Neutron detector array at IUAC: Design features and instrumentation developments

The characteristics and performance of the newly commissioned neutron detector array at IUAC are described. The array consists of 100 BC501 liquid scintillators mounted in a semi-spherical geometry and are kept at a distance of 175 cm from the reaction point. Each detector is a 5^″ × 5^″ cylindrical cell coupled to 5^″ diameter photomultiplier tube (PMT). Signal processing is realized using custom-designed home-made integrated electronic modules which perform neutron – gamma discrimination using zero cross timing and time-of-flight (TOF) technique. Compact custom built high voltage power supply developed using DC–DC converters are used to bias the detector. The neutrons are recorded in coincidence with fission fragments which are detected using multi-wire proportional counters mounted inside a 1 m diameter SS target chamber. The detectors and electronics have been tested off-line using radioactive sources and the results are presented.     

Implicit algorithms and their linearization for the transient incompressible Navier-Stokes equations

Email: na.asmith2{at}na-net.ornl.gov Email: na.silvester{at}na-net.ornl.gov The issue of appropriate time discretization methods for theunsteady incompressible Navier-Stokes equations is consideredfrom a practical perspective. Conventional implicit time-steppingalgorithms are not feasible for long-time simulations sincethey inherit the quadratic nonlinearity of the steady-stateequations. As a result, two new linearized versions of the ‘pure’algorithms are analyzed herein. These have similar stabilityproperties and comparable accuracy to the underlying nonlinearmethods.     

Erbium–ytterbium fibre laser emitting more than 13 W of power in 1.55 μm region

We report the work on erbium:ytterbium-doped double clad fibre laser (EYDFL), that is pumped at 976 nm. The maximum output power generated is 13.6 W in 1550 nm region with a slope efficiency of about 21%. To the best of our knowledge, this is the highest power reported from an EYDFL, that uses commercially available off-the-shelf large mode area Er:Yb-doped double-clad fibre.     

In vivo AND PHOTOPHYSICAL STUDIES ON PHOTOOXIDATIVE DAMAGE TO LENS PROTEINS AND THEIR PROTECTION BY RADIOPROTECTORS

Abstract— Photooxidation, whether initiated by an endogenous or exogenous sensitizer, is an important mechanism in light induced damage to the lens. One of the substrates for this damage is lens protein. A porphyrin sensitizer which binds to lens proteins [ mesotetra ( p -sulfonatophenyl) porphyrin (TPPS)] was found to photooxidize Skh-2 pigmented mice lens protein in vivo. Uroporphyrin, a model for a non-binding photosensitizer, did not induce photooxidative damage to the mouse lens.
The radioprotector 3-amino-2-hydroxypropyl phosphorothioate (WR-77913) was investigated as an agent to retard or negate in vivo photooxidative damage to the lens. Intraperitoneal injections of WR-77913 prior to irradiation reduced the TPPS induced photodestruction of lens protein in Skh-2 pigmented mice.
The mechanism of protection was also investigated. Thiols were found to quench both the triplet state of porphyrins and the reactive intermediate singlet oxygen on the order of 10⁵ and 10⁶ M ^-1 s¹ respectively. These are probably not fast enough to explain most of the protection afforded by thiols. An additional mechanism may be the accelerated photobleaching of porphyrins by thiols which protects tissue by reducing the absorptions due to the porphyrins.     

Linearly polarized intracavity passive Q-switched Yb-doped photonic crystal fibre laser

In this paper we report linearly polarized high average power passive Q-switched ytterbium-doped photonic crystal fibre laser with a Cr⁴⁺:YAG crystal as a saturable absorber. An average output power of 9.4 W with pulse duration of 64 ns and pulse repetition rate of 57.4 kHz with a slope efficiency of 52% was achieved. Measured polarization extinction ratio (PER) of the Q-switched laser output was 10.5 dB.