Development of a high-power water cooled beryllium target for use in accelerator-based boron neutron capture therapy.

In order for ABNCT (accelerator-based boron neutron capture therapy) to be successful, 10-16 kW or more must be dissipated from a target. Beryllium is well suited as a high-power target material. Beryllium has a thermal conductivity of 200 W/mK at 300 K which is comparable to aluminum, and it has one of the highest strength to weight ratios of any metal even at high temperatures (100 MPa at 600 degrees C). Submerged jet impingement cooling has been investigated as an effective means to remove averaged power densities on the order of 2 x 10(7) W/m2 with local power densities as high as 6 x 10(7) W/m2. Water velocities required to remove these power levels are in excess of 24 m/s with volumetric flow rates of nearly 100 GPM. Tests on a prototype target revealed that the heat transfer coefficient scaled as Re0.6. With jet-Reynolds numbers as high as 5.5 x 10(5) heat transfer coefficients of 2.6 x 10(5) W/m2K were achieved. With this type of cooling configuration 30 kW of power could be effectively removed from a beryllium target placed on the end of an accelerator. A beryllium target utilizing a proton beam of 3.7 MeV and cooled by submerged jet impingement could be used to deliver a dose of 13 RBE cGy/min mA to a tumor at a depth of 4 cm. With a beam power of 30 kW, 1500 cGy could be delivered in 14.2 min.