Proton-induced Nuclear Reactions Research Articles

Proton-induced reactions for 47Sc (and 46Sc) production: new nuclear cross section measurements on enriched titanium targets

Abstract47Sc is a theranostic radionuclide under the spotlight of the scientific community thanks to its potential for SPECT imaging and therapeutic applications. This work presents the recent measurements of proton-induced nuclear reaction cross-sections aimed at 47Sc production using enriched 48Ti, 49Ti and 50Ti targets from 23 up to 70 MeV. Since the co-production of contaminant isotopes is a key issue, and 46Sc is the main one having a longer half-life than 47Sc, the 48/49/50Ti(p,x)47Sc and 46Sc cross sections are presented and compared with the scarce literature data and TALYS estimations.

Technical note: Implementing MRI/CT-based elemental concentration data to Monte Carlo simulation for yielding positron emitters in proton therapy.

The elemental concentration (especially oxygen and carbon) and mass density must be accurately assigned to perform Monte Carlo (MC) simulations for predicting proton-induced nuclear reactions in the human body. We recently proposed an approach to quantify elemental concentrations and mass densities of human soft tissues from water content (WC) data obtained by quantitative magnetic resonance (MR) imaging (which we called "MRWC"). This study presents the first implementation of MRWC-derived elemental concentrations and mass densities as complementary inputs into MC simulations on a virtual head phantom, and demonstrates the simulation of positron emitter production yields in proton therapy. An MC code, PHITS, was used to simulate proton therapy with a monoenergetic 140 MeV beam for a digital head phantom provided by BrainWeb. Three different head images were synthesized as inputs: a conventional CT image, an ideal CT image as a reference, and a WC image coupled with the bone-only CT image for a hybrid approach (MRWC/CT). Thereafter, the performance of the MRWC/CT method was evaluated by comparing its accuracy in predicting the production yields of positron emitters (11C and 15O) with the gold-standard CT-only method. The MRWC/CT method could predict 11C and 15O production yield maps that closely resembled the corresponding reference maps, while the CT-only method failed. The structural similarity index measures between the reference and CT- or MRWC/CT-derived maps were improved from 0.67 (CT-only) to 0.87 (MRWC/CT) for 11C and 0.76 (CT-only) to 0.93 (MRWC/CT) for 15O. Furthermore, applying post-processing normalizations to account for elemental density variations in the production yields of positron emitters facilitated the determination of distal fall-off positions in depth activity profiles. At least in the head area, the MRWC/CT method demonstrated potential for more precise predictions of proton-induced positron emitter distributions via MC simulations than that of the CT-only method.

Excitation functions of proton-induced nuclear reactions on natCaCO3 up to 60 MeV

47Sc could be used in SPECT imaging and is also suitable for targeted therapy of small tumours. Application of 47Sc is quite promising as theranostic with its diagnostic pair 44Sc or 43Sc. Excitation functions for the production of 47Sc and its accompanying impurities through proton bombardment of natural calcium carbonate (natCaCO3) targets were experimentally evaluated and compared with both previous measurements and TALYS predictions. The integral production yields of 47Sc, as well as the main impurities 44m,46,48Sc, were calculated. The consistency of the results with available experimental data was verified for each reaction. The target yield was determined using the measured activity of the produced radionuclides.

γ-ray emission in proton-induced nuclear reactions on [formula omitted]C and Mylar targets over the incident energy range, Ep = 30 – 200 MeV. Astrophysical implications

We have measured the γ-ray line production cross sections in proton-induced nuclear reactions on various target nuclei (12C, 16O, 24Mg, 28Si, 56Fe) of chemical elements abundant in astrophysical sites (solar flares, the interstellar medium, cosmic compact objects) over the incident energy range of Ep = 30 – 200 MeV. We carried out experimental campaigns in joint collaboration at the K = 200 separated sector cyclotron of iThemba LABS using a high-energy resolution, high-efficiency detection array composed of 8 Compton-suppressed clover detectors comprising 32 HP-Ge crystals for recording the γ-ray energy spectra. In the current paper, we focus on γ-ray de-excitation lines produced in proton irradiations of natC and Mylar targets, in particular, on the prominent 4.439 and 6.129 MeV lines of 12C and 16O which are among the strongest lines emitted in solar flares and in interactions of low-energy cosmic rays (LECRs) with the gas and dust of the inner galaxy. We report new γ-ray production experimental cross section data for ten nuclear γ-ray lines that we compare to previous low-energy data sets from the literature, to the predictions of the TALYS code of nuclear reactions and to a semi-empirical compilation. In the first approach, performing calculations with default input parameters of TALYS we observed substantial deviations between the predicted cross sections and experimental data. Then, using modified optical model potential (OMP) and nuclear level deformation parameters as input data we generated theoretical excitation functions for the above two main lines fully consistent with experimental data. In contrast, the experimental data sets for the other eight analyzed lines from the two proton-irradiated targets exhibit significant deviations with the predicted cross section values. We also report line-shape experimental data for the line complex observed at Eγ = 4.44 MeV in irradiations of the two targets. Finally, we emphasize the astrophysical implications of our results.

Production of 11C, 13N and 15O in proton-induced nuclear reactions up to 200 MeV

Production cross sections of light positron emitters 11C (t1/2=20.36 min), 13N (t1/2=9.97 min) and 15O (t1/2=122 s) have been measured for proton-induced reactions on the main relevant constituents of the human body (C, N and O) from threshold up to 200 MeV of proton incident energy. This has been accomplished by means of two complementary experiments at the clinical proton treatment centers WPE (Essen) and HIT (Heidelberg), both in Germany. In the first case, the multi-foil activation technique was combined with PET imaging, a methodology previously developed at CNA (Seville, Spain). In the second experiment, aimed at energies below 50 MeV, the activation of single foils was measured with conventional LaBr3 detectors. In both cases the IAEA monitor reaction natCu(p,x)63Zn data was used for validation purposes.The most complete and accurate set of excitation functions for the production of light-positron emitters 11C, 13N and 15O in proton induced reactions on human tissue up to 200 MeV is presented. These data are needed for nuclear reaction model development and are extremely important to improve the accuracy of the PET range verification in proton radiotherapy. Seven excitation functions have been measured: 12C(p,x)11C, 14N(p,x)11C, 14N(p,x)13N, 14N(p,γ)15O, 16O(p,x)11C, 16O(p,x)13N and 16O(p,x)15O up to 200 MeV of proton incident energy.

Bayesian evaluation of residual production cross sections in proton-induced nuclear spallation reactions

Residual production cross sections in spallation reactions are key data for nuclear physics and related applications. Spallation reactions are very complex due to the wide range of incident energies and abundant fragments involved. Therefore, it is challenging to obtain accurate and complete energy-dependent residual cross sections. With the guidance of a simplified EPAX formula (sEPAX), the Bayesian neural network (BNN) technique is applied to form a new machine learning model (BNN + sEPAX) for predicting fragment cross sections in proton-induced nuclear spallation reactions. Three types of sample dataset for measured residual production cross sections in proton-induced nuclear spallation reactions are made, i.e. D1 consists of isotopic cross sections in reactions below 1 GeV/u, D2 consists of fragments excitation functions of reactions up to 2.6 GeV/u, and D3 is a hybrid of D1 and D2. With the constructed BNN and BNN + sEPAX models, the isotopic and mass cross section distributions are compared for the 356 MeV/u 40Ca + p and 1 GeV/u 136Xe + p reactions, and fragment excitation functions in 40Ca + p, 56Fe + p, 138Ba + p and 197Au + p reactions. It is found that the BNN model needs sufficient information to achieve good extrapolations, while the BNN + sEPAX model performs better extrapolations based on less information due to the physical guidance of the sEPAX formulas. It is suggested that the BNN + sEPAX model provides a new approach to predict the energy-dependent residual production cross sections produced in proton-induced nuclear spallation reactions of incident energies from tens of MeV/u up to several GeV/u.

Excitation functions of proton-induced nuclear reactions on ^{86}Sr, with particular emphasis on the formation of isomeric states in ^{86}Y and ^{85}Y

Cross sections of proton-induced nuclear reactions on enriched ^{mathrm {86}}Sr target were measured by the activation technique up to proton energies of 44 MeV. The isomeric cross-section ratios for ^{mathrm {86m,g}}Y and ^{mathrm {85m,g}}Y as a function of projectile energy were deduced from their measured data. The present experimental data for the nuclear reaction products, namely ^{mathrm {86m}}Y, ^{mathrm {86g+xm}}Y, ^{mathrm {85m}}Y, ^{mathrm {85g}}Y, ^{mathrm {84}}Rb and ^{mathrm {83}}Rb were compared with the results of nuclear model calculations using the code TALYS, which combines the statistical, precompound, and direct interactions. In general, the experimental cross-section data as well as the isomeric cross-section ratios are reproduced well by the model calculations, provided the input model parameters are properly chosen and the level structure of the product nucleus is thoughtfully considered. The quality of the agreement between experimental data and model calculations was numerically quantified. For products formed via emission of a light complex particle as well as multi-nucleons (e.g., alpha and 2p2n), the contribution of the latter process starts increasing when its energy threshold is crossed.

Excitation functions of natNi(p, x) reactions in the energy range of 75–100 MeV

Stacked-foil activation technique and high-resolution gamma spectrometry were used to investigate new excitation functions of proton-induced nuclear reactions on natNi targets in the energy range of 75–100 MeV. The stack foils were irradiated with 100 MeV protons at the separated-sector cyclotron of the Institute of Modern Physics, Chinese Academy of Sciences, China. The proton intensity for each nickel foil was determined using the natNi(p, x)57Ni monitor reaction. The cross-sections of the natNi(p, x)56Ni, 55,57,58Co, and 54Mn reactions were calculated and compared with the existing literature data presented in the Experimental Nuclear Reaction Data (EXFOR). Furthermore, evaluated nuclear data of the PADF-2007, ENDF/B-VIII.0, and JENDL-4.0/HE libraries as well as theoretical calculations of the TALYS code were used. Overall, our experimental data agree with the majority of the literature data. The results of TALYS code as well as the ENDF/B-VIII.0 and JENDL-4.0/HE libraries could reproduce most of the experimental trend, whereas the results of PADF-2007 library could not do so. The new experimental results provide cross-sections for proton-induced natNi reactions in the energy range of 75–100 MeV and could serve as a technical assistance for radionuclide production and radiation safety practices.

Collisions of Nucleons with Atoms: Calculated Cross Sections and Monte Carlo Simulation

After a summary description of the theory of elastic collisions of nucleons with atoms, we present the calculation of a generic database of differential and integrated cross sections for the simulation of multiple elastic collisions of protons and neutrons with kinetic energies larger than 100 keV. The relativistic plane-wave Born approximation, with binding and Coulomb-deflection corrections, has been used to calculate a database of proton-impact ionization of K-shell and L-, M-, and N-subshells of neutral atoms These databases cover the whole energy range of interest for all the elements in the periodic system, from hydrogen to einsteinium (Z = 1–99); they are provided as part of the penh distribution package. The Monte Carlo code system penh for the simulation of coupled electron-photon-proton transport is extended to account for the effect of the transport of neutrons (released in proton-induced nuclear reactions) in calculations of dose distributions from proton beams. A simplified description of neutron transport, in which neutron-induced nuclear reactions are described as a fractionally absorbing process, is shown to give simulated depth-dose distributions in good agreement with those generated by the Geant4 code. The proton-impact ionization database, combined with the description of atomic relaxation data and electron transport in penelope, allows the simulation of proton-induced x-ray emission spectra from targets with complex geometries.

Evaluation of production cross-sections for theranostic 67Cu radionuclide via proton-induced nuclear reaction on 68Zn target

Copper-67 (T1/2 = 61.83 h, Eβ−mean=141 keV, Iβ−total=100%; Eγ = 184.577 keV, Iγ = 48.7%) is a promising radionuclide for theranostic applications especially in radio immunotherapy. However, one of the main drawbacks for its application is related to its limited availability. Various nuclear reaction routes investigated in the last years can result in 67Cu production, although the use of proton beams is the method of choice taken into account in this work. The goal of this work is a revision of the cross-sections aimed at 67Cu yield, which were evaluated for the 68Zn(p,2p)67Cu reaction route up to 80 MeV proton energy. A well-defined statistical procedure, i.e., the Simultaneous Evaluation on KALMAN (SOK), combined with the least-squares concept, was used to obtain the evaluated data together with the covariance matrix. The obtained evaluated data were also compared to predictions provided by the nuclear reaction model codes TALYS and EMPIRE, and a partial agreement among them has been found. These data may be useful for both existing and potential applications in nuclear medicine, to achieve an improvement and validation of the various nuclear reaction models, and may also find applications in other fields (e.g., activation analysis and thin layer activation).

Single pencil beam benchmark of a module for Monte Carlo simulation of proton transport in the PENELOPE code.

PENH is a recently coded module for simulation of proton transport in conjunction with the Monte Carlo code PENELOPE. PENELOPE applies class II simulation to all type of interactions, in particular, to elastic collisions. PENH uses calculated differential cross sections for proton elastic collisions that include electron screening effects as well as nuclear structure effects. Proton-induced nuclear reactions are simulated from information in the ENDF-6 database or from alternative nuclear databases in ENDF format. The purpose of this work is to benchmark this module by simulating absorbed dose distributions from a single finite spot size proton pencil beam in water. Monte Carlo simulations with PENH are compared with simulation results from TOPAS Monte Carlo (v3.1p2) and RayStation Monte Carlo (v6). Different beam models are examined in terms of mean energy and energy spread to match the measured profiles. The phase-space file is derived from experimental measurements. Simulated absorbed dose distributions are compared to experimental data obtained with the ionization chamber array MatriXX 2D detector (IBA Dosimetry) in a water tank. The experiments were conducted with a clinical IBA pencil beam scanning dedicated nozzle. In all simulations a Fermi-Eyges phase-space representation of a single finite spot size proton pencil beam is used. In general, there is a good agreement between simulated results and experimental data up to a distance of 3cm from the central axis. In the core region (region where the dose is more than 10% of the maximum dose) PENH shows, overall, the smallest deviations from experimental data, with the largest radial rms (root mean square) smaller than 0.2. The results achieved by TOPAS and RayStation in that region are very close to those of PENH. For the halo region, that is the area of the dose distribution outside the core region reaching down to 0.01% of the maximum intensity, the largest rms achieved by TOPAS is always smaller than 0.5, yielding better results than the rest of the codes. The physics modeling of the PENELOPE/PENH code yields results consistent with measurements in the dose range relevant for proton therapy. The discrepancies between PENH appearing at distances larger than 3cm from the central-beam axis are accountable to the lack of neutron simulation in this code. In contradistinction, TOPAS has a better agreement with experimental data at large distances from the central-beam axis because of the simulation of neutrons.

Cross section analysis of proton-induced nuclear reactions of thorium

Production cross sections of 225,226,228Ac and 226,231Th by the proton bombardment on 232Th target at the proton energies from 10MeV to 155MeV are calculated with collective semi-classical nuclear level density model (CSCFGM) by using TALYS computer code. Collective nuclear level density effect on these reactions are investigated. The importance of collective effects (rotational and vibrational) on proton induced reactions are represented. Theoretical results are compared with the experimental data taken from EXFOR library, which shows a good agreement.

Evaluation of the activation of brass apertures in proton therapy using gamma-ray spectrometry and Monte Carlo simulations

Collimating apertures are used in proton therapy to laterally conform treatment fields to the target volume. While this is a standard technique in passive spreading treatment heads, patient-specific apertures can supplement pencil-beam scanning (PBS) techniques to sharpen the lateral dose fall-off. A radiation protection issue is that proton-induced nuclear reactions can lead to the formation of radionuclides in the apertures. In the experiments of the current study, cylindrical, thick brass targets were irradiated with quasi-monoenergetic proton fields of 100.0 MeV and of 226.7 MeV in PBS mode. The radioactivation of these two brass samples was characterised with a low-level gamma-ray spectrometer. The activation products were scored in a Monte Carlo simulation, too, and compared with the experimental activities. For the high-energy field, 63Zn, 60Cu, and 61Cu were the most important short-lived isotopes regarding the measured specific activity. After irradiation with the 100.0 MeV field, 62Cu, 63Zn, and 60Cu had the highest activity. Regarding long-lived isotopes, which determine the storage time of the used apertures, the isotopes 57Co, 65Zn, 54Mn, 56Co had the largest contribution to the activity. The relative difference of activities between simulation and experiment was typically between 10%–20% for short-lived nuclides and were up to a factor of five larger for long-lived nuclides. Summarising experiments and simulations for both incident proton energies, 62Cu was the most important detected residual nucleus regardless if specific activity or equivalent dose is considered.

Cyclotron Production and Separation of Scandium Radionuclides from Natural Titanium Metal and Titanium Dioxide Targets

Theranostic strategies involve select radionuclides that allow diagnostic imaging and tailored radionuclide therapy in the same patient. An example of a Food and Drug Administration-approved theranostic pair is the 68Ga- and 177Lu-labeled DOTATATE peptides, which are used to image neuroendocrine tumors, predict treatment response, and treat disease. However, when using radionuclides of 2 different elements, differences in the pharmacokinetic and pharmacodynamic profile of the agent can occur. Theranostic agents that incorporate the matched-pair radionuclides of scandium-43Sc/47Sc or 44Sc/47Sc-would guarantee identical chemistries and pharmacologic profiles. The aim of this study was to investigate production of 43,44,47Sc via proton-induced nuclear reactions on titanium nuclei using a 24-MeV cyclotron. Methods: Aluminum, niobium, and tantalum target holders were used with titanium foils and pressed TiO2 to produce scandium radionuclides with proton energies of up to 24 MeV. Irradiated targets were digested using NH4HF2 and HCl in a closed perfluoroalkoxy alkane vessel in 90 min. Scandium radionuclides were purified via ion-exchange chromatography using branched N,N,N',N'-tetra-2-ethylhexyldiglycolamide. The titanium target material was recovered via alkali precipitation with ammonia solution. Results: Titanium foil and TiO2 were digested with an average efficiency of 98% ± 3% and 95% ± 1%, respectively. The typical digestion time was 45 min for titanium foil and 75 min for TiO2 The average scandium recovery was 94% ± 3%, and the average titanium recoveries from digested titanium foil and TiO2 after precipitation as TiO2 were 108% ± 8% and 104% ± 5% of initial mass, respectively. Conclusion: This work demonstrated a robust method for the cyclotron production of scandium radionuclides that could be used with natural or enriched TiO2 target material.

New excitation functions for proton induced reactions on natural gadolinium up to 70 MeV with focus on 149Tb production

Terbium is one of the most interesting elements for new potential theranostics applications. Indeed, the physical properties of four of its radionuclides (149Tb, 152Tb, 155Tb, 161Tb) allow their use in each main applications of nuclear medicine. 149Tb is the lowest mass alpha emitter with suitable physical properties for receptor-targeted alpha therapy (TAT), and the only one among the radiolanthanides. Currently 149Tb is only produced through spallation reactions induced by high-energy proton beam coupled with mass separation to obtain suitable purity. The aim of the present work is to investigate the production of 149Tb using commercial cyclotrons by irradiation of natural gadolinium target. New excitation functions for proton-induced nuclear reactions on natural gadolinium have been measured. Our results extend current knowledge up to 70 MeV and are in good agreement with existing data at low energy. From this new set of data, production yield estimations are calculated and discussed.

Excitation function calculations in proton-induced nuclear reactions on Zn and Cu upto 80 MeV

Nuclear reaction model codes like the EMPIRE-3.2, the ALICE-1991 and the TALYS-1.9 have been used to calculate the excitation functions of 63Cu(p,n)63Zn, 65Cu(p,n)65Zn, 66Zn(p,n)66Ga, 67Zn(p,n)67Ga, 67Zn(p,2n)66Ga, 68Zn(p,n)68Ga and 68Zn(p,2n)67Ga reactions for incident proton energy range of 1–80 MeV. These codes compute reaction cross section using the direct, the compound and the pre-equilibrium (PEQ) processes as major nuclear reaction mechanisms. The computed results have been analyzed and compared with the available experimentally measured data and with the evaluated nuclear data files. Good agreements have been found between theoretically calculated and measured data.

Experimental investigation and theoretical evaluation of proton induced nuclear reactions on nickel

The cross-sections for proton-induced nuclear reactions on natural nickel were experimentally measured for the natNi(p,x)60,61,64Cu, natNi(p,x)55,57,58Co and natNi(p,x)57Ni reactions from their respective thresholds up to 17 MeV proton energy. The stacked-foil technique in combination with HPGe γ-ray spectroscopy was used. Three codes were used in the theoretical calculations namely ALICE-IPPE, EMPIRE-3.2.2 and TENDL-2017. Comparison of the present results with the earlier reported experimental data and with the code results were carried out.

Measurement of cross-sections of proton-induced nuclear reactions on 197Au focused on the production of the theranostic pair 197m,gHg

We measured cross-sections of the nuclear reactions 197Au(p,x)197mHg, 197gHg, 195mHg, 195gHg, 196m2Au, 196m1+gAu, 194m+gAu in the energy range of 6.4–35.3 MeV having used stacked-foil technique with high purity gold foils. The results were compared with previously published data and with prediction of the TALYS nuclear reaction model code adopted from the TENDL-2017 library. Thick target yields were deduced from the measured data. Production of the theranostic isomeric pair 197m,gHg is thoroughly discussed.

Vortex Target: A New Design for a Powder-in-Gas Target for Large-Scale Radionuclide Production

This paper presents a design and working principle for a combined powder-in-gas target. The excellent surface-to-volume ratio of micrometer-sized powder particles injected into a forced carrier-gas-driven environment provides optimal beam power-induced heat relief. Finely dispersed powders can be controlled by a combined pump-driven inward-spiraling gas flow and a fan structure in the center. Known proton-induced nuclear reactions on isotopically enriched materials such as 68Zn and 100Mo were taken into account to be conceptually remodeled as a powder-in-gas target assembly, which was compared to thick target designs. The small irradiation chambers that were modeled in our studies for powdery ‘thick’ targets with a mass thickness (g/cm2) comparable to 68Zn and 100Mo resulted in the need to load 2.5 and 12.6 grams of the isotopically enriched target material, respectively, into a convective 7-bar pressured helium cooling circuit for irradiation, with ion currents and entrance energies of 0.8 (13 MeV) and 2 mA (20 MeV), respectively. Current densities of ~2 μA/mm2 (20 MeV), induces power loads of up to 4 kW/cm2. Moreover, the design work showed that this powder-in-gas target concept could potentially be applied to other radionuclide production routes that involve powdery starting materials. Although the modeling work showed good convective heat relief expectations for micrometer-sized powder, more detailed mathematical investigation on the powder-in-gas target restrictions, electrostatic behavior, and erosion effects during irradiation are required for developing a real prototype assembly.

Calculation of reactions cross section for proton-induced nuclear reactions on Iodine-127 isotope

Radioisotope production for nuclear medicine is tomography devices. Both single photon emissions computed tomography (SPECT) and positron emission tomography (PET) is used for diagnosis in nuclear medicine we have calculated the reaction cross section and investigated the excitation functions for the formation of 127,126 125 I , 126,127,128 Xe , 126,125 Te isotopes in the interactions of proton particle with the nucleus of the iodine-127 isotope. The analysis shows that there is a variation of interaction cross-section with a variation of energy of the incident particle. The result shows that the plots of the 127 I (p,ng), and 127 I (p,2ng), graphs have full excitation curve. The productions confirm the presence of Xenon-127 and Xenon-126 isotopes are possible at the energy range of 0 to 30 MeV from the iodine-127 nucleus. Keywords : Cross-Section; Excitation function; Nuclear Reaction; Radioisotope; Statistical Multistep Reaction