Perspectives in science最新文献

The new general-purpose fixed target experiment SHiP (Search for Hidden Particles) at the CERN SPS (Super Proton Synchrotron) is aimed at research in the field of Beyond Standard Model (BSM) physics and of tau-neutrino physics. The Emulsion Neutrino Detector will be one of the main elements in the SHiP detector design. It is intended for search for Dark Matter scattering on electrons of nuclear emulsion and for tau-neutrino and anti tau-neutrino direct observation, and study their properties and the cross section. The main source of both hidden particle and tau-neutrino event fluxes is the decay of charmed particles produced in the SHiP proton target. The detection of the production and decay of charmed hadrons in the target will be performed through nuclear emulsion films employed in the Emulsion Cloud Chamber target structure. The paper describes the basic principles of the SHiP neutrino emulsion detector and some measures for its optimization.

The number (n) and diameter (d) of superheated droplets in bubble detectors of Type T-12 have been determined with high-energy heavy ions ⁵⁶Fe, ⁸⁴Kr and ¹³²Xe at HIMAC accelerator in the National Institute of Radiological Sciences (NIRS), Chiba Japan. The approach to determining the number and diameter of superheated droplets is based on determination of (1) the average gap distance (g) between two neighboring bubbles in a track of high-energy heavy ion and (2) the volume ratio (V_L/V) of superheated droplets to the whole volume of the detector. The volume ratio is known from preparation process of bubble detectors. The average gap distance can be obtained from the mean of gap distances measured between two neighboring bubbles in a track of heavy ion. From g and V_L/V one can obtain the two basic parameters n and d of the bubble detector, which are unknown due to invisibility of superheated droplets in bubble detector. Four batches of bubble detectors of Type T-12 were calibrated by this approach. It shows that the average gap distance of bubbles in the detectors is ∼1 mm, the volume density (number n) of superheated droplets in the detectors is ∼10⁶ cm⁻³ and the diameter of superheated droplets is in the range from ∼30 to 50 μm. It also shows that the two parameters n and d are different from batch to batch of the detectors when V_L/V is the same. Therefore, one should make a calibration of bubble detectors at accelerator with heavy ions before using the detectors. This property is similar to that of etch track detectors (SSNTD).

Absorbed dose during a CT exam can be estimated by the computed tomography dose index (CTDI). The aim of this study is to validate a simulated CTDI with measured data for a 16-slice CT system. To measure the CTDI we have used an ion chamber, electrometer and two polymethylmethacrylate (PMMA) phantoms (head and body). GATE (GEANT4 Application for Tomographic Emission) platform is a Monte Carlo code for medical physics applications, especially dosimetry studies. CTDI and CTDI_w were recorded to compare simulated results for different X-ray tube currents and voltages with experimental data at different positions in the phantom. The results obtained for all conditions applied show a difference less than 2.6% and 4.3% for head and body phantom, respectively. It was demonstrated that GATE is a good tool to simulate CTDI_w values and to study of the influence of tube current and voltage on the absorbed dose.

Two types of cascade nuclear track filters have been developed: (1) cascade filter made of polypropylene (PP) fiber membrane as preliminary filter and nuclear track membrane (NTM) as terminal filter; (2) Nylon tortuous-pore membrane as preliminary filter and NTM as terminal filter. Removal of solid particles by the cascade filters has been investigated. The solid particles studied include glass shards from broken ampoules and rubber fragments from rubber covers (plugs) of medical bottles. When an ampoule containing medicine is broken by emery wheel and by hands, large number of glass shards are produced and fall into the medicine. When a rubber cover is punctured by syringe needle, large number of rubber fragments are produced by friction between rubber and needle. The investigation shows that fiber or tortuous membranes alone usually cannot completely remove the microscopic particles due to existence of large gaps in the structure of the two common membranes. Nuclear track membranes alone and their cascade filters are superior to remove all solid particles bigger than the pore size of the track membrane. Removal efficiency for solid particles and flow rate of injections through the cascade filters have been calibrated and shown that both features above fulfill the requirements of Chinese regulations. The two types of cascade filters have been accepted for use in Chinese hospitals.

The relationship between different physical parameters of various polymers (e.g., CR-39, Lexan, and PET) used as Nuclear Track Detectors (NTDs) and their intrinsic detection thresholds were investigated. A strong correlation was found between the electrical resistivity and detection thresholds of the NTDs and from that an empirical relationship between the two established. The predicted value of the detection threshold for Perspex® obtained from that empirical formula is in good agreement with its experimentally determined value.

In this study, a portable radioactive plume monitor using a silicon photodiode was developed for the detection of a radioactive plume (e.g. ¹³¹I, ¹³⁴Cs and ¹³⁷Cs) in an emergency situation. It was found that the background count rate was proportional to ambient dose equivalent rate and the detection limit for the monitor at 20 μSv h⁻¹ as an ambient dose equivalent rate was evaluated to be 187 Bq m⁻³ using the ISO11929 method. These results suggest that the detection limit for the system can be decreased effectively by lead shielding with optimized thickness.

In this work, we propose to analyze the dosimetric properties of the glucose Electron Paramagnetic Resonance (EPR) system. This study consists of irradiating samples of glucose by megavoltage X photons and electrons delivered by a particle accelerator used in radiotherapy. After irradiation, the samples were analyzed by EPR. The measurements obtained on samples placed at different depth in a phantom of PolyMethyl Methacrylate “PMMA” have firstly identified the depths corresponding to the maximum dose deposition for both particles and samples used. Analysis by EPR showed that the threshold measurable dose for this dosimetric system is about 2 Gy. The variation of curves obtained from the peak-to-peak EPR intensity, or the results of the double integration of the spectrum as a function of the irradiation dose, are linear with a correlation coefficient exceeding 0.999. Glucose seems slightly more sensitive to megavoltage X photons than megavoltage electrons. The results reveal interesting potential dosimetry of the glucose/EPR system in the field of radiation therapy.

For gaining insight in the mode of action at the molecular level of glycans in biological systems precise knowledge of the structure of the glycans is indispensable. To obtain this fundamental information well-defined starting material, optimal fractionation methods and adequate identification techniques are essential. In this review, the emphasis is on the application of high resolution ¹H NMR spectroscopy to the structure determination of glycans of different origin. The power of ¹H NMR spectroscopy is the possibility to determine in a non-destructive way all structural parameters of glycans. This is illustrated for glycans that differ in structural complexity.

The Integrated Life Science Database Project of Japan funded a group of glycoscientists to carry out a project to integrate glycoscience databases using Semantic Web technologies. As a continuation of the previous project period, the Japan Consortium for Glycobiology and Glycotechnology Database (JCGGDB) developed several glycoscience-related databases. The GlycoProtDB database is among those being integrated, providing an important resource to understand protein glycosylation. Another database being integrated is GlycoEpitope, a comprehensive database of carbohydrate epitopes and antibodies. In the current project period, we started the development of GlyTouCan, the international glycan structure repository providing unique accession numbers to all glycan structures. Although such databases are sufficiently important in and of themselves, their integration with other—omics data such as the protein information in UniProt will be crucial to bring glycosciences to the forefront of life sciences. However, to integrate such disparate sets of data among different fields in a way such that future maintenance costs are minimal, standardized ontologies and formats must be established. Our latest project has attempted to define the minimal standards that are necessary to enable this integration. The technical challenges to integrate all these databases and the technologies to overcome these challenges will be described.