We report the results of several complementary radiation tests to qualify and calibrate a highly radiation sensitive Single-Mode (SM) Optical Fiber (OF) for distributed dosimetry application at CERN. The Radiation Induced Attenuation (RIA) is the physical phenomenon used to evaluate the Total Ionizing Dose (TID) received by the OF sensor. The radiation response tests comprise online RIA in the Near InfraRed (NIR) domain under $\rm {}^{60}Co \gamma -rays$ , X-rays and proton irradiations, as well as post mortem Optical Attenuation (OA) measurement to evaluate long term fading effects of the RIA. In this work, we focus on the effect of successive irradiations, dose rate dependence and effects related to the change of the irradiation temperature up to 45 °C. On the basis of our investigation, we conclude that the studied OF is a suitable TID sensor and that it is well adapted for distributed OF radiation dose sensing. It is fully compatible with commercially available SM Optical Time Domain Reflectometers (OTDR), with some noticeable advantages with respect to previously developed systems based on Multimode OFs. Finally, the OF we investigated has been selected for the distributed monitoring of low radiation dose levels at CERN in the injector chain (Proton Synchrotron Booster, Proton Synchrotron, Super Proton Synchrotron) and parts of the Large Hadron Collider (LHC).

Optical fibers hold promise for accurate dosimetry in small field proton therapy due to their superior spatial resolution and the lack of significant Cerenkov contamination in proton beams. One known drawback for most scintillation detectors is signal quenching in areas of high linear energy transfer, as is the case in the Bragg peak region of a proton beam. In this study, we investigated the potential of innovative optical fiber bulk materials using the sol-gel technique for dosimetry in proton therapy. This type of glass is made of amorphous silica (SiO $${}_{2}$$2 ) and is doped with Gd $${}^{3+}$$3 + ions and possesses very interesting light emission properties with a luminescence band around 314 nm when exposed to protons. The fibers were manufactured at the University of Lille and tested at the TRIUMF Proton Therapy facility with 8.2–62.9 MeV protons and 2–6 nA of extracted beam current. Dose-rate dependence and quenching were measured and compared to other silica-based fibers also made by sol-gel techniques and doped with Ce $${}^{3+}$$3 + and Cu $${}^{+}$$+ . The three fibers present strong luminescence in the UV (Gd) or visible (Cu,Ce) under irradiation, with the emission intensities related directly to the proton flux. In addition, the 0.5 mm diameter Gd $${}^{3+}$$3 + -doped fiber shows superior resolution of the Bragg peak, indicating significantly reduced quenching in comparison to the Ce $${}^{3+}$$3 + and Cu $${}^{+}$$+ fibers with a Birks’ constant, k $${}_{B}$$B , of (0.0162 $$\pm $$± 0.0003) cm/MeV in comparison to (0.0333 $$\pm $$± 0.0006) cm/MeV and (0.0352 $$\pm $$± 0.0003) cm/MeV, respectively. To our knowledge, this is the first report of such an interesting k $${}_{B}$$B for a silica-based optical fiber material, showing clearly that this fiber presents lower quenching than common plastic scintillators. This result demonstrates the high potential of this inorganic fiber material for proton therapy dosimetry.

With recent impressive clinical results of targeted alpha therapy using ²²⁵Ac, significant effort has been directed towards providing a reliable and sufficient supply of ²²⁵Ac to enable widespread using of ²²⁵Ac-radiopharmaceuticals. TRIUMF has begun production of ²²⁵Ac via spallation of thorium metal with 480 MeV protons. As part of this program, a new ²²⁵Ac-production target system capable of withstanding the power deposited by the proton beam was designed and its performance simulated over a range of potential operating parameters. Special attention was given to heat transfer and stresses within the target components. The target was successfully tested in two irradiations with a 72–73 µA proton beam for a duration of 36.5 h. The decay corrected activity at end of irradiation (average ± standard deviation) was (524 ± 21) MBq (14.2 mCi) and (86 ± 13) MBq (2.3 mCi) for ²²⁵Ac and ²²⁵Ra, respectively. These correspond to saturation yields of 72.5 MBq/µA for ²²⁵Ac and 17.6 MBq/µA for ²²⁵Ra. Longer irradiations and production scale-up are planned in the future.

Objective. To develop a bremsstrahlung target and megavoltage (MV) x-ray irradiation platform for ultrahigh dose-rate (UHDR) irradiation of small-animals on the Advanced Rare Isotope Laboratory (ARIEL) electron linac (e-linac) at TRIUMF. Approach. An electron-to-photon converter design for UHDR radiotherapy (RT) was centered around optimization of a tantalum–aluminum (Ta–Al) explosion-bonded target. Energy deposition within a homogeneous water-phantom and the target itself were evaluated using EGSnrc and FLUKA MC codes, respectively, for various target thicknesses (0.5–1.5 mm), beam energies ( E _e− = 8, 10 MeV) and electron (Gaussian) beam sizes ( 2 σ = 2–10 mm). Depth dose-rates in a 3D-printed mouse phantom were also calculated to infer the compatibility of the 10 MV dose distributions for FLASH-RT in small-animal models. Coupled thermo-mechanical FEA simulations in ANSYS were subsequently used to inform the stress–strain conditions and fatigue life of the target assembly. Main results. Dose-rates of up to 128 Gy s ⁻¹ at the phantom surface, or 85 Gy s ⁻¹ at 1 cm depth, were obtained for a 1 × 1 cm ² field size, 1 mm thick Ta target and 7.5 cm source-to-surface distance using the FLASH-mode beam ( E _e− = 10 MeV, 2 σ = 5 mm, P = 1 kW); furthermore, removal of the collimation assembly and using a shorter (3.5 cm) SSD afforded dose-rates >600 Gy s ⁻¹ , albeit at the expense of field conformality. Target temperatures were maintained below the tantalum, aluminum and cooling-water thresholds of 2000 °C, 300 °C and 100 °C, respectively, while the aluminum strain behavior remained everywhere elastic and helped ensure the converter survives its prescribed 5 yr operational lifetime. Significance. Effective design iteration, target cooling and failure mitigation have culminated in a robust target compatible with intensive transient (FLASH) and steady-state (diagnostic) applications. The ARIEL UHDR photon source will facilitate FLASH-RT experiments concerned with sub-second, pulsed or continuous beam irradiations at dose rates in excess of 40 Gy s ⁻¹ .

The potential of fiber-based sensors to monitor the fluence of atmospheric neutrons is evaluated through accelerated tests at the TRIUMF Neutron Facility (TNF) (BC, Canada), offering a flux approximatively 10⁹ higher than the reference spectrum observed under standard conditions in New York City, USA. The radiation-induced attenuation (RIA) at 1625 nm of a phosphorus-doped radiation sensitive optical fiber is shown to linearly increase with neutron fluence, allowing an in situ and easy monitoring of the neutron flux and fluence at this facility. Furthermore, our experiments show that the fiber response remains sensitive to the ionization processes, at least up to a fluence of 7.1 × 10¹¹ n cm⁻², as its radiation sensitivity coefficient (~3.36 dB km⁻¹ Gy⁻¹) under neutron exposure remains very similar to the one measured under X-rays (~3.8 dB km⁻¹ Gy⁻¹) at the same wavelength. The presented results open the way to the development of a point-like or even a distributed dosimeter for natural or man-made neutron-rich environments. The feasibility to measure the dose caused by the neutron exposure during stratospheric balloon experiments, or during outer space missions, is presented as a case study of a potential future application.