Tuning fractional PID controllers for a Steward platform based on frequency domain and artificial intelligence methods

In this paper, two methods to tune a fractional-order PI ^λ D ^μ controller for a mechatronic system are presented. The first method is based on a genetic algorithm to obtain the parameter values for the fractionalorder PI ^λ D ^μ controller by global optimization. The second method used to design the fractional-order PI ^λ D ^μ controller relies on an auto-tuning approach by meeting some specifications in the frequency domain. The real-time experiments are conducted using a Steward platform which consists of a table tilted by six servo-motors with a ball on the top of the table. The considered system is a 6 degrees of freedom (d.o.f.) motion platform. The feedback on the position of the ball is obtained from images acquired by a visual sensor mounted above the platform. The fractional-order controllers were implemented and the performances of the steward platform are analyzed.     

Beta-decay energies of neutron-rich nuclei in the mass region 142≦A≦150

The β-endpoint energies of 6 neutron-rich nuclei with mass numbersA=146 andA=147 have been measured with a plastic scintillator telescope at the on-line mass separator OSTIS. With theQ _β-values derived from these experiments and with those obtained in earlier studies, nuclear structure effects in this part of the nuclear chart are investigated. In addition, nuclear masses derived from the experimentalQ _β-values are compared with the predictions of theoretical mass calculations.     

New cooling methods for HPGE detectors and associated electronics

Summary Despite the on-going development of room temperature semiconductors for use as gamma-ray detectors, the only material which can provide a solution to the combined requirements of stability, high-energy resolution and high-detection efficiency (at useful energies) is still germanium (HPGe). These properties of HPGe gamma-ray detectors make them invaluable in meeting the demands of the newly emergent and increasingly important applications relating to homeland security and the interdiction of smuggled nuclear material. However, HPGe detectors require cooling to cryogenic temperatures (<120 K) to operate as gamma-ray detectors. Traditionally, this cooling has been accomplished with liquid nitrogen (LN2). The use of LN2 as a coolant is, at best, inconvenient. Maintenance, operating cost, availability at remote locations, and the hazardous nature of the material all combine to limit the practicality of a LN2-cooled device, no matter how desirable it might be from other standpoints. Mechanical methods of achieving cryogenic temperatures have existed for many years. The first mechanically-cooled HPGe systems appeared commercially in the early 1980s.¹ These systems had high cost, high power requirements, degraded system performance, were bulky in size, and unreliable. Other developments have produced prototype versions of portable (or transportable) mechanically-cooled HPGe systems. More recent advances in mechanical cooling technologies have the potential to make HPGe detectors easily adaptable to a wide variety of applications including battery-operated, truly man-portable systems for use in inspection, unattended monitoring, and Homeland Security. The major problems of mechanical coolers are degraded performance due to vibration and power consumption. The systems described here have reduced both of these to useable limits. The vibration or microphonic noise created in real-world systems is significantly reduced by optimizing the digital filter technology in the signal processing electronics associated with such detectors. Data presented here show reliability and performance results of the mechanically-cooled systems. These results show the improvements gained through the use of the optimally-matched digital filters.     

Efficiency for close geometries and extended sources of a p-type germanium detector with low-energy sensitivity

Typically, germanium detectors designed to have good sensitivity to low-energy photons and good efficiency at high energies are constructed from n-type crystals with a boron-implanted outer contact. These detectors usually exhibit inferior resolution and peak shape compared to ones made from p-type crystals. To overcome the resolution and peak-shape deficiencies, a new method of construction of a germanium detector element was developed. This has resulted in a gamma-ray detector with high sensitivity to photon energies from 14 keV to 2 MeV, while maintaining good resolution and peak shape over this energy range. Efficiency measurements, done according to the draft IEEE 325-2004 standard, show efficiencies typical of a GMX or n-type detector at low energies. The detectors are of large diameter suitable for counting extended samples such as filter papers. The Gaussian peak shape and good resolution typical of a GEM or p-type are maintained for the high count rates and peak separation needed for activation analysis.     

Improvement of spectral resolution in the presence of periodic noise and microphonics for hyper-pure germanium detector gamma-ray spectrometry using a new digital filter

The radiation dose of workers and patients resulting from inhaling radon and through the consumption of spring waters was examined in the hospital near the Héviz lake in Hungary. The radiation dose originating from radon was 2.15–3.95 mSv·y⁻¹ concerning workers at the spa. The radiation dose originating from radon in the case of those regularly taking a bath was an average of 0.75 mSv·y⁻¹. Due to the limited duration of treatments a bound effective dose of maximum 100 μSv·y⁻¹ may originate from radon and inhaling radon, while a maximum of 1.4 μSv·y⁻¹ may originate from ingestion of ²²²Rn, ²²⁶Ra, ²³⁴U and ²³⁸U radionuclides.     

Prompt (n,γ) Mass Measurements for the AVOGADRO Project

The aim of the AVOGADRO project is to replace the kilogram artefact by a high-purity, perfect single crystal of natural or isotope-enriched silicon. The isotopic composition and the impurities of the silicon crystal must, therefore, be known with highest possible accuracy and precision. The only method to obtain all this information without destruction of the massive samples is prompt (n,γ)-spectrometry. The measurements are performed at a thermal neutron guide of the ILL (Institut Max von Laue Paul Langevin) in Grenoble, France. The spectrometry of γ-radiation emitted by a nucleus promptly after thermal neutron capture allows a highly precise determination of atomic mass differences, as well as the determination of isotope abundances leading to the molar mass. The uncertainties assigned to the results for the respective atomic masses determined by the mass differences amount to up to 10⁻¹⁰, while the molar mass of an isotope-enriched Si single crystal has so far been determined with an uncertainty of 1 ⋅ 10⁻⁴. A direct comparison (for example, relative value of isotope abundances determined by (n,γ)-spectrometry omitting the thermal neutron cross section) furnishes a value of 7 ⋅ 10⁻⁵. The final aim of the AVOGADRO project is to provide a well specified crystal, which allows a more accurate value of the Avogadro constant to be determined. This constant is the key input parameter for tabulated values of fundamental constants and for a new definition of the unit of mass - the kilogram itself. This revised version was published online in July 2006 with corrections to the Cover Date.     

Advances in HPGe Detectors for Real-World Applications

Germanium detector use and crystal production has progressed to such a degree that the IEEE standard for the performance of the detector is no longer adequate to predict the efficacy for a different situation. The specifications of the standard do not predict how a detector will perform at other energies or geometries. One such geometry that is poorly predicted is extended sources. Many parts of the detector and electronics that can be changed to make the total system perform better for a specific case, but such changes can worsen the performance of the detector at the IEEE specification. Examples will be given for the efficiency, MDA, throughput, and resolution for different source—detector and crystal configurations.     

Deuterium isotope separation by tunable-laser predissociation of formaldehyde

A tunable ultraviolet laser has been used to investigate the deuterium enrichment resulting from the photopredissociation of formaldehyde. An enrichment factor of 254 ± 30 has been measured at 345.6 nm starting from a 4 Torr sample of natural formaldehyde.     

Beta-decay energy and nuclear mass of100Nb

Radiofrequency measurements of the zero-field hyperfine intervals in low levels of¹⁶⁷Er and^161,163Dy have been made as part of a systematic study of the second half of the 4f^N6s² configuration of the neutral rare-earth atoms. Almost no precise hfs data exist for this region, and a preliminary analysis indicates systematic differences between ab initio theory and experiment.