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NASA NTRS2018

Application Software Cybersecurity Scanning

Scanning software applications for cybersecurity vulnerabilities is a crucial step is assessing the overall health of the application, but how can this kind of scan be performed to give development teams the information they need to make informed design decisions? Two pilot cybersecurity scans were conducted in an attempt to answer this question. A scanning team composed of various subject matter experts was established and worked closely with the development team to perform these scans and capture metrics throughout the process. These interactions and metrics indicate that these scans can be performed in an unobtrusive way and still provide valuable information to development teams regarding the health of their application. This work is not definitive in nature but serves as a foundation for future work.

Barner, Lyle↗

DOE OSTI2015

System and method for compressive scanning electron microscopy

A scanning transmission electron microscopy (STEM) system is disclosed. The system may make use of an electron beam scanning system configured to generate a plurality of electron beam scans over substantially an entire sample, with each scan varying in electron-illumination intensity over a course of the scan. A signal acquisition system may be used for obtaining at least one of an image, a diffraction pattern, or a spectrum from the scans, the image, diffraction pattern, or spectrum representing only information from at least one of a select subplurality or linear combination of all pixel locations comprising the image. A dataset may be produced from the information. A subsystem may be used for mathematically analyzing the dataset to predict actual information that would have been produced by each pixel location of the image.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2022

Multi-scan computed tomography defect detectability

Systems and methods for representing internal defects of an object to determine defect detectability using a multi-scan computed tomography (CT) approach are disclosed. A defect-free object may be scanned using a CT machine. In one or more separate scans, phantom defects may be imaged and the resulting projections combined and reconstructed to represent internal defects. The air-normalized intensities of the object and the phantom defect may be used to represent voids and inclusions. Subtraction of materials may be represented by the quotient of the air-normalized intensities thereof, and the addition of materials may be represented by the product of the air-normalized intensities thereof. A void may be represented by subtracting a phantom defect scan from the object scan. An inclusion may be represented by creating a void, scanning an additional phantom defect, and adding the additional phantom defect in the volume created by the void.

Schiefelbein, Bryan E.↗

DOE OSTI2022

Exploring leakage in dielectric films via automated experiments in scanning probe microscopy

Here electronic conduction pathways in dielectric thin films are explored using automated experiments in scanning probe microscopy (SPM). In this study, we use large field of view scanning to identify the position of localized conductive spots and develop an SPM workflow to probe their dynamic behavior at higher spatial resolution as a function of time, voltage, and scanning process in an automated fashion. Using this approach, we observe the variable behaviors of the conductive spots in a 20-nm-thick ferroelectric Hf 0.54 Zr 0.48 O 2 film, where conductive spots disappear and reappear during continuous scanning. There are also fresh conductive spots that develop during scanning. The automated workflow is universal and can be integrated into a wide range of microscopy techniques, including SPM, electron microscopy, optical microscopy, and chemical imaging.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Lessons learned on the presentation of scan data

Technicians performed a radiological survey of a surplus metal tank to support disposition planning at an Oak Ridge, Tennessee site. The survey included radiation scans to identify contamination and, if identified, define the boundary and magnitude of contamination. Fixed-point 1-minute measurements were also collected at randomly selected locations for comparison against the site's free release limit of 5,000 disintegrations per minute per 100 cm² (dpm/100 cm²) (0.83 Bq/cm²). Scan data were recorded using a data logger as a means to document surveyor observation - logged data captured at 1-second intervals and converted to counts per minute (cpm) by the data logger software were presented in the project report. Both the qualitative scan data (in cpm) and the quantitative direct measurement (in dpm/100 cm²) were reported for completeness, so stakeholders had all available information to support disposition decisions. However, a new stakeholder - introduced to the project at the reporting phase of work - used the instrument efficiency and background data to convert the scan data from cpm to dpm/100 cm², then compared the converted results to the site limit. Many of the converted values exceeded 5,000 dpm/100 cm². This resulted in delays in tank disposition and additional project costs which could have been avoided if the proper use and interpretation of scan data, and implications of radon progeny buildup on oxidized metal surfaces, had been better communicated.

12 MANAGEMENT OF RADIOACTIVE AND NON-RADIOACTIVE W↗

DOE OSTI2017

Scanning Quantum Cryogenic Atom Microscope

Microscopic imaging of local magnetic fields provides a window into the organizing principles of complex and technologically relevant condensed-matter materials. However, a wide variety of intriguing strongly correlated and topologically nontrivial materials exhibit poorly understood phenomena outside the detection capability of state-of-the-art high-sensitivity high-resolution scanning probe magnetometers. We introduce a quantum-noise-limited scanning probe magnetometer that can operate from room-to-cryogenic temperatures with unprecedented dc-field sensitivity and micron-scale resolution. The Scanning Quantum Cryogenic Atom Microscope (SQCRAMscope) employs a magnetically levitated atomic Bose-Einstein condensate (BEC), thereby providing immunity to conductive and blackbody radiative heating. The SQCRAMscope has a field sensitivity of 1.4 nT per resolution-limited point (approximately 2 μm) or 6 nT/√Hz per point at its duty cycle. Furthermore, compared to point-by-point sensors, the long length of the BEC provides a naturally parallel measurement, allowing one to measure nearly 100 points with an effective field sensitivity of 600 pT/√Hz for each point during the same time as a point-by-point scanner measures these points sequentially. Moreover, it has a noise floor of 300 pT and provides nearly 2 orders of magnitude improvement in magnetic flux sensitivity (down to 10 -6 Φ 0 /√Hz) over previous atomic probe magnetometers capable of scanning near samples. These capabilities are carefully benchmarked by imaging magnetic fields arising from microfabricated wire patterns in a system where samples may be scanned, cryogenically cooled, and easily exchanged. We anticipate the SQCRAMscope will provide charge-transport images at temperatures from room temperature to 4 K in unconventional superconductors and topologically nontrivial materials.

74 ATOMIC AND MOLECULAR PHYSICS↗

DOE OSTI2015

Multienergy CT acquisition and reconstruction with a stepped tube potential scan

Purpose: Based on an energy-dependent property of matter, one may obtain a pseudomonochromatic attenuation map, a material composition image, an electron-density distribution, and an atomic number image using a dual- or multienergy computed tomography (CT) scan. Dual- and multienergy CT scans broaden the potential of x-ray CT imaging. The development of such systems is very useful in both medical and industrial investigations. In this paper, the authors propose a new dual- and multienergy CT system design (segmental multienergy CT, SegMECT) using an innovative scanning scheme that is conveniently implemented on a conventional single-energy CT system. The two-step-energy dual-energy CT can be regarded as a special case of SegMECT. A special reconstruction method is proposed to support SegMECT. Methods: In their SegMECT, a circular trajectory in a CT scan is angularly divided into several arcs. The x-ray source is set to a different tube voltage for each arc of the trajectory. Thus, the authors only need to make a few step changes to the x-ray energy during the scan to complete a multienergy data acquisition. With such a data set, the image reconstruction might suffer from severe limited-angle artifacts if using conventional reconstruction methods. To solve the problem, they present a new prior-image-based reconstruction technique using a total variance norm of a quotient image constraint. On the one hand, the prior extracts structural information from all of the projection data. On the other hand, the effect from a possibly imprecise intensity level of the prior can be mitigated by minimizing the total variance of a quotient image. Results: The authors present a new scheme for a SegMECT configuration and establish a reconstruction method for such a system. Both numerical simulation and a practical phantom experiment are conducted to validate the proposed reconstruction method and the effectiveness of the system design. The results demonstrate that the proposed SegMECT can provide both attenuation images and material decomposition images of reasonable image quality. Compared to existing methods, the new system configuration demonstrates advantages in simplicity of implementation, system cost, and dose control. Conclusions: This proposed SegMECT imaging approach has great potential for practical applications. It can be readily realized on a conventional CT system.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2015

Characterization and implementation of OSL dosimeters for use in evaluating the efficacy of organ-based tube current modulation for CT scans of the face and orbits

Purpose: The purpose of this work was to characterize commercially available optically stimulated luminescent (OSL) dosimeters for general clinical applications and apply the results to the development of a method to evaluate the efficacy of a vendor-specific organ-based tube current modulation application for both phantom and clinical computed tomography (CT) scans of the face and orbits. Methods: This study consisted of three components: (1) thorough characterization of the dosimeters for CT scans in phantom, including evaluations of depletion, fading, angular dependence, and conversion from counts to absorbed dose; (2) evaluation of the efficacy of using plastic glasses to position the dosimeters over the eyes in both phantom and clinical studies; and (3) preliminary dosimetry measurements made using organ-based tube current modulation in computed tomography dose index (CTDI) and anthropomorphic phantom studies. Results: (1) Depletion effects were found to have a linear relationship with the output of the OSL dosimeters (R{sup 2} = 0.96). Fading was found to affect dosimeter readings during the first two hours following exposure but had no effect during the remaining 60-h period observed. No significant angular dependence was observed for the exposure conditions used in this study (with p-values ranging from 0.9 to 0.26 for all t-tests). Dosimeter counts varied linearly with absorbed dose when measured in the center and 12 o’clock positions of the CTDI phantoms. These linear models of counts versus absorbed dose had overlapping 95% confidence intervals for the intercepts but not for the slopes. (2) When dosimeters were positioned using safety glasses, there was no adverse effect on image quality, and there was no statistically significant difference between this placement and placement of the dosimeters directly on the eyes of the phantom (p = 0.24). (3) When using organ-based tube current modulation, the dose to the lens of the eye was reduced between 19% and 43%, depending on the scan protocol used and the positioning of the phantom. Furthermore, the amount of dose reduction was significantly affected by the vertical position of the phantom, with the largest reduction in dose seen when the phantom was centered in the gantry. Conclusions: (1) An appropriate correction factor, specific to CT scanning, was developed to account for depletion and fading characteristics of the dosimeters. Additionally, an equation to convert dosimeter counts to absorbed dose was established. (2) The use of plastic safety glasses was validated as an appropriate positioning device when measuring dose to the lens of the eye. (3) The use of organ-based tube current modulation can reduce dose to the lens of the eye during CT scanning. The amount of dose reduction, however, is largely influenced by the positioning of the anatomy in the gantry.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2018

Automatic Organ Segmentation for CT Scans Based on Super-Pixel and Convolutional Neural Networks

Accurate segmentation of specific organ from computed tomography (CT) scans is a basic and crucial task for accurate diagnosis and treatment. To avoid time-consuming manual optimization and to help physicians distinguish diseases, an automatic organ segmentation framework is presented. The framework utilized convolution neural networks (CNN) to classify pixels. To reduce the redundant inputs, the simple linear iterative clustering (SLIC) of super-pixels and the support vector machine (SVM) classifier are introduced. To establish the perfect boundary of organs in one-pixel-level, the pixels need to be classified step-by-step. First, the SLIC is used to cut an image into grids and extract respective digital signatures. Next, the signature is classified by the SVM, and the rough edges are acquired. Finally, a precise boundary is obtained by the CNN, which is based on patches around each pixel-point. The framework is applied to abdominal CT scans of livers and high-resolution computed tomography (HRCT) scans of lungs. The experimental CT scans are derived from two public datasets (Sliver 07 and a Chinese local dataset). Experimental results show that the proposed method can precisely and efficiently detect the organs. This method consumes 38 s/slice for liver segmentation. The Dice coefficient of the liver segmentation results reaches to 97.43%. For lung segmentation, the Dice coefficient is 97.93%. This finding demonstrates that the proposed framework is a favorable method for lung segmentation of HRCT scans.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2018

Tribological Performance of Ni{sub 3}Al Matrix Composites Synthesized by Laser Melt Deposition Under Different Scanning Velocities

In order to study the effect of scanning velocity on the microstructure and tribological properties of Ni{sub 3}Al matrix composites containing graphene nanoplatelets (NGs), a series of NG samples are successfully synthesized by laser melt deposition under the various scanning velocities from 300 to 500 mm s{sup −1}. The sliding friction tests of NG against GCr15 steel balls are carried out under 10 N and 0.2 m s{sup −1} at room temperature. The microstructures, tribological properties and wear mechanisms of the NG samples are analyzed. The results show that the scanning velocity can be optimized to effectively control the surface hardness and relative density, as well as tribological performance of NG. The NG sample synthesized under scanning velocity of 450 mm s{sup −1} has a dense and fine microstructure as well as excellent properties such as higher relative density (98.6%), lower friction coefficient (0.23) and wear rate (5.5 × 10{sup −6} mm{sup 3} N{sup −1} m{sup −1}). The lower substrate layer with dense and stable structure plays an important role in supporting the upper glaze layer with rich graphene and oxides, as well as nanocrystalline structure, which contributes to the excellent friction-reducing and wear resistance performances of NG. The research results could be used to guide the selection of suitable scanning velocity and study the wear mechanisms of NG for having excellent tribological performance.

77 NANOSCIENCE AND NANOTECHNOLOGY↗

DOE OSTI2014

Spot Scanning Proton Therapy for Malignancies of the Base of Skull: Treatment Planning, Acute Toxicities, and Preliminary Clinical Outcomes

Purpose: To describe treatment planning techniques and early clinical outcomes in patients treated with spot scanning proton therapy for chordoma or chondrosarcoma of the skull base. Methods and Materials: From June 2010 through August 2011, 15 patients were treated with spot scanning proton therapy for chordoma (n=10) or chondrosarcoma (n=5) at a single institution. Toxicity was prospectively evaluated and scored weekly and at all follow-up visits according to Common Terminology Criteria for Adverse Events, version 3.0. Treatment planning techniques and dosimetric data were recorded and compared with those of passive scattering plans created with clinically applicable dose constraints. Results: Ten patients were treated with single-field-optimized scanning beam plans and 5 with multifield-optimized intensity modulated proton therapy. All but 2 patients received a simultaneous integrated boost as well. The mean prescribed radiation doses were 69.8 Gy (relative biological effectiveness [RBE]; range, 68-70 Gy [RBE]) for chordoma and 68.4 Gy (RBE) (range, 66-70) for chondrosarcoma. In comparison with passive scattering plans, spot scanning plans demonstrated improved high-dose conformality and sparing of temporal lobes and brainstem. Clinically, the most common acute toxicities included fatigue (grade 2 for 2 patients, grade 1 for 8 patients) and nausea (grade 2 for 2 patients, grade 1 for 6 patients). No toxicities of grades 3 to 5 were recorded. At a median follow-up time of 27 months (range, 13-42 months), 1 patient had experienced local recurrence and a second developed distant metastatic disease. Two patients had magnetic resonance imaging-documented temporal lobe changes, and a third patient developed facial numbness. No other subacute or late effects were recorded. Conclusions: In comparison to passive scattering, treatment plans for spot scanning proton therapy displayed improved high-dose conformality. Clinically, the treatment was well tolerated, and with short-term follow-up, disease control rates and toxicity profiles were favorable.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2016

Robustness of the Voluntary Breath-Hold Approach for the Treatment of Peripheral Lung Tumors Using Hypofractionated Pencil Beam Scanning Proton Therapy

Purpose: The safe clinical implementation of pencil beam scanning (PBS) proton therapy for lung tumors is complicated by the delivery uncertainties caused by breathing motion. The purpose of this feasibility study was to investigate whether a voluntary breath-hold technique could limit the delivery uncertainties resulting from interfractional motion. Methods and Materials: Data from 15 patients with peripheral lung tumors previously treated with stereotactic radiation therapy were included in this study. The patients had 1 computed tomographic (CT) scan in voluntary breath-hold acquired before treatment and 3 scans during the treatment course. PBS proton treatment plans with 2 fields (2F) and 3 fields (3F), respectively, were calculated based on the planning CT scan and subsequently recalculated on the 3 repeated CT scans. Recalculated plans were considered robust if the V{sub 95%} (volume receiving ≥95% of the prescribed dose) of the gross target volume (GTV) was within 5% of what was expected from the planning CT data throughout the simulated treatment. Results: A total of 14/15 simulated treatments for both 2F and 3F met the robustness criteria. Reduced V{sub 95%} was associated with baseline shifts (2F, P=.056; 3F, P=.008) and tumor size (2F, P=.025; 3F, P=.025). Smaller tumors with large baseline shifts were also at risk for reduced V{sub 95%} (interaction term baseline/size: 2F, P=.005; 3F, P=.002). Conclusions: The breath-hold approach is a realistic clinical option for treating lung tumors with PBS proton therapy. Potential risk factors for reduced V{sub 95%} are small targets in combination with large baseline shifts. On the basis of these results, the baseline shift of the tumor should be monitored (eg, through image guided therapy), and appropriate measures should be taken accordingly. The intrafractional motion needs to be investigated to confirm that the breath-hold approach is robust.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2016

Robust Proton Pencil Beam Scanning Treatment Planning for Rectal Cancer Radiation Therapy

Purpose: To investigate, in a treatment plan design and robustness study, whether proton pencil beam scanning (PBS) has the potential to offer advantages, relative to interfraction uncertainties, over photon volumetric modulated arc therapy (VMAT) in a locally advanced rectal cancer patient population. Methods and Materials: Ten patients received a planning CT scan, followed by an average of 4 weekly offline CT verification CT scans, which were rigidly co-registered to the planning CT. Clinical PBS plans were generated on the planning CT, using a single-field uniform-dose technique with single-posterior and parallel-opposed (LAT) fields geometries. The VMAT plans were generated on the planning CT using 2 6-MV, 220° coplanar arcs. Clinical plans were forward-calculated on verification CTs to assess robustness relative to anatomic changes. Setup errors were assessed by forward-calculating clinical plans with a ±5-mm (left–right, anterior–posterior, superior–inferior) isocenter shift on the planning CT. Differences in clinical target volume and organ at risk dose–volume histogram (DHV) indicators between plans were tested for significance using an appropriate Wilcoxon test (P<.05). Results: Dosimetrically, PBS plans were statistically different from VMAT plans, showing greater organ at risk sparing. However, the bladder was statistically identical among LAT and VMAT plans. The clinical target volume coverage was statistically identical among all plans. The robustness test found that all DVH indicators for PBS and VMAT plans were robust, except the LAT's genitalia (V5, V35). The verification CT plans showed that all DVH indicators were robust. Conclusions: Pencil beam scanning plans were found to be as robust as VMAT plans relative to interfractional changes during treatment when posterior beam angles and appropriate range margins are used. Pencil beam scanning dosimetric gains in the bowel (V15, V20) over VMAT suggest that using PBS to treat rectal cancer may reduce radiation treatment–related toxicity.

62 RADIOLOGY AND NUCLEAR MEDICINE↗

DOE OSTI2022

Symmetry Breaking with the SCAN Density Functional Describes Strong Correlation in the Singlet Carbon Dimer

The SCAN (strongly constrained and appropriately normed) meta-generalized gradient approximation (meta-GGA), which satisfies all 17 exact constraints that a meta-GGA can satisfy, accurately describes equilibrium bonds that are normally correlated. With symmetry breaking, it also accurately describes some sd equilibrium bonds that are strongly correlated. While sp equilibrium bonds are nearly always normally correlated, the C 2 singlet ground state is known from correlated wave function theory to be a rare case of strong correlation in an sp equilibrium bond. Earlier work that calculated atomization energies of the molecular sequence B 2 , C 2 , O 2 , and F 2 in the local spin density approximation (LSDA), the Perdew–Burke–Ernzerhof (PBE) GGA, and the SCAN meta-GGA, without symmetry breaking in the molecule, found that only SCAN was accurate enough to reveal an anomalous under-binding for C 2 . Here, this work shows that spin symmetry breaking in singlet C 2 , which involves the appearance of net up- and down-spin densities on opposite sides (not ends) of the bond, corrects that underbinding, with a small SCAN atomization-energy error more like that of the other three molecules, suggesting that symmetry breaking with an advanced density functional might reliably describe strong correlation. This article also discusses some general aspects of symmetry breaking and the insights into strong correlation that symmetry breaking can bring. The normally correlated low-lying triplet excited state has the right vertical excitation energy in SCAN but not in LSDA or PBE, where the triplet is a false ground state. Fractional occupation numbers are found only for the symmetry-unbroken singlet and only in LSDA and PBE GGA.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2024

Effects of open circuit immersion and vertex potential on potentiodynamic polarization scans of metallic biomaterials

Abstract Electrodes made of commercially pure titanium (CP-Ti) and a CoCrMo alloy are immersed at an open circuit in a phosphate buffer saline electrolyte at room temperature for different durations prior to electrochemical analyses. Open circuit potential measurements, electrochemical impedance spectroscopy measurements, and cyclic potentiodynamic polarization (CPP) scans are used to assess the impact of the immersion time on derived property values. Stable passivation layers formed on both materials during immersion. The corrosion potentials determined from the anodic legs of CPP scans become more cathodic, and the corrosion currents decrease to lower values after longer immersion times. Measured currents indicate the layers formed on CP-Ti stabilize during forward anodic scans and persist to the vertex potential, whereas passivation breakdown occurs during anodic scans with CoCrMo with active corrosion at voltages up to the vertex potential. The characteristics of the return cathodic legs of CPP scans represent the surface conditions at the vertex potential: characteristic corrosion property values derived from the test responses represent passive surfaces on CP-Ti and leached surfaces on CoCrMo rather than intrinsic properties of those materials.

36 MATERIALS SCIENCE↗

DOE OSTI2013

Development of the compact proton beam therapy system dedicated to spot scanning with real-time tumor-tracking technology

Hokkaido University and Hitachi Ltd. have started joint development of the Gated Spot Scanning Proton Therapy with Real-Time Tumor-Tracking System by integrating real-time tumor tracking technology (RTRT) and the proton therapy system dedicated to discrete spot scanning techniques under the {sup F}unding Program for World-Leading Innovative R and D on Science and Technology (FIRST Program){sup .} In this development, we have designed the synchrotron-based accelerator system by using the advantages of the spot scanning technique in order to realize a more compact and lower cost proton therapy system than the conventional system. In the gated irradiation, we have focused on the issues to maximize irradiation efficiency and minimize the dose errors caused by organ motion. In order to understand the interplay effect between scanning beam delivery and target motion, we conducted a simulation study. The newly designed system consists of the synchrotron, beam transport system, one compact rotating gantry treatment room with robotic couch, and one experimental room for future research. To improve the irradiation efficiency, the new control function which enables multiple gated irradiations per synchrotron cycle has been applied and its efficacy was confirmed by the irradiation time estimation. As for the interplay effect, we confirmed that the selection of a strict gating width and scan direction enables formation of the uniform dose distribution.

43 PARTICLE ACCELERATORS↗

DOE OSTI2013

Thermal conductivity profile determination in proton-irradiated ZrC by spatial and frequency scanning thermal wave methods

Using complementary thermal wave methods, the irradiation damaged region of zirconium carbide (ZrC) is characterized by quantifiably profiling the thermophysical property degradation. The ZrC sample was irradiated by a 2.6 MeV proton beam at 600 °C to a dose of 1.75 displacements per atom. Spatial scanning techniques including scanning thermal microscopy (SThM), lock-in infrared thermography (lock-in IRT), and photothermal radiometry (PTR) were used to directly map the in-depth profile of thermal conductivity on a cross section of the ZrC sample. The advantages and limitations of each system are discussed and compared, finding consistent results from all techniques. SThM provides the best resolution finding a very uniform thermal conductivity envelope in the damaged region measuring ∼52 ± 2 μm deep. Frequency-based scanning PTR provides quantification of the thermal parameters of the sample using the SThM measured profile to provide validation of a heating model. Measured irradiated and virgin thermal conductivities are found to be 11.9 ± 0.5 W m{sup −1} K{sup −1} and 26.7 ±1 W m{sup −1} K{sup −1}, respectively. A thermal resistance evidenced in the frequency spectra of the PTR results was calculated to be (1.58 ± 0.1) × 10{sup −6} m{sup 2} K W{sup −1}. The measured thermal conductivity values compare well with the thermal conductivity extracted from the SThM calibrated signal and the spatially scanned PTR. Combined spatial and frequency scanning techniques are shown to provide a valuable, complementary combination for thermal property characterization of proton-irradiated ZrC. Such methodology could be useful for other studies of ion-irradiated materials.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

DOE OSTI2014

A frequency and amplitude scanned quadrupole mass filter for the analysis of high m/z ions

Quadrupole mass filters (QMFs) are usually not used to analyze high m/z ions, due to the low frequency resonant circuit that is required to drive them. Here we describe a new approach to generating waveforms for QMFs. Instead of scanning the amplitude of a sine wave to measure the m/z spectrum, the frequency of a trapezoidal wave is digitally scanned. A synchronous, narrow-range (<0.2%) amplitude scan overlays the frequency scan to improve the sampling resolution. Because the frequency is the primary quantity that is scanned, there is, in principle, no upper m/z limit. The frequency signal is constructed from a stabilized base clock using a field programmable gate array. This signal drives integrating amplifiers which generate the trapezoidal waves. For a trapezoidal wave the harmonics can be minimized by selecting the appropriate rise and fall times. To achieve a high resolving power, the digital signal has low jitter, and the trapezoidal waveform is generated with high fidelity. The QMF was characterized with cesium iodide clusters. Singly and multiply charged clusters with z up to +5 were observed. A resolving power of ∼1200 (FWHM) was demonstrated over a broad m/z range. Resolution was lost above 20 000 Th, partly because of congestion due to overlapping multiply charged clusters. Ions were observed for m/z values well in excess of 150 000 Th.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗