Coincidence measurements on the decay of Tm (87 d)

The decay of ¹⁶⁸Tm(87 d) has been studied with Ge(Li) detectors in singles and in coincidence with a NaI detector. The energies and intensities of the following previously established transitions were obtained: 79.8, 99.3, 173.8, 184.4, 198.3, 273.0, 348.5, 4.22.2, 447.6, 546.8, 557.0, 631.7, 645.75, 673.7, 720.4, 730.7, 741.4, 748.25, 816.0, 821.1, 829.9, 914.8, 928.9, 1014.2, 1167.3, 1277.3, 1323.7, 1351.4 and 1461.5 keV. Additional γ-ray transitions at 284.5, 853.2, 1262.6 and 1489.7 keV were observed. These data were combined with the available internal conversion electron data to obtain internal conversion coefficients. Branching ratios for E2 transitions de-exciting levels in the gamma band and E1 transitions de-exciting the negative-parity states were calculated and compared with theoretical estimates. Prompt and delayed coincidence measurements were carried out using a 2 mm Ge(Li) detector and a 7.6 cm × 7.6 cm NaI detector. Gates were set at 79.8, 99.3, 184.4, 198.3 and 447.6 keV and on transitions in the region from 700 to 850 keV. The delayed coincidence measurements were made to investigate the population and decay of the 0.12 μsec state at 1094.1 keV and support the placement of the 348.5 keV transition in the decay scheme. A revised decay scheme is presented.     

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Semi-Resonant Interactions and Frequency Dividers

A theory describing the behavior of a system as it evolves slowly through internal nonlinear resonances is presented. The energy sharing process is seen to be quite complex as it depends crucially on both nonlinear and frequency detuning effects. Two phenomena are discussed in detail although the general ideas are applicable to many situations. Firstly we examine the interaction between the quadratically coupled oscillators whose natural frequencies are in the ratio 2:1 for a limited period of time. Such a system is shown to be an extremely useful switching device. Secondly we examine the time dependent Duffing equation and find that smooth forward and reverse transitions occur without the presence of dissipation.     

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Total synthesis of (+/-)fasicularin via a 2-amidoacrolein cycloaddition

The total synthesis of the cytotoxin fasicularin is described. The key steps include the following: (1) an intermolecular Diels-Alder cycloaddition of a 2-(triflamido)acrolein with the dioxolane ketal of trideca-1,3-dien-7-one to establish the trans-perhydroisoquinoline stereochemistry, (2) a stereoelectronically controlled hydride addition to a N(1)-C(2) iminium ion to introduce the equatorial hexyl substituent, and (3) elaboration of the pyrido ring by an internal aldol reaction.