Two of the most important observables for understanding Quark-Gluon Plasma (QGP) physics are quarkonia suppression and the energy loss process. Although, quarkonia are compound objects, it is usually advocated that their production at intermediate $p_{T}$ follows a behaviour similar to the one of single particles, like for instance D mesons. Ultimately, this kind of study will bring more information about the way in which the QGP thermalize the energy during the hadronization process. We will be  focus in explore the production of charmonia as function of  at mid-rapidity in central collision for lead-lead and proton-proton cases.

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1. Ralite¹, C. Koumeir², V. Metivier¹, N. Servagent¹

 

¹Laboratoire SUBATECH, IMT Atlantique, CNRS-IN2P3, Université de Nantes/Nantes/France

²GIP ARRONAX/Saint-Herblain/France

 

Heavy charged particle beams demonstrated strong ballistic advantages in cancer treatment by delivering a high and localized deposited dose to tumor cells (Bragg Peak). The development of particle therapy requires accurate online beam monitoring tools and experimental data for radiobiology field¹. In this frame, a radiobiology platform is in development at the cyclotron ARRONAX². First, the experimental set-up development to irradiate cells at the Spread-Out Bragg Peak (SOBP) with alpha particles is presented.  A second work exposes a non-invasive method to monitor online proton beams used in radiobiology experiments, investigating the feasibility to use the bremsstrahlung X-rays coming from a PMMA target, as a biological medium surrogate.

 

Alpha beam of 68MeV irradiated Chinese Hamster Ovary (CHO) cells placed at different step of the SOBP. The SOBP was built by weighted summing Bragg Peaks obtained with aluminium targets of different thicknesses which decreased the initial beam energy. Aluminium thicknesses and Bragg peak weight factor were determined with Monte-Carlo simulations. The set-up physic validation was performed by measuring the SOBP with radiochromic films.

Concerning the beam monitoring part, the experimental set-up irradiated a PMMA target with proton beams in the energy range of 17MeV/u to 50MeV. The detection of the bremsstrahlung X-rays coming from the target surface was performed by a silicon drift detector. A model based on the theoretical bremsstrahlung cross sections³ was developed to compare the experiment data to simulations. The differential cross sections were previously measured on carbon target in order to valid the model on a single element target and to compare the results to data available in the literature⁴.

 

            Radiochromic film results validated the experimental set-up to irradiate CHO cells at the SOBP with an alpha beam. According to simulations, the interest region of the SOBP was 760µm large in water with a dose homogeneity of 8%. The deposited dose delivered to cells were between 2Gy and 8Gy. However the set-up does not allow to monitor the deposited dose desired because of the radiation time and the intensity beam fluctuations.

Bremsstrahlung cross sections were in the range of 10 mbarns.keV^-1 to 1000 mbarn.keV^-1. A significate agreement was found with the model and the literature. Moreover, simulations fitted the bremsstrahlung spectra of the PMMA target confirming the significate sensibility of the method (10⁴ X-rays/nC detected). According to the set-up used, proton beam energy can be monitored with the bremsstrahlung X-rays because of the spectrum hardening. The PMMA thickness can also be monitored until a thickness limit where the bremsstrahlung yield saturates.

 

The experimental set-up to build the SOBP with alpha particles have to be improved to deliver the deposited dose faster to overcome the beam fluctuations and to control the deposited dose to cells.

The beam monitoring method described is only valid for the set-up used because of the detector efficiency and the X-ray attenuation, and should be improve by investigating other X-rays detectors. Fundamental studies are also expected to link the bremsstrahlung signal to the deposited dose in the biological medium, in order to apply the method to dosimetry applications in radiobiology and medical fields.

 

Keywords: Bremsstrahlung X-rays, Ion beam Monitoring, Radiobiology

 

References

1. L. Schwob et al, New beam monitoring tool for radiobiology experiments at the cyclotron Arronax, Radiation Protection Dosimetry, 166(1-4), 257-60, (2015).

2. F. Haddad et al. Arronax, a High Energy and High Intensity Cyclotron for Nuclear Medicine, Eur. J. Nucl. Med. Mol. Imaging, 35, 1377-1387, (2008).

3. K. Ishii et al, Continuous X-rays produced in light-ion-atom collisions, Radiation Physics and Chemistry, 75, 1135-1163, (2006).

4. K. Ishii et al, Theoretical detection limit of PIXE analysis using 20MeV proton beams, Nucl. Instr. and Meth. In Phys. Res. B, 417, 37-40, (2018).

 

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