Secondary isochron

That there is hope of finding terrestrial rocks somewhat older than 3,500 m.y. is implied in the secondary isochron study of igneous rocks about l,900-m.y.-old from the Churchill province in Canada (Doe, 1967). The slope of leads from three feldspars (A Pb/ Pb)/( A Pb/ Pb) is 0.521 the source age (t) may then be 3,800 m.y. 

For constant-frequency (sometimes referred to as isochronal) experiments on amorphous polymers, the highest temperature relaxation is the glass transition, also referred to as a, while secondary p and y relaxations are commonly observed. There also may be a 8 process. In this case all the relaxations are associated with the amorphous phase. The y and 8 relaxations (and in certain cases also the p relaxation) are below -100 °C. These relaxations would be missed if the only cooUng device available were a mechanical chiller that would cool to only -100 °C. Figure 5.18 illustrates the various loss peaks associated with the transitions in amorphous and crystalUne polymers. 

Many other secondary viscoelastic mehcanisms observed in the glassy state have been tentatively identified with various types of local molecular motions with less specific descriptions than in the case of the cyclohexyl group. Most of these identifications are based on isochronal rather than isothermal measurements. 

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