Y. Tzuk

Dynamics of the detonation products of lead azide. I. Hydrodynamics

The present paper is the first of a series reporting on a comprehensive study of the hydrodynamics, kinetics, and spectroscopy of the transient species formed following the detonation of lead azide (LA). The spatial and temporal behavior of the detonation products expanding into vacuum is obtained via high‐speed framing photography, transmission of a HeNe laser beam, and chemiluminescence from excited Pb atoms. The photography reveals that following the initiation of LA the products form an expanding, bell‐shaped cloud. The HeNe beam is attenuated when the cloud of products traverses its route. The attenuation starts 4–15 μs after initiation and depends on the height of the beam above the LA sample. The chemiluminescence consists of two components: the first, appearing 1–2 μs after initiation, is obtained from excited products formed by the detonation near the surface of the sample, while the second, starting 2–14 μs after initiation, originates from the expanding cloud of products.The intensity and the t...

The sudden expansion of a gas cloud into vacuum revisited

The sudden expansion into vacuum of a gas cloud, with initial centrally symmetric density and temperature profiles, is studied theoretically for different values of the specific heat ratio γ. Models treating the expansion are discussed, in particular, a model for isentropic expansion and a model for spatially isothermal expansion. For γ→1, the density of the gas obtained from the former model for late stages of the expansion, approaches a Gaussian spatial profile which is the exact solution to the latter model. A description by a Gaussian profile can be, for some important cases, approximately correct even for large deviations of γ from one. For a spherically symmetric flow, the maximum difference (for any given time and distance from the center of symmetry) between the densities obtained from the above two models is 11% for γ=7/5. For γ=1.28, which corresponds to the expansion of lead azide detonation products previously studied in the author’s laboratory, the difference is 9%. It is also shown that in p...

Preferential excitation and enhanced emission of Pb atoms following detonation of lead azide

Preferential excitation of the 3P°1 state of the lead atom and enhanced emission in the Pb(3P°1Pb(3P°1→1D2) transition at 722.9 nm have been observed following the detonation of lead azide, Pb(N3)2. The detonation is initiated by a short laser pulse and the products are expanded through a supersonic nozzle. It is suggested that the enhanced emission is due to preferential excitation of Pb(3P°1) via energy transfer from electronically excited N2 combined with the effect of self‐trapping of the emission from 3P°1 to the 3P0,1,2 states. The implications to short‐wavelength chemical lasers are discussed.

Multiple charge reaction cell for studies of primary explosives

A reaction cell for the detonation of primary explosives is described. The cell is 250 mm in diameter and contains 30 samples, which can be initiated consecutively using a laser beam. A manually driven mechanism is used to locate each charge in its turn in a central firing position without having to break the vacuum. Eight 3‐in. observation windows and four 0.25‐in. feedthrough ports allow recording and analysis of the emission resulting from the detonation products. The design provides a means for protection against accidental explosion. The cell is currently being used for spectroscopic studies of the gaseous reaction products obtained from the detonation of lead azide.

Dynamics of the detonation products of lead azide: III. Laser‐induced hole burning and flow visualization

The cloud of products formed following the detonation of lead azide (LA) contains solid particles. Utilizing a pulsed beam of a neodymium: yttrium aluminum garnet (Nd:YAG) laser, the particles are evaporated and hole burning through the opaque cloud is demonstrated. The characteristics of the hole and of the expanding cloud are monitored in real time by a HeNe beam, high‐speed framing photography and emission of excited Pb atoms. The hole is carried with the cloud and propagates at a constant velocity of 0.5–2.8 km/s, depending on the time and location of burning and given by d(h)/t(h), where d(h) is the distance from the LA sample to the center of the Nd:YAG beam and t(h) is the time from detonation to hole burning. The reduction in the number and size of the particles is monitored by scanning electron microscopy of the deposits formed on a substrate following the detonation. The propagation of the Nd:YAG laser pulse through the cloud is numerically modeled and provides an estimate of the increase in the...

Real-time measurement and control of particle-number density and size of the detonation products of lead azide

Time-resolved measurement and modeling of the number density and size of lead particles produced following the detonation of Lead Azide (LA) are presented. Particles expanding freely into vacuum through a supersonic nozzle or interacting with a barrier placed above the LA sample are monitored via attenuation of laser beams at 0.67, 1.3 and 10.6 µm. The attenuation depends on the conditions of expansion, but is always much more pronounced at 0.67 µm and 1.3 µm. From the ratio between the attenuations at 0.67 µm and 10.6 µm, the radius and number density of the particles are calculated applying Beers law and Mies theory. It is found that 20–90 µs following the detonation the attenuation at 32–36 mm above the LA sample is due to particles with radii of ≈0.9, ≈0.7 and ≈0.1 µm for free expansion into vacuum through the nozzle or near the barrier, respectively. Also, the expansion through the nozzle results in a transparent medium above the nozzle exit for the first few µs following the detonation. The effect of the nozzle is attributed to the fact that the velocity of the expanding detonation products is supersonic, which leads to compression and heating in the throat region, in contrast to the more familiar phenomenon of cooling at subsonic velocities. The dynamics of particles expanding under the different conditions and the mechanism of size reduction and elimination of particles is discussed.

Dynamics of the detonation products of lead azide. IV. Laser shadowgraphy of expanding species

Laser resonant shadowgraphy (LRS) and laser nonresonant shadowgraphy (LNRS) are used to monitor the detonation products of lead azide. Photographs of the cloud of products are obtained via illumination with a doubled dye laser tuned on‐resonance to the 3P1o‐3P0 transition of the Pb atom at 283.31 nm, and off‐resonance at 284.31 nm. The versatility of the diagnostics and its applicability to detonation products expanding into vacuum and into atmospheric pressure air are demonstrated. The LRS monitors the density gradients of both lead atoms and solid particles formed in the detonation, whereas the LNRS detects only the latter. Expansion into vacuum through a nozzle leads to an increase in the velocity (from ∼4.5 to ≳5 km/s) and density of the atoms and to a decrease in the density of the particles. The LRS measurements show that the expansion of both products in air is relatively slow (∼0.75 km/s) and leads to production of shock waves. From the shape of the shock waves created by an obstacle when the prod...

Laser-induced hole-burning and flow visualization in the cloud of products of detonated lead azide

Utilizing a pulsed beam of a Nd:YAG laser, hole burning through the opaque cloud of products formed following the detonation of lead azide is demonstrated. The characteristics of the hole and of the expanding cloud are monitored in real time by a HeNe beam and by high‐speed framing photography. The hole is carried with the cloud and propagates at a constant velocity of 0.5–2.8 km/s, depending on the time and location of burning. The hole burning is a result of eliminating solid particles from the cloud. The application of a laser to burn a hole in the detonation products from a solid explosive is demonstrated for the first time. This technique may serve as a method for flow visualization in an aerosol medium.

Overview Of Pulsed Premixed Short Wavelength Chemical Laser Concepts

All efforts to obtain short wavelength (< 1 gm) chemical lasers (SWCLs) have failed to date. The reasons for failure and possible ways to overcome the difficulties are discussed. In particular, a novel approach to obtaining SWCLs based on a premixed fuel-lasant capable of producing high energy pulses, is described. Electronically-excited nitrogen molecules are produced by detonation of metal azides. Lasing is expected via energy transfer from the nitrogen molecules to metal atoms or within the nitrogen molecules. Preliminary results obtained by detonation of lead azide are presented. Calculations based on a coupled hydrodynamic-kinetic model point out that the detonation should result in population inversion between potential laser levels of lead atoms.

Expansion of the detonation products of lead azide via a supersonic nozzle

The cloud of products formed following the detonation of lead azide (LA) contains gaseous species and solid particles. The dynamics of the detonation products expanding freely or through a supersonic nozzle into vacuum is unraveled via the temporal profiles of the pressure, the emission from Pb atoms and the attenuation of a He-Ne beam. The velocity of the fastest gaseous species is found from the onset of the pressure rise and the emission at a given distance from the LA sample, and the velocity of the fastest solid particles from the attenuation. In the free expansion, the respective velocities are 4.5±0.1 and 3.8±0.2 km/s and in the nozzle expansion 5.1±0.2 and 1.4±0.2 km/s. The expansion into atmospheric pressure air is also monitored and found to be much slower than that into vacuum. The utilization of nozzles as a means for obtaining a particle free, transparent medium of detonation products is stressed in the context of exploiting explosives for achieving chemical lasers in the visible wavelength region.