Low Energy Proton Beam Research Articles

155Tb production by cyclotrons: what level of 155Gd enrichment allows clinical applications?

Background155Tb represents a potentially useful radionuclide for diagnostic medical applications, but its production remains a challenging problem, in spite of the fact that many production routes have been already investigated and tested. A recent experimental campaign, conducted with low-energy proton beams impinging on a 155Gd target with 91.9% enrichment, demonstrated a significant co-production of 156gTb, a contaminant of great concern since its half-life is comparable to that of 155Tb and its high-energy γ emissions severely impact on the dose released and on the quality of the SPECT images. In the present investigation, the isotopic purity of the enriched 155Gd target necessary to minimize the co-production of contaminant radioisotopes, in particular 156gTb, was explored using various computational simulations.ResultsStarting from the recent experimental data obtained with a 91.9% 155Gd-enriched target, the co-production of other Tb radioisotopes besides 155Tb has been theoretically evaluated using the Talys code. It was found that 156Gd, with an isotopic content of 5.87%, was the principal contributor to the co-production of 156gTb. The analysis also demonstrated that the maximum amount of 156Gd admissible for 155Tb production with a radionuclidic purity higher than 99% was 1%. A less stringent condition was obtained through computational dosimetry analysis, suggesting that a 2% content of 156Gd in the target can be tolerated to limit the dose increase to the patient below the 10% limit. Moreover, it has been demonstrated that the imaging properties of the produced 155Tb are not severely affected by this level of impurity in the target.Conclusions155Tb can be produced with a quality suitable for medical applications using low-energy proton beams and 155Gd-enriched targets, if the 156Gd impurity content does not exceed 2%. Under these conditions, the dose increase due to the presence of contaminant radioisotopes remains below the 10% limit and good quality images, comparable to those of 111In, are guaranteed.

Gas sheet beam induced fluorescence based beam profile measurement for high intensity proton accelerators

The paper describes the design simulations, developmental details and characterization results of a dual gas sheet generator system for non-invasive beam profile measurement of high-intensity proton beams. The system is being developed for the Low Energy High Intensity Proton Accelerator facility at Bhabha Atomic Research Centre, India. To our knowledge, this is the first time an intense low energy proton beam was used to directly view the beam induced fluorescence of a gas sheet. The system works by generating two thin nitrogen gas sheets which produces fluorescence when a charged particle beam passes through them, thereby providing a visual representation of the beam's intensity profile. The gas sheets are generated at 45° to the beam axis, which allows the fluorescence created by the interaction to be viewed directly through a viewport or camera capture. The beam profile measurements were carried out with a typically 20 keV, 10 mA pulsed proton beam from an ECR ion source under different operating parameters like gas sheet pressure, beam current, beam energy and focusing magnetic field. The Geant4 simulation has been performed to study the scintillation process and optical transport. It may become useful to study methods of reconstructing the beam profile from image obtained.

Beam dynamic design and study of a linac with variable output energy for an AB-BNCT facility

The Accelerator-based Boron Neutron Capture Therapy (AB-BNCT) is being established worldwide as a future modality to start an era of in-hospital facilities. The most popular reaction for AB-BNCT is 7Li(p, n)7Be and high-flux neutron beams can be produced by bombarding lithium targets with low-energy proton beams. We chose the combined acceleration structure of Radio Frequency Quadrupole linac (RFQ) and Cross-bar H-mode DTL (CH-DTL) considering the compactness of the structure and the adjustment of output energy. The CW proton beam could be accelerated to 1.8 MeV by one RFQ cavity, and then to the final energy by one CH-DTL cavity. The output beam energy can be adjusted in the range of 2.2 MeV to 3.0 MeV with small beam loss and high beam quality, which could be achieved by controlling the feed power and RF phase of the CH-DTL. The variation of beam energy can meet requirements of the BNCT in treating tumors of different depths without adjusting structure of beam shaping assembly (BSA). The beam dynamics of the RFQ and DTL were completed to meet all requirements and the energy stability and adjustment method of output beam were investigated. In addition, we also performed the start-to-end beam tracking and error sensitivity analysis at last.

Development of an external PIGE method using nitrogen from atmospheric air as external beam current normalizer and its application to nondestructive quantification of total boron mass fraction in boron containing neutron absorbers

Beam current monitoring and normalization is a very important task in ion beam analysis experiments. Compared to current monitoring by conventional method, in situ or external beam current normalization is attractive in Particle Induced Gamma-ray Emission (PIGE), which involves simultaneous measurement of prompt gamma rays of analyte of interest and current normalizing element. In the present work, an external (in air) PIGE method has been standardized for quantification of low Z elements using nitrogen from atmospheric air as external current normalizer, in which 2313 keV of 14N(p,p’γ)14N is measured. It provides truly nondestructive and greener quantification method for low Z elements by external PIGE. The method was standardized by quantifying total boron mass fractions in ceramic/refractory boron-based samples using low energy proton beam from tandem accelerator. The samples were irradiated with 3.75 MeV proton beam and prompt gamma rays of analyte at 429, 718 and 2125 keV of 10B(p,αγ)7Be, 10B(p,p’γ)10B and 11B(p,p’γ)11B, respectively, and external current normalizers at 136 and 2313 keV were measured simultaneously using high resolution HPGe detector system. The obtained results were compared with external PIGE method using tantalum as external current normalizer, where 136 keV of 181Ta(p,p’γ)181Ta from beam exit window material (Ta) was used for current normalization. The developed method is found to be simple, rapid, convenient, reproducible, truly nondestructive and more economical as no additional beam monitoring instruments are required and it is especially advantageous for direct quantitative analysis of ‘as received’ samples.

An investigation of luminescence properties of CaF2: Dy nanophosphor irradiated with gamma rays and low energy proton beams

This paper reports the luminescence properties of nanocrystalline calcium fluoride doped with dysprosium (CaF2: Dy). The nanophosphor has been synthesized by the chemical co-precipitation technique and the dopant concentration has been optimized at 0.3 mol% using thermoluminescence (TL) intensity emitted post 50Gy gamma dose irradiation of samples doped with different dopant concentrations. X-ray diffraction shows the formation of crystalline particles with an average size of 49.233 nm. Photoluminescence (PL) emission spectrum shows the characteristic peaks at 455 nm, 482 nm, 573 nm corresponding to 4I15/2 to 6H15/2, 4F9/2 to 6H15/2 and 4F9/2 to 6H13/2 Dy3+ transitions respectively. PL excitation spectrum shows a peak at 327 nm which corresponds to the Dy3+ transition of 6H15/2 to 4L19/2. Gamma (of 1.25 MeV) and low energy proton beam (of 30 keV) irradiated nanophosphor shows a variation in TL glow curve structure and peak position with an increase in radiation dose/fluence. However, the nanophosphor shows a wide linear dose response for 60Co gamma radiation in the range 10 Gy - 1.5 kGy and for low energy proton beam in the fluence range of 1012–1014 ions/cm2. Srim 2013 has been used to calculate the ion beam parameters including the range of protons in CaF2: Dy 0.3 mol%. The nanophosphor CaF2: Dy could be further investigated as a potential dosimeter for gamma rays and proton beam by studying its TL properties for different energies of these radiations.

General Purpose Transistor Characterized as Dosimetry Sensor of Proton Beams.

A commercial pMOS transistor (MOSFET), 3N163 from Vishay (USA), has been characterized as a low-energy proton beam dosimeter. The top of the samples' housing has been removed to guarantee that protons reached the sensitive area, that is, the silicon die. Irradiations took place at the National Accelerator Centre (Seville, Spain). During irradiations, the transistors were biased to improve the sensitivity, and the silicon temperature was monitored activating the parasitic diode of the MOSFET. Bias voltages of 0, 1, 5, and 10 V were applied to four sets of three transistors, obtaining an averaged sensitivity that was linearly dependent on this voltage. In addition, the short-fading effect was studied, and the uncertainty of this effect was obtained. The bias voltage that provided an acceptable sensitivity, (11.4 ± 0.9) mV/Gy, minimizing the uncertainty due to the fading effect (-0.09 ± 0.11) Gy was 1 V for a total absorbed dose of 40 Gy. Therefore, this off-the-shelf electronic device presents promising characteristics as a dosimeter sensor for proton beams.

Monte Carlo study of nanoparticles effectiveness on the dose enhancement when irradiated by protons

Recently, the nanomedicine field has experienced considerable growth in research. The use of nanoparticles to enhance dose in radiation treatment was proposed and their potential effects can be indicated using Monte Carlo calculations. The main goal of this study focused on nanoparticles’ (NPs) effects on dose enhancement due to the low-energy protons because the majority of studies on NPs have been conducted for photon radiations. To investigate the effect of NPs on the Dose Enhancement Factor (DEF), a cell dimension phantom was modeled and spheres of NPs were localized inside that. Different NPs, such as Au, Pt, Ag, I, and Ta2O3, were located in the phantom, and the DEF was calculated by changing the source energy from 3 to 15 MeV. The purpose of investigating the low-energy proton beam is to clarify the effects around the Bragg peak in the presence of nanoparticles. For protons with an energy range of 3–15 MeV, it was discovered that Pt nanoparticles have a greater dose increase coefficient of about 1.8 times compared to the other nanoparticles. The findings indicated that the DEF values substantially depended on the NPs concentration, but that the DEF was not significantly affected by changes in concentration or nanoparticle size. Comparative calculations between water and soft tissue phantoms that were filled with NPs presented a difference of less than 2%. The obtained findings emphasized the importance of NPs and considered details, such as concentration, to demonstrate the potential of nanoparticles in improving treatment using protons.

Novel Ultraviolet and Ionizing Radiation Detectors Made From TiO Wide-Bandgap Semiconductor

We describe the fabrication and characterization of a novel ultraviolet (UV) and ionizing radiation detector using a polycrystalline TiO2 wide-bandgap semiconductor as the active material. The detector geometry we have developed and tested is a polycrystalline TiO2 thin film with planar electrode contacts for signal pickup. Several prototypes were fabricated using two single-step techniques. We present the dc characterization of these devices and the signal response to the UV light and low-energy proton beam irradiation. The detector prototypes show excellent dc characteristics and fast ac signal response at bias voltage as low as 50 V.

Production of radioisotopes for cancer imaging and treatment with compact linear accelerators

Accelerator-produced radioisotopes are widely used in modern medicine, for imaging, for cancer therapy, and for combinations of therapy and diagnostics (theragnostics). Clinical trials are well advanced for several radioisotope-based treatments that might open the way to a strong request of specific accelerator systems dedicated to radioisotope production. While cyclotrons are the standard tool in this domain, we explore here alternative options using linear accelerators. Compared to cyclotrons, linacs have the advantage of modularity, compactness, and reduced beam loss with lower shielding requirements. Although in general more expensive than cyclotrons, linacs are competitive in cost for production of low-energy proton beams, or of intense beams of heavier particles. After a review of radioisotopes of potential interest, in particular produced with low-energy protons or helium, this paper presents two linac-based isotope production systems. The first is a compact RFQ-based system for PET (Positron Emission Tomography) isotopes, and the second is an alpha-particle linac for production of alpha-emitters. The accelerator systems are described, together with calculations of production yields for different targets.

Absolute dose measurement and energy dependence of LiF dosimeters in proton therapy beam dosimetry

Background: For the purpose of patient dose monitoring, thermoluminescent dosimeters (TLDs) can report any dose point of interest as in vivo dosimetry. However, energy dependence of TLDs may perturb proton beam dosimetry, particularly for low-energy proton beams. The purpose of this study was to evaluate the energy dependence of TLDs for proton beams and influence on dosimetry.

Characterisation of a scintillating fibre-based hodoscope exposed to the CNAO low-energy proton beam

A 32 × 32 Bicron 1 mm2 polystyrene scintillating fibre-based beam hodoscope, with an entrance window of 6.3 × 6.3 cm2, has been designed and characterised for monitoring low-energy charged particle beams. The hodoscope, designed to fit into the 60 MeV/c negative muon beam at the RIKEN-RAL muon facility (UK) for the FAMU experiment, will enable muon counting for data normalisation. We describe a calibration technique to enable the detector to work as a muon stream counter by knowing the muon equivalent charge deposited in the detector. This value is obtained by exposing the detector to a single-proton beam at the CNAO hadron therapy synchrotron, with the energy set to have the same energy loss profile as 60 MeV/c negative muons.

Cross-section measurement for an optimized 61Cu production at an 18 MeV medical cyclotron from natural Zn and enriched 64Zn solid targets

The availability of novel medical radionuclides is a key point in the development of personalised nuclear medicine. In particular, copper radioisotopes are attracting considerable interest as they can be used to label various molecules of medical interest, such as proteins and peptides, and offer two of the most promising true theranostic pairs, namely 61Cu/67Cu and 64Cu/67Cu. Although 64Cu (t1/2 = 12.7006 h, β+: 17.6%, β−: 38.5%) is nowadays the most commonly used as a diagnostic radionuclide, 61Cu (t1/2 = 3.339 h, β+: 61%) features more favourable nuclear properties, such as a higher positron decay fraction and the absence of β− emissions. To date, the production of 61Cu has been carried out irradiating highly enriched 61Ni targets with a low energy proton beam. However, the use of the very expensive 61Ni targets requires an efficient recovery of the target material and makes this method quite inconvenient. Another promising production route is the proton irradiation of natural Zn or enriched 64Zn targets, exploiting the (p,α) nuclear reaction. Along this line, a research program is ongoing at the Bern medical cyclotron, equipped with an external beam transfer line and a solid target station. In this paper, we report on cross-section measurements of the 64Zn(p,α)61Cu nuclear reaction using natural Zn and enriched 64Zn material, which served as the basis to perform optimized 61Cu production tests with solid targets.

Characterising potential space suit textiles in proton beams using radiotherapy-based dosimetry

Four multi-layer textile samples for potential use in space suits, developed within the Planetary Exploration Textiles project of the European Space Agency, were exposed to a low energy proton beam, to characterise their effect on dose deposition in astronauts. Each textile stack contained all required layers for a potential space suit component. The influence of the textiles on proton beams was investigated using dosimetric equipment as utilised for medical purposes. The experiments were conducted at the synchrotron-based therapy and research centre MedAustron, Austria. To quantify the radiation characteristics, the water equivalent thickness of the fabrics was determined. A PEAKFINDERsystem (PTW, Freiburg, Germany) was positioned downstream of the textiles and the positions of the Bragg peaks were measured and compared to the range without any material in front. As reference values aluminium and lead plates were used and the results of the textiles were normalised to these materials. Furthermore, proton threshold energies for stopping protons in the suit materials were calculated. The position of the Bragg peak was shifted between 1.2mm to 2.6mm depending on the textile stacks. This corresponds to a proton threshold energy for the investigated stacks between 10–15MeV. The study showed that methods used in particle therapy are appropriate tools to quantify characteristics of space suit materials in proton beams. However, the effect of the investigated textiles on proton beams was comparable among the used fabrics.

High-frequency structure design and RF stability analysis of a 4-vane radio frequency quadrupole with pi-mode stabilizer loops

Compact accelerator-based neutron source facilities are garnering attention and play an important and expanding role in material and engineering sciences, as well as in neutron science education and training. Neutrons are produced by bombarding a low-energy proton beam onto a beryllium or lithium target. In such an accelerator-based neutron source, a radio frequency quadrupole (RFQ) is usually utilized to accelerate a high-intensity proton beam to a few MeV. This study mainly covers the high-frequency structure design optimizations of a 4-vane RFQ with pi-mode stabilizer loops (PISLs) and its RF stability analysis. A 176 MHz RFQ accelerator is designed to operate at a 10% duty factor and could accelerate an 80 mA proton beam from 65 keV to 2.5 MeV within a length of 5.3 m. The adoption of PISLs ensures high RF stability, eases the operation of the accelerator, and implies less stringent alignment and machining tolerances.

The Extended Field-aligned Suprathermal Proton Beam and Long-lasting Trapped Energetic Particle Population Observed Upstream of a Transient Interplanetary Shock

Abstract The properties of the suprathermal particle distributions observed upstream of interplanetary shocks depend not only on the properties of the shocks but also on the transport conditions encountered by the particles as they propagate away from the shocks. The confinement of particles in close proximity to the shocks, as well as particle scattering processes during propagation to the spacecraft, lead to the common observation of upstream diffuse particle distributions. We present observations of a rare extended anisotropic low-energy (≲30 keV) proton beam together with a trapped ≳500 keV proton population observed in association with the arrival of an oblique interplanetary shock at the Advanced Composition Explorer, the Interplanetary Monitoring Platform-8, and the Wind spacecraft on 2001 January 31. Continuous injection of particles by the traveling shock into a smooth radial magnetic field region formed in the tail of a modest high-speed solar wind stream produced an extended foreshock region of energetic particles. The absence of enhanced magnetic field fluctuations upstream of the shock results in the observation of a prolonged anisotropic field-aligned beam of ≲30 keV protons as well as a population of higher-energy (≳500 keV) protons with small pitch-angle cosine (μ ∼ 0) extending far from the shock.

Rb83/Kr83m production and cross-section measurement with 3.4 MeV and 20 MeV proton beams

$^{83m}\mathrm{Kr}$, with a short lifetime, is an ideal calibration source for liquid xenon or liquid argon detectors. The $^{83m}\mathrm{Kr}$ isomer can be generated through the decay of the $^{83}\mathrm{Rb}$ isotope, which is usually produced by proton beams bombarding natural krypton atoms. In this paper, we report a successful production of $^{83}\mathrm{Rb}/^{83m}\mathrm{Kr}$ with a proton beam energy of 3.4 MeV, and the first measurement of the production rate with such low-energy proton beams. Another production attempt is performed using the newly available 20 MeV proton beam in China, and the measured production rate is consistent with previous measurements. The produced $^{83m}\mathrm{Kr}$ source has been successfully injected into the PandaX-II liquid xenon detector, yielding enough statistics for detector calibration.

An Investigation of Luminescence Properties of Caf2: Dy Nanophosphor Irradiated with Gamma Rays and Low Energy Proton Beams

An Investigation of Luminescence Properties of Caf2: Dy Nanophosphor Irradiated with Gamma Rays and Low Energy Proton Beams

High-contrast low-dose proton radiography of thin samples at the Tandetron accelerator

We investigate the ability of using high-resolution position-sensitive pixel detector and standard non-scanning beams of low-energy protons in air as a flexible tool and simplified technique for density-sensitivity imaging of thin samples. Proton radiography can provide high contrast and low radiation dose delivered to the inspected sample. Density-sensitive contrast response can be provided by a single proton per imaging pixel. For this purpose, we use the silicon semiconductor high-resolution pixel detector Timepix3 to evaluate particle radiography of thin samples with monoenergetic low-energy proton beams from the Tandetron light-ion accelerator. Measurements were performed with various well-defined thin samples. A proton micro beam was used to test and evaluate the technique. Spatial information of the samples is provided by the imaging detector. Density-sensitive contrast is obtained from the measurement of small differences in the deposited energy of transmitted protons across the sample. The transmitted protons are detected with high spatial resolution in the pixel detector. The single particle tracks registered in the detector are analysed by detailed pattern recognition algorithms. Various of these track parameters of spectral response are used for imaging contrast. Resulting proton radiographies for various well-defined thin samples are presented.

Target manufacturing by Spark Plasma Sintering for efficient 89Zr production

Zirconium-89 (89Zr) is an emerging radionuclide for positron emission tomography (PET), with nuclear properties suitable for imaging slow biological processes in cellular targets. The 89Y(p,n)89Zr nuclear reaction is commonly exploited as the main production route with medical cyclotrons accelerating low-energy (< 20 MeV) and low-current (< 100 μA) proton beams. Usually, natural yttrium solid targets manufactured by different methods, including yttrium electrodeposition, yttrium sputtering, compressed yttrium powders, and foils, were employed. In this study, the Spark Plasma Sintering (SPS) technique has been investigated, for the first time, to manufacture yttrium solid targets for an efficient 89Zr radionuclide yield. The natural yttrium disc was bonded to a niobium backing plate using a commercial SPS apparatus and a prototype machine assembled at the University of Pavia. The resulting targets were irradiated in a TR19 cyclotron with a 12 MeV proton beam at 50 μA. A dedicated dissolution module, obtained from a commercial system, was used to develop an automated process for the purification and recovery of the produced 89Zr radionuclide. The production yield and recovery efficiency were measured and compared to 89Zr produced by irradiating standard yttrium foils. SPS manufactured targets withstand an average heat power density of approximately 650 W∙cm−2 for continuous irradiation up to 5 h without visible damage. A saturation yield of 14.12 ± 0.38 MBq/μAh was measured. The results showed that the obtained 89Zr production yield and quality were comparable to similar data obtained using standard yttrium foil targets. In conclusion, the present work demonstrates that the SPS technique might be a suitable technical manufacturing solution aimed at high-yield 89Zr radioisotope production.

Microdosimetry in low energy proton beam at therapeutic-equivalent fluence rate with silicon 3D-cylindrical microdetectors

In this work we show the first microdosimetry measurements on a low energy proton beam with therapeutic-equivalent fluence rates by using the second generation of 3D-cylindrical microdetectors. The sensors belong to an improved version of a novel silicon-based 3D-microdetector design with electrodes etched inside silicon, which were manufactured at the National Microelectronics Centre (IMB-CNM, CSIC) in Spain. A new microtechnology has been employed using quasi-toroid electrodes of 25 μm diameter and a depth of 20 μm within the silicon bulk, resulting in a well-defined cylindrical radiation sensitive volume. These detectors were tested at the 18 MeV proton beamline of the cyclotron at the National Accelerator Centre (CNA, Spain). They were assembled into an in-house low-noise readout electronics to assess their performance at a therapeutic-equivalent fluence rate. Microdosimetry spectra of lineal energy were recorded at several proton energies starting from 18 MeV by adding 50 μm thick tungsten foils gradually at the exit-window of the cyclotron external beamline, which corresponds to different depths along the Bragg curve. The experimental values in silicon cover from (5.7 ± 0.9) to (8.5 ± 0.4) keV μm−1 in the entrance to (27.4 ± 2.3) keV μm−1 in the distal edge. Pulse height energy spectra were crosschecked with Monte Carlo simulations and an excellent agreement was obtained. This work demonstrates the capability of the second generation 3D-microdetectors to assess accurate microdosimetric distributions at fluence rates as high as those used in clinical centers in proton therapy.