An empirical equation for the backscattering coefficient of electrons

Evaluation of dose perturbations around iodine-125 seed sources in supplemental external beam prostate radiotherapy

We investigated dose perturbations caused by 125I seeds in patients undergoing supplemental external beam radiotherapy (EBRT) for prostate cancer. We examined two types of nonradioactive seed models: model 6711 and model STM1251. All experiments were performed using a water-equivalent phantom. Radiochromic film was used to measure the dose distributions adjacent to the seeds upstream and downstream of the external beam source. Single and clusters of multiple seeds were placed in slots in a solid water (SW) slab to measure dose perturbations with separate versus dense seed placement at beam energies of 6 or 10 MV. Monte Carlo simulations (MCSs) were also performed to include the theoretical basis against film dosimetry. Distinct patterns of dose enhancement (buildup [BU]) were upstream, and dose reduction (builddown [BD]) were downstream of the radiation source. Model 6711 with lower photon beam energies produced larger dose perturbations of BU and BD than the model STM1251. The results showed the same tendency with different seed placements and beam energies. However, these differences were not observed in the rotational irradiation measurement, which replicated a clinical plan. Dose perturbations around seeds result in dose enhancement and dose reduction with varying impact depending on the photon beam energy and seed type. This has the potential to cancel out these perturbations using multiple beam direction fields.

Halide perovskites and perovskite related materials for particle radiation detection

Radiation detectors are widely used in physics, materials science, chemistry, and biology. Halide perovskites are known for their superior properties including tunable bandgaps and chemical compositions, high defect tolerance, solution-processable synthesis of films and crystals, and high carrier diffusion length. Recently, halide perovskites have attracted enormous interest as particle radiation detectors for both charged (α and β) and uncharged (neutrons) particles. Solid-state detectors based on single crystal perovskites can detect α particles and thermal neutrons with energy-resolved spectra. Halide perovskite scintillators are also able to detect β particles and fast neutrons. In this review, we briefly introduce the fundamentals of radiation detection and summarize the recent progress on halide perovskite detectors for particle radiation.

Energy calibration of charged particle detectors using discrete and continuous energy spectra of 137Cs

An improved method for energy calibration of particle detectors is presented utilizing both the discrete and continuous spectra from the conversion electrons and beta particles of a radioisotope of  ¹³⁷Cs. This method considers the instrument response against the discrete spectrum from the conversion electrons at 624.22 keV and the continuous spectrum from the beta particles emitted by the unique first forbidden transition in the energy range of approximately 120-513 keV. The instrument response is determined by fitting model functions to the measurements, from which the energy scale and energy resolution of the instrument are derived. Inclusion of the beta particles in this method enables a determination of the energy scale in a broader energy range as well as the DC-offset and non-linearity of the instrument. This is an improvement from the conventional method that only utilizes a mono-energetic peak from the conversion electrons. A detailed description of the procedure is provided, from constructing the model functions to determining the instrument response. Results of the method, as successfully applied to a space-borne instrument, are provided to demonstrate the method.

Design and test of a Faraday cup for low-charge measurement of electron beams from laser wakefield acceleration

Nowadays, laser wakefield acceleration is considered to be one of the perspective methods for GeV electron beam production. The combination of laser accelerated electrons and Compton backscattering of a probe light beam opens the possibility of creating the tabletop source of a femtosecond light beam in x-ray and gamma ranges. The project is aimed at creating a laser-driven Compton light source in ILP SB RAS in collaboration with BINP SB RAS. Production of 1-10 pC electron beams in sub-ps time range duration with energies up to 100 MeV is expected to be a result of the first stage of the project. Since the energy of electrons does not exceed 100 MeV, it allows the use of the Faraday cup (FC) with reasonable dimensions, instead of the commonly used integrating current transformer. The geometry of the FC has been optimized taking into account beam stopping simulation as well as a low capacity requirement. Simulation of high-frequency properties of the entire system was carried out. The system has been tested at the VEPP-5 electron linac. The results of developing and testing this FC are presented.

Generation and Beaming of Early Hot Electrons onto the Capsule in Laser-Driven Ignition Hohlraums

In hohlraums for inertial confinement fusion (ICF) implosions on the National Ignition Facility, suprathermal hot electrons, generated by laser plasma instabilities early in the laser pulse ("picket") while blowing down the laser entrance hole (LEH) windows, can preheat the capsule fuel. Hard x-ray imaging of a Bi capsule surrogate and of the hohlraum emissions, in conjunction with the measurement of time-resolved bremsstrahlung spectra, allows us to uncover for the first time the directionality of these hot electrons and infer the capsule preheat. Data and Monte Carlo calculations indicate that for most experiments the hot electrons are emitted nearly isotropically from the LEH. However, we have found cases where a significant fraction of the generated electrons are emitted in a collimated beam directly towards the capsule poles, where their local energy deposition is up to 10× higher than the average preheat value and acceptable levels for ICF implosions. The observed "beaming" is consistent with a recently unveiled multibeam stimulated Raman scattering model [P. Michel et al., Phys. Rev. Lett. 115, 055003 (2015)], where laser beams in a cone drive a common plasma wave on axis. Finally, we demonstrate that we can control the amount of generated hot electrons by changing the laser pulse shape and hohlraum plasma.

[Development of cloud chamber having thin-film entrance windows and proposal of practical training for beginners using X-ray equipment and unsealed radioactive material]

A cloud chamber is a detector that can visualize the tracks of charged particles. Hayashi, et al. suggested a visualization experiment in which X-rays generated by diagnostic X-ray equipment were directed into a cloud chamber; however, there was a problem in that the wall of the cloud chamber scattered the incoming X-rays. In this study, we developed a new cloud chamber with entrance windows. Because these windows are made of thin film, we were able to direct the X-rays through them without contamination by scattered X-rays from the cloud chamber wall. We have newly proposed an experiment in which beta-particles emitted from radioisotopes are directed into a cloud chamber. We place shielding material in the cloud chamber and visualize the various shielding effects seen with the material positioned in different ways. During the experiment, electrons scattered in the air were measured quantitatively using GM counters. We explained the physical phenomena in the cloud chamber using Monte Carlo simulation code EGS5. Because electrons follow a tortuous path in air, the shielding material must be placed appropriately to be able to effectively block their emissions. Visualization of the tracks of charged particles in this experiment proved effective for instructing not only trainee radiological technologists but also different types of healthcare professionals.

A special mini-extrapolation chamber for calibration of90Sr+90Y sources

90Sr+90Y applicators are commonly utilized in brachytherapy, including ophthalmic procedures. The recommended instruments for the calibration of these applicators are extrapolation chambers, which are ionization chambers that allow the variation of their sensitive volume. Using the extrapolation method, the absorbed dose rate at the applicator surface can be determined. The aim of the present work was to develop a mini-extrapolation chamber for the calibration of 90Sr+90Y beta ray applicators. The developed mini-chamber has a 3.0 cm outer diameter and is 11.3 cm in length. An aluminized polyester foil is used as the entrance window while the collecting electrode is made of graphited polymethylmethacrylate. This mini-chamber was tested in 90Sr+90Y radiation beams from a beta particle check source and with a plane ophthalmic applicator, showing adequate results.

Determination of the Kwall correction factor for a cylindrical ionization chamber to measure air-kerma in 60Co gamma beams

The factor Kwall to correct for photon attenuation and scatter in the wall of ionization chambers for 60Co air-kerma measurement has been traditionally determined by a procedure based on a linear extrapolation of the chamber current to zero wall thickness. Monte Carlo calculations by Rogers and Bielajew (1990 Phys. Med. Biol. 35 1065-78) provided evidence, mostly for chambers of cylindrical and spherical geometry, of appreciable deviations between the calculated values of Kwall and those obtained by the traditional extrapolation procedure. In the present work an experimental method other than the traditional extrapolation procedure was used to determine the Kwall factor. In this method the dependence of the ionization current in a cylindrical chamber was analysed as a function of an effective wall thickness in place of the physical (radial) wall thickness traditionally considered in this type of measurement. To this end the chamber wall was ideally divided into distinct regions and for each region an effective thickness to which the chamber current correlates was determined. A Monte Carlo calculation of attenuation and scatter effects in the different regions of the chamber wall was also made to compare calculation to measurement results. The Kwall values experimentally determined in this work agree within 0.2% with the Monte Carlo calculation. The agreement between these independent methods and the appreciable deviation (up to about 1%) between the results of both these methods and those obtained by the traditional extrapolation procedure support the conclusion that the two independent methods providing comparable results are correct and the traditional extrapolation procedure is likely to be wrong. The numerical results of the present study refer to a cylindrical cavity chamber like that adopted as the Italian national air-kerma standard at INMRI-ENEA (Italy). The method used in this study applies, however, to any other chamber of the same type.

Observation of nuclear excitation by electron transition in 197Au with synchrotron X rays and an avalanche photodiode

We have succeeded in observing nuclear excitation by electron transition (NEET) in 197Au by a new method. Monochromatic x-rays of synchrotron radiation were used to ionize the K shell of gold atoms in a target foil. The internal-conversion electrons emitted from excited nuclei were detected with a silicon avalanche photodiode. At a photon energy of 80.989 keV, the NEET probability in 197Au was determined to be (5.0+/-0.6)x10(-8) from a comparison of the event number per photon between NEET and the nuclear resonance at 77.351 keV.