Quasi-free electron scattering from 12C using Hartree-Fock wave functions

The energy spectrum and the angular correlation distributions for the reaction ¹²C(e, e'p)¹¹B are calculated within the framework of DWBA using spherical Hartree-Fock wave functions. A comparison with experiment and some of the earlier calculations is made. It is observed that a large spatial extent of the wave functions significantly improves the agreement.     

Neutron moderation in a bulk sample and its effects on PGNAA setup geometry

In a prompt gamma ray neutron activation analysis (PGNAA) setup, the neutron moderation in the bulk sample also plays a key role. This can even dominate the thermalization effects of the external moderator in some cases. In order to study the neutron moderation effect in the bulk sample, moderators with two different sizes of the sample were tested at the King Fahd University of Petroleum & Minerals (KFUPM) PGNAA facility. In these tests, the thermal neutron relative intensity and prompt gamma ray yield from the two moderators were measured using nuclear track detectors (NTDs) and NaI detector, respectively. As predicted by Monte Carlo simulations, the measured intensity of thermal neutron inside the large sample cavity due to the external moderator was smaller than that from the smaller sample cavity. Due to its larger size, additional thermalization of neutrons will take place in the larger sample. In spite of smaller thermal neutron yield from the external moderator at the large sample location, higher yield of the prompt gamma ray was observed as compared to that from the smaller sample. This confirms the significance of neutron moderation effects in the bulk sample and can thereby affect the PGNAA geometry size. This allows larger samples in conjunction with smaller moderators in the PGNAA setup.     

State selective laser photodissociation of Tl2 at 337.1 nm by optogalvanic spectroscopy

This paper reports the first time achievement of laser photolysis of thallium dimers by single photon absorption of N₂-laser light at 337.1 nm resulting in a large population inversion of thallium 7 ²S excited state with respect to 6 ²P state. The photodissociation nitrogen laser pulse is spatially and temporally overlapped with the tunable dye laser pulse that is used for confirming the production of selectively excited thallium atoms. The dye laser excites the thallium atoms from 7 ²S state to high lying Rydberg states that collisionally ionize giving an ion-current signal which is subsequently processed by a box-car average/integrator and recorded on the chart recorder. The photodissociation of Tl₂ to Tl(7 ²S ) state demonstrates the existence of the molecular dissociative state 1g that is correlated with Tl 7 ²S +6 ²P states. A complete absence of 6 ²P state population among the photolysis products indicates a 100% prompt population inversion between 7 ²S and 6 ²P atomic states.     

An241Am−Be source based thermal neutron activation analysis facility at KFUPM

An instrumental thermal neutron activation analysis facility based, on a 16 Ci²⁴¹ Am–Be source, a high resolution -ray spectrometry setup and a PC-based data acquisition system at KFUPM is described. The thermal neutron flux distribution was determined from the induced activities of high purity indium foils. The absolute thermal neutron flux was calculated from the activities of bare and cadmium-covered gold foils at a position of 3 cm from the soource at which the flux reaches a maximum. The facility tests were carried out with the determination of manganese concentrations in six types of industrially important steel samples. The result of 1.33% manganese in SS-304 steel sample was in excellent agreement with the literature value. The method is nondestructive, economical and ideal for bulk analysis.     

Measurements of sub-nanosecond lifetimes by means of nanosecond laser pulses

It is shown that the lifetimes of excited states of molecules which give a reasonably strong absorption (molar decadic extinction coefficient ∈ > 10⁴M^?1cm^?1) at the frequency of the ruby laser can be determined from the saturation of the optical transitions. This is illustrated for DDI (1,1'-diethyl-2,2'-dicarbocyanine iodide) in glycerol, which appears to have a lowest excited state with a lifetime of 110 psec. This value agrees fairly well with that calculated from the formula for the rate of internal conversion derived from Siebrand's work. Under favourable conditions lifetimes as short as 10 psec can be measured.     

Trace quantities of uranium in some Indian chewing tobaccos as determined by fission track analysis

The sandwiched pellet technique using Makrofol-E plastic track detectors has been employed to determine trace quantities of uranium in nine brands of flavored chewing tobaccos consumed by the Indian population. In this technique the nuclear reaction,²³⁵U(n,f), is used for the quantitative estimation of uranium. The maximum value of uranium (1.88 ppm) has been found in raw tobacco leaves (Surti), while the minimum (0.13 ppm) in Tulsi (Double Zero brand). Other seven brands showed intermediate values of U-contents which are also reported in this paper. These values are compared with the U-contents reported in the literature for other forms of tobaccos.     

Synthesis of polyfluoroaryl [2.2] cyclophanes

New and improved syntheses of 4,5,7,8-tetrafluoro- and 4,5,7,8,12,13,15,16-octafluoro[2.2]paracyclophanes are described. The preparation of the new compound, 4,5,7,8-tetrafluoro[2.2]metaparacyclophane, is outlined.     

Viscosity dependence of the fluorescence lifetimes of cryptocyanine,pinacyanol and DDI

Viscosity dependence of the fluorescence lifetimes of cryptocyanine, pinacyanol and I, I'-diethyl-2,2'-dicarbocyanine iodide (DDI) has been studied by making relative quantum yield measurements in five solvents. It has also been established. by means of flash kinetic spectroscopy, that, in rigid solvents, φ^o_F+φ^o_IC ≈ 1 for all three dyes, where φ^o_F and φ^o_IC stand for the intrinsic quantum yields of fluorescence emission and internal conversion, respectively. Values of the intrisic rate constant of internal conversion are also presented.     

Magnetic field effects on spin-rephasing in a photochemically produced radical pair investigated by a double-pulse technique using a nitrogen laser

The effect of an external magnetic field on the yield of the benzophenone ketyl radical has been investigated by a new, double-pulse technique. The technique and its variants can be used not only for studying geminate recombination of photochemically produced radical pairs but also for continuous photoelectric recording of fluorescence spectra of the free radicals which can be generated by nitrogen laser irradiation.