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Dense samples of cold Rydberg atoms have previously been observed to spontaneously evolve to a plasma, despite the fact that each atom may be bound by as much as 100 cm −1 . Initially, ionization is caused by blackbody photoionization and Rydberg-Rydberg collisions. After the first electrons leave the interaction region, the net positive charge traps subsequent electrons. As a result, rapid ionization starts to occur after 1 s caused by electron-Rydberg collisions. The resulting cold plasma expands slowly and persists for tens of microseconds. While the initial report on this process identified the key issues described above, it failed to resolve one key aspect of the evolution process. Specifically, redistribution of population to Rydberg states other than the one initially populated was not observed, a necessary mechanism to maintain the energy balance in the system. Here we report new and expanded observations showing such redistribution and confirming theoretical predictions concerning the evolution to a plasma. These measurements also indicate that, for high n states of purely cold Rydberg samples, the initial ionization process which leads to electron trapping is one involving the interactions between Rydberg atoms.

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Ripening changes were studied in plantains of three cultivars, two Horn types and one French type, and compared with those in bananas ripened under the same conditions. Bananas contained 1% starch when fully ripe and none when overripe, whereas plantains contained about 9% starch when fully ripe and 3 % when overripe (composition expressed as percentage fresh weight). Total sugar content was 23 % in fully ripe and overripe bananas but in plantains it increased from 20% when fully ripe to 27% when overripe. The ratio of glucose: fructose was approximately unity for bananas and plantains at all stages of ripeness. Sucrose comprised more than 70% of the total sugars in fully ripe bananas and plantains and about half of the total sugars in overripe fruits.