MeV Proton Beam Research Articles

Longitudinal dynamics study and optimization in the beam commissioning of the rapid cycling synchrotron in the China Spallation Neutron Source

The China Spallation Neutron Source (CSNS) is a high intensity proton accelerator-based facility, and its accelerator complex includes two main parts: a H- linac and a rapid cycling synchrotron (RCS). The RCS accumulates the 80 MeV proton beam, and accelerates it to 1.6 GeV, with a repetition rate of 25 Hz. The beam commissioning of RCS began in May, 2017 and reached the target beam power of 100 kW in February, 2020. The longitudinal beam dynamics study plays the key role in the commissioning. The study and optimization include the synchronicity between the ramping magnet field and the RF system, the mitigation of the high intensity effects to minimize the beam loss and the measurement of the longitudinal dynamics. Through the optimization of the bunch factor, the strong space charge effects with high intensity is mitigated, thus the RCS transmission efficiency arrives mostly at 100 %. The beam distribution is not affected by the phase loop with a new algorithm and the beam loss is smaller than the original one. The beam commissioning in longitudinal plane is reviewed in the paper.

FLASH Proton Pencil Beam Scanning Irradiation Minimizes Radiation-Induced Leg Contracture and Skin Toxicity in Mice.

Simple SummaryDose and efficacy of radiation therapy are limited by the toxicity to normal tissue adjacent to the treated tumor region. Recently, ultra-high dose rate radiotherapy (FLASH radiotherapy) has shown beneficial reduction of normal tissue damage while preserving similar tumor efficacy with electron, photon and scattered proton beam irradiation in preclinical models. Proton therapy is increasingly delivered by pencil beam scanning (PBS) technology, and we therefore set out to test PBS FLASH radiotherapy on normal tissue toxicity and tumor control in vivo in mouse using a clinical proton delivery system. This validation of the FLASH normal tissue-sparing hypothesis with a clinical delivery system provides supporting data for PBS FLASH radiotherapy and its potential role in improving radiotherapy outcomes. Ultra-high dose rate radiation has been reported to produce a more favorable toxicity and tumor control profile compared to conventional dose rates that are used for patient treatment. So far, the so-called FLASH effect has been validated for electron, photon and scattered proton beam, but not yet for proton pencil beam scanning (PBS). Because PBS is the state-of-the-art delivery modality for proton therapy and constitutes a wide and growing installation base, we determined the benefit of FLASH PBS on skin and soft tissue toxicity. Using a pencil beam scanning nozzle and the plateau region of a 250 MeV proton beam, a uniform physical dose of 35 Gy (toxicity study) or 15 Gy (tumor control study) was delivered to the right hind leg of mice at various dose rates: Sham, Conventional (Conv, 1 Gy/s), Flash60 (57 Gy/s) and Flash115 (115 Gy/s). Acute radiation effects were quantified by measurements of plasma and skin levels of TGF-β1 and skin toxicity scoring. Delayed irradiation response was defined by hind leg contracture as a surrogate of irradiation-induced skin and soft tissue toxicity and by plasma levels of 13 different cytokines (CXCL1, CXCL10, Eotaxin, IL1-beta, IL-6, MCP-1, Mip1alpha, TNF-alpha, TNF-beta, VEGF, G-CSF, GM-CSF and TGF- β1). Plasma and skin levels of TGF-β1, skin toxicity and leg contracture were all significantly decreased in FLASH compared to Conv groups of mice. FLASH and Conv PBS had similar efficacy with regards to growth control of MOC1 and MOC2 head and neck cancer cells transplanted into syngeneic, immunocompetent mice. These results demonstrate consistent delivery of FLASH PBS radiation from 1 to 115 Gy/s in a clinical gantry. Radiation response following delivery of 35 Gy indicates potential benefits of FLASH versus conventional PBS that are related to skin and soft tissue toxicity.

A Novel Approach to Design and Evaluate BNCT Neutron Beams Combining Physical, Radiobiological, and Dosimetric Figures of Merit.

Simple SummaryClinical potential and safety are presented as novel criteria to evaluate neutron beams designed for boron neutron capture therapy (BNCT). The presently used figures of merit are a set of physical quantities calculated in air, related to the neutron flux, the collimation, and the spectral characteristics. However, the capability of the beam to deliver an effective and safe treatment to patients should be the most important criterion in view of the clinical application. This work presents the design of a neutron beam produced by a proton accelerator coupled to a beryllium target and the use of new figures of merit to choose the best beam among different candidates. These figures of merit use tridimensional dosimetry simulated in phantoms and patients, to calculate the probability of tumor control without affecting healthy tissues, employing proper radiobiological models. Moreover, the dose absorbed by out-of-field healthy organs is used as a criterion to establish the safest beam for clinical treatments. Results show that beams that would be rejected by physical in-air quantities demonstrate a clinical performance comparable to existing neutron beams successfully used for patients, and that the presented criteria allow a clear selection of the most adequate beam among the ones presented.(1) Background:The quality of neutron beams for Boron Neutron Capture Therapy (BNCT) is currently defined by its physical characteristics in air. Recommendations exist to define whether a designed beam is useful for clinical treatment. This work presents a new way to evaluate neutron beams based on their clinical performance and on their safety, employing radiobiological quantities. (2) Methods: The case study is a neutron beam for deep-seated tumors from a 5 MeV proton beam coupled to a beryllium target. Physical Figures of Merit were used to design five beams; however, they did not allow a clear ranking of their quality in terms of therapeutic potential. The latter was then evaluated based on in-phantom dose distributions and on the calculation of the Uncomplicated Tumor Control Probability (UTCP). The safety of the beams was also evaluated calculating the in-patient out-of-beam dosimetry. (3) Results: All the beams ensured a UTCP comparable to the one of a clinical beam in phantom; the safety criterion allowed to choose the best candidate. When this was tested in the treatment planning of a real patient treated in Finland, the UTCP was still comparable to the one of the clinical beam. (4) Conclusions: Even when standard physical recommendations are not met, radiobiological and dosimetric criteria demonstrate to be a valid tool to select an effective and safe beam for patient treatment.

Lineal energy calibration of a mini-TEPC via the proton-edge technique

PurposeThe possibility to calibrate microdosimetric spectra using the proton- and electron-edge was proposed many years ago. It consists of two steps: first identifying the edge and a marker point on it and then ascribing the correct lineal energy value to the position of the edge in the event size spectrum. The purpose of this work is to study rigorously the marker identification for the proton-edge in the mini-TEPC spectra measured in neutron and in clinical proton fields, and the correspondent lineal energy value to assign to it. Materials and methodsMicrodosimetric measurements were performed with a cylindrical miniaturized tissue-equivalent proportional-counter (mini-TEPC) in neutron and gamma rays radiation fields at the CN accelerator of the Legnaro National Laboratories of the Italian National Institute for Nuclear Physics (LNL-INFN) and in the clinical 62 MeV proton beam of the Southern National Laboratories of INFN (LNS-INFN). The fitting of the proton-edge region of the microdosimetric spectra with a Fermi-like function was studied in both neutron and proton fields to identify the most precise marker point. The lineal energy value to ascribe to it was determined starting from the maximum energy deposit in protons obtained in FLUKA simulations. ResultsBoth in neutron radiation field and in clinical proton beams the flex and the intercept of the tangent through the inflection point are determined with similar precision. The flex was chosen as the most suitable marker of the proton-edge in sealed detectors because it is known to be less sensitive to pressure variations. The lineal energy value to ascribe to the flex position for 0.75 μm of propane depends on the irradiation geometry: 194 keV/μm for isotropic radiation fields and 165 keV/μm for mono-directional radiation fields orthogonal to the axis of the cylinder. The calibration values for the proton-edge have been converted in water by means of the mean stopping power ratio of water and propane for protons obtaining 171 keV/μm for isotropic radiation fields and 145 keV/μm for mono-directional radiation fields.

An accelerator facility for intermediate energy proton irradiation and testing of nuclear materials

The bulk irradiation of materials with 10–30 MeV protons promises to advance the study of radiation damage for fission and fusion power plants. Intermediate energy proton beams can now be dedicated to materials irradiation within university-scale laboratories. This paper describes the first such facility, with an Ionetix ION-12SC cyclotron producing 12 MeV proton beams. Samples are mm-scale tensile specimens with thicknesses up to 300 μm, mounted to a cooled beam target with control over temperature. A specialized tensile tester for radioactive specimens at high temperature (500+ °C) and/or vacuum represents the conditions in fission and fusion systems, while a digital image correlation system remotely measures strain. Overall, the facility provides university-scale irradiation and testing capability with intermediate energy protons to complement traditional in-core fission reactor and micro-scale ion irradiation. This facility demonstrates that bulk proton irradiation is a scalable and effective approach for nuclear materials research, down-selection, and qualification.

Characterization of the proton pulsed beam at CMAM

In this paper, the technicalities performed to obtain a pulsed beam at the CMAM facility will be explained. The pulsed beam has been characterized with an 8 MeV proton beam, using an existing equipment at CMAM: two pairs of electrostatic plates (RASTER) that deflect the beam, commonly used for homogeneous irradiation of large areas. A pulsed beam is used in many areas such as nuclear physics, material science and, in particular, for proton-therapy medical studies. Rectangular and pyramidal functions have been used to generate different pulses and characterize the response of the RASTER. The results point out that the pulses obtained are suitable for preclinical proton-therapy studies in the FLASH regime, which consists on fractionating the dose in time with short and intense pulses. The set-up for the characterization has been a function generator and a Si-PM outside the chamber.

The Metamorphosis of Radionuclide Production and Development at Paul Scherrer Institute

Radionuclide production and development has a long history at the Paul Scherrer Institute (PSI) and dates back to the founding times of its forerunner institutions: the Federal Institute for Reactor Research and the Swiss Institute for Nuclear Research. The facilities used for this purpose have evolved substantially over the last five decades. Many radiometals in use today, as radiopharmaceuticals, are for the diagnosis and treatment of disease, with the most popular means of detection being Positron Emission Tomography. These positron emitters are easily produced at low proton energies using medical cyclotrons, however, developments at these facilities are lacking. Currently, the fixed 72 MeV proton beam at PSI is degraded at IP2 irradiation station to provide the desired energy to irradiate targets to produce the likes of 44Sc, 43Sc and 64Cu as a proof of principle, which are of great interest to the nuclear medicine community. This development work can then be implemented at facilities containing medical cyclotrons. A history of the development of radionuclides at PSI, along with current development and projects with partner institutions, is described.

A proof-of-concept study of an in-situ partial-ring time-of-flight PET scanner for proton beam verification.

Development of a PET system capable of in-situ imaging requires a design that can accommodate the proton treatment beam nozzle. Among the several PET instrumentation approaches developed thus far, the dual-panel PET scanner is often used as it is simpler to develop and integrate within the proton therapy gantry. Partial-angle coverage of these systems can however lead to limited-angle artefacts in the reconstructed PET image. We have previously demonstrated via simulations that time-of-flight (TOF) reconstruction reduces the artifacts accompanying limited-angle data, and permits proton range measurement with 1-2 mm accuracy and precision. In this work we show measured results from a small proof-of-concept dual-panel PET system that uses TOF information to reconstruct PET data acquired after proton irradiation. The PET scanner comprises of two detector modules, each comprised of an array of 4×4×30 mm3 lanthanum bromide scintillator. Measurements are performed with an oxygen-rich gel-water, an adipose tissue equivalent material, and in vitro tissue phantoms. For each phantom measurement, 2 Gy dose was deposited using 54 - 100 MeV proton beams. For each phantom, a Monte Carlo simulation generating the expected distribution of PET isotope from the corresponding proton irradiation was also performed. Proton range was calculated by drawing multiple depth-profiles over a central region encompassing the proton dose deposition. For each profile, proton range was calculated using two techniques (a) 50% pick-off from the distal edge of the profile, and (b) comparing the measured and Monte Carlo profile to minimize the absolute sum of differences over the entire profile. A 10 min PET acquisition acquired with minimal delay post proton-irradiation is compared with a 10 min PET scan acquired after a 20 min delay. Measurements show that PET acquisition with minimal delay is necessary to collect 15O signal, and maximize 11C signal collection with a short PET acquisition. In comparison with the 50% pick-off technique, the shift technique is more robust and offers better precision in measuring the proton range for the different phantoms. Range measurements from PET images acquired with minimal delay, and the shift technique demonstrate the ability to achieve <1.5 mm accuracy and precision in estimating proton range.

Low-power proton beam extraction by the bright continuous laser using the 3-MeV negative-hydrogen linac in Japan Proton Accelerator Research Complex

ABSTRACT The Japan Atomic Energy Agency (JAEA) has designed a Transmutation Physics Experimental Facility (TEF-P) as an experimental facility in the Japan Proton Accelerator Research Complex (J-PARC). The TEF-P is a critical assembly driven by a low-power proton beam, a maximum of 10 W, which is extracted from a high-power beam source, such as 250 kW of 400 MeV proton beam of the J-PARC linac. To extract such a low-power proton beam from the high-power proton beam, we developed a laser charge exchange (LCE) device and employed its technique, which is one of the non-contact beam extraction techniques. To confirm the performance of the LCE device, a low-power proton beam was extracted using a negative-hydrogen linac having an energy of 3 MeV, and a bright continuous laser. A 0.57 mW proton beam was successfully extracted with a laser stripping efficiency of . These values obtained are in good agreement with the estimated values.

Technical Note: Design and commissioning of a water phantom for proton dosimetry in magnetic fields.

PurposeTo design and commission a water phantom suitable for constrained environments and magnetic fields for magnetic resonance (MR)‐guided proton therapy.MethodsA phantom was designed, to enable precise, remote controlled detector positioning in water within the constrained environment of a magnet for MR‐guided proton therapy. The phantom consists of a PMMA enclosure whose outer dimensions of 81×40×12.5cm3 were chosen to optimize space usage inside the 13.5‐cm bore gap of the magnet. The moving mechanism is based on a low‐height H‐shaped non‐ferromagnetic belt drive, driven by stepper motors located outside of the magnetic field. The control system and the associated electronics were designed in house, with similar features as available in commercial water phantoms. Reproducibility as well as accuracy of the phantom positioning were tested using a high‐precision Leica AT 402 laser tracker. Laterally integrated depth dose curves and lateral beam profiles at three depths were acquired repeatedly for a 148.2 MeV proton beam in water.ResultsThe phantom was successfully operated with and without applied magnetic fields. For complex movements, a positioning uncertainty within 0.16 mm was found with an absolute accuracy typically below 0.3 mm. Laterally integrated depth dose curves agreed within 0.1 mm with data taken using a commercial water phantom. The lateral beam offset determined from beam profile measurements agreed well with data from Monte Carlo simulations.ConclusionThe phantom is optimally suited for detector positioning and dosimetric experiments within constrained environments in high magnetic fields.

Simulation of a Neutron Source at the KFSH&RC CS-30 Cyclotron

The aim of this work is to optimize the parameters of the CS-30 cyclotron neutron source at King Faisal Specialist Hospital & Research Center (KFSH&RC). The CS-30 cyclotron is a positive ion machine capable of accelerating protons with internal and extracted beam currents up to 100μA and 60μA respectively. Geant4 simulation toolkit based on Monte Carlo methods was used to study and compare the energy spectra and the angular distributions of the neutrons resulting from a 26.5 MeV proton beam on a 0.5 cm thick target Beryllium-9 with a 0.15 cm Copper-63 back stop.

Study of the contribution of the 7Be(d, p) reaction to the 7Li problem in the Big-Bang Nucleosynthesis

Our research goal is to measure the cross section of the 7Be(d, p) reaction to find a solution for the cosmological the 7Li problem, which is an overestimation of the primordial 7Li abundance in the standard Big-Bang nucleosynthesis (BBN) model. We developed a method to produce an unstable 7Be target to measure the reaction in normal kinematics in a high-resolution measurement. We performed an experiment to produce the 7Be target and also to measure the cross section of the 7Be(d, p)8Be reaction with the produced 7Be target at the tandem facility, Kobe University. A 2.36 MeV proton beam irradiated a Li target to transmute 7Li particles to 7Be particles via the 7Li(p, n)7Be reaction. We produced 2.6×1013 7Be particles in the target after two days’ proton irradiation. After the target production, the beam ion was changed to deuterons with energies of 0.6, 1.0, and 1.6 MeV to measure the 7Be(d, p) reaction. The outgoing protons were measured by two ΔE-E silicon telescopes placed at 30° and 45°. We report the preliminary results of this experiment, including the 7Be(d, p) cross section.

Development of thallium bromide semiconductor detectors for particle-induced gamma-ray emission

A thallium bromide (TlBr) gamma-ray detector was developed for particle-induced gamma-ray emission (PIGE) applications. The PIGE spectrum of a lithium fluoride (LiF) crystal was obtained for the first time using the TlBr detector. This detector was fabricated using a zone-purified crystal with dimensions of approximately 2mm × 2mm × 5mm. An energy resolution of 2.3% full-width at half maximum for 511 keV gamma rays was obtained from the detector at room temperature. The LiF crystal target was irradiated with a 20 MeV proton beam at the Aomori Prefecture Quantum Science Center. Full-energy peaks of 478 keV and 197 keV were successfully detected from lithium and fluorine, respectively, using the TlBr detector in the PIGE experiment.

Preclinical Challenges in Proton Minibeam Radiotherapy: Physics and Biomedical Aspects

The concept of spatial fractionation in radiotherapy was developed for better sparing of normal tissue in the entrance channel of radiation. Spatial fractionation utilizing proton minibeam radiotherapy (pMBRT) promises to be advantageous compared to X-ray minibeams due to higher dose conformity at the tumor. Preclinical in vivo experiments conducted with pMBRT in mouse ear models or in rat brains support the prospects, but the research about the radiobiological mechanisms and the search for adequate application parameters delivering the most beneficial minibeam therapy is still in its infancy. Concerning preclinical research, we consider glioma, non-small cell lung cancer and hepatocellular carcinoma as the most promising targets and propose investigating the effects on healthy tissue, especially neuronal cells and abdominal organs. The experimental setups for preclinical pMBRT used so far follow different technological approaches, and experience technical limitations when addressing the current questions in the field. We review the crucial physics parameters necessary for proton minibeam production and link them to the technological challenges to be solved for providing an optimal research environment. We consider focusing of pencil or planar minibeams in a scanning approach superior compared to collimation due to less beam halos, higher peak-to-valley dose ratios and higher achievable dose rates. A possible solution to serve such a focusing system with a high-quality proton beam at all relevant energies is identified to be a 3 GHz radio-frequency linear accelerator. We propose using a 16 MeV proton beam from an existing tandem accelerator injected into a linear post-accelerator, boosted up to 70 MeV, and finally delivered to an imaging and positioning end-station suitable for small animal irradiation. Ion-optical simulations show that this combination can generate focused proton minibeams with sizes down to 0.1 mm at 18 nA mean proton current - sufficient for all relevant preclinical experiments. This technology is expected to offer powerful and versatile tools for unleashing structured and advanced preclinical pMBRT studies at the limits and also has the potential to enable a next step into precision tumor therapy.

Pairing of thorium with selected primary target materials in tandem configurations: Co-production of 225Ac/213Bi and 230U/226Th generators with a 70 MeV H[formula omitted] cyclotron

Several radionuclide production facilities based on a new generation of high-current, 70 MeV H− cyclotrons have been established in recent years and a number of new facilities are either under construction or being planned. In this study, the feasibility to produce 225Ac/213Bi and 230U/226Th generators via Th + p reactions at such a facility has been investigated. From the perspective of production yields, it has been found useful to compare the relevant reactions on thorium with those on other targets regularly employed in this energy region, in particular the natMg(p,x)22Na, natGa(p,x)68Ge, and natRb(p,x)82Sr reactions that have been exploited with 66 MeV proton beams at iThemba LABS for many years. Therefore, various tandem configurations of thorium with magnesium, gallium and rubidium are discussed based on the relevant nuclear data. In a few cases, the available data were judged to be insufficient in this energy region. New experimental cross sections are presented for 225Ac, 225Ra, and 230Pa in Th + p reactions as well as 22,24Na in natMg + p reactions. Integral yields have been derived for those radionuclides of main interest. Production yields expected from extended 70 MeV proton bombardments, on selected tandem-target configurations, are presented for 22Na, 68Ge, 82Sr, 225Ac, and 230Pa. It is concluded that 225Ac/213Bi generators can, in principle, be added to a production programme based at a 70 MeV H− cyclotron facility as the production rate is of similar magnitude to those of other well-established radionuclides in this energy region. Also, radio-contaminant levels for 225Ac are similar to those found in higher proton-energy windows. The scope for 230U/226Th generators, via bulk production of the precursor 230Pa, seems to be more limited due to a lower yield but can nevertheless be produced in clinically relevant quantities.

Optical Properties of YAG:Ce and GGG:Ce Scintillation Crystals Irradiated with a High Fluence Proton Beam

In this paper, we report on the study of the optical properties of YAG:Ce and GGG:Ce garnet crystals after irradiation in a 660~MeV proton beam with a fluence up to 8.9$\times$10$^{14}$ protons/cm$^2$. We found that the transparency of both crystals fell by no more than 7\% in the region of their own luminescence. The light yield of a YAG:Ce sample, measured one year after irradiation, dropped by about 35\%.

Dose-dependent Changes After Proton and Photon Irradiation in a Zebrafish Model.

The importance of hadron therapy in the cancer management is growing. We aimed to refine the biological effect detection using a vertebrate model. Embryos at 24 and 72 h postfertilization were irradiated at the entrance plateau and the mid spread-out Bragg peak of a 150 MeV proton beam and with reference photons. Radiation-induced DNA double-strand breaks (DSB) and histopathological changes of the eye, muscles and brain were evaluated; deterioration of specific organs (eye, yolk sac, body) was measured. More and longer-lasting DSBs occurred in eye and muscle cells due to proton versus photon beams, albeit in different numbers. Edema, necrosis and tissue disorganization, (especially in the eye) were observed. Dose-dependent morphological deteriorations were detected at ≥10 Gy dose levels, with relative biological effectiveness between 0.99±0.07 (length) and 1.12±0.19 (eye). Quantitative assessment of radiation induced changes in zebrafish embryos proved to be beneficial for the radiobiological characterization of proton beams.

Key Clinical Concepts from Multi-Institutional Experience with Dedicated Fixed Low-Energy Proton Ocular Beamlines

Proton beam treatment for ocular tumors has been well established with dedicated eye beamlines internationally. Given the emergence of universal, high-energy, non-fixed beamline options, we share key practices for uveal melanoma (UM) treatment planning and delivery. We focus particularly on practical clinical and physics concepts to minimize important ocular side effects. Practices were studied from two well-established international dedicated proton ocular institutions with very longstanding facilities, both using fixed, low-energy, ocular beamlines to treat eye tumors only. Since the 1970s and 1980s until now, the respective cyclotrons produce 67.5 and 60.0 MeV proton beams (range up to 3 cm). In total 5927 ocular patients, 93% with UM, have been treated. Standard UM dose is 56 Gray Equivalent (GyE) and 57.2 GyE, respectively, delivered in 4 fractions. Planning and delivery procedures were analyzed as a bi-institutional effort to communicate key concepts to newer developing proton centers. Normal eye tissue sparing is related to critical beam characteristics provided in the setting of low-energy dedicated eye beamlines. Both centers offer a very sharp dose fall off (distal ∼1 mm and lateral ∼1.1-1.6 mm), high dose homogeneity, excellent range precision and short treatment time (∼0.5-2 minutes). Planned doses to critical ocular structures are independent predictors of ocular complications such as vision loss and neovascular glaucoma, including the following parameters: 28 GyE to macula [P<.0001], optic nerve [P<0.0004], lens [P<.0001], and ciliary body [P<.0001]. A systematic tumor/critical structure dose evaluation is used to optimize treatment parameters, i.e. lateral margin, distal range, gaze angle, and aperture shape. New high-energy non-dedicated beam designs, which degrade energy to deliver ocular treatment, may require significant beam adjustment and treatment planning procedures to achieve adequate characteristics. Regarding UM dose, a common regimen is 60 GyE in 4 fractions globally. Unrandomized early retrospective data shows lower local tumor control with 48 GyE (P = 0.02). Critical structures including the retina, lacrimal gland, cornea, tear ducts, lids, bony orbit, and limbal stem cells are methodically evaluated to minimize side effects. Eyelid toxicity is reduced by institutional retraction techniques or treatment through closed lids. Experienced international specialty proton ocular centers with dedicated, low-energy, fixed eyelines, provide important practical concepts for consideration by developing centers to optimize high-energy universal beamline designs for eye treatments. As new centers with different beam designs emerge globally, key clinical and treatment planning/delivery practices will need to be applied, particularly to reduce potential normal tissue toxicity for ocular patients.

The p(20)+Be reaction as a source of fusion relevant neutrons

The p(20)+Be neutron source reaction was investigated at the Nuclear Physics Institute of the Czech Academy of Sciences using the 20 MeV proton beam on thick beryllium target (thickness of 8 mm). Neutron field in close source-to-sample distances was determined by means of the activation foils technique; set of ten activation foils (Al, Ti, Co, Fe, Ni, Y, In, Nb, Lu, Au) was utilized. Neutron spectrum reconstruction from reaction rates obtained using the gamma-spectroscopy method (semiconductor HPGe detectors) was performed utilizing the modified version of SAND-II unfolding code and relevant activation cross-sections from the EAF-2010 nuclear database. Determined neutron energy spectra were validated against the MCNPX calculations. Developed p(20)+Be neutron field with broad spectrum represents a useful tool for the cross-section data validation within the ITER and IFMIF-DONES research programs (≥ 12 MeV), neutron-hardness tests of microelectronics, study of material damage, and calibration of new detection systems.

22 dB Signal-to-Noise Ratio Real-Time Proton Sound Detector for Experimental Beam Range Verification

This paper presents the design and experimental characterization of a Proton Sound Detector (ProSD), a device that physically captures and senses the weak acoustic signal emitted by the fast energy deposition at the end of the same proton beam range. The measured acoustic signal Time-of-Flight provides a very accurate (13 μm accuracy) measure of the proton beam penetration depth in water, improving the proton range verification accuracy w.r.t. previous works in pre-clinical scenarios. This suggests interesting possibilities for high-accuracy and real-time beam monitoring and calibration in hadron-therapy for cancer treatment. The detector has been fully characterized and tested with a physical 20 MeV proton beam in a water energy absorber. The ProSD and the water tank have been mounted in front of the exit layer of a 20 MeV 120 ns pulse time-width proton beam. A clear sinusoidal-like acoustic signal of 5 Pa and 2.3 MHz frequency has been detected at 12 dB SNR with 0.8 Gy single shot dose. After averaging 10 beam shots the achieved Signal-to-Noise-Ratio is 22 dB allowing a ±7.5 μm precision vs. previously reported ±45μm ionoacoustic precision.