E Takacs

A high efficiency ultrahigh vacuum compatible flat field spectrometer for extreme ultraviolet wavelengths

A custom, flat field, extreme ultraviolet spectrometer built specifically for use with low power light sources that operate under ultrahigh vacuum conditions is reported. The spectral range of the spectrometer extends from 4 nm to 40 nm. The instrument optimizes the light gathering power and signal-to-noise ratio while achieving good resolution. A detailed description of the spectrometer and design considerations are presented, as well as a procedure that could be used to obtain a synthetic wavelength calibration with the aid of only a single known spectral feature. This synthetic wavelength calibration is compared to a standard wavelength calibration obtained from previously reported spectral lines of Xe, Ar, and Ne ions recorded with this spectrometer.

Overview of the electron beam ion trap program at NIST

This paper surveys the ongoing physics experiments at the Electron Beam Ion Trap (EBIT) facility at NIST, with particular attention paid to the underlying physical principles involved. In addition, some new data on the performance of our EBIT are presented, including results related to the determination of the trap width, ion temperature, and number of highly charged ions in the trap.

First measurement of Lyman alpha x-ray lines in hydrogen-like vanadium: results and implications for precision wavelength metrology and tests of QED

The first measurement of hydrogen-like vanadium x-ray Lyman alpha transitions has been made. The measurement was made on an absolute scale, fully independent of atomic structure calculations. Sufficient signal was obtained to reduce the statistical uncertainty to a small fraction of the total uncertainty budget. Potential sources of systematic error due to Doppler shifts were eliminated by performing the measurement on trapped ions. The energies for Ly α1 (1s-2p3/2) and Ly α2 (1s-2p1/2) are found to be 5443.95(25) eV and 5431.10(25) eV, respectively. These results are within approximately 1.5 σ (experimental) of the theoretical values 5443.63 eV and 5430.70 eV. The results are discussed in terms of their relation to the Lamb shift and the development of an x-ray wavelength standard based on a compact source of trapped highly charged ions.

Fabry-Perot spectroscopy of a visible magnetic dipole transition in Ba34+

Abstract We are using Fabry-Perot interferometry to study visible lines from highly-charged ions created and trapped within an electron beam ion trap (EBIT). The 3d 4 5 D 2 – 5 D 3 titanium-like barium (Ba 34+ ) line at 3932(2) A was recently measured in Ref. [1] (C.A. Morgan et al., Phys. Rev. Lett. 74 (1995) 1716) using a grating monochromator. We present preliminary Fabry-Perot spectra of this line with significantly improved resolution. The Doppler-broadened 1 A line width is consistent with an expected ion temperature of less than 1 keV. We discuss the possibility of resolving Zeeman splittings, and of using these visible lines as a diagnostic in high temperature, low density plasmas, like those that exist in tokamaks and the EBIT itself.

Helium-like titanium x-ray spectrum as a probe of QED computation

We discuss the first absolute energy measurements of the intercombination and forbidden transitions ( xyz ,, ) in trapped Ti 20+ ions to 15 parts per million accuracy. We present new measurements on helium-like titanium, in which the orbital radius is reduced and QED terms are magnified by the increased nuclear charge. The measured transition energies are higher than predicted.

X-ray measurements in helium-like atoms increased discrepancy between experiment and theoretical QED

A recent 15 parts per million (ppm) experiment on muonic hydrogen () found a major discrepancy with quantum electrodynamics (QED) and independent nuclear size determinations. Here we find a significant discrepancy in a different type of exotic atom: a medium-Z nucleus with two electrons. Investigation of the data collected is able to discriminate between available QED formulations and reveals a pattern of discrepancy of almost six standard errors of experimental results from the most recent theoretical predictions, with a functional dependence proportional to Zn where . In both the muonic and highly charged systems, the sign of the discrepancy is the same, with the measured transition energy higher than predicted. Some consequences are possible or probable, and some are more speculative. This may give insight into effective nuclear radii, the Rydberg, the fine-structure constant, or unexpectedly large QED terms.

Laboratory astrophysics and microanalysis with NTD-germanium-based X-ray microcalorimeters

Abstract With the ability to create cosmic plasma conditions in the laboratory it is possible to investigate the dependencies of key diagnostic X-ray lines on density, temperature, and excitation conditions that exist in astrophysical sources with X-ray optics and a high-resolution X-ray microcalorimeter. The same instrumentation can be coupled to scanning electron microscopes or X-ray fluorescence probes to analyze the elemental and chemical composition of electronic, biological, geological and particulate materials. We describe how our microcalorimeter and X-ray optics provide significantly improved capabilities for laboratory astrophysics and microanalysis.

Population based ranking of frameless CT-MRI registration methods

BACKGROUND Clinical practice often requires simultaneous information obtained by two different imaging modalities. Registration algorithms are commonly used for this purpose. Automated procedures are very helpful in cases when the same kind of registration has to be performed on images of a high number of subjects. Radiotherapists would prefer to use the best automated method to assist therapy planning, however there are not accepted procedures for ranking the different registration algorithms. PURPOSE We were interested in developing a method to measure the population level performance of CT-MRI registration algorithms by a parameter of values in the [0,1] interval. MATERIALS AND METHODS Pairs of CT and MRI images were collected from 1051 subjects. Results of an automated registration were corrected manually until a radiologist and a neurosurgeon expert both accepted the result as good. This way 1051 registered MRI images were produced by the same pair of experts to be used as gold standards for the evaluation of the performance of other registration algorithms. Pearson correlation coefficient, mutual information, normalized mutual information, Kullback-Leibler divergence, L1 norm and square L2 norm (dis)similarity measures were tested for sensitivity to indicate the extent of (dis)similarity of a pair of individual mismatched images. RESULTS The square Hellinger distance proved suitable to grade the performance of registration algorithms at population level providing the developers with a valuable tool to rank algorithms. CONCLUSIONS The developed procedure provides an objective method to find the registration algorithm performing the best on the population level out of newly constructed or available preselected ones.

Pinhole X-Ray Camera Photographs of an ECR Ion Source Plasma

A 70-μm pinhole and an X-ray CCD camera in single-photon counting mode were used to obtain spatially and spectrally resolved images of an electron-cyclotron-resonance ion-source-generated plasma. The method has good spatial resolution, as well as the capability of postprocessed energy filtering of the images. The X-ray images clearly show the spatial positions of different sources of the X-ray photons: bremsstrahlung, characteristic lines of the plasma ions, and X-rays emitted from the wall.

Cascade transition X-rays from electron capture into highly charged ions in collisions with neutral gas targets

Abstract X-rays originating from a series of the cascades after electron capture into highly excited Rydberg states have been observed from low energy, highly charged Kr q + ions ( q =27–36) colliding with neutral Ar atoms. The intensity ratio between L ( n =3→2) X-rays and the sum of M X-rays ( n =4→3, n =5→3, n =6→3, etc.) is drastically changed from Kr 27+ to Kr 28+ and constant for higher ion charge states ( q =29–36). This feature can be understood to be due to the metastable states formed during cascades after electron capture into Kr 27+ ions. This is also supported by time-dependent population calculations.