Mm In Profile Research Articles

TH-CD-201-10: Highly Efficient Synchronized High-Speed Scintillation Camera System for Measuring Proton Range, SOBP and Dose Distributions in a 2D-Plane

Purpose: Proton therapy (PT) delivery is complex and extremely dynamic. Therefore, quality assurance testing is vital, but highly time-consuming. We have developed a High-Speed Scintillation-Camera-System (HS-SCS) for simultaneously measuring multiple beam characteristics. Methods: High-speed camera was placed in a light-tight housing and dual-layer neutron shield. HS-SCS is synchronized with a synchrocyclotron to capture individual proton-beam-pulses (PBPs) at ∼504 frames/sec. The PBPs from synchrocyclotron trigger the HS-SCS to open its shutter for programmed exposure-time. Light emissions within 30×30×5cm3 plastic-scintillator (BC-408) were captured by a CCD-camera as individual images revealing dose-deposition in a 2D-plane with a resolution of 0.7mm for range and SOBP measurements and 1.67mm for profiles. The CCD response as well as signal to noise ratio (SNR) was characterized for varying exposure times, gains for different light intensities using a TV-Optoliner system. Software tools were developed to analyze ∼5000 images to extract different beam parameters. Quenching correction-factors were established by comparing scintillation Bragg-Peaks with water scanned ionization-chamber measurements. Quenching corrected Bragg-peaks were integrated to ascertain proton-beam range (PBR), width of Spared-Out-Bragg-Peak (MOD) and distal

Estimating groundwater recharge based on mass balance evaluation of unsaturated zone in a coastal catchment characterized by tropical rainforest weather conditions

Estimation of recharge is necessary for evaluating water resources in the north Kelantan catchment of Malaysia due to rapid development and consequently over-drafting of available groundwater. In order to determine the amount of recharge, a study of natural salts (i.e., chloride and sulfate) was conducted to estimate groundwater recharge rates. Studies of the chloride mass balance (CMB) and sulfate mass balance (SMB) were carried out in the unsaturated zone under rainforest weather conditions with a relatively shallow groundwater table. Ten soil profiles in different parts of the catchment representing a range of soil textures were selected for the study. The CMB results showed that the mean recharge rate is 527.87 mm/year. The highest and lowest calculated recharge rates in the study area were 8 and 31 % of local rainfall. Times required to accumulate chloride/sulfate beneath the natural ecosystem highly depend on profile texture and the CMB age is maximized at KP94 and KT121 sites to be 15.01 and 14.15 years, respectively. The SMB method produced lower recharge rates than those based on chloride, yielding an average of 364.60 mm/year, with values ranging between 7 and 26 % of local rainfall and the SMB age is 21.01 years at KP94 site. Mobilization decreases with fine texture and low permeability and increases with coarse texture and high permeability. In this way, low permeability of surface geology not only controls the recharge rate but also causes high buffering in holding salts. Nevertheless, higher sulfate concentration in profile may be due to different dissolution or sorption processes which are required to be studied thoroughly. Based on two types of scenarios representing natural water movement in unsaturated zone using HYDRUS-1D, recharge rates were simulated to be 419 mm in profile with overlain fine texture soil and 636 mm in profile characterizing with single coarse texture for a total time of 213 days. Our study suggests the feasibility of using the mass balance methods in tropical rainforest weather conditions. The information may improve the accuracy of prediction of possible groundwater pollution and groundwater management in the future.