Reliability of the data on the cross sections of the partial photoneutron reaction for <Superscript>63,65</Superscript>Cu and <Superscript>80</Superscript>Se nuclei

The cross sections of partial photoneutron reactions are evaluated for the ^63,65Cu and ⁸⁰Se isotopes. The cross sections are free of systematic uncertainties from shortcomings of the experimental methods for neutron multiplicity sorting based on measurements of neutron energy used in experiments with quasimonoenergetic annihilation photon beams. An experimental-theoretical method is used to evaluate cross sections σ^eval(γ, in)= F_i^theor σ^exp(γ, xn), where ratios F_i^theor = σ^theor(γ, in)/σ^theor(γ, xn) = σ^theor(γ, in)/σ^theor[(γ, 1n) + 2(γ, 2n) + …] are calculated using a combined model of photonuclear reactions, and σ^exp(γ, xn) is the experimental cross section of the neutron yield reaction free from neutron multiplicity sorting problems. The cross sections are evaluated for reactions (γ, 1n) and (γ, 2n) for the ^63,65Cu and ⁸⁰Se isotopes, and for the total photoneutron reaction σ(γ, Sn) = σ[(γ, 1n) + (γ, 2n) + …]. It is shown that noticeable deviations of the experimental cross sections from the evaluated values result from the unreliable sorting of neutrons between the channels with multiplicities 1 and 2.     

Cross sections of the photoneutron reaction for <Superscript>141</Superscript>Pr and <Superscript>186</Superscript>W nuclei,estimated from physical criteria of data reliability

Using objective physical criteria for data reliability, cross sections of partial photoneutron reactions (γ, 1n), (γ, 2n) and (γ, 3n) that are free of the shortcomings of neutron multiplicity sorting methods used on beams of quasimonoenergetic annihilation photons are obtained for ¹⁴¹Pr and ¹⁸⁶W nuclei. Evaluation is performed using the experimental–theoretical method (ETM), based on the experimental cross section of neutron yield reaction σ^exp(γ, xn) = σ^exp(γ, 1n) + 2 σ^exp(γ, 2ⁿ) + 3 σexp(γ, 3n) + … and ratios F _i ^theor= σ^theor(γ, in)/σ^theor(γ, xn) calculated within the combined model (CM) of photonuclear reactions, which stipulates that σ^eval(γ, in) = F _i ^theor σ^exp(γ, xn). It is found that for ¹⁴¹Pr and ¹⁸⁶W, ratios F ^exp _i do not contradict the data reliability criteria only at energies up to ~21 and ~22 MeV, respectively. At the same time, there are notable discrepancies between F _i ^theor and F ^exp _i, and thus between the evaluated and experimental cross sections of reactions. It is shown that the discrepancies between the evaluated and experimental cross sections are due to the assumed unreliable experimental distribution of neutrons in the channels with multiplicities 1, 2, and 3.     

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.     

Reliable cross sections of partial photoneutron reactions on 188,189Os isotopes free of neutron multiplicity sorting problems

Experimental data on the cross sections of partial photoneutron reactions, obtained for ^188,189Os isotopes using quasimonoenergetic annihilation photon beams and neutron multiplicity sorting method, are analyzed. Using special criteria (transition multiplicity functions F _i = σ(γ, in)/σ(γ, xn), the ratios of the cross section of the corresponding partial reaction to the total neutron yield reaction’s cross section σ(γ, xn) = σ(γ, 1n)+ 2σ(γ, 2n) + 3σ(γ, 3n) free of the problems associated with experimental neutron multiplicity sorting), it is demonstrated that the data contain significant systematic errors. New data are evaluated for cross sections of partial photoneutron reactions (γ, 1n), (γ, 2n), (γ, 3n) and total photoneutron reaction (γ, sn) for ^188,189Os isotopes within an experimental-theoretical approach proposed earlier. It is shown that the significant systematic errors in the experimental cross sections of partial reactions can be attributed to the ambiguity of the relation between the photoneutrons’ multiplicity and their kinetic energy.     

Frequency Dependence of the Dielectric Loss Angle in Disordered Semiconductors in the Terahertz Frequency Range

Frequency dependence of the real part of the conductivity σ₁(ω) in the region of the transition from almost linear (s < 1) to quadratic (s ≈ 2) can indicate a change in the conduction mechanism (the transition from the variable-range to the fixed-range hopping with increasing frequency); in this case, the sharpness of the change in the slope of the frequency characteristic is related to the dependence of the preexponential factor of the resonance integral on the intercenter distance in the pair. The frequency dependence of the imaginary part of the conductivity σ₂(ω) has no kink in the vicinity of the transition frequency ωcr, remaining almost linear. A large dielectric loss angle |cotγ| = |σ₂|/σ₁ can indicate that the imaginary part of the conductivity at ω < ω_cr is defined by the larger zero-phonon contribution in σ₂^res the region of weak variation in the loss angle γ(ω), which significantly exceeds the relaxation contribution σ₂^res.     

(γ, p) cross sections and isospin splitting of the giant dipole resonance in N = 50 nuclei

The differential (e, e'p) cross sections of ⁸⁸Sr, ⁸⁹Y, ⁹⁰Zr and ⁹²Mo have been measured at θ = 90°. The results are used to obtain the (γ, p) cross sections by correcting with the angular distribution data. The (γ, p) cross sections are compared with the (γ, n) cross sections. A resonance corresponding to the T_< GDR is found and another resonance is separated by fitting a Lorentz line with a width equal to that of the (γ, n) GDR. The ratios σ(γ, p)/σ(γ, n) and σ(γ, p₀)/σ(γ, p) show differences between the two resonances. The two GDR resonances are studied from the isospin splitting point of view. The sum rule and splitting energy of the (γ, p) GDR agree well with theory. However, when the sum of the (γ, p) and (γ, n) experimental data is taken, the results are too large to be explained by the T_> GDR.     

Physical criteria for the reliability of data on the photodisintegration of the <Superscript>89</Superscript>Y nucleus

Experimental photonuclear reaction cross sections obtained in experiments using quasimonoenergetic annihilation, monoenergetic tagged photons, and bremsstrahlung γ-radiation are analyzed using physical criteria for the reliability of data on the ⁸⁹Y nucleus. It is found that the reliability of data on the cross sections of partial reactions (γ, 1n) and (γ, 2n), obtained by means of photoneutron multiplicity sorting, is highly doubtful. Reliable cross sections of reactions (γ, 1n) and (γ, 2n) are obtained using the experimental–theoretical method (ETM) for evaluating using both experimental cross sections of neutron yield reaction σ^exp(γ, xn) that are free of neutron multiplicity problems, and theoretically calculated F _i ^theor ratios of the cross sections of definite (i) partial reactions to cross section σ^theor(γ, xn). It is shown that the evaluated cross sections differ noticeably from the experimental data.     

High-spin states in106Cd

Levels of¹⁰⁶Cd, populated by¹⁰⁴Pd(α, 2nγ)¹⁰⁶Cd have been studied measuring direct and delayedγ-ray spectra,γ-γ coincidences andγ-ray angular distributions. A decay level scheme is proposed including states up to 4659.8 keV. IntenseE2 transition cascades have been observed. The half-life of an isomeric level located at 4659.8 keV has been measured:T _1/2= 62±6ns. Nuclear Reactions ¹⁰⁴Pd(α, 2nγ),E _α=31MeV; measuredE _γ,I _γ,γ-γ coinc, σ(θ)T _1/2.¹⁰⁶Cd deduced levels,J, π, Enriched targets. Ge(Li) detectors.     

Applications of the Bloch–Siegert Shift in Solid-State Proton-Dipolar-Decoupled19F MAS NMR

In solid-state proton-dipolar-decoupled¹⁹F MAS NMR spectroscopy,¹⁹F chemical-shift data need to be corrected for the Bloch–Siegert shift. Assigning the single sharp¹⁹F resonance of 2-fluoroadamantane to its proton-coupled¹⁹F shift of −174.4 ppm results in chemical-shift referencing that is independent of the amplitude of the proton-decoupling field. The Bloch–Siegert shift is also a useful tool to characterize the amplitude and homogeneity of the proton-decoupling field,H_1H, and to monitor probe performance. Considerable inhomogeneity inH_1Halong the long axis of the right-cylinder sample rotor was detected. In our commercial 7 mm H– F MAS probe, the proton field strength,[formula], decreases to 25% of the maximum value across the usable sample volume. Measurement of the Bloch–Siegert shift revealed that the proton-decoupling field strength decreases during the first few scans of an acquisition. Reductions in the proton field strengths can exceed 10%, and they are explained by the heating of the RF coil circuitry which is caused by high-power proton decoupling. The extent of reduction in field amplitude is a function of the decoupling duty cycle. Losses in[formula]can be avoided by tuning the probe proton RF circuitry at the operating temperature of the probe, using the Bloch–Siegert shift as an optimization parameter.     

A study of the photoneutron contribution to the giant dipole resonance in doubly even Mo isotopes

By using a variable monochromatic photon beam, the partial photoneutron cross sections σ(γ, n) + σ(γ, pn), σ(γ, 2n) and σ(γ, 3n) are determined in the region of the giant dipole resonance for the doubly even Mo isotopes ⁹²Mo, ⁹⁴Mo, ⁹⁶Mo, ⁹⁸Mo and ¹⁰⁰Mo. Measured integrated photoneutron cross sections are compared with available integrated photoproton cross sections as a function of A. Broadening of the giant dipole resonance as A increases is observed in good agreement with the predictions of the dynamic collective model. A tentative study of some isospin splitting effects is also carried out.     

Angular distributions of photoneutrons from the 207, 208Pb(γ, n0) reactions

Angular distributions of photoneutrons from the ^{207, 208}Pb(γ, n₀) reactions were measured at 11 angles around θ = 90°. The γ-source, E_γ = 7–11.4 MeV, contained discrete lines (ΔE ? 30 eV) obtained from n-capture and was used in conjunction with a high-resolution ³He spectrometer. Strong evidence for an E2 contribution and for E2-E1 and possibly E1-M1 interference was obtained in both ²⁰⁷Pb and ²⁰⁸Pb. The results are compared with calculations using a direct-semidirect model which involved an E1 and isoscalar E2 giant resonances. The results indicate that this model could explain only certain features of the data while most of the other features remain unexplained.     

Structure of even-even actinides in the interacting boson model and the N = 152 subshell closure

We show that a wide range of deformed actinides can be described in terms of an interacting boson model hamiltonian with three parameters, two of them [including the coefficient of the only SU(3) symmetry breaking term] remaining almost constant over the whole region. In addition to ground γ₁ and β₁ spectra, B(E2:0_g⁺ → 2_g⁺) values are well reproduced with no extra adjustable parameters for nuclei with 136⩽N⩽146, while for nuclei beyond N = 146 an effective boson number has to be considered in order to fit the observed in the B(E2:0⁺_g → 2⁺_g) values, which is due to the presensce of a subshell closure at N = 152. The sensitive dependence of the B(E2:0_g⁺→2_g⁺) values on the effective boson numbers is emphasized. β₁ → ground and β₁ → ground transitions are fitted by breaking the SU(3) symmetry of the E2 transition operator.     

Projectile Z dependence of double K-shell ionization in light elements by hydrogen- and helium-ion bombardment

The K² X-rays from Be, B and O atoms by H- and He-ion bombardment were measured. The ratio of σ_2K(He) to σ_2K(H) exhibits the projectile Z⁴₁ dependence. This is the first observation of the Z₁-dependence of σ_2K predicted by the Coulomb excitation.     

Collective polynuclear superradiance rather thanstimulated emission of Mössbauer radiation from125m2Te and 123m2Te

Acts attributed to single-particle stimulated emission, ^125m2Te(γ,2γ)^125m1Te, had been observed previously in a Be^125m2Te sample as a variation of the line intensity at Eγ=109.27 keV and by the appearance of a line of double energy at E_2γ=218.54 keV. This effect occurred when the sample temperature, T was lowered from 300 to 4 K. In the present work, the first observation is reported of stimulated emission events in the reaction ^123m2Te(γ,2γ)^123m1Te which were registered from a Mg₃ ^123m2TeO⁶ sample when cooled in a similar fashion. It is shown here that the mechanism of these experimentally observed events is polynuclear superradiance rather than a single-particle stimulated emission of Mössbauer radiation as earlier suggested.     

Unbounded generalizations of standard von Neumann algebras

The primary purpose of this paper is to study unbounded operator algebras called standard EW^#-algebras which are generalizations of standard von Neumann algebras to the unbounded case.The first part is an investigation of the weak, σ-weak, strong and σ-strong topologies on a standard EW^#-algebra. It is showed that the weak and σ-weak topologies on a standard EW^#-algebra coincide.The second part is a study of a locally convex topology called _∞L^ω₂-topology on a standard EW^#-algebra U. It is proved that U is a GB¹-algebra under the topology.The third part is an investigation of isomorphisms of standard EW^#-algebras. It is showed that if standard EW^#-algebras U and B are isomorphic then U and B are spatially isomorphic.     

Conductivity of a periodic two-component system of rhombic type

The conductivity and the distribution of electric field, current, and charge density in a periodic two-component system composed of rhombs with an arbitrary vertex angle of 2α are investigated. The effective conductivity of such a medium is represented by a tensor with components σ _eff ¹¹ (α) and σ _eff ²² (α) in the principal axes that satisfy the Dykhne relation σ _eff ¹¹ (α) σ _eff ²² (α)=σ ₁σ₂, where σ₁, σ₂ are the isotropic conductivities of media 1 and 2. In addition, the relation σ _eff ²² (α)=σ _eff ¹¹ (π/2?α) is satisfied. The principal axes are directed along the diagonals of the rhombs. It is shown that there are three lines in the rectangle 0<α ≤π/2,?1<Z<1((Z=σ₁?σ₂)/(σ ₁+σ₂)) on which the charge density is expressed in terms elliptic functions. An explicit expression is obtained for all physical quantities on these lines.     

129Xe contact shift in oxygen gas

We have determined the temperature dependence of σ₁ of ¹²⁹Xe in oxygen gas. These results were obtained by measurement of the resonance frequency of ¹²⁹Xe in gas samples of known densities in Xe and O₂. The shift of the resonance frequency due to Xe-Xe interactions has been measured in pure Xe gas samples with improved precision. This allows the determination of σ₁(Xe-O₂) by subtracting out the known effect of Xe-Xe interactions in mixed Xe-O₂ samples. σ₁(Xe-O₂) values are reported here for the temperature range 220 to 440 K. The values of σ₁(Xe-O₂) are adequately described by the polynomial function in p.p.m. amagat^-1 σ₁(Xe-O₂) = - 1·061 + 3·64 × 10^-3τ - 2·19 × 10^-5τ² + 9·58 × 10^-8τ³ - 2·08 × 10^-10τ⁴, where τ = (T - 300 K). It is found that the temperature dependence of σ₁(Xe-O₂) can be interpreted in terms of a contact interaction between Xe and the paramagnetic O₂ molecule.     

Impurity thermodynamics of a Heisenberg antiferromagnet - Mn:FeF2

The temperature dependence of the ⁵⁵Mn and ¹⁹F NMR in antiferromagnetic FeF₂ with 1% Mn impurities was used to determine the magnetizations σ_i, σ_nn and σ_nnn vs. T for the impurity and neighboring Fe ions. σ_i vs. T was found to be well described by an effective field theory in agreement with the thermodynamic Greens' function prediction for an impurity mode below the host-magnon band. The magnitude of the FeMn nnn exchange interaction J′₂ in Fe:MnF₂ and Mn:FeF₂ differ slightly from each other but the nn interaction J′₁ changes sign.     

Energy spectrum of photons produced by neutrino (antineutrino) scattering on electrons. Effect of possible neutrino oscillations

The energy spectrum of photons emitted in neutrino (antineutrino) scattering on electrons at E_v ? m_v is calculated with the assumption that the neutral electron flow has an arbitrary (V, A) structure. The result obtained is generalized to the case of possible neutrino oscillations, \(v_e \begin{array}{*{20}c} { - \to } \\ { \leftarrow - } \\ \end{array} v_\mu , \overline v _e \begin{array}{*{20}c} { - \to } \\ { \leftarrow - } \\ \end{array} \overline v _\mu \) , at an arbitrary neutrino mixing angle. Using the Weinberg-Salam model (sin²θ_W = 0.23) estimates of the sections dσ_γ/dω and σ_γ are obtained with consideration of the reactor antineutrino flux \(\bar v_e \) . The contributions from charged and neutral lepton fluxes and their interference to dσ_γ/dω are compared.     

A study of the photoneutron contribution to the giant dipole resonance of nuclei in the 64 ≦ A ≦ 86 mass region

The partial photoneutron cross sections [σ(γ, n) + σ(γ, pn)] and σ(γ, 2n) of ⁶⁴Zn, Ga, ^70,72,74,76Ge, ⁷⁵As and ^76,78,80,82Se were measured with a monochromatic photon beam and a high efficiency neutron detecting system in the photon-energy range 8 ≦ E ≦ 30 Me V. Integrated cross sections are discussed. The evolution of the GDR as observed through the neutron exit channel only, is tentatively interpreted either in terms of isospin splitting or in terms of the dynamic collective model.