately. For the emission of electrons from different atomic shells the formulas become rather complicated, because of interference effects. The electron andγ-quantum spectra in all of the three second order processes are discussed in detail for the decay of the isomeric level in Xe¹³¹.     

Der Zerfall des Mn52m

Mn^52m(T _1/2=21 m) was produced by irradiating iron-foiles with deuterons ofE _d =9 MeV. Coincidences ofγ-rays with the main 1434 keV-transition had been sought for with the aid of a scintillation fast-slow-coincidence circuit. There was no evidence ofγ-lines which had been found earlier byKatoh et al. atγ-energies 700, 940, 1020, 1150, 1370, 1520 keV. If these transitions exist, their relative intensities are less than 0.7% (700 keV) and 0.3% (all others) per decay of Mn^52m.     

The spin cut-off factor for60Co

Nine experimental isomeric cross-section ratios for the reactions⁵⁹Co(n, γ)⁶⁰Co,⁶⁰Ni(n,p)⁶⁰Co, and⁶³Cu(n,α)⁶⁰Co are analysed in terms of statistical theory by means of the method ofHuizenga andVandenbosch. Theγ-cascades are treated by a new model which was recently published. The results confirm the energy dependence of the spin cut-off factor for⁶⁰Coσ～U^1/4 which should not be neglected. As a mean value (σ=4.3±0.3 is obtained forU=B _n =7.5 MeV in good agreement with a nuclear moment of inertia for a rigid sphere.     

Über die Bestimmung des Spin-Abschneidekoeffizienten σ

A value ofσ=3, 5±1 is obtained for the spin cut off coefficient in the Fermi gas level density formula from a comparison of calculated and experimental (n, γ)-intensities feeding the observed levels of deformed nuclei in the rare earths region. The model used for the computations is tested at two nuclei with compound states of low spin (I _c =1/2) and high spin (I _c =13/2 or 15/2). The calculations can help to determine spins of nuclear levels in some cases.     

The structure of a vortex line and the lower critical field in superconducting alloys

The structure of an isolated vortex line, and the lower critical fieldH _c 1, is calculated by means of the generalized Ginzburg-Landau (GL) theory for arbitrary values of the GL-parameterk(≧1/√2) and the mean free pathl at temperaturesT in the vicinity ofT _c . The free energy functional including the corrections of order [1?(T/T _c )] to the GL-functional is derived exactly. The corresponding Euler-Lagrange equations determining the zero-order (GL) contributions and the corrections of order [1?(T/T _c )] to the order parameter,f(r), and the superfluid velocity,v(r), have been solved numerically. The shapes of the first-order corrections off(r), v(r), and the magnetic field,h(r) are found to depend markedly, for a given value ofκ, on a second parameter,α=0.882(ξ ₀ /l) (whereξ ₀ is theBCS-coherence-distance). The deviations from the GL-solutions become largest forh(r) at parameter valuesk≈ 1 andα ≈ 0(the deviation ofh(0) is about 6% atT=0.9T _c forκ=1 andα=0). The ratioH _c1/H _c (where the thermodynamic criticalH _c has the BCS-temperature-dependence) is found to increase slightly in the “clean” limit (α=0), and to decrease slightly in the “dirty” limit (α=∞) asT decreases (the variation ofH _c 1/H _c is always less than 3% for arbitrary values ofκ andα asT decreases fromT _c to 0.9T _c ).     

Halbwertszeit,Elektroneneinfangverhältnis und β-Spektrum des Tl204

Half-life,P _L /P _K -capture ratio andβ-spectrum of Tl²⁰⁴ were studied with a scintillation spectrometer. To avoid source absorption and scattering troubles, the Tl²⁰⁴ source was built in in the lattice of NaJ(Tl)-crystals. The half-life measurements were performed over a period of 2,2 years, and we obtained a half-life of 3.81±0.04 years. TheP _L /P _K -capture ratio was determined at 0.41±0.03. This ratio gives a desintegration energy of 442 _?24 ⁺³⁰ keV for the unique first forbidden electron capture decay of Tl²⁰⁴. For the branching ratio of electron capture toβ ^?-decay we found a value of (2.15±0.06)% and for the ratio ofK-capture toβ ^?-decay a value of (1.53±0.05)%. Theβ ^?-spectrum of Tl²⁰⁴ was measured from 200 down to 6 keV and yields an experimental shape factor which deviates below an energy of ～90 keV from the theoretical shape factorq ² L ₀+9L ₁. Reasons for this deviation which is opposite to the one obtained with magnetic spectrometers are discussed.     

Zeitliches Abklingen und Anisotropie von p-Terphenyl- undp-Terphenyl-Anthrazen-Mischkristallen bei Beschuß mit α-Teilchen

The time dependence of scintillation intensity from single crystals ofp-terphenyl and mixed crystals ofp-terphenyl and anthracene after bombarding with α-particles was investigated at the two temperaturesT=296 °K andT=92 °K. For the crystals ofp-terphenyl the time dependence of the scintillation anisotropy was also measured. Using the formulas given byKing andVoltz the decay curves ofp-terphenyl were decomposed into two components. Good agreement between experiment and theory was found. The ratio of the prompt intensity to the delayed intensity was determined to be 1∶2 atT=296 °K and 1∶3 atT=92 °K. The diffusion constants for triplet excitons were calculated to beD _T(296 °K)≈10^?5 cm² sec^?1 andD _T(92 °K)≈ 2×10^?6 cm² sec^?1, and the triplet-triplet interaction rate constantsχ _tt(296 °K)≈ 2.5×10^?11 cm³ sec^?1 andχ _tt(92 °K)≈0.5×10^?11 cm³ sec^?1.