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Over the past few decades, tetrafluoroethane (TFE, R134a Freon)-based gases have been widely used in the operation of phenolic resistive plate chambers (RPCs) in many high-energy experiments. However, TFE has a high global warming potential (GWP); therefore, a search for new eco-friendly gases to replace traditional TFE-based ones is now unavoidable. In this research, we present cosmic-ray test results of a prototype RPC for the SHiP (search for hidden particles) experiment using 1.6- and 1.4-mm-thick RPC electrodes containing mixtures of various gases, including 1,3,3,3-tetrafluoropropene (HFO1234ze), CO2, iC4H10 and SF6. We compare the performance data gathered with these new gas mixtures with those gathered with a traditional TFE-based gas used for RPCs in compact muon solenoid (CMS) and a toroidal LHC apparatus (ATLAS) experiments. The addition of CO2 to the HFO1234ze-based gas was found to be fairly effective in reducing the working-point high voltage (HVWP) for RPC operation. The results of our experiments lead us to the conclusion that adding 40% CO2 or less, when combined with HFO1234ze-based gas, is conducive to reliable detector performance for SHiP single-gap phenolic RPCs.

The main goals of the Search for Hidden Particles (SHiP) experiment are to observe hidden particles and to run a high-statistics study of tau neutrino events. Two different types of resistive plate chambers (RPCs) will be used in the future SHiP experiment: one for triggers to select the decayed muons emitted via tau neutrino interactions and one for precision time measurements of charged particles, which are expected from the decays of hidden particles. In the present research, we constructed and tested a prototype RPC module to study the fundamental detector performance of the muon trigger RPCs in the tau neutrino detector of the SHiP experiment. The required detector characteristics, such as the intrinsic noise rate, the time response, and the spatial resolution, were proven through the test of the present prototype detector with cosmic muons.

In the past several decades, many studies have been conducted to search for non-baryonic dark matter, such as weakly interactive massive particles (WIMPs). In the search for WIMPs, charged particles incident on the detector are background particles because WIMPs are neutral. Charged particles originate from various sources, such as cosmic rays and laboratory materials surrounding the main detector. Therefore, a veto that discriminates charged particles can improve the particle-detection efficiency of the entire experiment for detecting WIMPs. Here, we investigate in the thickness range of 1 mm to 5 mm, the optimal thickness of a polystyrene scintillator as a chargedparticle veto detector. We found that 3-mm-thick polystyrene provides the best performance to veto charged particles and the charged-particle background in the search for the WIMP signal. Furthermore, we fabricated 3-mm-thick and 5-mm-thick polystyrene charged particle veto detectors that will be used in an underground laboratory in the search for WIMP dark matter. After exposing those detectors are the actual beam line, we compared the rate of charged particles measured using those detectors and the rate simulated through a Monte Carlo simulation.

LaPO4:RE3+(RE = Tb or Ce) phosphor powders were synthesized with different activator ion concentrations by using the solid-state reaction method. The effect of the activator ion concentration on the structural, morphological, and luminescent properties of lanthanide-phosphate phosphors was investigated. XRD patterns revealed that the synthesized phosphors with different activator ions showed a monoclinic structure with a main (120) diffraction peak for both activator ions. The crystallite size was estimated by using the Scherrer formula, and the maximum size was obtained at 0.01 mol of Ce3+ions and at 0 mol of Tb3+ions. The emission spectra of Tb3+-doped LaPO4 phosphors under excitation at 210 nm exhibited one intense green band at 548 nm and three weak lines peaking at 493, 590, and 640 nm, respectively. The intensities of all the emission bands reached their maxima at 0.10 mol of Tb3+ ions. As for the Ce3+-doped LaPO4 phosphors, two strong emission bands were observed, one each at 324 and 340 nm, and the energy difference between the two peaks was 0.18 eV. These results suggest that multicolor emission can be realized by controlling the concentrations of the activator ions incorporated into the host lattice.

Identification of gamma rays and neutrons is a fundamental technique used in elementary particle physics experiments, such as the search for dark matter, double beta decay, etc. The pulse shape discrimination (PSD) methods with liquid and crystal scintillators, a well-known technology, have been under development for several decades. The PSD methods with crystal scintillators are known to be less stable and less effective than PSD methods with liquid crystals. Here, an improved PSD technique with a CsI crystal scintillator based on the well-known PSD methods with liquid scintillators is introduced. In this study, we found the possibility that the proposed PSD with a CsI crystal scintillator provides a performance to discriminate gamma rays and neutrons equivalent to that of a PSD with a liquid scintillator.

The elastic scatterings of 6Li + 24Mg and 6Li + 28Si systems at Elab = 240 MeV have been analyzed within the framework of the eikonal model by using the tangential velocity at the distance of closest approach. The calculated results, taking into account the tangential velocity, show good agreement with the observed data. The diffractive oscillatory structures at the forward angles can be explained by the strong interference between the near- and the far-side scattering amplitudes. Deep real potentials and rather weak imaginary ones are required to describe these systems. The refractive patterns of the large-angle cross sections, dominated by far-side scattering, can be shown to be sensitive to the real part of the optical potential at small radius. We investigate the effect of the tangential velocity on the phase shifts and the cross sections.

We report on the electrical characteristics for the metal-insulator-semiconductor (MIS) structure of low-dielectric-constant SiOC(−H) films. The SiOC(−H) thin films were deposited on p-Si(100) substrates by using a plasma-enhanced atomic layer deposition (PEALD) system. To improve the structural and the electrical characteristics, we post-treated the SiOC(−H) films deposited using PEALD with ultraviolet (UV) irradiation for various time intervals. The radical intensities in the bulk plasma were observed to be influenced strongly by the radio-frequency (rf) power. A complete dissociation of the trimethylsilane (TMS) precursor took place for rf powers greater than 300 W. As the UV treatment time was increased, the bonding structure of the SiOC(−H) film clearly separated to Si-O-Si and Si-O-C bonds. Also, the fixed charge density and the interface state density on the SiOC(−H)/p-Si(100) interface decreased as the UV treatment time was increased to 6 min. Therefore, we were able to minimize the defects and to reduce the interface charge by adjusting the UV dose.

Estimating the radioactivity induced by patient-specific devices installed near the patient skin is important, because patients are directly exposed during the treatment. This study evaluated the radioactivity induced by a brass collimator and a PMMA range compensator in a proton beam and identified the radionuclides produced by nuclear interactions with the proton beam and with the patient-specific devices. The total dose rate depended on the radionuclides, which had short decay times and 1 hour later their activities reach about one-fiftieth of the initial values in the cases of both PMMA and brass. Although the radioactivity induced by proton therapy can affect patients during the radiotherapy, the total radiation dose is much smaller than the prescribed dose for cancer treatment, and the treatment time is very short. Therefore, the radioactivity induced by patient-specific devices should be negligible.

We report on the electrical characteristics of the metal-insulator-semiconductor (MIS) structure of low-dielectric-constant SiOC(-H) films. SiOC(-H) thin films were deposited on p-Si(100) substrates by using a plasma-enhanced chemical vapor deposition (PECVD) system. The frequency dependence of the capacitance-voltage (C-V) and the conductance-voltage (G/ω-V) characteristics of the A1/SiOC(-H)/p-Si(100)/Al MIS structures was analyzed. C-V and G/ω-V measurements were carried out over a frequency range of 1 kHz to 5 MHz. Based on our analysis, the C-V and the G/ω-V characteristics confirmed that the surface states and the series resistance were important parameters that strongly influenced the electrical properties of the A1/SiOC(-H)/p-Si(100)/Al MIS structures.

The interconnection of copper (Cu) with low-dielectric-constant interlayer films (low-k) is crucial to improving integrated circuit performance. Integration challenges with new ultra-low-k generation materials include electrical-property and reliability issues. In this study, low-dielectric-constant SiOC(-H) films were deposited on p-type Si(100) substrates by using plasma-enhanced chemical vapor deposition (PECVD) with dimethyldimethoxysilane (DMDMOS) and oxygen gas as precursors. The deposited SiOC(-H) films were then annealed at temperatures from 250 to 450 C in a vacuum. The electrical conduction in the low-dielectric-constant SiOC(-H) films depended on two main conduction mechanisms: Schottky emission (SE) and Poole-Frenkel (PF) emission. We calculated the Schottky barrier height at the interface between the Cu and the SiOC(-H) film for SE conduction and the trap potential well in the SiOC(-H) films for PF conduction. These calculations showed that the leakage current densities were linearly related to the square root of the applied electric field.

Many customs inspection machines based on particle detector techniques have been researched and developed. An inspector with a proper scanning speed of an inspector will provide better efficiency. This report attempted to optimize the scanning parameters for container inspectors with segmented detectors for gamma rays from radioactive isotopes for custom inspections executed on higher-density objects hidden in imported iron containers. This calculation method provided good results for segmented detectors such as a resistive plate chamber (RPC), segmented photomultiplier tube (PMT), cathode stripe chamber (CSC), pixelized semiconductor detectors, etc. We estimate the proper scanning speed for the best combinations of the intensity of the gamma ray, the distance between the detector and the gamma ray source, the size of a pixel in the detector, the scanning speed, etc. to get a sufficient resolution. We used an RPC, whose pixel size is a few cm and whose gamma-ray detection efficiency is 0.18, as a reference detector for our calculation. Also we used Co emitting two kinds of gamma rays with kinetic energies of 1.17 MeV and 1.33 MeV, as a gamma ray source.

A study of the ambient gamma ray exposure rate is an essential part of underground astro-particle and astro-nuclear physics experiments. The daily variation of the ambient gamma ray exposure rate has been measured at a gamma-ray monitoring post in the mid-Korean peninsula from 2003 to 2006 by using a sinusoidal function with two free parameters, an amplitude and a phase, as a function of the time. The shifted phase indicates that the besttted sine curve starts 3 hours and 7 minutes delayed from 0:00 o'clock. The maximum and the minimum ambient gamma exposure rates appear at 9:07 am and at 9:07 pm in the besttted sinusoidal curve for the daily variation of ambient gamma ray rate. Also, we will provide some information for the daily gamma ray exposure rate.

A study of the ambient gamma ray exposure rate is essential as a background for underground particle physics experiments such as the neutrino and the non-bayonic dark matter experiments. Here, we report patterns for the daily and the annual variations of the ambient gamma ray exposure rate measured at the Cheongju Regional Radiation Monitoring Post from January 2003 to December 2006 by using a pressurized ionization chamber. The daily ambient gamma ray exposure rate appears to have a sinusoidal pattern with an annual average daily variation of 0.17 μR/h. The maximum ambient gamma exposure rate appears from 7 : 30 am to 9 : 30 am and the minimum from 7 : 30 pm to 10 : 30 pm. The annual average of the ambient gamma ray rate was 12.78 μR with an annual variation of 1 μR/h for the years from 2003 to 2006. The fluctuation in the seasonal variation was 7.8 percent while the fluctuation the daily varition was 1.3 percent during the years from 2003 to 2006.