Target Irradiation Research Articles

Extraction chromatography of 225Ac and lanthanides on N,N-dioctyldiglycolamic acid /1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide solvent impregnated resin

The alpha-emitter 225Ac (t1/2 = 9.92 d) is currently under development for targeted alpha-particle therapy of cancer, and accelerator production of 225Ac via proton irradiation of thorium targets requires robust separations of 225Ac from chemically similar fission product lanthanides. Additionally, the lanthanide elements represent critical components in modern technologies, and radiolanthanides such as 140Nd (t1/2 = 3.37 d) also have potential application in the field of nuclear medicine. The ionic liquid, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ([Bmim][NTf2]), combined with the diglycolamide extractant, N,N-dioctyldiglycolamic acid (DODGAA), was adsorbed on macroporous resin support to produce a solvent impregnated resin (SIR) that was investigated for separations of 225Ac and lanthanides. The equilibrium distribution coefficients (Kd) of the rare earth elements (Sc(III), Y(III), Ln(III)), 225Ac(III), Th(IV), and U(VI) on the prepared DODGAA/[Bmim][NTf2]-SIR were determined from batch adsorption experiments in HCl and HNO3 media. The DODGAA/[Bmim][NTf2]-SIR exhibited preferential uptake of the heavier lanthanide elements while allowing for the separation of the lighter lanthanides. Column separations utilizing the DODGAA/[Bmim][NTf2]-SIR were effective at separating the lighter lanthanides from each other, and separating 225Ac from a mixture of lanthanides, 213Bi, and 225Ra without the need for additional complexing agents.

Radiochemical separation of no-carrier-added 186Re from proton irradiated tungsten target

Rhenium-186 [t½ = 3.7 d, 1.07 MeV β−-particles, 137 keV γ-ray] is an emerging radioisotope which holds tremendous potential in preparation of theranostic radiopharmaceuticals. This radioisotope was produced in a no-carrier-added form by irradiation of enriched 186W target via 186W(p, n) 186Re reaction in a pelletron. A facile radiochemical separation procedure based on selective solvent extraction in methylethyl ketone medium followed by column chromatography using mesoporous alumina sorbent has been developed to obtain 186Re in a form suitable for radiopharmaceutical preparation. This approach is expected to promote widespread utilization of this radioisotope for the benefit of cancer patients.

Compression and Burning of a Thermonuclear Target upon Shock Ignition under the Conditions of Laser Beam Irradiation Symmetry Violation

The influence of heating homogeneity violations in a laser thermonuclear target designed for shock ignition on the target compression and burning has been studied. We have performed our studies based on two-dimensional hydrodynamic simulations when modeling the target heating homogeneity violations due to various factors of symmetry violation of the target irradiation by a finite number of laser beams. The gains have been calculated at various perturbation amplitudes of the spatial distribution of absorbed energy in the target for two characteristic cases—low and high dominant perturbation modes. The first and second cases refer, respectively, to the factors of regular irradiation homogeneity violation due to a finite number of laser beams and a target offset from the focusing point and the factors of stochastic irradiation homogeneity violation related to laser beam energy imbalance, beam mispointing, and beam mistiming. We show that for a target designed for shock ignition the factors of regular irradiation homogeneity violation are much more dangerous than those for a spark ignition target.

Monte Carlo simulation-based design of an electron-linear accelerator-based neutron source for boron neutron capture therapy

Characteristics of a beam-shaping assembly that utilizes photo-neutrons from irradiation of a tungsten target by electrons from an accelerator were examined to produce a beam of neutrons suitable for boron neutron capture therapy. The epithermal neutron flux per kilowatt of electron-beam power almost increased to a maximum as the energy of the initial electrons was increased to 42.5 MeV, but the fast-neutron dose and the photon dose per epithermal neutron hardly changed on varying the energy of the initial electrons.

Effect of the spot size on ionization and degree of plasma shielding in plumes induced by irradiation of a copper target by multiple short laser pulses

The plasma plume expansion into argon background gas at atmospheric pressure induced by irradiation of a copper target with a burst of three short laser pulses at 266 nm wavelength is studied numerically for the laser spot diameters ranging from 20 μm to 500 µm. The computational model includes a thermal model of the irradiated target and a kinetic model of plume expansion. The kinetic model is implemented in the form of the direct simulation Monte Carlo method that is redesigned to account for ionization and absorption of laser radiation in the plume. The irradiation conditions are chosen to do not induce ionization and absorption during the first pulse in the burst independently of the laser spot size. During the second pulse, the ionization is initiated in the vicinity of the irradiated target behind the shock wave that is generated during that pulse and propagates through the vapor plume created by the preceding pulse. The simulations show that the degree of ionization and plasma shielding during the second and subsequent pulses strongly increases with increasing the laser spot size. It is explained by different rates of expansion between pulses in the plumes generated at various spot sizes. At a relatively small spot size, the rapid drop of density and temperature in the plume induced by the first pulse can preclude plasma ignition during the second and further pulses. These results suggest that the use of lasers with the spot sizes that are in the order of tens of micrometers can be favorable for mitigating the effect of plasma shielding in multi-pulse laser ablation when the plumes induced by individual laser pulses strongly interact with each other.

Production of 100-TW single attosecond x-ray pulse

Attosecond light sources have provided insight into the fastest atomic-scale electronic dynamics. True attosecond-pump–attosecond-probe experiments require a single attosecond pulse at high intensity and large photon energy, a challenge that has yet to be conquered. Here we show 100-TW single attosecond x-ray pulses with unprecedented intensity of 10 21 W / c m 2 and duration 8.0 as can be produced by intense laser irradiation of a capacitor-nanofoil target composed of two separate nanofoils. In the interaction, a strong electrostatic potential develops between the two foils, which drags electrons out of the second foil and piles them up in vacuum, forming an ultradense relativistic electron nanobunch. This nanobunch reaches both high density and high energy in only half a laser cycle and smears out in others, resulting in coherent synchrotron emission of a single, intense attosecond pulse. Such a pulse enables the capture and control of electron motion at the picometer–attosecond scale.

Exact location of sensorimotor cortex injury after photochemical modulation; evidence of stroke based on stereological and morphometric studies in mice.

The integrity of the structural cerebral cortex is disrupted after stroke either at the macroscopic or microscopic levels. Therefore, many attempts have been gathered to circumvent stroke-associated problems in the brain tissue. The current study was aimed to design an animal model of photochemical stroke using rose bengal (RB) plus laser irradiation (L) after 10, 15, and 20min (´) and evaluate its effect on the cerebral tissue using unbiased stereological quantitative methods and morphometric histological analysis. Photochemical stroke was induced by intraperitoneal injection of RB dye and further activation through the exposure of the right sensorimotor cortex with the green laser radiation (100mW; 532nm). Mice were randomly allocated into 4 groups (each in 15) as follows: control (10μg/gbw RB), RB + 10'L, RB + 15'L, and RB + 20'L. Target irradiation site was adjusted to 2mm lateral to the bregma. Vernier caliper morphometric evaluation, cresyl violet staining, and unbiased stereological assays including Cavalier's principle and point counting techniques were used to monitor the pathological changes and lesion volume on days 1, 3, and 7 after the ischemia induction. Our data showed that the mean diameter of the lesion site and lesion infarct volume in the group RB + 20'L) was significantly increased relative to the other groups (P< 0.05). Notably, the lesion volume and diameter in the group RB + 15'L was larger compared with the group RB + 10'L and control mice (P< 0.05). Data showed an increased acute inflammatory response such as hyperemia and edema 3days after ischemic induction while the intensity of acute changes and lesion volume were reduced and replaced with necrotic and chronic pathological changes including astrogliosis on day 7. It is concluded that the laser irradiation of RB-injected mice at a distinct time period could induce the magnificent degenerative effects on the cerebral cortex which is similar to the stroke condition.

Expansion of laser-induced plume after the passage of a counter shock wave through a background gas

Double-pulsed laser ablation with two targets and lasers in a background gas is a method to form nanoparticle complex. Effects of pulse delay between two lasers on plume expansion dynamics are discussed. The germanium and silicon targets were set parallel to each other and irradiated by two YAG lasers. The germanium target was irradiated followed by irradiation of the silicon target with delay time, td. We found that the expansion distance of delayed silicon plume is enhanced for 2 µs ≤ td ≤ 50 µs, compared to that when only the silicon target is irradiated. For td = 200 µs, the expansion distance of delayed silicon plume is similar to that when only the silicon target is irradiated. We discuss the expansion dynamics of the delayed silicon plume based on the effect of the density distribution induced by the primary germanium plume. Our results indicate that the effect of primary germanium plume remains up to about td = 50 µs, and it disappears by td = 200 µs.

3-Dimensional target coverage assessment for MRI guided esophageal cancer radiotherapy

PurposeThis study aimed to quantify the coverage probability for esophageal cancer radiotherapy as a function of a preset margin for online MR-guided and (CB)CT-guided radiotherapy. MethodsThirty esophageal cancer patients underwent six T2-weighted MRI scans, 1 prior to treatment and 5 during neoadjuvant chemoradiotherapy at weekly intervals. Gross tumor volume (GTV) and clinical target volume (CTV) were delineated on each individual scan. Follow-up scans were rigidly aligned to the bony anatomy and to the clinical target volume itself, mimicking two online set-up correction strategies: a conventional CBCT-guided set-up and a MR-guided set-up, respectively. Geometric coverage probability of the propagated CTVs was assessed for both set-up strategies by expanding the reference CTV with an isotropic margin varying from 0 mm to 15 mm with an increment of 1 mm. ResultsA margin of 10 mm could resolve the interfractional changes for 118 out of the 132 (89%) analyzed fractions when applying a bone-match registration, whereas the CTV was adequately covered in 123 (93%) fractions when the registration was directly performed at the CTV itself (soft-tissue registration). Closer analyses revealed that target coverage violation predominantly occurred for distal tumors near the junction and into the cardia. ConclusionOnline MR-guided soft-tissue registration protocols exhibited modest improvements of the geometric target coverage probability as compared to online CBCT-guided bone match protocols. Therefore, highly conformal target irradiation using online MR-guidance can only be achieved by implementing on-table adaptive workflows where new treatment plans are daily generated based on the anatomy of the day.

The impact of isocentric shifts on delivery accuracy during the irradiation of small cerebral targets-Quantification and possible corrections.

PurposeTo assess the impact of isocenter shifts due to linac gantry and table rotation during cranial stereotactic radiosurgery on D98, target volume coverage (TVC), conformity (CI), and gradient index (GI).MethodsWinston‐Lutz (WL) checks were performed on two Elekta Synergy linacs. A stereotactic quality assurance (QA) plan was applied to the ArcCHECK phantom to assess the impact of isocenter shift corrections on Gamma pass rates. These corrections included gantry sag, distance of collimator and couch axes to the gantry axis, and distance between cone‐beam computed tomography (CBCT) isocenter and treatment beam (MV) isocenter. We applied the shifts via script to the treatment plan in Pinnacle 16.2. In a planning study, isocenter and mechanical rotation axis shifts of 0.25 to 2 mm were applied to stereotactic plans of spherical planning target volumes (PTVs) of various volumes. The shifts determined via WL measurements were applied to 16 patient plans with PTV sizes between 0.22 and 10.4 cm3.ResultsArcCHECK measurements of a stereotactic treatment showed significant increases in Gamma pass rate for all three measurements (up to 3.8 percentage points) after correction of measured isocenter deviations. For spherical targets of 1 cm3, CI was most severely affected by increasing the distance of the CBCT isocenter (1.22 to 1.62). Gradient index increased with an isocenter‐collimator axis distance of 1.5 mm (3.84 vs 4.62). D98 (normalized to reference) dropped to 0.85 (CBCT), 0.92 (table axis), 0.95 (collimator axis), and 0.98 (gantry sag), with similar but smaller changes for larger targets. Applying measured shifts to patient plans lead to relevant drops in D98 and TVC (7%) for targets below 2 cm3 treated on linac 1.ConclusionMechanical deviations during gantry, collimator, and table rotation may adversely affect the treatment of small stereotactic lesions. Adjustments of beam isocenters in the treatment planning system (TPS) can be used to both quantify their impact and for prospective correction of treatment plans.

Excitation functions of deuteron-induced nuclear reactions on erbium in the energy range of 4–24 MeV

Excitation functions for the natEr(d,x)163,165,166,167,168,170Tm and natEr(d,x)171Er nuclear reactions were measured from the respective thresholds up to 24 MeV by using a stacked-foil activation technique combined with HPGe γ-ray spectrometry. Measured data show a partial agreement when compared with the available literature data, theoretical data extracted from the TENDL-2019 library, and predicted data by the model code EMPIRE-3.2.2. Estimated physical thick target yields of the reaction products show close values to the directly measured ones available in the literature. The deduced yield curves indicate that a typical irradiation (Ed = 15 MeV, Id = 100 µA, tirr = 72 h) of enriched 167Er target by a low energy deuteron cyclotron is suitable to obtain more than a hundred GBq activity of 167Tm with negligible impurity from 168Tm. Measured data of 170Er(d,p)171Er reaction have great significance to improve the predicting capability of the model code.

Emittance measurement along transport beam line for laser driven protons

Particle emittance quantifies the ability to focus and transport a beam, and is one of the most important parameters for a beamline. The emittance of a proton beam produced by ultraintense laser irradiation of a micron-thick flat solid target has been measured systematically for the first time, using three different methods at different positions along the transport beamline: pepper-pot method, quadrupole triplet scan technique, and single-shot emittance measurement. Emittance growth is shown both in experiments and in simulations using CST. An over 3-fold emittance growth was found for 5 MeV laser-driven protons with an energy spread of $\ifmmode\pm\else\textpm\fi{}2%$ and divergence of $\ifmmode\pm\else\textpm\fi{}20\text{ }\text{ }\mathrm{mrad}$ after being transported 5.9 m in the experiment, due to the energy spread and angular dispersion of the protons.

Increasing analyzable steel thickness for thin layer activation experiments

The thin layer activation technique (TLA) is very effective in wear analysis for tribological systems where disassembly is costly or impractical. Since its development in the 1970s, TLA has been applied through direct irradiation of solid targets using ionizing particle beams to obtain an activation with a specific profile. This profile is then used to measure wear in a variety of experiments. These experiments rely heavily on how deep the normalized activation occurs. Depths of $$30\,\upmu {\text{m}}$$ to $$50\,\upmu {\text{m}}$$ are obtained for constant activation by the standard method, which for many experiments is sufficient. However, many others would benefit greatly from a $$300\,\upmu {\text{m}}$$ constant activation layer, such as high-performance engines, softer alloys (brakes), and oil transport systems. Achieving this aim was the goal of this paper. First, we needed to find an adequate irradiation line for the TLA technique. Then, another technique/system was developed (the Attenuation Wheel), which would bring the depth of constant activation from $$50\,\upmu {\text{m}}$$ to $$300\,\upmu {\text{m}}$$.

The impact of the field width on VMAT plan quality and the assessment of half field method.

PurposeThe goal of this work is to investigate the field width dependence of the volumetric modulated arc therapy (VMAT) plan quality and to propose a half field method to irradiate large volumes effectively with VMAT.Materials and methodsWe compared four different VMAT methods; namely three full field (3ff), four full field (4ff), three half field (3hf), four half field (4hf). To evaluate the impact of the field width on VMAT plan quality, 12 different size PTVs were created in the virtual phantom and treatment plans generated for each PTV were compared. The effectiveness of our half field method was tested using computed tomography (CT) data of 10 nasopharyngeal carcinoma patients.ResultsIn the virtual phantom study, organs at risk (OAR) mean dose, the maximum point dose, and Homogeneity Index (HI) were found to be field width dependent. Conformation Number (CN) was not significantly affected. In the clinical study, 4hf plans obtained statistically significant dose reduction at brainstem (P < 0.001), right parotid (P = 0.034), oral cavity (P < 0.001), larynx (P = 0.003), cochlea (P = 0.017), lips (P = 0.024), and Body‐PTV (P = 0.04) compared to 4ff plans.ConclusionOur results indicate that VMAT plan quality is dependent on the field width. Half field VMAT method, with the help of reduced field width, shows a clear advantage for the irradiation of large size targets compared to traditionally used full field VMAT plans.

Dosimetric impact of rotational errors on the quality of VMAT‐SRS for multiple brain metastases: Comparison between single‐ and two‐isocenter treatment planning techniques

PurposeIn the absence of a 6D couch and/or assuming considerable intrafractional patient motion, rotational errors could affect target coverage and OAR‐sparing especially in multiple metastases VMAT‐SRS cranial cases, which often involve the concurrent irradiation of off‐axis targets. This work aims to study the dosimetric impact of rotational errors in such applications, under a comparative perspective between the single‐ and two‐isocenter treatment techniques.MethodsTen patients (36 metastases) were included in this study. Challenging cases were only considered, with several targets lying in close proximity to OARs. Two multiarc VMAT plans per patient were prepared, involving one and two isocenters, serving as the reference plans. Different degrees of angular offsets at various orientations were introduced, simulating rotational errors. Resulting dose distributions were evaluated and compared using commonly employed dose‐volume and plan quality indices.ResultsFor single‐isocenter plans and 1⁰ rotations, plan quality indices, such as coverage, conformity index and D95%, deteriorated significantly (>5%) for distant targets from the isocenter (at> 4–6 cm). Contrarily, for two‐isocenter plans, target distances to nearest isocenter were always shorter (≤4 cm), and, consequently, 1⁰ errors were well‐tolerated. In the most extreme case considered (2⁰ around all axes) conformity index deteriorated by on‐average 7.2%/cm of distance to isocenter, if one isocenter is used, and 2.6%/cm, for plans involving two isocenters. The effect is, however, strongly associated with target volume. Regarding OARs, for single‐isocenter plans, significant increase (up to 63%) in Dmax and D0.02cc values was observed for any angle of rotation. Plans that could be considered clinically unacceptable were obtained even for the smallest angle considered, although rarer for the two‐isocenter planning approach.ConclusionLimiting the lesion‐to‐isocenter distance to ≤4 cm by introducing additional isocenter(s) appears to partly mitigate severe target underdosage, especially for smaller target sizes. If OAR‐sparing is also a concern, more stringent rotational error tolerances apply.

Design of target irradiation and diagnostic chamber to study ps-laser generated plasma as a source of singly charged ions for external injection into an electron beam ion source.

High repetition-rate (∼10 kHz) ps-lasers are becoming available on the market with reasonable cost and may offer several advantages compared to ns-lasers by generating nearly continuous beams of singly charged ions appropriate for the "slow" injection mode into the Electron Beam Ion Source (EBIS). To evaluate these advantages, we will perform studies of a ps-laser generated plasma using a laser with a pulse duration of 8 ps and energy up to 5 mJ per pulse. A vacuum chamber equipped with a 3D target positioner, a focusing lens, and a Faraday Cup has been designed and built for this study. Lens-to-target distance variations have been measured using a laser tracker over the whole range of horizontal and vertical translation for all five targets we will use. The variations were found to be within ±150 µm. This degree of "target flatness" should be acceptable for our experimental conditions. Ion currents and ion pulse durations of various elements (from Al to Ta) will be measured for different target irradiation conditions (focal spot size and laser pulse energy). The results obtained will allow us to specify all parameters and geometry of a laser ion source based on a ps-laser to provide external ion injection into the relativistic heavy ion collider EBIS.

EUV induced, low temperature plasmas, produced in an aerosol target

In this work spectral investigations of low temperature plasmas, created by photoionization of aerosol targets, were performed. A laser produced plasma (LPP) source of extreme ultraviolet (EUV) was used as a source of ionizing radiation. The source was driven by a 10 Hz Nd:YAG laser system, delivering pulses of energy up to 10 J with a time duration of approximately 10 ns. The aerosol target was formed using a specially prepared system composed a mist ultrasonic generator and a solenoid valve. The mist was created inside a small cell containing a small portion of methanol and filled with a He gas. The valve coupled to this cell allowed to inject the aerosol into a vacuum chamber synchronously with the EUV pulse. Low temperature plasmas created by the EUV irradiation of the aerosol target were investigated mainly by spectral measurements. The spectra, acquired in the UV/VIS range, were composed of lines corresponding to radiative transitions in atoms and singly charged ions originating from the He gas and dissociation products of the methanol. Spectral measurements were performed also for aerosol targets created from solutions of various inorganic salts in the methanol. In this case, additional lines corresponding to decomposition products of these salts were detected.

Laser-Induced Synthesis of Pure Zinc Oxide Nanoflakes

Nanostructured zinc oxide (ZnO) has received immense attention as a low-cost and non-toxic photo-active material for different applications such as photocatalysis, photovoltaics, photonic and bio-medical fields. Herein, facile crystalline ZnO nanoflakes were prepared by homogeneous precipitation followed by laser-induced recrystallization and without the use of any organic ligand. The effect of laser type and wavelength on the recrystallization process was studied adopting a pulsed nitrogen laser (λ=337 nm) and a continuous argon laser (λ=488 nm). The pulsed nitrogen laser features a pulse duration of 150±1 ns, pulse energy of 1.3±0.3 mJ, and a target irradiance of 5.7±0.5 kW/cm2 while the continuous argon laser provides an irradiance of 10±0.3 mW/cm2. The morphology, structure and optical properties of the prepared nanostructures were studied using a scanning electron microscope (SEM), X-ray diffraction (XRD), UV-Visible, photoluminescence (PL), and Raman spectroscopy. The results confirm the formation of pure ZnO nanoflakes of the wurtzite structure. The laser-induced evolution of ZnO nanoflakes depends on the nature of the precipitating agent, laser energy and exposure time. The ZnO nanoflakes prepared using urea-assisted homogeneous precipitation is more advantageous than that precipitated with NaOH. Moreover, the pulsed nitrogen laser of higher irradiance demonstrated an enhanced formation of ZnO nanoflakes after 90 min of irradiation. The laser irradiation provides a facile synthetic route to pure ZnO nanostructures for various applications.

Identification of radionuclides in cooling circuit of Cyclone 18/9-HC

In the present work the patterns of relationship of photonic radiation dose rate from Cyclone 18/9HC water cooling system were studied at production of positron-emitting nuclides. Reaction (n, p) was shown to be the main source of activation nuclides in cyclotron cooling water at 18F production, resulting in formation of 16N (T1/2 = 7 s) from 16О. In water targets with high accumulated dose, when beam partially irradiates a target body, proton-induced reactions: 16О(p, α)11С and 18О(p, n)18F take place. Fluoride 18F–, carbonate 11СО32– and hydrocarbonate Н11СО3– anions, formed in proton-induced activation reactions, efficiently precipitate on anion-exchanging resin during water circulation resulting in circuit purification from the named radionuclides. Activation of cooling water does not occur at irradiation of gas targets. Projected annual dose for cyclotron operator from cooling water activation is less than 1 % of annual dose limit for personnel from technogeneous radioactive sources. In order to minimize operator`s accumulated doses it is recommended to decrease the duration of personnel activities at the distance less than 1 meter from heat exchanger during 18F production. At operation of water targets with absorbed dose higher than 2500 μA·h it is desirable to conduct the preventive maintenance of water cooling system not earlier than in half an hour after the end of irradiation and with mandatory dosimetry control. To decrease the activation of impurities it is essential to use only deionized water in cooling circuit. In case of its specific conductivity increase due to corrosion the coolant should be replaced promptly.

Ion sputtering for preparation of thin MAX and MXene phases

Thin films of MAX and MXene phases were prepared by ion beam sputtering followed by thermal annealing in vacuum. For this purpose, a Low Energy Ion Facility (LEIF) using heavy ions for target irradiation was developed, and the DC ion beam sputtering method was implemented. The process for preparing MAX and MXene thin composites consists of two steps. First step: bombarding the elemental targets with low-energy ions (either all targets together, each with the corresponding size, or each target separately and repeatedly); it results in synthesis of either homogeneous layers of mixed phases or multilayer arrays of individual phases. Second step: thermal annealing under vacuum with a suitable temperature and time to induce a diffusion process, mutual phase interaction and finally the formation of MAX or MXene composites with the desired structure. After installation of the LEIF system and the introduction of the two-step method, i.e. DC ion sputtering with subsequent thermal processing, the first Ti-based MAX and MXene carbides, Ti2SnC and Ti2C, in thin films of composites were prepared and analyzed.