Optimum Beam Energy Research Articles

X‐ray energy optimization in minibeam radiation therapy

The purpose of this work is to assess which energy in minibeam radiation therapy provides the best compromise between the deposited dose in the tumor and the sparing of the healthy tissues. Monte Carlo simulations (PENELOPE 2006) have been used as a method to calculate the ratio of the peak-to-valley doses (PVDR) in the healthy tissues and in the tumor for different beam energies. The maximization of the ratio of PVDR in the healthy tissues and in the tumor has been used as a criterion. The main result of this work is that, for the parameters being used in preclinical trials (minibeam sizes of 600 microm and 1200 microm center-to-center separation), the optimum beam energy is 375 keV. The conclusion is that this is the energy of minibeams that should be used in the preclinical studies.

SU‐GG‐I‐133: Low Dose Dual Energy Breast Imaging with An Energy Resolving Photon Counting Detector

Purpose: To investigate the feasibility of low dose dual energy imaging with an energy resolving photon counting detector using a single exposure / single kVp technique for the measurement of breast density (the percentage of glandular breast tissue) in mammography. Method and Materials: An analytical simulation model was developed to determine the mean glandular dose required to quantify breast density with a novel energy resolving photon counting detector to within an accuracy of 1%. The detector was modeled as a 3 mm thick layer of CdZnTe. All detected photons above 15 keV were counted and separated into either a low or high energy bin as determined by a user defined threshold. Only stochastic x‐ray noise sources were considered. The breast was modeled as a semicircle 10 cm in radius with homogenous equal thicknesses of adipose and glandular tissues, corresponding to a density of 50%. Polyenergetic spectra from a tungsten target anode x‐ray tube were simulated from 20 – 150 kVp. Tube filtration was 1.0 mm Be and 0.5 mm Al. At each kVp, the threshold energy was varied to determine the optimal dual energy SNR in the breast density image. Results: For a 4.2 cm breast, the optimal beam energy determined from simulation was determined to be 95 kVp with a threshold separating low and high energy beam spectra at 30 keV. The predicted required minimal mean glandular dose for the dual energy image was low (< 1 μGy), and the corresponding incident photon fluence was approximately 10,000 photons per square millimeter. Conclusion: The results suggest that breast density, a quantity strongly associated with the risk of breast cancer, can be accurately measured at low dose, with an energy counting photon counting detector.

Monte Carlo simulation of a realistic anatomical phantom described by triangle meshes: Application to prostate brachytherapy imaging

Purpose Monte Carlo codes can simulate the transport of radiation within matter with high accuracy and can be used to study medical applications of ionising radiations. The aim of our work was to develop a Monte Carlo code capable of generating projection images of the human body. In order to obtain clinically realistic images a detailed anthropomorphic phantom was prepared. These two simulation tools are intended to study the multiple applications of imaging in radiotherapy, from image guided treatments to portal imaging. Methods We adapted the general-purpose code PENELOPE 2006 to simulate a radiation source, an ideal digital detector, and a realistic model of the patient anatomy. The anthropomorphic phantom was developed using computer-aided design tools, and is based on the NCAT phantom. The surface of each organ is modelled using a closed triangle mesh, and the full phantom contains 330 organs and more than 5 million triangles. A novel object-oriented geometry package, which includes an octree structure to sort the triangles, has been developed to use this complex geometry with PENELOPE. Results As an example of the capabilities of the new code, projection images of the human pelvis region were simulated. Radioactive seeds were included inside the phantom’s prostate. Therefore, the resulting simulated images resemble what would be obtained in a clinical procedure to assess the positioning of the seeds in a prostate brachytherapy treatment. Conclusions The new code can produce projection images of the human body that are comparable to those obtained by a real imaging system (within the limitations of the anatomical phantom and the detector model). The simulated images can be used to study and optimise an imaging task (i.e., maximise the object detectability, minimise the delivered dose, find the optimum beam energy, etc.). Since PENELOPE can simulate radiation from 50 eV to 1 GeV, the code can also be used to simulate radiotherapy treatments and portal imaging. Using the octree data structure, the new geometry model does not significantly increase the computing time when compared to the simulation of a much simpler quadric geometry. In conclusion, we have shown that it is feasible to use PENELOPE and a complex triangle mesh geometry to simulate real medical physics applications.

Ion beam capture and charge breeding in electron cyclotron resonance ion source plasmas

Beam capture of injected ions and charge breeding in electron cyclotron resonance (ECR) charge breeder ion source plasmas has been investigated utilizing an ECR plasma modeling code, the generalized ECR ion source model, and a Monte Carlo beam capture code. Beam capturing dynamics, charge breeding in the plasma, and the extracted charged ion states are described. Optimization of ion beam energy is performed for (1) high beam capture efficiency and (2) high charge state ion beam extractions. A sample case study for ANL-ECR has been performed. Ions entering ECR ion source plasma are slowed down mostly by the background ions. Assuming Maxwellian plasma ions, maximum beam energy loss occurs when the beam velocity is around the background thermal velocity in magnitude. It is also found that beam capture location affects charge state distribution. For instance, with a majority of beam ions captured near the middle of the device higher currents for higher charge states are obtained. The beam ions captured near the entry have a higher probability of backstreaming after they are captured. For this reason, the optimum beam energy of the injected Ar(+) beam ions for charge breeding is generally higher than the optimum input beam energy for maximum beam energy loss.

Excitation function for the production ofBh262(Z=107) in the odd-Z-projectile reactionPb208(Mn55,n)

The excitation function for production of $^{262}\mathrm{Bh}$ in the odd-Z-projectile reaction $^{208}\mathrm{Pb}$($^{55}\mathrm{Mn}$, $n)$ has been measured at three projectile energies using the Berkeley Gas-filled Separator at the Lawrence Berkeley National Laboratory 88-Inch Cyclotron. In total, 33 decay chains originating from $^{262}\mathrm{Bh}$ and 2 decay chains originating from $^{261}\mathrm{Bh}$ were observed. The measured decay properties are in good agreement with previous reports. The maximum cross section of ${540}_{\ensuremath{-}150}^{+180}$ pb is observed at a lab-frame center-of-target energy of 264.0 MeV and is more than five times larger than that expected based on previously reported results for production of $^{262}\mathrm{Bh}$ in the analogous even-Z-projectile reaction $^{209}\mathrm{Bi}$($^{54}\mathrm{Cr}$, $n)$. Our results indicate that the optimum beam energy in one-neutron-out heavy-ion fusion reactions can be estimated simply using the optimum energy rule proposed by \ifmmode \acute{S}\else \'{S}\fi{}wi\k{a}tecki, Siwek-Wilczy\ifmmode \acute{n}\else \'{n}\fi{}ska, and Wilczy\ifmmode \acute{n}\else \'{n}\fi{}ski.

Study of neutral-beam etching conditions for the fabrication of 7-nm-diameter nanocolumn structures using ferritin iron-core masks

We fabricated nanocolumn structure by using a low energy neutral beam and a ferritin iron-core mask. By using Cl2 gas plasma for generating neutral beam, we obtained a better etching profile than with SF6 gas plasma. Though Cl2:SF6=90:10 enabled faster etching than Cl2 gas without degrading the etching profile when the etching depth was 25 nm, a mixture with any quantity of SF6 gas resulted in a poor etching profile when the etching depth was 50 nm. The beam energy was optimized for the 50-nm depth using Cl2 gas by changing the rf bias power to the bottom electrode of the neutral-beam source. Using the optimum beam energy, extremely high etching selectivity of the Si to ferritin iron-core masks (about 80) as well as highly anisotropic etching profile could be realized. As a result, the diameter of the top of the Si nanocolumn structure was 7 nm, which was identical to that of the iron core in the ferritin. Additionally, the etching profile was almost vertical. We were also able to achieve a high aspect ratio of about 4.6. It is very difficult for conventional plasma etching processes to fabricate such fine structure, because the high-energy photons enhanced the etching of the iron-core mask in the conventional plasma processes.

Primary beam energy dependence of properties in ion beam sputtered spin–valve films

Spin–valve films with the structure Ta/NiFe/FeCo/Cu(18–30 Å)/FeCo/FeMn–70 Å/Ta were deposited using a Veeco ion beam deposition (IBD) system, model IBD-350. The physical properties of these spin–valve films as a function of primary ion beam energy have been studied in a primary ion beam energy range of 600–1500 eV. Xe was used as the working gas. The optimal ion beam energy range for the best spin-valve performance has been found to be around 600 eV. Giant magnetoresistance (GMR) values of ΔR/R∼8% have been measured for the spin–valve films deposited in this energy range. A strong dependence on beam energy of magnetic properties for these spin–valve films has been observed in the energy range from 600 to 1500 eV. ΔR/R for spin–valve films with a Cu layer thickness of 22 Å decreases from 7.5% at 600 eV monotonically to 6.1% at 1500 eV with increasing ion beam energy. Interlayer coupling field increases from 20 Oe at 600 eV to 37 Oe at 1500 eV. Further reduction in the interlayer coupling field to 13 Oe and an increase in ΔR/R to 8% have been achieved by depositing the free layer at 1000 eV and the rest of the layers at 600 eV. These are consistent with the improvement in crystallographic orientation and crystallinity of these spin–valve films.

Aspects on the Optimal Photon Beam Energy for Radiation Therapy

The selection of optimal photon beam energy is investigated both for realistic clinical bremsstrahlung beams and for monoenergetic photon beams. The photon energies covered in this investigation range from 60

Prospects for charge-exchange-recombination-based measurements on International Thermonuclear Experimental Reactor using a helium diagnostic neutral beam

Several important measurements in the International Thermonuclear Experimental Reactor (ITER) diagnostic mission, including the primary one of core helium ash density, are expected to be addressed using active spectroscopic techniques. These methods rely on the use of a dedicated diagnostic neutral beam (DNB) which has been optimized for the dual requirements of beam penetration and charge exchange cross section. For hydrogenic beams, this results in an optimal beam energy of ∼100 keV/amu. Signal-to-noise estimates using realistic geometries and the existing ITER profile and equilibrium data have confirmed the stringent requirements on beam quality and intensity to satisfy the stated ITER measurement precisions. In this article we consider the use of a neutral helium DNB for making active spectroscopic measurements on ITER, since helium beams offer better penetration in dense plasma for a given energy, and the prospects for given source performance may also be improved. Drawbacks include the more difficult absolute calibration of the beam density profile as well as the fundamental problem of uniquely identifying the source (fusion-based ash, beam core fuelling, or edge DNB neutralizer/source efflux) of the observed He charge-exchange recombination line in order to unambiguously characterize core helium buildup and confinement on ITER.

Electron beam lithography for 0.13 μm manufacturing

General requirements for the use of electron beam lithography in direct write manufacturing of silicon integrated circuits are discussed. 50 keV is suggested as an optimum beam energy, since this is the minimum beam energy that can achieve high aspect ratio structures (4:1) in single layer resists in a manufacturing environment. Higher beam energies result in an inefficient exposure process requiring larger currents; this combination will lead to excessive resist and wafer heating. Lower voltages will require the use of top surface imaging or multilayer resists, which have concerns of processing complexity, resist charging, and defects. At 50 keV, some form of proximity correction is required to achieve reasonable control of critical dimensions. While one of the principle arguments for low voltage lithography is that it avoids the need for proximity correction, proximity correction is a solvable problem for large chips and is therefore a less risky approach than developing a reliable surface imaging resist technology. From a quick review of available resists and recent resist progress, it appears that a sensitivity of 5 μC/cm2 at 50 kV is the best that will be achieved in the next several years. Neglecting overheads, for a design point of 40 8 in. wafers/h, a peak beam current of 13 μA for a raster scan or projection tool is required. One of the major challenges of designing a tool with such high beam currents is controlling space charge effects so that there is minimal impact on lithographic quality. After discussing the characteristics of various high speed electron beam writers that have been made to date, it will be concluded that there are two types of systems that have the best chance of meeting all of the requirements—a projection system such as SCALPEL, and a multibeam system with hundreds of independently blanked beamlets. These systems minimize space charge effects by spreading out the electrons through a larger volume of space, allowing a larger total beam current. However, in order to make these systems a commercial reality, a great deal of innovation, research, and development are still required.

A digital readout system for the SYRMEP silicon strip detectors

The SYRMEP project (SYnchrotron Radiation for MEdical Physics) intends to improve mammography performances using two non-traditional means: synchrotron radiation and silicon detectors. A silicon crystal (the monochromator) allows to choose the optimal beam energy that leads to the maximum signal to noise ratio, while the detectors are arranged to form a matrix of pixels and coupled to low noise high-gain VLSI integrated circuits making the single photon counting technique possible. We present the data acquisition system implemented to read out the VLSI circuit with particular emphasis on two dedicated CAMAC modules that generate the control signals and store the chip digital output on memories that can be accessed via the CAMAC bus. It has been useful in testing the chip performances and can be considered a prototype of the final SYRMEP data acquisition system.

Electron beam pumping of CdZnSe quantum well laser structures using a variable energy electron beam

In this paper we present experimental results on electron beam pumping of MBE and MOVPE lasers with CdZnSe single quantum wells. Laser emission in the gree and blue occurs under pulsed excitation, with threshold power densities typically less than 2 kW/cm2 at low temperatures. Threshold curves obtained at different electron beam energies show that there is an optimum electron beam energy for wells at a given depth below the surface. This suggests that it is possible to match the electron beam energy to a given structure. Results are broadly consistent with Monte Carlo calculations of the depth dependence of the energy deposition of the electron beam.

An optimal target-filter system for electron beam generated X-ray spectra

An electron beam generated X-ray spectrum consists of characteristic X-rays of the target and continuous bremsstrahlung. The percentage of characteristic X-rays over the entire energy spectrum depends on the beam energy and the filter thickness. To determine the optimal electron beam energy and filter thickness, one can either conduct many experimental measurements, or perform a series of Monte Carlo simulations. Monte Carlo simulations are shown to be an efficient tool for determining the optimal target-filter system for electron beam generated X-ray spectra. Three of the most commonly used low-energy X-ray metal targets (Cu, Zn and Mo) are chosen for this study to illustrate the power of Monte Carlo simulations.

Innovation leads the way to attractive inertial fusion energy reactors–Prometheus-L and Prometheus-H

Abstract Two conceptual inertial fusion energy (IFE) reactor design studies employing innovative system concepts have been completed for the US Department of Energy. These concepts enable power plants with inertially confined plasmas to be economically competitive with other energy sources and provide safety and environmental advantages. A KrF driver employs 960 electric discharge laser amplifiers to enhance driver reliability and target illumination with a loss of one or more amplifiers. A non-linear laser architecture uses Raman accumulator cells to combine and enhance the beam quality and stimulated Brillouin scattering cells for beam compression. Optical delay switchyards maximize the utilization of beam energy to provide proper beam pulse forms to the target. Grazing incidence metal mirrors are the final optical elements that employ a high rigidity SiC support structure and graded thickness aluminum reflective surface material to obtain a life-of-plant optical element with a direct line-of-sight to the target within 20 m of the target. Sixty of these laser beamlines symmetrically illuminate the direct-drive target. A performance and economic systems code determined the optimum laser beam energy as 4 MJ corresponding to a target gain of 124. When pulsed at 5.65 Hz, the fusion power is 2807 MW. To reduce the cost of traditional, lengthy, multiple-beam heavy ion drivers, a single-beam LINAC driver with storage rings was adopted. A charge state of two was used to shorten the length and cost of the driver. An ion energy of 4 GeV reduced the number of beams. The LINAC is rapidly pulsed 18 times. Pulses are contained in storage rings and combined to form 2 prepulse and 12 main beams. These are subdivided to illuminate the indirectly driven target from two sides. Triplet coil sets ballistically focus the beams on the outside of the blanket. Channel transport is proposed to deliver the beams in two 6 mm diameter channels to the target. A total beam energy of 7 MJ is delivered to the target to obtain a gain of 103 and fusion power of 1818 MW at 3.54 Hz. A common reactor design is used for the laser and heavy ion beam systems. Low activation SiC material is used for the first wall and blanket systems. The first wall is protected with a thin film of liquid lead that is evaporated by each microexplosion and recondensed between explosions, thus providing protection and vacuum pumping of target debris. A lithium oxide breeder is cooled with low pressure, high temperature helium that minimizes stored energy and improves system safety and activation. The plant Level of Safety Assurance is one, and waste disposal is class C or better. Double-walled steam generators maintain low tritium permeation to the environment. High-temperature helium and first wall lead coolants are used with a 42% efficient, advanced Rankine cycle to deliver a power output of 1000 MW for both plant designs. All systems were optimized to deliver the lowest cost of electricity.

Modeling of a diagnostic neutral beam for ITER

A neutral hydrogen beam has been modeled to serve as an energetic particle source for the measurement of ion temperature profiles via charge-exchange recombination spectroscopy. Calculation of the neutral beam attenuation uses the multistep ionization cross sections of Boley, Janev, and Post. Whereas beam penetration toward the center of the discharge increases with increasing beam energy, the relevant charge-exchange cross section for the familiar C 5+ n=8–7 transition decreases above 50 keV, leading to an optimum beam energy that yields the maximum charge exchange brightness for each set of plasma conditions. This energy is in the range of 100–150 keV. As a consequence of the high plasma density, temperature, and machine size, the detected signal is dominated by visible bremsstrahlung integrated along the detector sightline, placing a premium on beam intensity, beam current density, and beam chopping with synchronous detection.

Enhancement of the neutral beam stopping cross-section due to circulating fast ions in a toroidal plasma

The beam stopping cross-section in a toroidal system is enhanced by the interaction between injected neutral beams and circulating fast ions generated by the injection. The ionization rate due to the fast ion impact and the fast ion charge exchange is evaluated by a simplified three-dimensional model. This enhancement will be conspicuous in beam driven steady state operation of next generation tokamaks such as ITER and FER. If this effect were taken into consideration in the reactor studies, the optimum beam energy and the wall load due to the beam shinethrough would be changed.

Numerical Investigations of Electron Beam Energy Deposition into the Gas Medium of an Excimer Laser

Electron beam propagation in a dense gas medium is numerically investigated. All the main phenomena that determine electron beam behavior in a gas (scattering and energy losses of the electrons on the gas atom molecules, ionization and excitation, electron thermalization, beam pinching, and influence of a magnetic guide field) are taken into account. The initial beam energy and the gas chamber dimensions are varied in a wide range: typical gas mixtures for the excimer lasers are considered. Graphs are given that allow the choice of the optimal electron beam energy that provides the maximum efficiency of the beam energy deposition into the gas, depending on the gas chamber dimensions.

Three-dimensional treatment planning for para-aortic node irradiation in patients with cervical cancer

Three-dimensional treatment planning has been used by four cooperating centers to prepare and analyze multiple treatment plans on two cervix cancer patients. One patient had biopsy-proven and CT-demonstrable metastasis to the para-aortic nodes, while the other was at high risk for metastatic involvement of para-aortic nodes. Volume dose distributions were analyzed, and an attempt was made to define the role of 3-D treatment planning to the para-aortic region, where moderate to high doses (50–66 Gy) are required to sterilize microscopic and gross metastasis. Plans were prepared using the 3-D capabilities for tailoring fields to the target volumes, but using standard field arrangements (3-D standard), and with full utilization of the 3-D capabilities (3-D unconstrained). In some but not all 3-D unconstrained plans, higher doses were delivered to the large nodal volume and to the volume containing gross nodal disease than in plans analyzed but not prepared with full 3-D capability (3-D standard). The small bowel was the major dose limiting organ. Its tolerance would have been exceeded in all plans which prescribed 66 Gy to the gross nodal mass, although some reduction in small bowel near-maximum dose was achieved in the 3-D unconstrained plans. All plans were able to limit doses to other normal organs to tolerance levels or less, with significant reductions seen in doses to spinal cord, kidneys, and large bowel in the 3-D unconstrained plans, as compared to the 3-D standard plans. A high probability of small bowel injury was detected in one of four 3-D standard plans prescribed to receive 50 Gy to the large para-aortic nodal volume; the small bowel dose was reduced to an acceptable level in the corresponding 3-D unconstrained plan. An optimum beam energy for treating this site was not identified, with plans using 4, 6, 10, 15, 18, and 25 MV photons all being equally acceptable. Attempts to deliver moderate or high doses (50–66 Gy) to this region should be made only after careful analysis of the plan with techniques similar to those employed in this study.

Electron beam induced current study of thin silicon layers on insulator substrate

If a thickness of a semiconductor is smaller than the penetration depth of the electron beam, e.g. in silicon on insulator (SOI) structures, only a small portion of incident electrons energy , which is lost in a superficial silicon layer separated by the oxide from the substrate, contributes to the electron beam induced current (EBIC). Because the energy loss distribution of primary beam is not uniform and varies with beam energy, it is not straightforward to predict the optimum conditions for using this technique. Moreover, the energy losses in an ohmic or Schottky contact complicate this prediction. None of the existing theories, which are based on an assumption of a point-like region of electron beam generation, can be used satisfactorily on SOI structures. We have used a Monte Carlo technique which provide a simulation of the electron beam interactions with thin multilayer structures. The EBIC current was calculated using a simple one dimensional geometry, i.e. depletion layer separating electron- hole pairs spreads out to infinity in x- and y-direction. A point-type generation function with location being an actual location of an incident electron energy loss event has been assumed. A collection efficiency of electron-hole pairs was assumed to be 100% for carriers generated within the depletion layer, and inversely proportional to the exponential function of depth with the effective diffusion length as a parameter outside this layer. A series of simulations were performed for various thicknesses of superficial silicon layer. The geometries used for simulations were chosen to match the "real" samples used in the experimental part of this work. The theoretical data presented in Fig. 1 show how significandy the gain decreases with a decrease in superficial layer thickness in comparison with bulk material. Moreover, there is an optimum beam energy at which the gain reaches its maximum value for particular silicon thickness.

Self-consistent analysis of steady state Tokamaks sustained by beam-driven and bootstrap currents

Beam-driven steady state Tokamaks of moderate size (R0=4.55 m) are analyzed by an optimizing beam current drive analysis code, which consistently includes MHD equilibrium, kink and ballooning stability analysis, bootstrap current, global power balance and toroidal momentum balance calculations. The maximum Q values attained are Q=7-9 with fusion powers of Pf=500-800 MW. L-mode confinement given by Kaye-Goldston scaling is sufficient to sustain steady state conditions. The Q value is nearly doubled due to the bootstrap current and the Ti>Te feature of beam-driven Tokamaks. The optimum beam energy is 1.0-1.2 MeV and the toroidal rotation effects are negligible.