Initial thermal radiation

The overall duration of the emission of initial thermal energy varies with energy between values of a fraction of a second for low energies and values of tens of seconds for the higher energies (10 Mt and higher). 

As already mentioned, it is assumed that about 35 per cent of the energy released is transmitted as initial thermal radiation. 

The total energy deposited on objects on the ground and for unit surface is, then, approximately proportional to the inverse of the cube of the distance in air. 

It can be assumed that any combustible material catches fire for a value of this specific energy equal to 40 J cm-2 (= 400 kJ m- ). 

For an explosion of 1 Mt, about 40 J cm at 3000 m in air from the explosion centre can be observed. Other values can be obtained by the simple scaling laws above. 

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Fay and Lewis (1977) used spherical gas samples inside soap bubbles whose volumes ranged from 20 to 190 cm. Typically, a sphere was ignited with resistance wire, and the combustion process was then filmed with a high-speed camera. The fireball s maximum height and diameter, as well as the time needed to complete combustion, were evaluated. The fireball s thermal radiation was sensed by a radiation detector. Figure 6.3 relates fireball burning time and size to initial propane... 

The first published examples of hydrosilation, which appeared about 30 years ago, noted that they were observed to proceed by free-radical mechanisms initiated thermally (about 300°C) (J), by acyl peroxides (4), by azonitriles (5), by ultraviolet light (6), or by y radiation (7). The first hint that catalysts known to be effective for hydrogenation might also be effective for hydrosilation was found in a French patent (8) (1949) which stated that catalysts may be chosen from compounds and salts of the elements of Groups IIA, IVA, IB, and IIB of the periodic table and metals of Group VIII and certain of their salts. No example to demonstrate this was included in the patent. 

Aldehydes are oxidized by dioxygen by the chain mechanism in reactions brought about in different ways initiated, thermal, photochemical, and induced by radiation as well as in the presence of transition metal compounds [4-8]. Oxidation chains are usually very long from 200 to 50,000 units [4], Acyl radicals add dioxygen very rapidly with a rate constant of 10s—109 Lmol V1 [4], Therefore, the initiated chain oxidation of aldehyde includes the following elementary steps at high dioxygen pressures [4-7] ... 

The radical polymerization of ethylene, in practice, is initiated by free-radical initiators, although radiation-induced,155 210 photoinduced,211-213 and thermal213,214 initiations are also possible. The temperature of high-pressure polymerization should not exceed 350°C since above this temperature a rapid exothermic (AH = —30.4kcal/mol) thermal decomposition of ethylene can take place leading to a runaway reaction ... 

Radiological warfare(RW) may be defined as the employment of agents or weapons to produce residual radioactive contamination,as distinguished from the initial effects of a nuclear explosionfblast, thermal, and initial nuclear radiation) defense against such warfare (Ref 12,p 233)... 

In the flame of a mixture of gas and air, the gas is also heated before the flame front, but this heating occurs in the presence of oxygen and the pieces of hydrocarbon molecules that could become the initial centers of formation of soot are immediately oxidized. As a result the thermal radiation of the flame of the mixture turns out to be significantly lower and the temperature significantly higher than in the flame of a non-premixed gas, although the... 

A basic requirement of the ESR technique is the presence of molecules or atoms containing unpaired electrons. Such species can be generated in polymeric systems by homolytic chemical scission reactions or by polymerization processes involving unsaturated monomers. These reactions can be initiated thermally, photochemically, or with a free-radical initiator, and, in the case of scission, by mechanical stress applied to the system. Therefore, ESR can be used to study free-radical-initiated polymerization processes and the degradation of polymers induced by heat, light, high-energy radiation, or the application of stress. 

Free radicals and atoms appear as intermediates in a wide range of processes. Almost all photochemical reactions initiated by radiation in the visible or ne2ur ultraviolet regions of the spectrum are propagated by radicals or atoms (but see Section 1.4 for the photochemical formation of ions). Similarly, combustion processes are believed to occur predominantly by a radical mechanism, as are a large number of other thermal reactions. 

Although the output of primer is known to consist of hot particles, a pressure pulse (in some cases a shock wave), and thermal radiation, no general quantitative requirement for initiation of lead azide is known to designers. Failures occur in igniting the primer, but once the primer bums, it always ignites the azide. Primer mixtures are complex, empirically determined compositions for which no general quantitative relationships are known. This situation makes it difficult to optimize them for a particular requirement, or to determine the cause of failures, except by trial and error. 

In the special case of a cavity filled in with a high-temperature thermal radiation, the initial distribution over modes reads v (0) = (-)/ , where the constant 0 is proportional to the temperature. Then ... 

B. Surface Burst. A surface burst weapon is detonated on or slightly above the surface of the earth so that the fireball actually touches the land or water surface. The area affected by blast, thermal radiation, and initial nuclear radiation will be less extensive than for an air burst of similar yield, except in the region of ground zero where destruction is concentrated. In contrast with airbursts, local fallout can be a hazard over a much larger downwind area than that which is affected by blast and thermal radiation. 

C. Subsurface Burst. A subsurface burst weapon is detonated beneath the surface of land or water. Cratering will generally result from an underground burst, just as for a surface burst. If the burst does not penetrate the surface, the only other hazard will be from ground or water shock. If the burst is shallow enough to penetrate the surface, blast, thermal, and initial nuclear radiation effects will be present, but will be less than for a surface burst of comparable yield. Local fallout will be very heavy if penetration occurs. 

E. Enhanced Radiation (ER) Weapons. An enhanced radiation weapon has an output in which neutrons and x-rays are made to constitute a substantial portion of the total energy released. An ER weapon s total energy would be partitioned as follows 30% as blast 20% as thermal 45% as initial radiation and 5% as residual radiation. A 3-kiloton ER weapon will produce the nuclear radiation of a 10-kiloton fission weapon and the blast and thermal radiation of a 1-kiloton fission device. 

The ultimate loss of the HAS activity occurs by destruction of the heterocycle initiated thermally, photochemically, chemically or by high-energy radiation. An intramolecular H-abstraction from the p-carbon atom in thermolysis of 2,2,6,6-tetramethyl-4-oxo-piperidinyl-l-oxyl 133 via a general reaction (Eq. 8) was proposed as a pathway of thermal selfdestruction of the piperidine cycle [25] (Scheme 25). The respective hydroxylamine was isolated in the yield of 66.5%. The biradical intermediate 137 either dimerizes to nitroxide 138 or thermolyses via 139 to a nitrogen-free fragment 140 (phorone) and nitric oxide. 

These equations are commonly called pyrolysis relations, in reference to the thermal (as opposed to a possibly chemical or photonic) nature of the initiating step(s) in the condensed phase decomposition process. It can be seen that while the second, simpler pyrolysis expression with constant coefficient As) preserves the important Arrhenius exponential temperature dependent term, it ignores the effect of the initial temperature, condensed phase heat release and thermal radiation parameters present in the more comprehensive zero-order pyrolysis relation. These terms To, Qc, and qr) make a significant difference when it comes to sensitivity parameter and unsteady combustion considerations. It is also important to note the factor of 2, which relates the apparent "surface" activation energy Es to the actual "bulk" activation energy Ec, Es- E /1. Failure to recognize this factor of two hindered progress in some cases as attempts were... 

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