Large-area Beam Research Articles

Radiological evaluation of lead apron integrity in five selected hospitals in Abuja, Nigeria

Background: The general consensus is that any exposure to ionising radiation carries a risk. Diagnostic radiology is the largest (87%) contributor to man-made ionising radiation, therefore any economical and socially acceptable means ofreducing dose without compromising the diagnostic value of the procedure must be worth implementing.Aim: This study is aimed at evaluating lead apron integrity in five selected Hospitals in Abuja, Nigeria.Methodology: The methodology approach includes the application of a large area beam for transmission measurement with the placement of OSLD before and behind the ten (10) lead aprons to determine the entrance and exit dose as well as the transmission factor. In this study, lead apron consisting of 0.25mm and 0.35mm thickness were examined.Results: The result shows that the transmittance factor of the entrance and exit dose through the lead equivalent aprons is directly proportional to the age of the apron with NHA1 having the highest transmission factor (0.83) and oldest age (16 years). WGH2 has the lowest transfer factor (0.12) and the least age (1 year).Conclusion: Lead aprons loses their attenuation capability over time and should be replace after 15 years at most for effective protection against ionizing radiation.

RADIOLOGICAL EVALUATION OF LEAD APRON INTEGRITY IN FIVE SELECTED HOSPITALS IN ABUJA, NIGERIA

Background: The general consensus is that any exposure to ionising radiation carries a risk. Diagnostic radiology is the largest (87%) contributor to man-made ionising radiation, therefore any economical and socially acceptable means of reducing dose without compromising the diagnostic value of the procedure must be worth implementing. Aim: This study is aimed at evaluating lead apron integrity in five selected Hospitals in Abuja, Nigeria. Methodology: The methodology approach includes the application of a large area beam for transmission measurement with the placement of OSLD before and behind the ten (10) lead aprons to determine the entrance and exit dose as well as the transmission factor. In this study, a lead apron consisting of 0.25mm and 0.35mm thickness were examined. Results: The result shows that the transmittance factor of the entrance and exit dose through the lead equivalent aprons is directly proportional to the age of the apron with NHA1 having the highest transmission factor (0.83) and oldest age (16 years). WGH2 has the lowest transfer factor (0.12) and the least age (1 year). Conclusion: Lead aprons loses their attenuation capability over time and should be replaced after 15 years at most for effective protection against ionizing radiation.

A large beam high efficiency radio frequency neutron spin flipper.

A design for a radio frequency (RF) neutron spin flipper obtained from magneto-static and neutron spin transport simulations is presented. The RF flipper constructed from this design provides a flipping probability of 0.999 or better for a beam size 6cm wide and 15cm high and a wavelength band between 0.4 and 0.6nm. Three permanent magnet guide field sections with air gaps provide a linear field gradient along the beam propagation direction over a large cross-sectional area. An RF oscillator based on coupling the resonant coil of a Hartley oscillator to the excitation coil was developed, which provides a higher current and, thereby, a larger RF amplitude, as compared to a conventional RF power amplifier. Two opaque He3 neutron spin filters were employed to measure the flipping probability of the flipper with very high precision. A spatially uniform flipping probability of 0.9995(2) or higher was measured over the large cross-sectional area neutron guide. This RF neutron spin flipper will be employed in a polychromatic beam reflectometer at the National Institute of Standards and Technology Center for Neutron Research. This design can be applied to other polarized neutron instruments or applications requiring a very high continuous flipping probability of the neutron spin for a large cross-sectional area beam.

Transverse profile shaping of a charged-particle beam using multipole magnets - Formation of hollow beams -

The use of multipole magnets enables us to transform the transverse profile of a charged-particle beam into various ones that can never be formed through linear beam optics. To date, the formation of a large-area beam with a uniform transverse intensity distribution has been realized using octupole magnets for uniform beam irradiation. Here, we report the first demonstration of the hollow-beam formation using multipole magnets in a beam transport line. Results of beam-formation experiments and tracking simulations are shown. The hollow beam has a steep peak at the edge of the beam and thus has a high contrast between the edge peak and the intensity near the beam center.

Micro-ion beam-induced luminescence spectroscopy for evaluating SiAlON scintillators

Ion beam-induced luminescence (IBIL) spectroscopy was used for luminescent material characterization and analysis for the investigation of new scintillator families. Under continuous 3 MeV proton microbeam irradiation, the crystal structures of α-SiAlON:Eu, β-SiAlON:Eu, and CaAlSiN3 (CASN) emitted bright luminescence at peak wavelengths of 605, 540, and 670 nm, respectively. As the irradiation progressed, the IBIL intensity of the conventional ZnS:Ag scintillator decreased sharply, whereas that of the SiAlONs and CASN remained within the detection limit. IBIL spectroscopy was performed on individual grains of the SiAlON scintillators. IBIL imaging and spectroscopy of two grains of β-SiAlON:Eu showed that the main peak in the IBIL spectrum of β-SiAlON:Eu obtained from a large-area beam scan consisted of several small peaks, which were observed in spectra from individual grains. Our experimental results suggest that microscopic spectroscopy of IBIL is an effective tool for microscopic material characterization of luminescent targets.

Development of a large active area beam telescope based on the SiD microstrip sensor

A beam telescope as one of the most important and often requested test beam equipment provides particle tracking to test beam users. At the DESY II test beam facility, a new beam telescope called Lycorisbased on a microstrip sensor has been designed to address the user demands for momentum measurement in a 1T solenoid magnet or large area tracking with limited space (3.5cm between the potential user device and the magnet inner wall). Lycorisis designed to provide a high-precision resolution of at least ∼10µm along the bending direction, and a large active area of 10×10cm2 to cover at least 90% of the beam particles at energies of 1-6GeV. The microstrip sensor was originally designed for the Silicon Detector (SiD) at the International Linear Collider (ILC), which adopted a hybrid-less design, i.e. a second metallization layer is used to route signals from strips to the bump-bonded ASIC, and from the ASIC to a wire-bond pad to the outside. This hybrid-less arrangement eliminates the need for a complex hybrid design, and its functioning is first-time tested in this project. The performance of the sensor modules was firstly tested in the lab then at the DESY II test beam facility in August/September 2018, and the results will be presented here. In addition, a summary will be given at the end with an overview of the ongoing test beam campaign of the Lycorisprototype in February 2019.

Real-time SPR imaging based on a large area beam from a wavelength-swept laser.

We demonstrate a real-time surface plasmon resonance imaging (SPRi) system based on a wavelength-swept laser. Compared to conventional spectral-modulation SPRi using white light source and spectral filtering, the proposed system has a higher scan rate to detect rapid changes in refractive index and a higher output power for large-area illumination. This SPRi system achieves scan rates faster than 12Hz, simultaneously obtaining SPR dip positions over full illumination fields of 12×12 mm. Using the wavelength-swept laser, two-dimensional biomolecular array imaging can be acquired with a high dynamic detection range (7.67×10-3 refractive index unit (RIU)) as well as high sensitivity (6501nm/RIU) and resolution (1.89×10-6 RIU).

A large area diamond-based beam tagging hodoscope for ion therapy monitoring

The MoniDiam project is part of the French national collaboration CLaRyS (Contrôle en Ligne de l’hAdronthérapie par RaYonnements Secondaires) for on-line monitoring of hadron therapy. It relies on the imaging of nuclear reaction products that is related to the ion range. The goal here is to provide large area beam detectors with a high detection efficiency for carbon or proton beams giving time and position measurement at 100 MHz count rates (beam tagging hodoscope). High radiation hardness and intrinsic electronic properties make diamonds reliable and very fast detectors with a good signal to noise ratio. Commercial Chemical Vapor Deposited (CVD) poly-crystalline, heteroepitaxial and monocrystalline diamonds were studied. Their applicability as a particle detector was investigated using α and β radioactive sources, 95 MeV/u carbon ion beams at GANIL and 8.5 keV X-ray photon bunches from ESRF. This facility offers the unique capability of providing a focused (~1 μm) beam in bunches of 100 ps duration, with an almost uniform energy deposition in the irradiated detector volume, therefore mimicking the interaction of single ions. A signal rise time resolution ranging from 20 to 90 ps rms and an energy resolution of 7 to 9% were measured using diamonds with aluminum disk shaped surface metallization. This enabled us to conclude that polycrystalline CVD diamond detectors are good candidates for our beam tagging hodoscope development. Recently, double-side stripped metallized diamonds were tested using the XBIC (X Rays Beam Induced Current) set-up of the ID21 beamline at ESRF which permits us to evaluate the capability of diamond to be used as position sensitive detector. The final detector will consist in a mosaic arrangement of double-side stripped diamond sensors read out by a dedicated fast-integrated electronics of several hundreds of channels.

Study of electron beam uniformity in large-area multi-aperture diode with arc plasma cathode

The use of plasma emission cathode in the conjunction with a multiple apertured electron optical system (EOS) is promising for the multi-MW class electron beams of a large cross-sectional area. In a multi-aperture source, the beam parameters could be raised simply due to increase of the number of apertures (i.e. an effective emission area), if a uniformity of the electron emission over a large-area plasma cathode is ensured. In the presented paper, the cross-sectional distribution of the emission current density was investigated using the X-ray diagnostic technique for two versions of the diode-type EOS, with electrodes performed as flat molybdenum “grids”. The first one had 241 apertures arranged hexagonally inside a circle with a diameter of 8.3 cm and the second had 499 apertures within a circle of 11.8cm diameter. The emission plasma is produced using a single arc-discharge plasma generator placed on the axis at 20 cm from the EOS. It was demonstrated that multi-aperture systems with a single on-axis plasma generator can be effectively employed to obtain large-area beams, even in the presence of the guiding magnetic field. All apertures are emitting in the 499-apertured EOS. The beam current density is quite uniform up to the radius 2.5cm and gradually decreases to the periphery.

Study on ion irradiation response of Gafchromic films for the intensity distribution measurement of a large-area beam

It is required to precisely evaluate the large-area transverse intensity distribution of various ion beams applied to materials and biological research at an azimuthally-varying-field cyclotron in Japan Atomic Energy Agency. The response of radiochromic films, Gafchromic HD-810 and EBT2, was, therefore, investigated using proton and several heavy-ion beams for developing a measurement technique of the transverse beam intensity distribution. The optical density of the films increased linearly with the particle fluence of the beam in a low-fluence region. The linear-response range of the fluence was strongly dependent on ion species. By analyzing the film response to absorbed dose, it was found that the sensitivity of the film decreased for heavy-ion beams. The practical fluence range of the Gafchromic film HD-810 for an arbitrary ion beam was determined from the measurement result. The present technique with the use of the two types of Gafchromic films enables us to measure the intensity distribution of a large-area ion beam easily in a wide fluence range. Using the technique, we measured the relative intensity distribution of a large-area ion beam focused by multipole magnets and evaluated its size and uniformity.

Negative ion source development for fusion application (invited)

Giant negative ion sources, producing high-current of several tens amps with high energy of several hundreds keV to 1 MeV, are required for a neutral beam injector (NBI) in a fusion device. The giant negative ion sources are cesium-seeded plasma sources, in which the negative ions are produced on the cesium-covered surface. Their characteristic features are discussed with the views of large-volume plasma production, large-area beam acceleration, and high-voltage dc holding. The international thermonuclear experimental reactor NBI employs a 1 MeV-40 A of deuterium negative ion source, and intensive development programs for the rf-driven source plasma production and the multistage electrostatic acceleration are in progress, including the long pulse operation for 3600 s. Present status of the development, as well as the achievements of the giant negative ion sources in the working injectors, is also summarized.

Long pulse large area beam extraction with a rf driven H−∕D− source

IPP Garching is heavily involved in the development of the rf driven H(-)/D(-) ion source for the ITER NBI. After the successful demonstration of the required physical parameters, the experimental conditions have been extended to long pulses and large area beam extraction. This paper contains descriptions of the source and power supply modifications necessitated for long pulses as well as the latest results including the first 1 h pulse. Suppression of the coextracted electron current is a key issue. Experiments with potential control, different magnetic filter fields, and cesium handling to suppress the electrons and stabilize the currents are also reported.

Homogeneous near surface activity distribution by double energy activation for TLA

Thin layer activation (TLA) is a versatile tool for activating thin surface layers in order to study real-time the surface loss by wear, corrosion or erosion processes of the activated parts, without disassembling or stopping running mechanical structures or equipment. The research problem is the determination of the irradiation parameters to produce point-like or large area optimal activity-depth distribution in the sample. Different activity-depth profiles can be produced depending on the type of the investigated material and the nuclear reaction used. To produce activity that is independent of the depth up to a certain depth is desirable when the material removed from the surface by wear, corrosion or erosion can be collected completely. By applying dual energy irradiation the thickness of this quasi-constant activity layer can be increased or the deviation of the activity distribution from a constant value can be minimized. In the main, parts made of metals and alloys are suitable for direct activation, but by using secondary particle implantation the wear of other materials can also be studied in a surface range a few micrometers thick.In most practical cases activation of a point-like spot (several mm2) is enough to monitor the wear, corrosion or erosion, but for special problems relatively large surfaces areas of complicated spatial geometry need to be activated uniformly. Two ways are available for fulfilling this task, (1) production of large area beam spot or scanning the beam over the surface in question from the accelerator side, or (2) a programmed 3D movement of the sample from the target side. Taking into account the large variability of tasks occurring in practice, the latter method was chosen as the routine solution in our cyclotron laboratory.

Thin layer activation of large areas for wear study

Thin layer activation (TLA) method is a versatile tool for activating thin surface layers (from several micrometers to millimeters range) in order to study the wear, corrosion or erosion processes of the activated parts without disassembling or stopping the running equipment in question. Mainly parts made of metals and alloys are suitable for direct activation, but by using secondary particle implantation other materials can also be measured in micrometer thick surface range [F. Ditrói, I. Mahunka, Nucl. Instrum. Meth. Phys. Res. B 113 (1996) 415; F. Ditrói, I. Mahunka, Wear 219 (1998) 78]. In most practical cases the activation of a point-like spot (several square millimeters) is enough to monitor the wear, corrosion or erosion, but by special problems relatively great surface of complicated spatial geometry should be activated uniformly. Two ways are available for fulfilling this task: (1) production of large area beam spot or scanning the beam over the surface in question from the accelerator side, or (2) a programmed 3D movement of the sample from the target side. Taking into account the large variability of tasks occurring in our practice, the latter method was chosen as routine solution in our cyclotron laboratory.

Polarized (3) He Spin Filters for Slow Neutron Physics.

Polarized (3)He spin filters are needed for a variety of experiments with slow neutrons. Their demonstrated utility for highly accurate determination of neutron polarization are critical to the next generation of betadecay correlation coefficient measurements. In addition, they are broadband devices that can polarize large area and high divergence neutron beams with little gamma-ray background, and allow for an additional spin-flip for systematic tests. These attributes are relevant to all neutron sources, but are particularly well-matched to time of flight analysis at spallation sources. There are several issues in the practical use of (3)He spin filters for slow neutron physics. Besides the essential goal of maximizing the (3)He polarization, we also seek to decrease the constraints on cell lifetimes and magnetic field homogeneity. In addition, cells with highly uniform gas thickness are required to produce the spatially uniform neutron polarization needed for beta-decay correlation coefficient experiments. We are currently employing spin-exchange (SE) and metastability-exchange (ME) optical pumping to polarize (3)He, but will focus on SE. We will discuss the recent demonstration of 75 % (3)He polarization, temperature-dependent relaxation mechanism of unknown origin, cell development, spectrally narrowed lasers, and hybrid spin-exchange optical pumping.

Fly's Eye Beam

JPSA Laser’s new Fly’s Eye Beam Homogenizer converts the characteristically non-uniform beam of a UV Excimer laser into a homogeneous beam with 95% uniformity while utilizing >80% of the laser power. This long working distance single element array easily adapts to most commercial excimer lasers, and offers optimum price/performance ratio (single element for lowest cost and lowest beam loss). The JPSA Fly’s Eye Beam Homogenizer’s long working distance — typically between 1–2 meters — provides a beam size ranging from 8mm to 1.5cm. It is easily re-imaged due to the long working distance and slow optical F-number.Excimer laser beams are not perfectly uniform in intensity over the area of the beam and therefore only a portion of the area of the beam is usable for high-uniformity materials processing. In some cases, only the most uniform section or “filet” of the beam will be selected for use, and the non-uniform section of the laser beam will be discarded. Due to the premium price associated with UV photons, high beam utilisation in many cases is a key economic factor. Beam shaping optics and beam homogenisers can be employed to shape the beam and simultaneously make the laser energy uniform so that the maximum amount of the available laser power can be used. The resultant uniform, large area beam can then be subdivided using near-field imaging to project complex patterns onto a part or make simultaneous multiple laser ablations, a key advantage of UV Excimer lasers. Visit www.three-fives.com for the latest advanced semiconductor industry news

Evaluation of the transmitted exposure through lead equivalent aprons used in a radiology department, including the contribution from backscatter

A study was conducted to evaluate the radiation transmission through lead equivalent aprons that are used in a radiology department. A large area beam (poor geometry) was employed for the transmission measurements, and backscatter was simulated by placing 7" of Lucite behind each apron. Separate ionization chambers were used to measure the incident and transmitted x-ray beams. Transmission measurements were made at 70 kVp and 100 kVp through aprons and protective shields from eight different vendors that were marked 0.25 mm and 0.5 mm lead equivalent. Transmissions through 0.254 mm and 0.508 mm of pure lead were also measured and were compared with the transmissions through the lead equivalent materials. In addition, the area densities of the aprons were measured to compare radiation transmission with respect to the weights of the aprons. At 70 kVp, the transmission through 0.254 mm of pure lead was 5.4% and the transmissions through the 0.25 mm lead equivalent materials were 4.3% to 10.2% with a mean value of 7.1% and a standard deviation (s.d.) of 1.4%. At 100 kVp, the values were 15% for 0.254 mm pure lead and 12.3% to 20.7% (mean 16.8%, s.d. 2.1%) for the 0.25 mm lead equivalent materials. The transmission through the 0.508 mm pure lead sample was 0.9% at 70 kVp, and the corresponding transmissions through the 0.5 mm lead equivalent materials were 0.6% to 1.6% (mean 1.0%, s.d. 0.2%). At 100 kVp, the transmission through the 0.508 mm lead sample was 5% and those through the 0.5 mm lead equivalent materials were 3.5% to 6.7% (mean 4.9%, s.d. 0.7%). The radiation transmissions at 70 kVp, through two "lead-free" 0.5 mm lead equivalent aprons, were 1.7% and 1.9% and at 100 kVp the transmissions were 6.1% and 6.8%, respectively. This study indicates that there is a need to establish methods for acceptance testing of aprons and a need to establish acceptance limits for the x-ray transmission of aprons at specific kVp values. There is also a need for the establishment of appropriate methods and frequencies of routine quality assurance testing of radiation protection aprons.

Improvement of a large negative ion source for the Large Helical Device neutral beam injector

For compensation of the magnetically deflected beamlets, a new type of grid system has been applied to a large negative ion source of a negative-ion-based neutral beam injector in the Large Helical Device (LHD) fusion experimental machine. Corresponding to deviation of the negative ion beamlet trajectory due to the electron suppression magnetic field at the extraction grid, the exit aperture of the extraction grid is displaced to cancel the beamlet deflection by electrostatic lens effect. As a result, the beamlet deflection was suppressed less than 2 mrad in a wide range of energy of 110–180 keV, and the port-through efficiency of the injected beam was improved to 90%–95% from 70%–75% in the case of the previous compensation by the grounded grid aperture displacement. The injected beam power was increased to 3.5 MW with an energy of 165 keV using one injector. To improve beam uniformity of the large area beam, individual arc currents through filaments are controlled for uniform plasma production, with independent 12 arc power supplies connected to 12 filament power supplies. The initial results show good controllability of the individual arc current distribution at a high arc power. The improvement of the ion source performance would lead to an increase in the injection power in the following LHD experimental campaign.

Recent developments of long pulse RF ion sources for NBI systems

For the new radial injector of the Wendelstein 7-AS stellerator, two medium size 40 kW RF sources (‘W7-AS RF source’) have been built and tested. A positive hydrogen ion beam of 28 A at 50 kV with a proton fraction of 60% has been extracted. For future injection systems, in particular those based on negative ions, large area beam extraction and long pulse capability up to cw operation are envisaged. At IPP two different design concepts of RF sources are being investigated in order to meet these requirements: in the first one, the plasma is generated in one or two small circular RF sources (‘drivers’), which are mounted onto the back plate of a 30 l expansion volume (‘bucket’) with magnetic multi-cusp confinement of the plasma (‘Type 6-1’ and ‘Type 6-2’ respectively). In the second concept the plasma is generated inside the bucket by an internal RF coil, which is insulated by a quartz tube (‘Type 5’). In both cases the applicability for negative as well as for positive ion production is being tested. The next application will be in the positive ion based injectors in the third injector of JET and in the W7X stellerator.

RF ion source for low energy ion implantation — beam profile control of a large-area ion source using 500-MHz discharge

In order to fabricate ULSI devices on large wafers up to 300 mm in diameter, an ion implantation system that can transport a high-current ion beam with low energy and suppress the charge-up on the wafer is necessary. Both problems come from the space charge effect; to solve them it is convenient to use a large-area ribbon-beam ion source, because it leads a low current density and low charge-up on the wafer. However, handling of the large-area beam is not easy and beam profile control on the wafer is even more difficult. This article is concerned with a method for controlling the beam profile of the large-area ribbon-beam ion source in RF plasma production. As the size of the ion-source chamber is comparable to the RF wavelength, then the ion-beam profile can be controlled by adjusting the size of the variable windows into the chamber for the RF wave. Accordingly, less than 2% spread in uniformity of the large-area ion beam is achieved.