Design of the double focusing magnet for mass separation of a ¹¹C⁺ radioactive ion beam

At NIRS, re-acceleration of unstable ¹¹C ion beam with the synchrotron for cancer therapy, HIMAC has been pursuit in order to enable the real-time imaging of irradiation distribution of carbon ion into malignant tumour. Up to now ¹¹C⁶⁺ ion beam has been tried with very limited intensities of ∼10⁵ per pulse created with the use of a nuclear reaction of accelerated ¹²C⁶⁺ ion beams by the HIMAC (so-called "Projectile Fragment Separation Scheme"). It was not possible to attain good enough signal to noise ratio to obtain a diagnosable imaging. Recently, the usage of ¹¹C ion beams, produced by irradiation of a high intensity proton beam coming from a cyclotron has been investigated. For this purpose, we have studied the separation of the molecular ¹¹CO₂⁺ ion beam from the overwhelming ¹²CO₂⁺ ion beam with the use of a double focusing magnet. The design of the double focusing magnet to supply ¹¹C⁴⁺ radioactive ion beam to the HIMAC injector to re-accelerate the ions for the cancer therapy will be presented. (author)