Dosimetry

EBT3 GAFchromic films calibrated at INFN-LNL are currently used for dose assessment in the TOP-IMPLART accelerator.

Before implementing this dosimetry system, EBT3 films have been studied in terms of LET and dose rate dependence of the response at low energy.

LET dependence has been evaluated as Relative Effectiveness (RE) for 5 MeV proton beam with respect to gamma rays of the ENEA-Casaccia 60Co source. Dose rate dependence has been investigated in the (2.1- 40) Gy/min. The results of the study will be published on Medical Physics Journal.

LIF crystals and films

Irradiation of LiF crystals and films for solid state luminescent detectors

Lithium fluoride (LiF) is a well-known dosimeter material and it is sensitive to any kind of ionising radiation. Proton beams are used to irradiate at room temperature LiF crystals and thin films (produced at TECFIS MNF Laboratory) in the fluence range from 10¹⁰ to 10¹⁵ protons/cm². The irradiation of LiF induces the formation of primary and aggregate color centers, which are stable at room temperature. The aggregate visible-emitting F₂ and F₃⁺ color centers (two electrons bound to two and three close anion vacancies, respectively) possess almost overlapping absorption bands around 450 nm. Under optical pumping in this spectral region they simultaneously emit broad photoluminescence bands peaked at 678 nm and 541 nm for F₂ and F₃⁺color centers, respectively.

Proton Dosimetry

Color centers photoluminescence intensity is measured (TECFIS-MNF) both in LiF crystals and LiF films only 1 mm thick grown by thermal evaporation on glass and silicon substrates. They show linear optical response as a function of dose from 10³ to 10⁶ Gy and the results are encouraging for using LiF-based detectors for proton dosimetry over several orders of magnitude of dose range [M. Piccinini et al, J.Lum. 156 (2014) 170-174]. Experiments in the dose range from 1 to 20 Gy are in progress.

Proton beam and Bragg peak imaging

By optical fluorescence microscopy, it is possible to record the transversal proton beam intensity profile by acquiring the photoluminescence image of irradiated LiF. It showed to be a versatile radiation imaging detector, as it can store information about the proton beam intensity on a large area (> 1 cm²) with sub-micrometric spatial resolution and revealing even subtle intensity differences.

Moreover, using cleaved LiF crystals and LiF films grown on Si(100) substrates irradiated in a particular geometry allows one to measure the color centers distribution along the proton penetration depth (proportional to the linear energy transfer, LET) and directly imaging the Bragg peak with a conventional fluorescence microscope. Such measurements are very precise and an important check of beam dynamics calculations.

DOSIMETRY

SUBSYSTEMS

INJECTOR LEBT SCDTL CCL RF SYSTEM DIAGNOSTICS DOSIMETRY CONTROL SYSTEM RADIOPROTECTION