Speakers
Description
The ion-acoustic effect generates images of the ion-dose distribution
from the ultrasound produced when an energetic, fast pulse of ionizing
particles interact in an appropriate medium. We recorded the light excited in a liquid scintillator as a cross-check of the waves simultaneously
recorded using ultrasonic sensors.
In earlier work we used ANSYS ZEMAX in non-nequential ray-tracing
mode to simulate the optical image, from two orthogonal directions, that
would be recorded in our phantom filled with UltimaGoldXR liquid scintillator. Our ultrasonic characterisation of UltimaGoldXR (acoustic attenuation coefficient at 22 ◦C was $$
0.19f^{1.75} $$
, where f is frequency in range 1.5 to 3.5 MHz. The
speed of sound was 1479 m/s) demonstrated that it was an appropriate
medium in which to generate and detect an ion-acoustic signal and we
used the LION beamline at the Centre for Advanced Laser Applications,
Garching to generate proton beams with nominal peak energies from 10
to 20 MeV.
Here we compare measurements made of the deposited energy as a
function of depth, estimated by Monte Carlo modelling of particle transport starting with entry dose measured 5 cm before entry into the phantom
using radiochromic film stacks, with a ZEMAX simulation that includes
absorption and scattering from black anodized surfaces, black Kapton and
a realistic model of the optical system including coatings on the lenses. We
evaluate the correlation between the two different methods of determining
the three-dimensional energy profile. This work updates our previous simulation which assumed an ideal beam from the accelerator and we discuss
the challenges of measuring and simulating the complexities of the real
3D beam profile within the liquid scintillator.