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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 307 records · Page 17
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

New Advanced Source Identification Algorithm (ASIA-NEW) for radiation monitors with plastic detectors

Radiation Portal Monitors (RPM) with plastic detectors represent the main instruments used for primary border (customs) radiation control. RPM are widely used because they are simple, reliable, relatively inexpensive and have a high sensitivity. However, experience using the RPM in various countries has revealed the systems have some grave shortcomings. There is a dramatic decrease of the probability of detection of radioactive sources under high suppression of the natural gamma background (radiation control of heavy cargoes, containers and, especially, trains). NORM (Naturally Occurring Radioactive Material) existing in objects under control trigger the so-called 'nuisance alarms', requiring a secondary inspection for source verification. At a number of sites, the rate of such alarms is so high it significantly complicates the work of customs and border officers. This paper presents a brief description of new variant of algorithm ASIA-New (New Advanced Source Identification Algorithm), which was developed by the authors and based on some experimental test results. It also demonstrates results of different tests and the capability of a new system to overcome the shortcomings stated above. New electronics and ASIA-New enables RPM to detect radioactive sources under a high background suppression (tested at 15-30%) and to verify the detected NORM (KCl) and the artificial isotopes (Co-57, Ba-133 and other). New variant of ASIA is based on physical principles and does not require a lot of special tests to attain statistical data for its parameters. That is why this system can be easily installed into any RPM with plastic detectors. This algorithm was tested for 1,395 passages of different transports (cars, trucks and trailers) without radioactive sources. It also was tested for 4,015 passages of these transports with radioactive sources of different activity (Co-57, Ba-133, Cs-137, Co-60, Ra-226, Th-232) and these sources masked by NORM (K-40) as well. (authors)

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2016

Review—hexagonal boron nitride epilayers: Growth, optical properties and device applications

This paper provides a brief overview on recent advances made in authors’ laboratory in epitaxial growth and optical studies of hexagonal boron nitride (h-BN) epilayers and heterostructures. Photoluminescence spectroscopy has been employed to probe the optical properties of h-BN. It was observed that the near band edge emission of h-BN is unusually high and is more than two orders of magnitude higher than that of high quality AlN epilayers. It was shown that the unique quasi-2D nature induced by the layered structure of h-BN results in high optical absorption and emission. The impurity related and near band-edge transitions in h-BN epilayers were probed for materials synthesized under varying ammonia flow rates. Our results have identified that the most dominant impurities and deep level defects in h-BN epilayers are related to nitrogen vacancies. By growing h-BN under high ammonia flow rates, nitrogen vacancy related defects can be eliminated and epilayers exhibiting pure free exciton emission have been obtained. Deep UV and thermal neutron detectors based on h-BN epilayers were shown to possess unique features. Lastly, it is our belief that h-BN will lead to many potential applications from deep UV emitters and detectors, radiation detectors, to novel 2D photonic and electronic devices.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Liquid chromatography detection unit, system, and method

An embodiment of a liquid chromatography detection unit includes a fluid channel and a radiation detector. The radiation detector is operable to image a distribution of a radiolabeled compound as the distribution travels along the fluid channel. An embodiment of a liquid chromatography system includes an injector, a separation column, and a radiation detector. The injector is operable to inject a sample that includes a radiolabeled compound into a solvent stream. The position sensitive radiation detector is operable to image a distribution of the radiolabeled compound as the distribution travels along a fluid channel. An embodiment of a method of liquid chromatography includes injecting a sample that comprises radiolabeled compounds into a solvent. The radiolabeled compounds are then separated. A position sensitive radiation detector is employed to image distributions of the radiolabeled compounds as the radiolabeled compounds travel along a fluid channel.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2026

Electron/hadron separation with the TRD based on GaAs pixel detectors

Transition Radiation Detectors (TRDs) are widely used for particle identification in both high-energy physics and astroparticle physics. They are typically equipped with gaseous detectors. The main limitation of these types of detectors is that TR photons and ionization losses cannot be decoupled, which significantly reduces the particle separation power. Recent advancements in the development of pixel detectors based on GaAs sensors offer a unique opportunity to effectively detect TR photons and separate them from ionization losses. Such detectors represent novel devices that combine precise tracking capabilities with particle identification (PID) properties. The present work is dedicated to an experimental study of particle identification properties of the TRD prototype based on 500 μ m-thick GaAs sensor bonded to a Timepix3 chip. Studies were performed at the CERN SPS and it was shown that at a particle momentum of 20 GeV/c, the probability of misidentifying a hadron as an electron is below 10 −2 for an electron detection efficiency of 98%–99%, and it is 1 . 6⋅10 −4 for electron detection efficiency of 90%. This performance surpasses the electron/hadron rejection power of all known TRDs by an order of magnitude for the same detector length.

GaAs detectors↗
NASA NTRS1974

High field CdS detector for infrared radiation

An infrared radiation detector including a cadmium sulfide platelet having a cathode formed on one of its ends and an anode formed on its other end is presented. The platelet is suitably doped such that stationary high-field domains are formed adjacent the cathode when based in the negative differential conductivity region. A negative potential is applied to the cathode such that a high-field domain is formed adjacent to the cathode. A potential measuring probe is located between the cathode and the anode at the edge of the high-field domain and means are provided for measuring the potential at the probe whereby this measurement is indicative of the infrared radiation striking the platelet.

Tyagi, R. C.↗
DOE OSTI2016

Charge Carrier Diffusion Length Determination in 4H-SiC Schottky Alpha Detectors

When developing semiconductor radiation detectors detailed characterization of the detector behavior is required. The ability of a semiconductor radiation detector to collect the charge liberated by incident ionizing radiation is a critical characteristic. Several factors influence the charge collection efficiency of a semiconductor radiation detector, including electron-hole trapping, applied electric field strength, and dopant concentrations and dimensions of low doped regions. Applying a reverse bias electric potential to a low doped semiconductor region creates a free charge carrier depleted region and establishes an electric field which can remove subsequently freed charge in the form of an electrical signal. When ionizing radiation is incident upon a semiconductor electron-hole pairs are generated. These charge carriers are created along the path of the ionizing radiation regardless of the doping concentration. However, only the charge freed in the low doped epitaxial region of a detector will be collected as a result of the applied electric field. When the electric field is insufficient to develop a depleted region equal to or larger than the range of the ionizing radiation in the detector material some charge freed by the ionizing radiation outside of the sensitive region will be lost, thus potentially resulting in less than complete charge collection. The incomplete collection of charge complicates the analysis of the incident particle energy spectrum. Charge freed in the highly doped bulk region beyond the low doped epitaxial region may diffuse back into the low doped depleted region and be subsequently included in the integral pulse. The amount of charge collected as a result of this diffusion mechanism is dependent upon the diffusion length of the charge carriers in the material. The diffusion length is subsequently dependent on the material properties of the detector including the number of defects, trapping centers, and temperature. In order to fully characterize the properties of 4H-SiC as a radiation detector the diffusion length was calculated by adjusting the theoretical diffusion length value used in the calculation of the charge collection efficiency to agree with empirically observed charge collection efficiencies. The discrepancy between the observed and theoretical charge collection efficiency at 50 to 150 volts applied bias indicates an unexplained charge collection phenomenon which is contributing to the larger than predicted charge collection efficiency of the detectors. This voltage range corresponds to an intermediate applied bias, indicating that either the theoretical depletion width is too short, the diffusion length varies with the composition of the region that the charge carriers are diffusing through, or some other phenomenon is involved. If the charge carrier diffusion length varies depending on whether or not the diffusing charge is freed in unbiased epitaxy or bulk layer, then a function describing the variation of the diffusion layer could be determined by measuring the diffusion length at the applied voltages used previously, but over a range of epitaxial layer thicknesses. Future work includes the characterization of the effects of high temperature operation on the diffusion length of 4H-SiC in addition to measuring the effects of varying energy alpha emitter electrodeposition on the observed diffusion length. Additional Schottky barrier contacts, namely those with a nickel-platinum contact, will be tested in various sizes which have been developed in order to eliminate certain failure mechanisms and explore the potential effects of Schottky contact size on charge collection efficiency. (authors)

36 MATERIALS SCIENCE↗
DOE OSTI2026

The ePIC dual-radiator RICH detector

The dual radiator Ring Imaging Cherenkov (dRICH) detector is required to provide continuous hadron identification from ≈3 GeV/c up to ≈50 GeV/c, and to supplement electron and positron identification from a few hundred MeV/c up to about 15 GeV/c, in the forward (ion-side) end-cap of the ePIC experiment. Such an extended momentum range imposes the use of two radiators, gas and aerogel. The common imaging system, that ensures compactness and cost-effectiveness, is based on SiPM sensors to work in a high non-uniform magnetic field. During the R&D phase, the dual radiator principle and the single component performance have been validated. A status overview of the project is presented. The design and technological choices are discussed together with the results obtained from laboratory characterization of the component demonstrators and beam tests of the evolving prototypes.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗