Correlation studies of fission fragment neutron multiplicities

We calculate neutron multiplicities from fission fragments with specified mass numbers for events having a specified total fragment kinetic energy. The shape evolution from the initial compound nucleus to the scission configurations is obtained with the Metropolis walk method on the five-dimensional potential-energy landscape, calculated with the macroscopic-microscopic method for the three-quadratic-surface shape family. Shape-dependent microscopic level densities are used to guide the random walk, to partition the intrinsic excitation energy between the two proto-fragments at scission, and to determine the spectrum of the neutrons evaporated from the fragments. The contributions to the total excitation energy of the resulting fragments from statistical excitation and shape distortion at scission is studied. Good agreement is obtained with available experimental data on neutron multiplicities in correlation with fission fragments from $^{235}$U(n$_{\rm th}$,f). At higher neutron energies a superlong fission mode appears which affects the dependence of the observables on the total fragment kinetic energy.Comment: 12 pages, 10 figure

Radiographic spectrum of adult pulmonary tuberculosis in a developed country

AbstractSetting. Bispebjerg Hospital, Department of Pulmonary Medicine P. The referral centre of adult tuberculosis in the municipality of Copenhagen, Denmark.Objective. To evaluate the radiographic spectrum of pulmonary tuberculosis (TB) in adults in a low-prevalence country and to correlate radiographic appearances with bacteriological results, clinical and demographic data.Design. Retrospective review of medical files on 548 cases with pulmonary TB according to the criteria of WHO.Results. Usual radiographic pattern of reactivating TB, with upper lobe involvement, was found in 92% (n=504). eight percent (n=44) showed unusual X-ray patterns for adults, such as isolated lower lobe infiltrations (n=19), hilar adenopathy (n=10), miliary TB (n=7), tuberculoma (n=2), pleural effusion (n=1) and normal chest X-ray (n=3). Eighty-nine percent of cases with cavitary lesions were positive by microscopy.Conclusion. The risk of missing a diagnosis of pulmonary TB may be high if patients present with an X-ray unusual for TB, but this is fortunately seen only in 8% of cases of pulmonary tuberculosis. Unusual X-ray is more commonly found in patients with concomitant disease, such as diabetes and cancer.If chest X-ray shows cavities, but the smear is negative for Mycobacterium, TB is unlikely and further diagnostic procedures should be performed without waiting for culture results

Microscopic Structure of Rotational Damping

The damping of collective rotational motion is studied microscopically, making use of shell model calculations based on the cranked Nilsson deformed mean-field and on residual two-body interactions, and focusing on the shape of the gamma-gamma correlation spectra and on its systematic behavior. It is shown that the spectral shape is directly related to the damping width of collective rotation, \Gammarot, and to the spreading width of many-particle many-hole configurations, \Gammamu. The rotational damping width is affected by the shell structure, and is very sensitive to the position of the Fermi surface, besides mass number, spin and deformation. This produces a rich variety of features in the rotational damping phenomena

Linear response of light deformed nuclei investigated by self-consistent quasiparticle random-phase-approximation

We present a calculation of the properties of vibrational states in deformed, axially--symmetric even--even nuclei, within the framework of a fully self--consistent Quasparticle Random Phase Approximation (QRPA). The same Skyrme energy density and density-dependent pairing functionals are used to calculate the mean field and the residual interaction in the particle-hole and particle-particle channels. We have tested our software in the case of spherical nuclei against fully self consistent calculations published in the literature, finding excellent agreement. We investigate the consequences of neglecting the spin-orbit and Coulomb residual interactions in QRPA. Furthermore we discuss the improvement obtained in the QRPA result associated with the removal of spurious modes. Isoscalar and isovector responses in the deformed ${}^{24-26}$Mg, $^{34}$Mg isotopes are presented and compared to experimental findings

Barrier penetration and rotational damping of thermally excited superdeformed nuclei

We construct a microscopic model of thermally excited superdeformed states that describes both the barrier penetration mechanism, leading to the decay-out transitions to normal deformed states, and the rotational damping causing fragmentation of rotational E2 transitions. We describe the barrier penetration by means of a tunneling path in the two-dimensional deformation energy surface, which is calculated with the cranked Nilsson-Strutinsky model. The individual excited superdeformed states and associated E2 transition strengths are calculated by the shell model diagonalization of the many-particle many-hole excitations interacting with the delta-type residual two-body force. The effect of the decay-out on the excited superdeformed states are discussed in detail for $^{152}$Dy, $^{143}$Eu and $^{192}$Hg.Comment: 33pages, 32 figures, submitted to Nucl.Phys.

Poisson and Porter-Thomas Fluctuations in off-Yrast Rotational Transitions

Fluctuations associated with stretched E2 transitions from high spin levels in nuclei around $^{168}$Yb are investigated by a cranked shell model extended to include residual two-body interactions. It is found that the gamma-ray energies behave like random variables and the energy spectra show the Poisson fluctuation, in the cranked mean field model without the residual interaction. With two-body residual interaction included, discrete transition pattern with unmixed rotational bands is still valid up to around 600 keV above yrast, in good agreement with experiments. At higher excitation energy, a gradual onset of rotational damping emerges. At 1.8 MeV above yrast, complete damping is observed with GOE type fluctuations for both energy levels and transition strengths(Porter-Thomas fluctuations).Comment: 21 pages, phyzzx, YITP/K-99