Radiation protection challenges in the upgrade, autopsy and disposal of the LHC beam dump.

The upgrade of the Large Hadron Collider spare beam dumps (Target Dump External, TDE) and the autopsy of the old operational TDE required to perform several activities in a high-radiation environment posing significant radiation protection challenges due to the residual activation of the equipment. To ensure high safety standards and to respect the ALARA principle, these challenges were addressed using the advanced Monte Carlo techniques to predict the residual ambient dose equivalent rate and the radionuclide inventory at different steps of the interventions. The CERN HSE-RP group makes extensive use of the FLUKA and ActiWiz codes to produce accurate estimates. This work aims to provide an overview of the radiation protection studies to optimise the interventions (ALARA) and to reduce the radiological risk for personnel and environment.

Radiation protection challenges for the Large Hadron Collider upgrade.

In the context of the so-called Long Shutdown 3 (2026-2028), the Large Hadron Collider will be upgraded to the High-Luminosity Large Hadron Collider, allowing for approximately five more instantaneous collisions. The upgrade, maintenance and decommissioning of equipment will be mainly performed in the experimental insertions of Points 1 and 5, requiring to perform multiple interventions in high-residual radiation environment. This poses complex radiological challenges that the CERN Radiation Protection group is called to address. Radiation protection studies are performed to plan and optimise (ALARA) these future interventions using the advanced Monte Carlo techniques and tools such as FLUKA, ActiWiz, SESAME and the FCC method. This paper aims to provide an overview of the studies conducted to estimate the residual radiation field in the experimental insertions, the activation levels in terms of multiple of the Swiss clearance limits/specific activity and to provide preliminary considerations on the upgrade/decommissioning of key equipment.

Assessment of emission data and transmission factors supporting radiation protection in the use of 225Ac.

PURPOSE: 225Ac is the most promising alpha emitter for radiopharmaceutical therapy. Labeling PSMA, it showed to be effective in the treatment of prostate cancer and research is undergoing in order to improve its production capacity. Currently, there are still few data published concerning operational radiation protection in its use, both in clinics and in radiopharmacy, and even some basic data are not readily available. This papers aims to estimate the emission gamma-ray constant of 225Ac when at equilibrium with its descendants, and the transmission factors for a broad beam of the gamma-rays emitted by 225Ac and its descendants. MATERIALS & METHODS: Monte Carlo simulations were performed using FLUKA 4.2, considering firstly the source in air, in absence of any shielding, and secondly by adding an increasing thicknesses of Lead, Concrete or Tungsten. In order to obtain statistically meaningful results, high-statistics simulations were performed by sampling up to 1010 primary decay events. As the shielding thickness increased, an appropriate variance reduction technique (importance biasing) was applied. RESULTS: The specific gamma ray emission constant for 225Ac at equilibrium with descendants resulted (3.26 ± 0.03) × 10-5 mSv/h per 1 MBq at a distance of 100 cm. The transmission factors are presented in detail and data have been appropriately interpolated and fitting parameters are reported. CONCLUSIONS: The attenuation curves show a clear bi-exponential trend: performing shielding calculations by adopting a simple approach based on a single value of Half Value Layer (HVL) or Tenth Value Layer (TVL) cannot provide adequate results. In conclusion, our results may be useful in the design of shielded hot cells or accessories necessary for operational radiation protection.

Modeling of a Cyclotron Target for the Production of 11C with Geant4.

BACKGROUND: In medical cyclotron facilities, 11C is produced according to the 14N(p,α)11C reaction and widely employed in studies of prostate and brain cancers by Positron Emission Tomography. It is known from literature that the 11C-target assembly shows a reduction in efficiency during time, meaning a decrease of activity produced at the end of bombardment. This effect might depend on aspects which are still not completely known. OBJECTIVE: Possible causes of the loss of performance of the 11C-target assembly were addressed by Monte Carlo simulations. METHODS: Geant4 was used to model the 11C-target assembly of a GE PETtrace cyclotron. The physical and transport parameters to be used in the energy range of medical applications were extracted from literature data and 11C routine productions. The Monte Carlo assessment of 11C saturation yield was performed varying several parameters such as the proton energy and the angle of the target assembly with respect to the proton beam. RESULTS: The estimated 11C saturation yield is in agreement with IAEA data at the energy of interest, while it is about 35% greater than the experimental value. A more comprehensive modeling of the target system, including thermodynamic effect, is required. The energy absorbed in the inner layer of the target chamber was up to 46.5 J/mm2 under typical irradiation conditions. CONCLUSION: This study shows that Geant4 is potentially a useful tool to design and optimize targetry for PET radionuclide productions. Tests to choose the Geant4 physics libraries should be performed before using this tool with different energies and materials.

Radiation Protection Studies for Medical Particle Accelerators using Fluka Monte Carlo Code.

Radiation protection (RP) in the use of medical cyclotrons involves many aspects both in the routine use and for the decommissioning of a site. Guidelines for site planning and installation, as well as for RP assessment, are given in international documents; however, the latter typically offer analytic methods of calculation of shielding and materials activation, in approximate or idealised geometry set-ups. The availability of Monte Carlo (MC) codes with accurate up-to-date libraries for transport and interaction of neutrons and charged particles at energies below 250 MeV, together with the continuously increasing power of modern computers, makes the systematic use of simulations with realistic geometries possible, yielding equipment and site-specific evaluation of the source terms, shielding requirements and all quantities relevant to RP at the same time. In this work, the well-known FLUKA MC code was used to simulate different aspects of RP in the use of biomedical accelerators, particularly for the production of medical radioisotopes. In the context of the Young Professionals Award, held at the IRPA 14 conference, only a part of the complete work is presented. In particular, the simulation of the GE PETtrace cyclotron (16.5 MeV) installed at S. Orsola-Malpighi University Hospital evaluated the effective dose distribution around the equipment; the effective number of neutrons produced per incident proton and their spectral distribution; the activation of the structure of the cyclotron and the vault walls; the activation of the ambient air, in particular the production of 41Ar. The simulations were validated, in terms of physical and transport parameters to be used at the energy range of interest, through an extensive measurement campaign of the neutron environmental dose equivalent using a rem-counter and TLD dosemeters. The validated model was then used in the design and the licensing request of a new Positron Emission Tomography facility.

Assessment of the neutron dose field around a biomedical cyclotron: FLUKA simulation and experimental measurements.

In the planning of a new cyclotron facility, an accurate knowledge of the radiation field around the accelerator is fundamental for the design of shielding, the protection of workers, the general public and the environment. Monte Carlo simulations can be very useful in this process, and their use is constantly increasing. However, few data have been published so far as regards the proper validation of Monte Carlo simulation against experimental measurements, particularly in the energy range of biomedical cyclotrons. In this work a detailed model of an existing installation of a GE PETtrace 16.5MeV cyclotron was developed using FLUKA. An extensive measurement campaign of the neutron ambient dose equivalent H∗(10) in marked positions around the cyclotron was conducted using a neutron rem-counter probe and CR39 neutron detectors. Data from a previous measurement campaign performed by our group using TLDs were also re-evaluated. The FLUKA model was then validated by comparing the results of high-statistics simulations with experimental data. In 10 out of 12 measurement locations, FLUKA simulations were in agreement within uncertainties with all the three different sets of experimental data; in the remaining 2 positions, the agreement was with 2/3 of the measurements. Our work allows to quantitatively validate our FLUKA simulation setup and confirms that Monte Carlo technique can produce accurate results in the energy range of biomedical cyclotrons.

Experimental measurement and Monte Carlo assessment of Argon-41 production in a PET cyclotron facility.

In a medical cyclotron facility, (41)Ar (t1/2 = 109.34 m) is produced by the activation of air due to the neutron flux during irradiation, according to the (40)Ar(n,γ)(41)Ar reaction; this is particularly relevant in widely diffused high beam current cyclotrons for the production of PET radionuclides. While theoretical estimations of the (41)Ar production have been published, no data are available on direct experimental measurements for a biomedical cyclotron. In this work, we describe a sampling methodology and report the results of an extensive measurement campaign. Furthermore, the experimental results are compared with Monte Carlo simulations performed with the FLUKA code. To measure (41)Ar activity, air samples were taken inside the cyclotron bunker in sealed Marinelli beakers, during the routine production of (18)F with a 16.5 MeV GE-PETtrace cyclotron; this sampling thus reproduces a situation of absence of air changes. Samples analysis was performed in a gamma-ray spectrometry system equipped with HPGe detector. Monte Carlo assessment of the (41)Ar saturation yield was performed directly using the standard FLUKA score RESNUCLE, and off-line by the convolution of neutron fluence with cross section data. The average (41)Ar saturation yield per one liter of air of (41)Ar, measured in gamma-ray spectrometry, resulted to be 3.0 ± 0.6 Bq/µA*dm(3) while simulations gave a result of 6.9 ± 0.3 Bq/µA*dm(3) in the direct assessment and 6.92 ± 0.22 Bq/µA*dm(3) by the convolution neutron fluence-to-cross section.

Bis(4-benzyloxyphenyl)iodonium salts as effective precursors for the no-carrier-added radiosynthesis of 4-[¹8F]fluorophenol.

4-[¹8F]Fluorophenol is a very useful intermediate compound for building-up more complex molecules bearing a 4-[¹8F]fluorophenoxy moiety. Bis(4-benzyloxyphenyl)iodonium salts proved very effective as labeling precursors for the radiosynthesis of this compound in no-carrier-added form. Starting from the bromide salt and performing the radiofluorination by conventional heating, 4-[¹8F]fluorophenol was obtained in an overall RCY of 43 ± 12% while a yield of 52 ± 3% was achieved more reliably starting from the tosylate salt and employing microwave heating.