The following plot shows an early experiment for spinodal in Al-Zn. The intensity of the the X-ray reaches a maximum at a particular wavenumber or wavelength.

* ( A ) 100 50 25 70 4 60 Aged at 65 .C I 0.5 min. 2 5.0 " 50 3 34.5 " 4 65.0 40 Intensity (cps) 30 20 10 4 O 2 B ( cm" )( x 10- ? ) Fig. 11-The evolution of the small-angle X-ray spectrum from an Al-Zn sample. Note the crossover point. It repre- sents a wavelength in the sample that is neither being ampli- fied or disappearing. 24