Improvement of energy resolution in time-of-flight method for high energy neutron measurement

In the time-of-flight measurement of high energy neutrons, the time resolution is often required to be as good as possible. For improvement of the energy resolution, the time-of-flight study was made by the use of Li (p, n) reaction at forward angles. Two types of detectors were tested. One was a liquid organic scintillator NE-213 5 inches (127 mm) in diameter and 127 mm thick connected with three Hamamatsu H2431 photomultipliers 2 inches (51 mm) in diameter. The other was NE-213 of the same size with a Hamamatsu R1250 127 mm in diameter. The experiment was made at pi2 beam line of 12 GeV proton synchrotron in High Energy Accelerator Research Organization (KEK). The incident proton energy was 800 MeV, and the flight path was 5 m. Two neutron detectors were set at 0 and 5 degrees, respectively. The time resolutions for prompt gamma rays were 0.5 ns for NE-213 with three H2431s and 1.0 ns for NE-213 with R1250. The energy resolutions for 800 MeV neutrons were derived from these values were 70 and 100 MeV, respectively. 12 Refs

A fixation guide for the accurate insertion of fibular segments in mandibular reconstruction

Background: Computer-aided design and computer-assisted manufacturing (CAD/CAM) of cutting guides are now being used in mandibular reconstruction with fibular bone flaps. Improvements in guide design and accuracy are needed to increase the benefits to patients. Cutting guides have become popular, but fixation guides are rarely considered. Materials and methods: The aim of this study was to determine whether using a fixation guide would contribute to better accuracy in mandibular reconstruction. Mandibular segmental osteotomies and fibular reconstructions were performed using model surgery. Models were divided into two groups: without or with a fixation guide (n = 13 for each group). After reconstruction, the distances between reference points such as the condylion laterale (Cl), gonion, and mental tubercle (T) were measured and compared with those of the preoperative virtual plan. Deviations in final positions between the two groups were analyzed. Results: The mean deviations were 2.61 mm (range 0.05–7.65 mm) and 2.05 mm (range 0.07–8.52 mm) in the groups without and with a fixation guide, respectively. The overall results were significantly better when a fixation guide was used (p = 0.03). Distances including the Cl reference points such as ClCl (p = 0.02) and Cl–T (p = 0.001) were particularly improved. Conclusions: Using a fixation guide together with a cutting guide makes mandibular reconstruction more accurate, particularly for positioning the Cl reference points. Therefore, when a CAD/CAM-produced cutting guide is used in preparation for surgery, it is recommended to use a fixation guide as well for more accuracy