Experimentelle Untersuchung von Elektronen-Photonen-Kaskaden in Blei-Szintillator-Anordnungen für Primärenergien zwischen 100 und 440 MeV

Showers generated by electrons of 200 and 440 MeV energy in single lead plates of 2, 5, and 10 radiation lengths are measured in scintillator material (NE 102 A) varying between 1.24 and 10.5 g/cm². The mean energy deposited in a scintillator is derived fromNagel's Monte-Carlo calculations. The photon contributionn _γ to the total pulseheight is of the order 15% near shower maximum t_max, it dominates the electron contributionn _e in a 3 cm thick scintillator for shower depthst ≧ 4.2 · t_max. The slope of the total ionizationn _e+n _γ behind the shower maximum can be approximated byn(t) ～ exp(?0.264t). The shower absorption in scintillator depends on the thicknessx (g/cm²) as exp (?0.068x). An arrangement of counter trays, scintillators and lead plates is calibrated with electrons between 100 and 440 MeV energy. A suitably defined track-lengthS is shown to give minimum error in energy measurement and to depend linearly on electron energy. The track-length constant of 22 MeV/r.l. is compared with the results of other authors.     

Cross sections of the reactions16O(γ,x)13 N and16O (γ,x)11 C,and Yield of12C (γ, t) up to 55 MeV

Yield curves of the reactions¹⁶O (γ, x)¹¹C,¹⁶O (γ, x)¹³N and¹²C(γ, t) have been measured relative to¹²C(γ, n)¹¹C with bremsstrahlung. The cross section σ[¹⁶O(γ, x)¹¹C] has a shape similar to σ[¹⁶O(γ, t)] and shows a broad maximum near 38 MeV. Differences between σ[¹⁶O(γ, x)¹³ N] and σ[¹⁶O(γ, t)] point to a reaction mechanism via quadrupole absorption in¹⁶O. The yield of¹²C(γ, t) exceeds the¹⁶O(γ,t) yield by a factor of two.     

Using a chiral anomaly to determine the number of colors

The N_c dependence of PPPγ vertices, where P is a pseudoscalar meson and N_c is the number of colors, is analyzed with allowance for the N_c dependence of the quark charges. It is shown that the reactions Kγ → Kπ and π^±γ → π^±η and the decay η → π⁺π^?γ are the best processes for determining N_c. The cross section σ(π^?γ → π^?η) as measured by using the VES facility at IHEP agrees with the value of N_c=3.     

Transient bi-fractional diffusion: space-time coupling inducing the coexistence of two fractional diffusions

Anomalous diffusion is researched within the framework of the coupled continuous time random walk model, in which the space-time coupling is considered through the correlated function g(t) ~ t ^γ , 0 ≤ γ< 2, and the probability density function ω(t) of a particle’s transition time t follows a power law for large t: ω(t) ~ t ^{? (1 + α)},1 <α< 2. The bi-fractional generalized master equation is derived analytically which can be applied to describe the transient bi-fractional diffusion phenomenon which is induced by the space-time coupling and the asymptotic behavior of ω(t). Numerical results show that for the transient bi-fractional diffusion, there is a transition from one fractional diffusion to another one in the diffusive process.     

Zum Kernphotoeffekt am Ar40 und Ar38

Liquid Argon was irradiated with bremsstrahlung from 18 to 31 MeV endpoint energy in steps of 2 MeV. The yields of the reactions Ar⁴⁰(γ, n)+(γ, p) and Ar³⁸(γ, n) were measured by detecting the 269a and the 35d rest activity with a low-level-counter. Cross section curves for the (γ, n)-processes could be found from the yield values, and they allowed together withσ _N, σ(γ, p) andσ(γ, np) a determination ofσ(γ, 2n) and σ_γabs for Ar⁴⁰. The integrated cross section forσ(γ, n) from threshold to 33 MeV yields (200±40) MeVmb for Ar⁴⁰ and (210±40) MeVmb for Ar³⁸, the corresponding value for σ_γabs being (450±60) MeVmb for Ar⁴⁰.     

Kernphotoeffekt an Aluminium und Fluor mit der Lithium-Resonanz-Strahlung

Fragments from thermal fission of U²³⁵ have been slowed down in purified Ar and N₂. Ionization by reactor radiation produced sufficient free electrons in the gas to permit formation of negative fission product ions by electron attachment. These negative ions were collected in an ionization chamber. Theγ-radiation of the activated electrode showed that mainly J and Te had been collected. By analysis of theγ-spectra the independent fission yieldsη(J¹³⁵)=(4,6±1,1)% andη(Te¹³⁵)=(1,5±1,1)% were found. In the derivation of this result an estimated valueη(Te¹³⁴)=(6±0,7)% was used.     

Kern-Isomerie bei In116

The short lived indium isomer produced by thermal neutron capture is confirmed to be In¹¹⁶. A new determination of half-live andγ energy yieldsT _1/2=(2.17α0.07) sec andE _γ=(164±1) keV. From measurement of theK shell conversion coefficient follows that the multipolarity of the transition isE 3, leading to a spin and parity assignment of 8^? for the isomeric level.     

Long-time relaxation phenomena in Pb<Subscript>0.94</Subscript>Ba<Subscript>0.06</Subscript>Sc<Subscript>0.5</Subscript>Nb<Subscript>0.5</Subscript>O<Subscript>3</Subscript> (PBSN-6) single crystals

Long-time polarization relaxation in the temperature range where PBSN-6 single crystals reside in the relaxor state was studied. An analysis of the time dependence of the permittivity ε′(t) performed at measuring frequencies from 1 Hz to 1 kHz in weak electric fields E₀ showed that the relaxation (or freezing) times derived by extrapolating relations of the type ε′(t) ～ log(t/t₀) and ε′(t) ～ exp{?[ln(t/t₀)]_β} range from 10⁸ to 10¹¹ min and depend substantially on the bias voltage applied to the sample. A study of the pattern of the dielectric response in moderate and strong infralow-frequency fields revealed that, after a sample was maintained under a bias lower than the coercive force, it no longer exhibited the additional anomalies in the amplitude dependences of the effective loss tangent tan_eff(E₀) than were observed in a thermally recuperated sample.     

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.     

Gamow Vectors and Borel Summability in a Class of Quantum Systems

We analyze the detailed time dependence of the wave function ψ(x,t) for one dimensional Hamiltonians \(H=-\partial_{x}^{2}+V(x)\) where V (for example modeling barriers or wells) and ψ(x,0) are compactly supported.We show that the dispersive part of ψ(x,t) is the Borel sum of its asymptotic series in powers of t ^?1/2, t→∞. The remainder, the difference between ψ and the Borel sum, i.e., the exponential part of the transseries of ψ, is a convergent expansion of the form \(\sum_{k=0}^{\infty}g_{k}\Gamma_{k}(x)e^{-\gamma_{k} t}\), where Γ _k are the Gamow vectors of H, and iγ _k are the associated resonances; generically, all g _k are nonzero. For large k, γ _k ～const?klog?k+k ² π ² i/4. The effect of the Gamow vectors is visible when time is not very large, and the decomposition defines rigorously resonances and Gamow vectors in a nonperturbative regime, in a physically relevant way.The decomposition allows for calculating ψ for moderate and large t, to any prescribed exponential accuracy, using optimal truncation of power series plus finitely many Gamow vectors contributions.The analytic structure of ψ is perhaps surprising: in general (even in simple examples such as square wells), ψ(x,t) turns out to be C ^∞ in t but nowhere analytic on ?⁺. In fact, ψ is t-analytic in a sector in the lower half plane and has the whole of ?⁺ a natural boundary. In the dual space, we analyze the resurgent structure of ψ.     

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.     

Untersuchung des Vanadium-52-Zerfalls

Theγ-rays of the decay of V⁵² were investigated with NaJ crystals andγ-γ-cascades had been sought for by a fast-slow coincidence circuit. Threeγ-transitions of energyγ ₁=0,935 (0,14%),γ ₂=1,331 (0,9%),γ ₃=1,531 MeV (0,16%), respectively, in coincidence with the 1,434 MeV transition could be detected. It is concluded that there are four branches of V⁵² β-decay:β ₀=2,47MeV (98,8%, logft=5,1),β ₁=1,53 MeV (0,14%, logft=7,0),β ₂=1,14 MeV (0,9%, logft=5,7),β ₃=0,94 MeV (0,16%, logft=6,1). Spin and parity of V⁵² ground level is concluded to be 3+.     

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.     

Long Time,Large Scale Limit of the Wigner Transform for a System of Linear Oscillators in One Dimension

We consider the long time, large scale behavior of the Wigner transform W _? (t,x,k) of the wave function corresponding to a discrete wave equation on a 1-d integer lattice, with a weak multiplicative noise. This model has been introduced in Basile et al. in Phys. Rev. Lett. 96 (2006) to describe a system of interacting linear oscillators with a weak noise that conserves locally the kinetic energy and the momentum. The kinetic limit for the Wigner transform has been shown in Basile et al. in Arch. Rat. Mech. 195(1):171–203 (2009). In the present paper we prove that in the unpinned case there exists γ ₀>0 such that for any γ∈(0,γ ₀] the weak limit of W _? (t/? ^3/2γ ,x/? ^γ ,k), as ??1, satisfies a one dimensional fractional heat equation \(\partial_{t} W(t,x)=-\hat{c}(-\partial_{x}^{2})^{3/4}W(t,x)\) with \(\hat{c}>0\). In the pinned case an analogous result can be claimed for W _? (t/? ^2γ ,x/? ^γ ,k) but the limit satisfies then the usual heat equation.     

Untersuchungen über den nichtresonanten Anteil der Li7 (p,γ)-Strahlung

The angular distributions of the 17,6 MeVγ-rays from the reaction Li⁷(p,γ) Be⁸ have been measured betweenE _p=0,4 MeV andE _p=0,65 MeV. The known strong asymmetry resulting from interference of the 441 keV-resonance radiation and the nonresonant radiation, and a cos² Θ-term, slowly increasing with energy have been observed. According to our results the nonresonant radiation is predominantly due tos-wave capture, but in addition to this a small contribution ofp-waves must be considered.     

<Emphasis Type="Italic">η</Emphasis> Physics with the crystal ball detector

The experimental results obtained with the Crystal Ball detector for the physics of η-meson decays are reviewed. The η → 3π ⁰ Dalitz plot slope and the η → π ⁰ γγ decay width are measured with a high accuracy using 3 × 10⁷ η decays. Upper limits on the η → 3γ, η → 2π ⁰ γ, and η → 3π ⁰ γ C-forbidden decays are found. The sensitivity of these upper limits to C violation is estimated. An upper limit on the η → 4π ⁰ C P-forbidden decay is found for the first time and the sensitivity of this value to C P violation is estimated.     

Transition form factors and light-cone distribution amplitudes of pseudoscalar mesons in the chiral quark model

It is shown that a chiral quark model of the Nambu-Jona-Lasinio type can be used to describe “soft”-momentum parts of the amplitudes with large momentum transfer. As a sample, the processes γ* → γ(π, η, η′), where one of the photons, γ*, has large spacelike virtuality, are investigated. The γ* → γ(π, η, η′) transition form factors are calculated for a wide region of the momentum transfer. The results are consistent with the calculations performed in the instanton-induced chiral quark model and agree with experimental data. The distribution amplitudes of pseudoscalar mesons are derived.     

Energy spectra of secondary particles in γ families and their sensitivity to the spectrum of primary cosmic rays

Spectra of secondary particles (γ-rays) in γ-families detected in the X-ray chambers in the Pamirs (H = 600 g cm^?2) have been analyzed. These γ-ray spectra show a bend at the energy E* _γ ≈ (ΣE _γ )^min, where (ΣE _γ )^min is the lowest total energy of γ-rays in the families above which γ-families were selected. The bend is not related to the knee in the spectrum of primary particles; it is due to the use of the ΣE _γ selection criterion. The E _γ spectrum slope is sensitive to the spectrum of the primary cosmic rays in the region E _γ ≥ (ΣE _γ )^min.     

Die Messung der β-γ-Winkelkorrelation bei Au198

The energy dependence of theβ ?γ asymmetry coefficient has been measured. No anomaly at lowβ energies as reported by other authors was found. Theξ-approximation holds andε W/p ² Ν ₁₂=0.027±0.007 was obtained. The matrix elements of theβ transition are discussed.