Measurement of Angular Distributions of Gamma Rays from the Inelastic Scattering of 14.1-MeV Neutrons by Carbon and Oxygen Nuclei

The results obtained by measuring the angular and energy distributions of gamma rays originating from the inelastic scattering of 14.1-MeV neutrons by carbon and oxygen nuclei are presented. The measurements in question were performed by the tagged-neutron method in a beam of an ING-27 standard portable neutron generator. The angular distributions of gamma rays emitted by the 2⁺ state of ¹²С at 4.43 MeVand the 3^? state of ¹⁶O at 6.13 MeV were obtained.     

Femtosecond Laser–Matter Interactions: Theory,Experiments, and Applications,by Eugene G. Gamaly

The Mössbauer effect, the recoilless absorption and emission of gamma rays by nuclei embedded in solids, has its origin in the properties of the solid state. The nature of this connection is dealt with in some detail and the various effects of the crystalline environment on the nuclear energy levels is described. The importance of these effects as contributions to the study of the physical and chemical properties of crystals is discussed, and applications which depend on the intrinsic energy resolution of the effect are described. The recoilless nuclear resonant scattering and diffraction of gamma rays is also dealt with in some detail.     

Investigation of Inelastic Neutron Scattering on 27Al Nuclei

The results obtained by measuring the angular and energy distributions of gamma rays produced in reactions induced by the inelastic scattering of 14.1-MeV neutrons on ²⁷Al nuclei are presented. The respective measurements were performed by the tagged-neutron method in a beam from the ING-27 compact neutron generator. The angular distributions were obtained for gamma rays emitted from the 844-keV 1/2⁺, 1015-keV 3/2⁺, 2212-keV 7/2⁺, and 3004-keV 9/2⁺ states of ²⁷ Al nuclei.

     

Mechanisms of excitation of <Emphasis Type="Italic">T</Emphasis>-odd correlations for prescission gamma rays and structure of these correlations

Conditions for the appearance and observation of prescission gamma rays emitted by a fissioning nucleus prior to its separation into fission fragments were investigated within quantum-mechanical fission theory. It is shown that these conditions are realizable in the gamma decay of isovector electric giant dipole resonances in a fissile nucleus that are excited because of nonadiabaticity of the collective deformation motion of the nucleus at the ultimate stages of its prefission evolution. Angular and energy distributions of prescission gamma rays emitted by unpolarized fissioning nuclei are analyzed. Features of T-odd correlations in angular distributions of gamma rays arising in the fission of unpolarized target nuclei that is induced by polarized cold neutrons are investigated, and it is shown that these correlations are similar in nature to T-odd ROT correlations discovered earlier for alpha particles emitted in the ternary fission of nuclei.     

Neutron Resonance States in Overdense Crystals

New three-body resonances appeared in the neutron scattering on two nuclei fixed in nodes of overdense crystalline lattice have been calculated for the iron group isotopes. These resonances are strongly dependent on the lattice parameters and characteristics of two-body resonances in neutron–nucleus subsystems. The effective forces created by the neutron resonance rescatterings supplement the Coulomb forces between nuclei of the crystalline lattice. These effective resonance interactions occur only at certain distances between nuclei and are accompanied by gamma radiation.     

Evolution of the giant dipole resonance in excited 120Sn and 208Pb nuclei populated by inelastic alpha scattering

The evolution of the giant dipole resonance (GDR) in ¹²⁰Sn and ²⁰⁸Pb nuclei at excitation energies in the range of 30–130 MeV and 40–110 MeV, respectively, were studied by measuring high energy γ rays from the decay of the resonance. The excited states were populated by inelastic scattering of α particles at beam energies of 40 and 50 MeV/nucleon for ¹²⁰Sn and 40 MeV/nucleon for ²⁰⁸Pb. A systematic increase of the resonance width with increasing excitation energy was observed for both nuclei. The observed width evolution was compared to calculations employing a model that adiabatically couples the collective excitation to the nuclear shape, and to a model based on the collisional damping of nucleons. The adiabatic coupling model described the width evolution in both nuclei well, whereas the collisional damping calculation could describe the width evolution only in ²⁰⁸Pb. Light-particle inelastic scattering populates low angular momentum states in the target nucleus. The observed width increase is therefore interpreted to be predominantly due to fluctuations in the nuclear shape induced by temperature. This interpretation is consistent with the adiabatic model calculations and with recent angular momentum-gated measurements of the GDR in excited Sn isotopes.     

Investigations of positronium formation and destruction using 3gamma/2gammaannihilation-ratio measurements

Positronium (Ps) produced by 4 to 40 eV positrons colliding with Ne, Ar, Kr, CO2, and O2 is investigated by measuring the ratio of signals of two gamma rays in coincidence resulting from (a) three gamma annihilation of ortho-Ps and (b) two annihilation gamma rays due to para-Ps decay and destruction of ortho-Ps at an aluminum scattering cell surface. These ratios provide evidence that relates to the kinetic energy dependence of ortho-Ps interactions with an aluminum surface, the Ps formation potential at this surface, and the fact that Ps is being formed with inner orbital electrons for CO2 and O2.     

Compilation of low-energy gamma rays

A compilation of selected nuclear gamma rays has been prepared in order to identify the most attractive candidate nuclei for a gamma-ray laser. The compilation consists of two parts: (1) a listing of selected gamma rays emanating from an isomeric state and (2) a listing of selected gamma rays following the decay of an energy level close to the isomeric state. The compilation is based on the latest “Nuclear Data Sheets” (Ref. 1) for each A-chain available on 1 January 1987.     

Understanding Quantum Phase Transitions,edited by Lincoln Carr

The concept of the superdeformed shape is first introduced classically as the most stable configuration of a rapidly rotating deformable body and is then applied to nuclei. The shape of nuclei are determined by a competition between the collective energy of the core, to which classical considerations apply quite well, and the quantal energies of the valence nucleons, which may be evaluated by the Nilsson model. The result of this competition is that slowly rotating nuclei can be either oblate or prolate but rapidly rotating nuclei can have a superdeformed prolate shape, with a 2:1 ratio of axes particularly favoured.

The evidence for superdeformation in nuclei is described under four headings. Firstly, some light nuclei are superdeformed in their ground state or in an excited state. Secondly, some nuclei pass through a well defined superdeformed shape on the way to fission. Thirdly, studies of the excitation functions of elastic and inelastic scattering of identical heavy ions provide evidence of a nuclear molecule in a superdeformed shape. Finally, recent analyses of gamma rays from nuclei formed in a very high spin state by a heavy ion collision provide conclusive evidence for superdeformation.     

Polarimetry of short-pulse gamma rays produced through inverse Compton scattering of circularly polarized laser beams

We have developed a polarimetry of ultrashort pulse gamma rays based on the fact that gamma rays penetrating in the forward direction through a magnetized iron carry information on the helicity of the original gamma rays. Polarized, short-pulse gamma rays of (1.1+/-0.2)x10(6)/bunch with a time duration of 31 ps and a maximum energy of 55.9 MeV were produced via Compton scattering of a circularly polarized laser beam of 532 nm off an electron beam of 1.28 GeV. The first demonstration of asymmetry measurements of short-pulse gamma rays was conducted using longitudinally magnetized iron of 15 cm length. It is found that the gamma-ray intensity is in good agreement with the simulated value of 1.0x10(6). Varying the degree of laser polarization, the asymmetry for 100% laser polarization was derived to be (1.29+/-0.12)%, which is also consistent with the expected value of 1.3%.     

Spins of198Au levels from the (n, γ) reaction using polarized neutrons and polarized197Au nuclei

The¹⁹⁷Au(n, γ) reaction was studied with the aid of polarized thermal neutron beams. Two kinds of experimental data were obtained: i) circular polarization of gamma rays of high energy due to capture of polarized neutrons by unoriented¹⁹⁷Au nuclei, and ii) angular distribution of such gamma rays observed after capture of polarized neutrons by polarized¹⁹⁷Au nuclei. Spins of several levels of¹⁹⁸Au could be uniquely assigned or could be restricted. The sign of the hyperfine field of Au in AuFe has been determined to be negative.     

Observation of the gamma resonance of a long-lived <Superscript>109<Emphasis Type="Italic">m</Emphasis></Superscript>Ag isomer using a gravitational gamma-ray spectrometer

Experiments confirming the previous data on the small real width of the γ resonance of ^109m Ag have been performed with a gravitational gamma-ray spectrometer. The achieved resolution is eight orders of magnitude higher than that of Mössbauer spectrometers using gamma rays from a ⁵⁷Fe nuclide. The theoretically predicted broadening of the Mössbauer gamma line of ^109m Ag by five orders of magnitude (due to the dipole-dipole interaction between the magnetic moments of neighboring nuclei) has not been observed.     

Gamma ray and π0 production from hydrogen and complex nuclei by 270–375 MeV gamma rays

Measurements are reported on the differential cross section for secondary gamma ray production on hydrogen and nuclear targets at 90° in the laboratory through the interactions of primary gamma rays in the energy range 270–375 MeV. A difference method using bremsstrahlung beams at different end point energies was employed. The gamma ray detector was a high resolution Nal(Tl) spectrometer and time of flight discrimination was used to reject neutrons. For incident gamma rays in the range 270–375 MeV the first pion nucleon resonance is strongly excited and the observed gamma ray yields are consistent with those expected due to an admixture of coherent and incoherent π⁰ photoproduction in the resonance region. The experiment marks the first successful use of a large Nal(Tl) crystals as a gamma ray spectrometer at a high energy electron linear accelerator, despite the low duty cycle and its accompanying difficulties for such detectors.     

Small broadening of the Mössbauer gamma line of the isomer <Superscript>109<Emphasis Type="Italic">m</Emphasis></Superscript>Ag as yet another indication of the protracted character of the emission of photons from nuclei and their absorption

Nine experiments performed to date by three research groups in order to observe the Mössbauer effect in the case of gamma rays emitted by the long-lived isomer ^109m Ag yielded results suggesting an anomalously small broadening of the Mössbauer gamma line of this isomer. In turn, this indicates that the emission of photons from nuclei and their resonance absorption cannot proceed within a time interval much shorter than the characteristic time of the change in the energy of hyperfine dipole—dipole interaction, because the photon energy would otherwise be determined by the sum of the instantaneous value of the energy of this interaction and the nuclear-transition energy, in which case the broadening of the Mössbauer gamma line would reach five to six orders of magnitude, as opposed to one to two orders of magnitude broadening observed experimentally.     

M1 gamma strength for zirconium nuclei in the photoneutron channel

Photoneutron cross sections were measured for 91Zr, 92Zr, and 94Zr near the neutron separation energy with quasimonochromatic gamma rays. The data exhibit some extra components around the neutron threshold. A coherent analysis of the photoneutron data for 92Zr together with the neutron capture on 91Zr based on the microscopic Hartree-Fock-Bogoliubov plus quasiparticle random-phase approximation model for the E1 strength has revealed the presence of an M1 resonance at 9 MeV. The microscopic approach systematically shows the same M1 strength in the photoneutron cross section for 91Zr and 94Zr. The total M1 strength is about 75% larger than the strength predicted by the systematics, being qualitatively consistent with the giant M1 resonance observed in the inelastic proton scattering.     

Diffusive and Shock-Drift Acceleration in Relativistic Shocks

It is accepted that the shock acceleration mechanism can explain the non-thermal cosmic rays in supernova remnants, active galactic nuclei and gamma ray bursts. Especially, the importance of relativistic shock acceleration of cosmic rays in extragalactic sources is an important subject of study. In this work we will discuss the shock acceleration mechanism and will review the properties of non-relativistic and relativistic shocks, particularly focusing on relativistic Monte Carlo simulation studies.     

Determination of partial structure factors using resonant nuclear scattering

A method based on nuclear scattering of gamma rays produced by filtering of synchrotron radiation is suggested for the determination of partial structure factors in multielement disordered systems. Theoretical treatment of the problem is given for binary system in the kinematical approach.     

Quantal radiation from macroscopic rotation

Macroscopic rotation of deformed excited nuclei may under certain conditions be accompanied by radiation of quasi-discrete gamma rays which resemble the cascade of transitions between nuclear rotational states.     

On the connection between gamma radiation and radio radiation in pulsars

A model proposed for radio radiation from a pulsar suggests that coherent radio radiation is generated in a vacuum gap over the polar cap of a neutron star. In this model, x and gamma rays from the pulsar are generated due to the inverse Compton scattering of radio radiation by ultrarelativistic electrons accelerated in the gap.     

射线检测管道垢厚方法的研究进展

报告了我国开展射线检测原油管道垢厚的研究进展. 介绍了γ射线透射检测垢厚的基本原理、 模拟实验装置及主要研究成果. 研究表明, 研制透射型测垢仪是可行的. 另外, 还给出了南京大学关于表面型中子测垢仪和γ射线测垢仪的初步预研结果.