Absolute cross sections for isotopically identified products formed in multinucleon transfer in the (136)Xe+(198)Pt system at ∼8 MeV/nucleon are reported. The isotopic distributions obtained using a ...large acceptance spectrometer demonstrated the production of the "hard-to-reach" neutron-rich isotopes for Z<78 around the N=126 shell closure far from stability. The main contribution to the formation of these exotic nuclei is shown to arise in collisions with a small kinetic energy dissipation. The present experimental finding corroborates for the first time recent predictions that multinucleon transfer reactions would be the optimum method to populate and characterize neutron-rich isotopes around N=126 which are crucial for understanding both astrophysically relevant processes and the evolution of "magic" numbers far from stability.
Some patients have noted a foul odor during radiation therapy sessions, but the cause of the odor remains unknown. Since we suspected that this phenomenon is due to ozone generated by ionizing ...radiation, this experimental study measured ozone concentrations in the treatment room and in a coiled polyvinyl chloride (PVC) tube placed within the radiation field.
We measured ozone concentrations using an ultraviolet absorption method and an ozone monitor. A PVC tube (inner diameter 7 mm, outer diameter 10 mm) was used to mimic the environment of the nasal cavity. The tube (790 cm) was coiled and set between two 4-cm-thick (for X-rays) or 2-cm-thick (for electron beams) water-equivalent solid phantoms. The sampling tube of the ozone monitor was inserted into the PVC tube, and the joint was sealed to prevent environmental air contamination. To measure ozone concentrations in the atmosphere, the sampling tube supplied with the unit was used. A linac was used on a full-sized treatment field (40 cm × 40 cm at a source-to-axis distance of 100 cm). The effect of an electron beam on ozone concentrations was also evaluated with a full-sized treatment field (40 cm × 40 cm at a source-to-surface distance of 100 cm).
Ozone levels in the treatment room were undetectable before the start of daily treatment but reached 0.008 parts per million (ppm) or more at 1 h after the start of treatment. Concentrations then remained nearly constant at 0.010-0.015 ppm throughout the day. The maximum ozone concentration in the PVC tube was only 0.006 ppm, even when it was irradiated at 2400 monitor units/min. Depending on the X-ray dose rate, the concentration increased to a maximum of 0.010 ppm with oxygen flowing into the other end of the tube at 1.5 L/min. Ozone concentrations in the PVC tube did not differ significantly between X-ray and electron-beam irradiation.
Only traces of ozone were found in the PVC tube that was used to mimic the nasal passages during radiation, these concentrations were too low for human perception. However, ozone concentrations did reach potentially detectable levels in the treatment room.
The detrimental influence of oxygen on the performance and reliability of V/III nitride based devices is well known. However, the influence of oxygen on the nature of the incorporation of other ...co-dopants, such as rare earth ions, has been largely overlooked in GaN. Here, we report the first comprehensive study of the critical role that oxygen has on Eu in GaN, as well as atomic scale observation of diffusion and local concentration of both atoms in the crystal lattice. We find that oxygen plays an integral role in the location, stability, and local defect structure around the Eu ions that were doped into the GaN host. Although the availability of oxygen is essential for these properties, it renders the material incompatible with GaN-based devices. However, the utilization of the normally occurring oxygen in GaN is promoted through structural manipulation, reducing its concentration by 2 orders of magnitude, while maintaining both the material quality and the favorable optical properties of the Eu ions. These findings open the way for full integration of RE dopants for optoelectronic functionalities in the existing GaN platform.
•A Multiple Coulomb scattering of a proton causing image blurring is studied.•A phantom with several tissue surrogates is irradiated.•A proton scattering angle is calculated using direction and ...position information.•Clinically relevant proton beam energies were studied.•Using proton direction gives factor 2 less statistics than proton position.
Proton radiography is a novel imaging modality that allows direct measurement of the proton energy loss in various tissues. Currently, due to the conversion of so-called Hounsfield units from X-ray Computed Tomography (CT) into relative proton stopping powers (RPSP), the uncertainties of RPSP are 3–5% or higher, which need to be minimized down to 1% to make the proton treatment plans more accurate.
In this work, we simulated a proton radiography system, with position-sensitive detectors (PSDs) and a residual energy detector (RED). The simulations were built using Geant4, a Monte Carlo simulation toolkit. A phantom, consisting of several materials was placed between the PSDs of various Water Equivalent Thicknesses (WET), corresponding to an ideal detector, a gaseous detector, silicon and plastic scintillator detectors. The energy loss radiograph and the scattering angle distributions of the protons were studied for proton beam energies of 150MeV, 190MeV and 230MeV. To improve the image quality deteriorated by the multiple Coulomb scattering (MCS), protons with small angles were selected. Two ways of calculating a scattering angle were considered using the proton’s direction and position.
A scattering angle cut of 8.7mrad was applied giving an optimal balance between quality and efficiency of the radiographic image. For the three proton beam energies, the number of protons used in image reconstruction with the direction method was half the number of protons kept using the position method.
•136Xe+198Pt shows a comparable contribution of proton pick-up and stripping.•Proton stripping channels in 136Xe+198Pt show enhanced cross sections.•Mass distributions of proton stripping channels in ...136Xe+198Pt shift to heavy side.
Multinucleon transfer reactions between two heavy ions are an important tool for production and investigation of exotic neutron-rich nuclei, which are difficult to access by other methods. The 136Xe+198Pt system is a candidate to efficiently produce neutron-rich nuclei around the neutron magic number N=126 for the KEK isotope separation project. In order to confirm this, measurements of the production cross sections with the large acceptance magnetic spectrometer VAMOS++ and de-excitation gamma rays from target-like fragments using the high efficiency germanium array EXOGAM at GANIL are reported. The measured isotopic distributions of the projectile-like fragments are compared with GRAZING calculations. The proton stripping channels show rough agreements between measurements and calculations. For the proton pick-up channels, the measured distributions are shifted toward the heavier masses and show enhanced cross sections in transfers of two or more protons.
Introduction The quality of cancer treatment with protons critically depends on the accurate determination of proton stopping powers (PSPs) of traversed tissues. Nowadays, proton treatment planning ...is based on stopping powers derived from X-ray Computed Tomography (CT) images leading to systematic uncertainties in the proton range in a patient of 3–4% and even up to 10% in regions containing bone. This may cause no dose in parts of the tumor and overdose in healthy tissues. Purpose In order to reduce the uncertainty in the translation of the X-ray CT image into a map of PSPs, we study proton radiography imaging as it delivers PSPs directly, without using a model. Materials and methods Using the Geant4 toolkit we simulate the proton radiography system with two position sensitive detectors and an energy detector. The imaged object is placed between the position detectors. The energy loss radiographs of the phantom with various, including tissue-like, materials are obtained. The multiple Coulomb scattering of a proton passing through various materials blurs the energy loss radiography image, but selecting protons travelling along almost straight paths decreases the blurring. Results Our simulations show that considering protons with small scattering angles increases sharpness between the material boundaries in the energy loss radiographs, and materials with small density differences are distinguished. Conclusion Proton radiography provides a direct information on PSPs of tissues inside the human body improving the accuracy of the calculation of the dose deposition by protons in a patient. Disclosure Authors have no relevant financial or nonfinancial relationships to disclose.
The quality of cancer treatment with protons critically depends on an accurate prediction of the proton stopping powers for the tissues traversed by the protons. Today, treatment planning in proton ...radiotherapy is based on stopping power calculations from densities of X-ray Computed Tomography (CT) images. This causes systematic uncertainties in the calculated proton range in a patient of typically 3-4%, but can become even 10% in bone regions 1,2,3,4,5,6,7,8. This may lead to no dose in parts of the tumor and too high dose in healthy tissues 1. A direct measurement of proton stopping powers with high-energy protons will allow reducing these uncertainties and will improve the quality of the treatment. Several studies have shown that a sufficiently accurate radiograph can be obtained by tracking individual protons traversing a phantom (patient) 4,6,10. Our studies benefit from the gas-filled time projection chambers based on GridPix technology 2, developed at Nikhef, capable of tracking a single proton. A BaF sub(2) crystal measuring the residual energy of protons was used. Proton radiographs of phantom consisting of different tissue-like materials were measured with a 30x30 mm super(2) 150 MeV proton beam. Measurements were simulated with the Geant4 toolkit.First experimental and simulated energy radiographs are in very good agreement 3. In this paper we focus on simulation studies of the proton scattering angle as it affects the position resolution of the proton energy loss radiograph. By selecting protons with a small scattering angle, the image quality can be improved significantly.
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