New beam monitoring tool for radiobiology experiments at the cyclotron ARRONAX

Abstract

The ARRONAX cyclotron is able to deliver alpha particles at 68 MeV. In the frame of radiological research, a new method is studied to infer in situ the deposited dose: it is based on the online measurement of the bremsstrahlung (>1 keV) produced by the interaction of the incident particle with the medium. Experiments are made using bombarded poly(methyl methacrylate) (PMMA)-equivalent water targets in order to characterise this continuous X-ray spectrum. The intensity of the bremsstrahlung spectrum allows for the beam monitoring. A simulation code of the bremsstrahlung has been built, and a good agreement is found with the experimental spectra. With this simulation, it is possible to predict the sensibility of this method: it varies with the target thickness, showing a good sensibility for thin target (<1000 µm) and saturation for thicker ones. Bremsstrahlung spectrum also shows a sensibility on the target's chemical composition.

Bremsstrahlung X-rays as a non-invasive tool for ion beam monitoring

“…The SDD promotes the detection of the Xrays with low-energies and can minimize the targetdetector distance (due to its compact design). These points improve the sensitivity of the measured bremsstrahlung signal, as predicted by Schwob et al [24]. The significant measured signal (>10 4 Xrays/nC) allows the use of the bremsstrahlung Xrays as a non-invasive tool for ion beam monitoring in case of radiobiology experiment.…”

“…The differential bremsstrahlung cross section 𝑑 2 𝜎 𝐵𝑟 𝑑𝛺𝑑ℎ𝜈 decreases while the photon energy ℎ𝜈 increases [25,29].To improve the statistics of the detected X-rays, the detection of low-energy photons has to be maximized. The SDD seems well adapted as its detection efficiency is optimal between 3 and 14 keV (as shown in Figure 1) [24]. The SDD detector efficiency is determined according to the model of Mohanty et al [31].…”

“…Previous works performed at the ARRONAX facility proved the capability of bremsstrahlung X-rays to monitor the deposited dose induced by an alpha beam of 68 MeV [24]. The sensitivity found with an HPGe detector was around 90 X-rays/Gy.…”

“…The sensitivity found with an HPGe detector was around 90 X-rays/Gy. The present work follows the ones of Schwob et al [24]. We modified the experimental set-up to increase the number of detected photons emitted from a Polymethyl Methacrylate (PMMA) target used as a biological medium surrogate thanks to its effective atomic number close to water.…”

“…The dependence of the bremsstrahlung signal with the medium thickness and the beam energy was studied. The latter properties are of importance to monitor the deposited dose and the beam energy into radiobiology experiments [24]. The beam energy dependence of the bremsstrahlung spectrum shape was also studied.…”