Target Irradiation Research Articles

Capacitive tracer design to mitigate incomplete I-V curves in outdoor tests

The capacitance technique is the most straightforward and low-cost technique to trace the I-V curve of photovoltaic (PV) modules. Nevertheless, the sweep speed and number of samples to measure the I-V curve depend on the device under test (DUT), capacitance size, switching dynamic, lighting conditions, Etc. Therefore, two performance indexes were proposed to evaluate the I-V curve quality. The indexes were estimated from a circuital model considering the transient capacitance charging process as a function of the target irradiance levels and parameters of the DUT and tracer. In this way, a capacitance range is estimated to mitigate the likelihood of measuring incomplete curves in the Isc and Voc regions. Finally, the capacitance sizing design in terms of both indexes for monitoring PV technologies was validated in outdoor tests.

Compact high-flux X-ray source based on irradiation of solid targets by gigahertz and megahertz bursts of femtosecond laser pulses

In this study, we demonstrate the significant increase in the hard X-ray yield (more than 1011 photons/s in 4π solid angle in 6 - 40 keV range) that can be achieved in an ambient air environment when solid targets are irradiated by sequences of high average power (90 W) bursts of femtosecond laser pulses, generated in GHz burst laser amplifier operated at high repetition rate (100 kHz). The combination of the prepulse and ∼ 10 times greater driving pulse not only enhances X-ray generation efficiency (∼ 10−6) by more than two orders of magnitude compared to the single pulse regime but also protects a target allowing continuous operation for 3 hours with only 30% predictable and gradual drop of X-ray yield. In addition, we show that X-ray yield enhancement becomes around 6 times more pronounced at higher repetition rates (100 kHz compared to < 5 kHz). The simplicity and relative cost-effectiveness of the presented X-ray source makes it an attractive solution for future applications in ultrafast X-ray imaging and spectroscopy.

ASSESSMENT OF OPERATION SAFETY OF THE RSG-GAS REACTOR TO SERVE RADIOISOTOPE TARGET IRRADIATION

The RSG-GAS multipurpose reactor is operated to serve the utilization in the field of radioisotope production and NAA, material research. The reactor actually has power of 30 MW thermal, but upon considerations of efficiency and of most users requirements, the reactor is mostly operated at the power of 15 MW thermal, 5 days a week to produce a primary radioisotope from target of 2 grams U-235. To guarantee the safe operation and optimum utilization, a safety procedure was established. The paper is intended to assesst the operation safety in serving radioisotope target irradiation at its cycle operation. Assessment was carried out for core numbers 102 – 105. The result shows that excess reactivity and shutdown margin reactivity are safe to provide the target irradiation in the core for each cycle operation.

A Model for Radiolysis in a Flowing-Water Target during High-Intensity Proton Irradiation.

At the Facility for Rare Isotope Beams (FRIB), interactions between heavy-ion beams and beam-dump water will create a wide variety of radionuclides which can be accessed by a technique known as “isotope harvesting”. However, irradiation of water is always accompanied by the creation of numerous radical, ionic, and molecular radiolysis products. Some of the radiolysis products have sufficiently long lifetimes to accumulate in the irradiated water and affect the harvesting chemistry. Here we investigate the formation of hydrogen peroxide, molecular hydrogen, and molecular oxygen during a high-intensity proton irradiation of a flowing-water isotope-harvesting target and compare the experimental results to simulations. The simulations kinetically model the chemical reactions occurring in the homogeneous phase of radiolysis in flowing water and establish an “effective yield”. In both the experiment and simulations, the bulk quantities of H2, H2O2, and O2 are considerably lower than predicted by primary radiolysis yields (escape yields), meaning that in the high beam intensity regime the homogeneous phase reactions have a considerable impact on the overall chemical composition of the water. Further, it could be shown that for radiation which is characterized by a limited linear energy transfer, such as the here applied protons, the bulk outcome of the microscopic kinetic modeling could be estimated by a simplified steady-state model.

Neutronic Evaluation of Using a Thorium Sulfate Solution in an Aqueous Homogeneous Reactor

Radioisotope 99 Mo is one of the most essential radioisotopes in nuclear medicine. Its production in an Aqueous Homogeneous Reactor (AHR) could be potentially advantageous compared to the traditional technology, based on target irradiation in a heterogeneous reactor. An AHR conceptual design using low-enriched uranium for the production of 99 Mo has been studied in depth. So far, the possibility of replacing uranium with a non-uranium fuel, specifically a mixture of 232 Th and 233 U, has not been evaluated in the conceptual design. Therefore, the studies conducted in this article aim to evaluate the neutronic behavior of the AHR conceptual design using thorium sulfate solution. Here, the 232 Th- 233 U composition to guarantee ten years of operation without refueling, conversion ratio, medical isotopes production levels, and reactor kinetic parameters were evaluated, using the computational code MCNP6. It was obtained that 14 % 233 U enrichment guarantees the reactor operation for ten years without refueling. The conversion ratio was calculated at 0.14. The calculated 99 Mo production in the AHR conceptual design resulted in 24.4 % higher with uranium fuel than with thorium fuel.

Nonlocal Heat Transfer in a Laser Inertial Confinement Fusion for the Direct Irradiation Scheme

High gradients of electron temperature appear in plasma corona under direct laser irradiation of inertial confinement fusion targets. This results in nonlocality of heat transport. Such effect influence the efficiency of laser absorption, redistribute heat fluxes and could preheat plasma ahead the front shock wave, therefore alter the compression adiabat. Ignition requires a specially tuned compression dynamics, so such an effect should be taken into account. Target simulations with nonlocal models show the decrease of compression efficiency and hot-spot parameters degradation compared to local models: Spitzer–Härm model with and without flux-limiter.

Suppression of Stimulated Brillouin Scattering in Laser Plasma under Conditions of Multifrequency Target Irradiation

Suppression of Stimulated Brillouin Scattering in Laser Plasma under Conditions of Multifrequency Target Irradiation

Experimental and simulation studies of thermal transport based on plasma flow motion in laser-ablated dense regions of Au and CH

A practical experimental method is proposed to investigate thermal transport by characterizing the motion of plasma flows through a x-ray spectroscopic technique using tracers. By simultaneously measuring multiple parameters, namely, the mass-ablation rate, the temporal evolution of plasma flow velocities and trajectories and the temperature, it is possible to observe a variety of physical processes, such as shock wave compression, heating by thermal waves, and plasma thermal expansion, and to determine their relative importance in different phases during the irradiation of CH and Au targets. From a comparison with hydrodynamic simulations, we find significant differences in the motion of the plasma flows between CH and Au, which can be attributed to different sensitivities to the thermal transport process. There are also differences in the ablation and electron temperature histories of the two materials. These results confirm that velocities and trajectories of plasma motion can provide useful evidence in the investigation of thermal conduction, and the approach presented here deserves more attention in the context of inertial confinement fusion and high-energy-density physics.

An alternative radiochemical separation strategy for isolation of Ac and Ra isotopes from high energy proton irradiated thorium targets for further application in Targeted Alpha Therapy (TAT)

Targeted Alpha Therapy (TAT) has shown very high potential for the treatment of cancers that were not responsive to other therapy options (e.g., β− therapy and chemotherapy). The main constraint to the widespread use of TAT in clinics is the limited availability of alpha-emitting radionuclides. One of the most promising candidates for TAT is 225Ac (t1/2 = 9.92 days), which can be used directly in combination with selective biomolecules (e.g., antibodies, peptides, etc.) or be a generator source of 213Bi (t1/2 = 45.6 min), another shorter-lived TAT radionuclide. Several strategies are currently under investigation to increase the supply of 225Ac. One of the most attractive options is the irradiation of natural thorium-232 targets with high-energy protons (≥100 MeV). However, there are several challenges associated with this production method including the development of an efficient radiochemical purification method.During irradiation of natural thorium with proton energy above 100 MeV, several Ra isotopes (223,224,225Ra) are produced. 223Ra (t1/2 = 11.43 days) is used for the treatment of bone metastases and can also be used as a generator source for 211Pb. Additionally, 225Ra (t1/2 = 14.9 days) can be a valuable source of isotopically pure 225Ac.In the present work, we address the radiochemical separation aspects of isolating Ac and Ra isotopes from irradiated thorium targets.

Specificity of micro- and nanoproducts of titanium laser ablation in pure water

Laser ablation of titanium in distilled water at high and low power densities of copper vapour laser beam in the focal spot on a target surface is experimentally studied. Ablation regimes with different pulsed energy inputs and target irradiation times are investigated. The morphology and elemental and phase compositions of micro- and nanoaggregates obtained in different irradiation regimes are studied using electron microscopy, X-ray diffraction analysis, and Raman spectroscopy. The ablation products are found to be practically totally in the X-ray amorphous state.

Radiomodulation in Mixed, Complex Cancer Pain by Triple Target Irradiation in the Brain: A Preliminary Experience.

IntroductionUp to 30% of terminally ill cancer patients experiencing intense pain might be refractory to opioid treatment. Complex cancer pain can be a mixture of somatic, visceral, and neuropathic pain with few or no effective alternatives to ameliorate pain. Radiosurgery to treat refractory pain in cancer has been reported with different degrees of success. Radiomodulation in pain could be defined as a fast (<72 h), substantial (>50%) pain relief by focal irradiation to a peripheric, and/or central mediated pain circuitry. Based on our previous experience, mixed, refractory cancer pain is usually unresponsive to single target irradiation of the hypophysis. We treated three patients using a multi-target approach.MethodsThree terminally ill oncological patients experiencing refractory, complex, mixed pain from bone, abdomen, thorax, and brachial plexus were treated with triple target irradiation which consisted of irradiating with a maximum dose (Dmax) of 90 Gy to the hypophysis using either an 8 mm collimator with gamma ray (Infini) (Shenzhen, China: Masep Medical Company) or a 7.5 circular collimator with Cyberknife (Sunnyvale, CA: Accuray Inc.), the other two targets were the mesial structures of the thalamus bilaterally using a 4 mm collimator with Infini and the 5 mm circular collimator with CK delivering 90 Gy Dmax to each region. Patients had a VAS of 10 despite the best medical treatment.A correlation was made between the 45 Gy and 20 Gy isodose curves of the two different technologies to the Morel stereotactic atlas of the thalamus and basal ganglia for further understanding of dose distribution reconstructions in accordance with the São Paulo-Würzburg atlas of the Human Brain Project were performed. Lastly, a scoping review of the literature regarding radiosurgery for oncological pain was performed.ResultsRadiomodulation effect was achieved in all patients; case 1 had a VAS of five at 72 h, three at 15 days, and three at the time of death (21 days after treatment). Case 2 had a VAS of six at 72 h, five at 15 days, and four at the time of death (29 days after treatment). Case 3 had a VAS of five at 72 h, six at 15 days, and six at the time of death (30 days). Morphine rescues for cases 1 and 2 were reduced to 84%, and 70% for case 3. Overall, there were no adverse effects to treatment although excessive sleepiness was reported by one patient. After reading the title and abstract, only 14 studies remained eligible for full-text evaluation, and only nine studies met inclusion criteria after full-text reading. For most reports (seven), the target was the hypophysis and in two reports, the target was the thalamus either with single or bilateral irradiation.ConclusionsIn complex, for refractory oncological pain of mixed nature (nociceptive, neuropathic, and visceral), very few, if any, treatment alternatives are currently available. We provide a small proof of concept that multitarget intracranial radiosurgery might be effective in ameliorating pain in this population. The doses administered per target are the lowest that have shown effectiveness thus far, a different strategy might be needed as opposed to single target “large” dose approach that has been tried in the past for complex mixed refractory oncological pain. By no means, in our experience, these treatments traduce in elimination of pain, clinical results might make pain to be more bearable and respond better to pain medication.

Laser ablation assisted synthesis of graphene/CuO nanocomposite: effect of laser fluence

ABSTRACT The role of laser fluence on the properties of graphene/CuO nanocomposite, prepared by pulsed laser ablation method was studied experimentally. Ablation processes were carried out with the fundamental wavelength of a Q-switched Nd:YAG laser. First, the graphene nanosheets were synthesized by irradiation of a graphite target in distilled water. Then, a Cu target was irradiated by the same laser pulses in the graphene suspension. Three samples of graphene/CuO nanocomposites were formed by different fluences of laser pulse. Results indicate that decoration of graphene with CuO nanoparticles was performed in all nanocomposite samples. As the laser fluence increased, adhesion of graphene nanosheets was enhanced, and the size of CuO nanoparticles was decreased, while the rate of their production was increased. According to the results, it can be concluded that the laser fluence is an effective tool to control the characteristics of laser ablation produced nanocomposites.

Electron-positron pairs and radioactive nuclei production by irradiation of high-Z target with γ -photon flash generated by an ultra-intense laser in the λ3 regime

This paper studies the interaction of laser-driven $\ensuremath{\gamma}$ photons and high-energy charged particles with high-Z targets through Monte Carlo simulations. The interacting particles are taken from particle-in-cell simulations of the interaction of a tightly focused ultra-intense laser pulse with a titanium target. Lead is chosen as the secondary high-Z target because of its high cross-section of the giant dipole resonance and electron-positron pair production. The results reveal an ultra-short, ultra-relativistic collimated positron population and their energy spectra, angular distribution, and temporal profile are found. We investigate the target thickness dependence of the resulting total numbers and total kinetic energies of various particle species emitted from the lead target irradiated with laser-generated $\ensuremath{\gamma}$ photons and charged particles separately. We plot the charts of residual high-Z nuclides generated by irradiation of the lead target. Because of the short pulse duration, the $\ensuremath{\gamma}$ photon, electron-positron, and neutron sources could find applications in material science, nuclear physics, laboratory astrophysics, and as injectors in laser-based accelerators of charged particles.

Recovery of 177Lu from Irradiated HfO2 Targets for Nuclear Medicine Purposes.

A new method of production of one of the most widely used isotopes in nuclear medicine, 177Lu, with high chemical purity was developed; this method includes irradiation of the HfO2 target with bremsstrahlung photons. The irradiated target was dissolved in HF and then diluted and placed onto a column filled with LN resin. Quantitative sorption of 177Lu could be observed during this process. The column later was rinsed with the mixture of 0.1 M HF and 1 M HNO3 and then 2 M HNO3 to remove impurities. Quantitative desorption of 177Lu was achieved by using 6 M HNO3. The developed method of 177Lu production ensures high purification of this isotope from macroquantities of hafnium and zirconium and radioactive impurities of carrier-free yttrium. The content of 177mLu in 177Lu in photonuclear production was determined. Due to high chemical and radionuclide purity, 177Lu obtained by the developed method can be used in nuclear medicine.

Design optimization of an electron-to-photon conversion target for ultra-high dose rate x-ray (FLASH) experiments at TRIUMF

Objective. To develop a bremsstrahlung target and megavoltage (MV) x-ray irradiation platform for ultrahigh dose-rate (UHDR) irradiation of small-animals on the Advanced Rare Isotope Laboratory (ARIEL) electron linac (e-linac) at TRIUMF. Approach. An electron-to-photon converter design for UHDR radiotherapy (RT) was centered around optimization of a tantalum–aluminum (Ta–Al) explosion-bonded target. Energy deposition within a homogeneous water-phantom and the target itself were evaluated using EGSnrc and FLUKA MC codes, respectively, for various target thicknesses (0.5–1.5 mm), beam energies (E e− = 8, 10 MeV) and electron (Gaussian) beam sizes ( = 2–10 mm). Depth dose-rates in a 3D-printed mouse phantom were also calculated to infer the compatibility of the 10 MV dose distributions for FLASH-RT in small-animal models. Coupled thermo-mechanical FEA simulations in ANSYS were subsequently used to inform the stress–strain conditions and fatigue life of the target assembly. Main results. Dose-rates of up to 128 Gy s−1 at the phantom surface, or 85 Gy s−1 at 1 cm depth, were obtained for a 1 × 1 cm2 field size, 1 mm thick Ta target and 7.5 cm source-to-surface distance using the FLASH-mode beam (E e− = 10 MeV, 2 = 5 mm, P = 1 kW); furthermore, removal of the collimation assembly and using a shorter (3.5 cm) SSD afforded dose-rates >600 Gy s−1, albeit at the expense of field conformality. Target temperatures were maintained below the tantalum, aluminum and cooling-water thresholds of 2000 °C, 300 °C and 100 °C, respectively, while the aluminum strain behavior remained everywhere elastic and helped ensure the converter survives its prescribed 5 yr operational lifetime. Significance. Effective design iteration, target cooling and failure mitigation have culminated in a robust target compatible with intensive transient (FLASH) and steady-state (diagnostic) applications. The ARIEL UHDR photon source will facilitate FLASH-RT experiments concerned with sub-second, pulsed or continuous beam irradiations at dose rates in excess of 40 Gy s−1.

Exploration of producing Uranium-232 for use as a tracer in uranium fuels

This study examines the production of 232U via neutron irradiation. Uranium-232 is considered for use as a tracer in nuclear fuel. However, a source of 232U is needed. This study examines the production of 232U via neutron irradiation of targets constructed out of either 231Pa or 230Th in the High Flux Isotope Reactor. HFIR targets were modeled in MCNP to determine 232U yield in protactinium and thorium targets. Flux tallies were used inside the targets to determine the neutron flux inside each target. This flux was then used in SCALE 6.2 ORIGEN to determine the 232U yield, as well as the buildup of the byproduct 233U. Several 230Th enrichments were examined to determine how 232U yield is affected by 230Th enrichment, as well as the effects of the presence of 232Th. The buildup of 228Th and 229Th in thorium targets was also examined, as these isotopes may impact the feasibility of recycling of thorium target materials.

Two-dimensional parametric design of short pulse laser driven iron opacity experiments

High intensity short pulse lasers are commonly used to create high temperature and high density plasmas. These plasmas are used to study fundamental properties such as the equation of state and opacity. The targets often use small-diameter, thin buried layers of the materials of interest, surrounded by a tamper of low atomic number material such as plastic. Computational modeling is used to design and interpret experiments with short pulse lasers. Most of the modeling to date has assumed one-dimensional plane-parallel geometry. In this paper, the effects of radial gradients in the irradiation of thin planar targets are studied with one- and two-dimensional radiation/hydrodynamic simulations. It is found that the main effect of radial gradients is the averaging of plasma conditions and x-ray emission over the pattern of irradiation. Differences between one- and two-dimensional simulations arise because the plasma conditions and x-ray emission are, in general, nonlinear functions of the temperature of the plasma and thereby also nonlinear functions of the irradiation intensity. The differences increase with the ratio of the buried layer radius to the laser spot radius. The root mean square difference in the inferred iron L-shell opacity is less than 30% when the ratio is less than 1.0 and about 70% when the ratio is 1.5.

Measurement of the Yield of Protactinium Radioisotopes 230,232,233Pa on Irradiation of ThO2 Targets by 1,2H AND 3,4He Nuclei

Measurement of the Yield of Protactinium Radioisotopes 230,232,233Pa on Irradiation of ThO2 Targets by 1,2H AND 3,4He Nuclei

Terahertz Emission Enhanced by a Laser Irradiating on a T-Type Target

The generation of high field terahertz emission based on the interaction between an ultra-intense laser and solid targets has been widely studied in recent years because of its wide potential applications in biological imaging and material science. Here, a novel scheme is proposed to enhance the terahertz emission, in which a linearly polarized laser pulse irradiates a T-type target including a longitudinal target followed by a transverse target. By using two-dimensional particle-in-cell simulations, we find that the electron beam, modulated by the direct laser acceleration via the interaction of the laser with the longitudinal solid target, plays a crucial role in enhancing the intensity of terahertz emission and controlling its spatial distribution. Compared with the single-layer target, the maximum radiated electromagnetic field’s intensity passing through the spatial probe point is enhanced by about one order of magnitude, corresponding to the terahertz emission power increasing by two orders of magnitude or so. In addition, the proposed scheme is robust with respect to the thickness and length of the target. Such a scheme may provide important theoretical and data support for the enhancement of terahertz emission efficiency based on the ultra-intense laser irradiation of solid targets.

Optimization of 68Ga production at an 18 MeV medical cyclotron with solid targets by means of cross-section measurement of 66Ga, 67Ga and 68Ga

The future development of personalized nuclear medicine relies on the availability of novel medical radionuclides. In particular, radiometals are attracting considerable interest since they can be used to label both proteins and peptides. Among them, the β+-emitter 68Ga is widely used in nuclear medicine for positron emission tomography (PET). It is used in theranostics as the diagnostic partner of the therapeutic β−-emitters 177Lu and 90Y for the treatment of a wide range of diseases, including prostate cancer. Currently, 68Ga is usually obtained via 68Ge/68Ga generators. However, their availability, high price and limited produced radioactivity per elution are a major barrier for a wider use of the 68Ga-based diagnostic radiotracers. A promising solution is the production of 68Ga by means of proton irradiation of enriched 68Zn liquid or solid targets. Along this line, a research program is ongoing at the Bern medical cyclotron, equipped with a solid target station. In this paper, we report on the measurements of 68Ga, 67Ga and 66Ga production cross-sections using natural Zn and enriched 68Zn material, which served as the basis to perform optimized 68Ga production tests with enriched 68Zn solid targets.