FIG. 2.

Photograph of the cabinet ¹³⁷Cs irradiator showing the position of the cell culture flasks that were irradiated with exponentially increasing and decreasing dose rates. The desired dose-rate pattern is achieved by varying the level of mercury in the attenuator (24). Each layer of flasks receives successively lower extrapolated initial dose rates as the distance from the ¹³⁷Cs source increases, however the dose rate increase and decrease half times are the same at each position.