The Sloan-Kettering Institute CS-15 compact cyclotron was the first prototype built by the Cyclotron Corporation. The description of the RF system for this machine has been reported by Hendry( The original automatic frequency control used a stable tuned frequency discriminator. However, for various reasons, into service. this unit had never been put In addition, unlike the newer model machines which employed a series pass tube for anode voltage control and regulationc2), our anode supply did not have such a device. Therefore the long term drift down of dee voltage had been quite appreciable. As a result, the external beam current was very unstable and a full time operator had to sit before the console constantly making necessary adjustments.

1. The results of a calorimetric determination of the energy flux of 22·5-MeV X rays relative to ionization measurements have been reported. 2. The energy flux has been related to the rontgen as measured according to a specified convention. 3. The absolute number of quanta/cm.2-r as a function of energy has been obtained from the experimental data and compared with calculated values. 4. A method of obtaining the energy absorbed in water in ergs per gm/r utilising this calorimetric energy flux determination together with existing dose distribution measurements has been outlined. A value has been calculated in terms of the ergs/gm.-r (M) and the ergs/gm-e.s.u./c.c. 5. An alternative convention for evaluation of the rontgen from depth-dose measurements is presented in the appendix.