No abstract

No abstract

In this work, a neutron spectrometric system based on a set of moderating spheres with thermoluminescence detectors (TLD) is presented. The system at the Nuclear Regulatory Authority (ARN) Dosimetry Laboratory consists of 12 solid spheres made of high-density polyethylene (p = 0.95 g x cm(-3)), with diameters ranging from 2" to 12" and TLD sensitive to thermal and gamma radiation, namely TLD-600 and TLD-700, located at the centre of the spheres. The neutron response matrix for this Bonner Sphere Spectrometer (BSS) was calculated using the MCNP-IVB code and the library ENDF/B-VI in the energy range between thermal neutrons and 100 MeV. The neutron spectrum was obtained using the LOUH182 unfolding code. The improvement in sensitivity of the system is based on the election of a different heating cycle of the TLD that allows an increase in sensitivity by a factor of 2.6 compared with the standard laboratory treatment. The system response for the calibration with an Am-Be source is presented.

The authors present a family of exact solutions of the four-dimensional Einstein field equations obtained by means of the application of the inverse scattering technique followed by a Kaluza-Klein dimensional reduction. They describe the collision of gravitational solitons on four-dimensional Friedmann-Robertson-Walker backgrounds with a material content consisting of a perfect fluid with a barotropic equation of state. They investigate the behaviour of the stress-energy tensor and show that the collision can form voids and halos. Applications to the Brans-Dicke theory and the problem of geodesic focusing are also considered.