The plane-wave shock initiation of a plastic-bonded RDX explosive, initial density 1.60 g/cc, has been investigated by measurement of shock buildup to detonation using the explosive wedge technique. Impedance-match techniques were employed to determine the pressure and particle velocity associated with the shock in the explosive. Using a graphical representation in which the shock distance and time coordinates are referred to the beginning of detonation, a similarity between overlapping portions of buildup curves from different experiments, having different initial shock pressures, has been observed. While closer study of the data of this paper did not support the assumption of identical buildup curves, certain implications of such behavior, which have relevance to various models of initiation, are subject to experimental evaluation.

The plane-wave shock initiation of a large particle size tetryl has been studied at five pressing densities between 1.30 and 1.70 g/cc. The explosive wedge technique was used to observe shock buildup to detonation for a number of initial shock strengths, obtaining shock position data as a function of time. Single-curve buildup was assumed to determine values of the initial shock velocity in the explosive and these were used in the impedance-match solution to compute the initial shock parameters in the explosive. Quantitative expression of the measured time of shock run in terms of the computed shock strength leads to a set of initiation relations characteristic of the test explosive. Comparison of these initiation curves for different densities of tetryl suggests that at least two initiation mechanisms are effective in low-density tetryl. This interpretation is illustrated by discussing the data in terms of two theories of initiation which have appeared in the literature.

Relatively simple and accurate delayed-coincidence apparatus for the measurement of isomeric half-lives in the millisecond range is described. Practical aspects of the statistics of delayed-coincidence counting are discussed. Half-life measurements of Ta181m (17.83±0.10 μsec) and Y88m (300.5±5.0 μsec) are described.

The decay of the isotope Ba 133 , produced by pile neutron irradiation of Ba 132 , has been studied with a magnetic lens and scintillation spectrometers. Gamma rays of 0.079, 0.302, and 0.355 Mev have been measured, with relative intensities 1.00:0.71:2.1 and J£-conversion coefficients of 1.3±0.5, O.llrLO.07, and 0.07±0.05, respectively. Conversion electrons from weak transitions of energies 0.158 and 0.276 Mev have been observed and assigned to Ba 133 . Gamma-gamma coincidences have been measured and a decay scheme is proposed. The K/L capture ratio for Ba 133 is shown to be greater than 1.5.