Cooling grain model

Note. The closure temperature (see later discussion) depends on grain size and cooling rate here it is calculated for a radius of 0.1 mm and a cooling rate of 5 K/Myr (Brady, 1995). Cylinder shape model means that the grains are treated as infinitely long cylinders with diffusion along the cross section (in the plane Ic). 

The only 25-mm Gun used by the Japanese was Type 96 Model 2 AA-A/Tk Gun. It was multiple-barreled, air-cooled, magazine-fed, automatic weapon. Used different projectiles, but the same propellant which consisted of 120g of single-perforated graphited cylindrical grains of NC (p 446)... 

The rates at which parent bodies cooled also provide constraints on thermal models. A method for determining the cooling rates for iron meteorites is described in Box 11.2. A similar method for chondrite cooling rates is also based on the compositions of metal grains. Cooling rates can also be estimated from knowing the blocking temperatures of various radioisotope systems. 

Figure 7. A and B. Map and topographic cross-sectional view of sample locations from Shuster et al. s (2005) study of incision of the Kliniklini valley, Coast Mountains, British Columbia. C. Model thermal histories for each sample, derived from 4He/3He evolution of step-heating experiments on proton-irradiated samples, and bulk grain (U-Th)/He dates. Samples from the valley bottom require rapid cooling, from 80 °C to surface temperatures, at 1.8 0.2 Ma, and samples from higher elevations require thermal histories with progressively smaller extents of cooling (beginning at 1.8 Ma) with elevation. The highest sample (TEKI-23) was at surface temperature before the 1.8 Ma cooling event experienced by the other samples. Collectively, these data are interpreted to be the result of -2 km incision at 1.8 Ma. After Shuster et al. (2005).

The grains that formed in the solar nebula are believed to have been produced by direct condensation as the nebular gas cooled (see also Chapter 4). If the thermodynamic properties of the reactants and mineral products are known, it is possible to model the condensation of solids by allowing a gas of any initial composition to cool. Larimer (1967) pioneered the application of this technique to the condensation of minerals in the solar nebula. A limitation of it is that minerals whose thermodynamic properties have not been determined cannot be included in the modeling, and computer limitations generally require that the number of minerals that are included in any model must be restricted. 

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