Field comparison of two different passive radon detectors

The present paper describes field performance of two different passive radon monitor devices formed, respectively, by a CR-39 track detector enclosed in a diffusion chamber and a cellulose nitrate detector (LR-115) in a heat-sealed polyethylene bag. The most important scope of these investigations was to study the performance of these detectors directly in the field. To this end, two different types of radon monitors mentioned above have been exposed simultaneously in 100 school rooms within the Italian region Friuli Venezia Giulia. Finally, the accuracy of their responses has been evaluated by exposing them under extreme humidity conditions and/or together with other radon measurement instruments.     

A comparison of layered metal-semiconductor optical position sensitive detectors

Position sensitive detectors (PSDs), utilize the lateral photovoltaic effect to produce an electrical output that varies linearly with the position of a light spot incident on a semiconductor junction. In fabricating PSDs, two key elements are optimized: the sensitivity, (mV/increment) and the linearity of the electrical output. Sensitivity is optimized by varying properties of the junction layers, particularly resistivity, while linearity is determined primarily by junction uniformity. In this paper, Schottky barrier PSDs are fabricated from the electron-beam deposition of titanium, tantalum and aluminum on to p-type silicon substrates. Devices were tested under focused broad-band white light and the sensitivities and linearities, for the different metals with varying thicknesses, are compared. Overall, Ti and Ta PSDs performed very well over a large range of film thicknesses, 50 to 2000 /spl Aring/, while Al was more limited. The best of all the devices fabricated so far was one with 380 /spl Aring/ film of Ti, giving a sensitivity, or output, of 10.62 mV/mm while maintaining excellent linearity and spatial resolution. The best aluminum devices were obtained with a 100 /spl Aring/ film and resulted in a sensitivity of 8.84 mV/mm and a spatial resolution of better than 10 /spl mu/m. Of the tantalum devices, film thicknesses of around 200 /spl Aring/ produced the highest sensitivities.     

An anomalous change in the supercooling of vapor in spontaneous condensation

Spontaneous condensation of vapor at transonic velocities in the subsonic part of a flow in contrast to condensation in all the remaining regions of the flow leads not to an increase, but rather to a decrease in temperature and not to a drop, but rather to a rise in the supercooling of vapor. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 2, pp. 215–217, March–April, 1998.     

Quantitative comparison of adhesion in metal-to-plastic systems

A peel test device was used to monitor metal-polymer adhesion. This technique showed variations in the resulting force within 1%, and enabled the ranking of many systems. A change in the 50 nm-adhesion layer resulted in a variation of the fracture energy by a factor 2.3. A change of the substrate led to a change in adhesion by a factor 40. The peeling results were also combined with attenuated total reflectance Fourier transform infra-red measurements to provide qualitative insight of the bonds at the substrate surface. Differences were also visible after surface pretreatment by plasma or sputter etching with different gases, as changes in interaction bonds as well as in adhesion were observed.     

A comparison of Schottky barrier position-sensitive detectors as a function of light wavelength

Position-sensitive detectors (PSDs), are single continuous optical sensors that utilize the lateral photovoltaic effect to produce an electrical output that varies linearly with light spot position. This work reports further on the results from Schottky barrier PSDs fabricated from thin films of tantalum, titanium, and aluminum. The optimal thickness of the Schottky metals was determined, trading off light transmissivity and proper Schottky barrier formation. The objective of this work was to determine if devices performed particularly well or poorly under certain light sources and, if so, at what thickness of film. Each device has been tested in one dimension under 5 mW of red laser light, focused broad-band light, as well as filtered red, green, and blue light. It was found that all devices generally responded well to the filtered red light and worst under the green light source. The extent to which this is true depends on the Schottky metal used and its thickness. It was also found that the detector response changed over time. Most interestingly, the tantalum Schottky barrier devices either improved or remained the same while the titanium devices deteriorated noticeably.     

Quantitative comparison of the efficiency of mechanochemical reactors

A simple method is proposed for the comparison of the mechanical dose rates of different mills, based on measuring the ignition time of a mechanically-induced self-propagating reaction (MSR). Specifically, a SPEX 8000 Mixer Mill with round-ended and flat-ended milling vials and a Fritsch Pulverisette-6 planetary mill are compared, using the ignition of MSR between Zn and S powders as the test reaction. The method facilitates the comparison of reaction kinetics data obtained by using different milling equipment.     

A comparison of performance between organic scintillation crystals and moderated He-based detectors for fission neutron detection

Direct detection of fast neutrons using organic scintillators is one alternative to moderated thermal neutron detectors deployed to detect fission neutrons—a relevant question in light of dwindling ³He supplies. Recent developments in materials science have demonstrated the capability to grow larger crystals in reasonable times. In light of these developments, this study compares the relative performance of a ³He-based neutron module from a commercially available portal monitor with a theoretical organic scintillator of similar overall size. Stilbene serves as a benchmark with its performance estimated from a combination of energy deposition modeled by radiation transport calculations and an assumption of the lowest neutron energy at which pulse shape discrimination can effectively separate neutron and gamma-ray events. Before intrinsic detection efficiencies on par with moderated detector systems can be achieved, the results point to the need for further advances including significant increases in detector size, especially thickness, and/or lower pulse shape discrimination thresholds.     

Operational comparison of TLD albedo dosemeters and solid state nuclear tracks detectors in fuel fabrication facilities

The authors carried out an operational study that compared the use of TLD albedo dosemeters and solid state nuclear tracks detector in plutonium environments of Japan Nuclear Cycle Development Institute, Tokai Works. A selected group of workers engaged in the fabrication process of MOX (Plutonium-Uranium mixed oxide) fuel wore both TLD albedo dosemeters and solid state nuclear tracks detectors. The TL readings were generally proportional to the counted etch-pits, and thus the dose equivalent results obtained from TLD albedo dosemeter agreed with those from solid state nuclear tracks detector within a factor of 1.5. This result indicates that, in the workplaces of the MOX fuel plants, the neutron spectrum remained almost constant in terms of time and space, and the appropriate range of field-specific correction with spectrum variations was small in albedo dosimetry.     

A comparison of the performance of irradiated p-in-n and n-in-n silicon microstrip detectors read out with fast binary electronics

Both n-strip on n-bulk and p-strip on n-bulk silicon microstrip detectors have been irradiated at the CERN PS to a fluence of 3×10¹⁴ pcm⁻² and their post-irradiation performance compared using fast binary readout electronics. Results are presented for test beam measurements of the efficiency and resolution as a function of bias voltage made at the CERN SPS, and for noise measurements giving detector strip quality. The detectors come from four different manufacturers and were made as prototypes for the SemiConductor Tracker of the ATLAS experiment at the CERN LHC.     

Quantitative comparison between microfluidic and microtiter plate formats for cell-based assays

In this paper, we compare a quantitative cell-based assay measuring the intracellular Ca2+ response to the agonist uridine 5'-triphosphate in Chinese hamster ovary cells, in both microfluidic and microtiter formats. The study demonstrates that, under appropriate hydrodynamic conditions, there is an excellent agreement between traditional well-plate assays and those obtained on-chip for both suspended immobilized cells and cultured adherent cells. We also demonstrate that the on-chip assay, using adherent cells, provides the possibility of faster screening protocols with the potential for resolving subcellular information about local Ca2+ flux.     

Reliability assessment of smoke detectors

A preliminary analysis of smoke detector test data is reported. The data corresponds to the threshold limit test (i.e. minimum aerosol concentration for operation of the detector) carried out using the smoke detector tester developed by UKAEA, Harwell.Differences in response levels of different detector types are discussed assuming that response levels follow normal and Weibull distributions. Based on a quality control criterion a pass/fail criterion is proposed.     

Characterization of liquid scintillation detectors

Five scintillation detectors of different scintillator size and type were characterized. The pulse height scale was calibrated in terms of electron light output units using photon sources. The response functions for time-of-flight (TOF)-selected monoenergetic neutrons were experimentally determined and also simulated with the NRESP code over a wide energy range. A comparison of the measured and calculated response functions allows individual characteristics of the detectors to be determined and the response matrix to be reliably derived. Various applications are discussed.     

Simulation-based comparison of cell design concepts for phase change random access memory

The RESET operation of different design concepts for phase change random access memory (PCRAM) cell is studied and compared using a three dimensional simulation model. This numerical algorithm comprises four interacting sub-models, which describe the electrical, thermal, phase change, and percolation dynamics in the PCRAM devices during the switching operation. The so-called vertical, confined, and lateral cell geometries are evaluated in terms of their current requirements for RESET operations, which is one of the most critical issues for an achievement of high integration densities. The advantages of the confined and lateral cell architecture as compared to the conventional vertical cell concept are explored, demonstrating their benefits of advanced thermal management and minimized current defined area. The simulation results agree well with experimental features of the RESET operation for the PCRAM design concepts studied.