A study of positron annihilation of cyclodextrins

The authors have studied α- and #betta#-cyclodextrins by peak counting and lifetime methods. Lifetime measurements were done for α-cyclodextrin sample under the following conditions: 1) as-received or exposed to a wet atmosphere, 2) heated (800C) and evacuated for more than one day, 3) in nitrogen at atmospheric pressure, 4) in oxygen at 1, 2, 3.5 and 4.5 atmospheres pressure. The same experiment was also performed with #betta#-cyclodextrin under almost the same conditions. The I3 of the oxygen-adsorbed samples decreased as a function of the oxygen pressure. In the peak counting experiment, a decrease in peak counting rate was observed both in α- and #betta#-cyclodextrins as a function of the oxygen pressure only. The results are interpreted in terms of relations betwen pole-radius of cyclodextrins and various gases and the free volume seen from the positron in the sample and its interaction with adsorbed oxygen molecule. (Auth.)