High-resolution X-ray Detectors Research Articles

Superconducting Sn/Sn-oxide/Sn tunneling junctions as high-resolution x-ray detectors

In a superconducting detector, the energy resolution is expected to be superior than in a semiconductor detector, owing to the thousand times smaller energy gap Δ. The performance of Sn/Sn-oxide/Sn tunneling junctions (operated in the Giaever mode at T=0.32 K) exposed to 6-keV x-ray photons of a 55Fe source is presented. The best energy resolution observed is 67 eV (FWHM). Extrapolating to vanishing electronic noise, an intrinsic resolution of 0.7% (FWHM) is obtained. This is an order of magnitude worse than expected from the statistics of the 2.5×106 primary electron charges produced, and is believed to be due to geometrical effects in the films. The energy response of the detector is nonlinear, owing to the self-recombination of the free charge carriers. At a fixed bias voltage, the pulses generated in either film of the junction were observed to have the same sign. If the junctions are evaporated onto a silicon substrate, most of the pulses originate, via phonon backscattering, from x-ray photons interacting in the substrate. Quasiparticle diffusion is essential in explaining the observed data.

X-ray computed tomography with 50-μm resolution

Diagnostic-quality x-ray computed tomography (CT) images, with spatial resolution of 0.05–0.1 mm, have now been made of small laboratory animals with a micro-CT scanner incorporating a patented, high-resolution x-ray detector. The images show clearly defined internal organ structure and tumors in intact rodents.

Antiprotonic atoms in gaseousH2and He and in liquidH2

Antiprotons were brought to rest in targets of gaseous ${\mathrm{H}}_{2}$ and gaseous He at temperatures of 30 K and also in a target of liquid ${\mathrm{H}}_{2}$. High-resolution x-ray detectors were used to measure the energies of x rays from $\overline{\mathrm{p}}$-He and to search for x rays from $\overline{\mathrm{p}}$-H. The $\overline{\mathrm{p}}$-He data are compared with similar measurements at different densities and with the theoretical predictions of Landua and Klempt. The $\overline{\mathrm{p}}$-H data provide upper limits for the yields of $\mathrm{nP}\ensuremath{\rightarrow}1S$ x rays in liquid and gaseous hydrogen.

State-of-the-Art X-Ray Detectors Fabricated on PCG Grown Mercuric Iodide Platelets.

ABSTRACTRecent developments on HgI2 detectors fabricated from platelets grown by the Polymer Controller Growth (PCG) technique have resulted in a better understanding of this remarkable process and provide increased hope for the future of room temperature operable, high resolution x-ray detectors. The benefits of PCG are higher purity using reagent grade materials, better control of stoichiometry, rapid growth, and simplified fabrication. This latter benefit is even more significant when the extreme fragility of HgI2 crystals is considered. The problems of device resolution crystal stability and uniformity, and control ot platelet growth were investigated under a NASA funded program. HgI2 devices fabricated from PCG platelets gave room temperature energy resolutions under 400 eV (FWHM) for the 5.9 eV Mn x-ray. Models for the polymer assisted transport are discussed along with an analysis of spectra obtained from PCG grown devices. Reproducibility has been demonstrated both for platelet growth and device performance.

Solid-State Room-Temperature Energy-Dispersive X-Ray Detectors

Over the last several years there has been growing interest directed toward high-resolution energy-dispersive x-ray detectors which operate at room temperature. The goal has been to develop a detector which combines the advantages of room-temperature operation characteristic of scintillation and proportional counters with the excellent energy resolution of silicon and germanium cryogenically cooled spectrometers. The elimination of the cryogenic coolant and the associated vacuum cryostat will permit the design and construction of really miniature and practically convenient x-ray detection systems which will find applications In already existing instruments as well as in various new fields.

Improved performance of HgI 2 spectrometers in the low energy X-ray region

High resolution X-ray detectors with areas up to 20 mm 2 have been fabricated from a 100 g HgI 2 single crystal. The 1.5 keV aluminum K α X-ray line is clearly resolved with the detectors operating at room temperature.

Studies of gamma-ray transitions in 146Eu

The decay of 146Gd to levels of 146Eu has been studied using high resolution X-ray and γ-ray detectors. γ–γ directional correlation studies, using X and γ-ray Ge(Li) detectors, were made to assign the spins of the low lying states in 146Eu. γ–γ coincidence experiments with two Ge(Li) detectors and between Eu X rays and γ rays were performed to pin down the levels of 146Eu. On the basis of these measurements, Jπ of 4−, 3−, 2−, and 1− have been assigned respectively to the ground, 115.66, 230.51, and 385.11 keV states in 146Eu. More accurate evaluation of the E2 admixtures in the M1 transitions, 114.85, 115.66, and 154.60 keV, have been obtained. Based on the above results a tentative level scheme for 146Eu has been proposed.

High-resolution Hgl2 x-ray spectrometers

Several high-resolution HgI2 x-ray detectors have been made from single crystals grown from the vapor phase. Hole and electron transport properties and detector electrical characteristics are described. Measured mobility-lifetime product for electrons is 8×10−5 cm2/V with a μe of 3 cm2/V sec. The mean energy per electron-hole pair is 4.33 eV at 122 keV. Detectors up to 1 mm3 are described, and a resolution as low as 850 eV at 300 °K in air has been obtained for 5.9-keV x rays, which suggests possible x-ray flourescence detection applications.

Si(Li) Coaxial Detectors

Lithium drifted silicon coaxial detectors have been fabricated from 19 mm diameter material with volumes up to 5 cm3. Essentially single line response, the double escape peak, is observed for gamma rays interacting by pair production. Resolutions (FWHM) of 5 keV and approximately 10 keV have been observed for incident gamma rays of 2.62 and 7.64 MeV. Slices, 2 to 3 mm thick, have been taken from such coaxial detectors and used as low capacity, high resolution X-ray detectors. A FWHM of 300 eV has been obtained at 6.4 keV using a detector with an active area slightly greater than 200 mm2.