Figure 2
Experimental approach for observing the SPIRE. (a) The pulse shape as measured by a beam intensity monitor and (b) the Bragg curve as measured by an ionisation chamber. (c) Schematic of the experimental setup for the SPIRE measurement using an LFH. A 100 MeV pulsed proton beam produced by an FFA was injected into the water phantom at a frequency of 30 Hz. The temperature of the water was kept at 22 °C. A gold marker with a diameter of 2 mm was placed on the beam axis and the SPIRE emitted from the marker was collected by the LFH. The residual range at the marker was changed by stacking acrylic plates on the phantom surface. For each beam pulse, the shape of the pulse was monitored by counting the lost protons, stray neutrons and gamma-rays using an EJ-200 plastic scintillator mounted at the exit of the vacuum beam duct. For each separate run, the scintillator signal height was converted to the number of protons measured using the Faraday cup. (d) Photograph of the gold marker and hydrophone setup in the water phantom. A stand with a conical tip with a slit was made to support the gold marker underwater. The stand was made of ABS resin that had an acoustic impedance close to that of water. The hydrophones were mounted on an XY stage that can scan in a plane parallel to the beam direction; they were set at position where the pressure amplitude is maximized. (e) Photograph of the LFH. A PZT piezoelectric ceramic processed into a spherical shape was used to improve the sensitivity. The focal length was set to 25 mm to have the maximum solid angle centred at the marker while keeping a sufficient distance from the proton beam.
