Design and construction of a facility for neutron activation analysis using the 14 MeV neutron generator at HMS Sultan

The potential for using a small, sealed tube, DT neutron generator for neutron activation analysis has been well documented but not well demonstrated, except for 14 MeV activation analysis. This paper describes the design, construction and characterization of a neutron irradiation facility incorporating a small sealed tube DT neutron generator producing 14 MeV neutrons with fluence rates of 2·10⁸ s⁻¹ in 4π (steady state) and 10¹¹ s⁻¹ in 4π (pulsed). Monte Carlo modeling using MCNP4c and McBend9 has been used to optimize the design of this facility, including the location of a thermal irradiation facility for conventional neutron activation analysis. A significant factor in designing the facility has been the requirement to conform with Ionising Radiation Regulations and the design has been optimized to keep potential radiation doses to less that 1 μSv/h at the external walls of the facility. Activation of gold foils has been used for flux characterization and the experimental results agree well with the modeling.     

Synthesis, spectroscopy, and theoretical calculations for a series of push-pull [14]-pyridoannulenes

Three new isomeric dipyridoannulenes were synthesized and characterized. These molecules possess differing conjugation pathways between the substituent alkoxy donating groups and the pyridyl acceptor groups. Optical absorption and emission properties of the dipyridoannulenes and their corresponding acyclic precursors were measured and correlated to structural differences and used to evaluate conjugation effectiveness and charge-transfer pathways. Optical properties of protonated dipyridoannulenes were also measured and found to be somewhat insensitive to the degree of protonation. Density functional studies of these systems at the B3LYP/6-31G* level provided insight into their stabilities, polarities, and quinoidal character. An analysis of the HOMO and LUMO molecular orbitals provided further information regarding charge-transfer behavior. These systems are good metal binding candidates, as the pyridine moiety can act as both an electron-acceptor and a site for metal coordination.     

On The Orders of Automorphism Groups of Finite Groups

In the Kourovka notebook, Deaconescu asks whether |AutG|(|G|)for all finite groups G, where denotes the Euler totient function,and whether G is cyclic whenever |AutG|. Both questions areanswered in the negative in this paper. Moreover, |AutG|/(|G|)can be made arbitrarily small. 2000 Mathematics Subject Classification20E36 (primary), 20F28 (secondary).     

Assembly of a tri-silver metallo-capsule incorporating a tripodal tris-pyridyl ligand

A trinuclear metallo-capsule has been assembled from a new tripodal pyridyl ligand and three silver(I) ions; the X-ray structure shows the presence of a Ag-Ag interaction in the solid state giving rise to a non-symmetric capsule arrangement while NMR evidence indicates that the structure in solution is symmetrical.