Distance between exposed object and exposure source
The suspension was filled in 0.4 ml polypropylene microcentrifuge tubes of 0.4 cm diameter and 4.5 cm length with a 0.05 ml air gap remaining at the top after capping. In the first experiment, sample tubes were placed in a stationary Styrofoam sample holder with the long axis of each tube parallel to the E-fieldvector. For all further experiments, a rotating sample holder was used to achieve identical exposure of all tubes. They were inserted in radial holes in a Styrofoam disk held in the vertical position by a long Teflon shaft of 2.5 cm diameter turned at 2 rpm by a motor shielded by RF-absorbing material. The vertical rotation (reversed every minute) caused a continuous mixing of the suspension.
In the first experiment, irradiation was interrupted every 10 min in order to measure the temperature of the samples. In all further experiments, the temperature was continuously monitored using an LCOF probe. The matchedthermal profile control samples were heated in a water bath (first experiment) or in a hot air incubator with a rotating sample holder.