Li Junli

Force collision and next event estimation of pulse height tallies

Pulse height cannot be easily tallied with commonly used analog transport methods when the recording cells are much smaller than the whole particle transport system. This paper presents a new trasport scheme and applies it to a simple modeling problem of an industrial CT. The results show that for an important class of problems, FC-NEE is much more efficient than geometry splitting with Russian roulette, DXTRAN or conventional analog transport methods. The new method has been tested on an MCNP benchmark.

Adjustment of chest wall thickness of voxel phantom for numerical efficiency calibration of lung counters

A modification method was implemented to adjust the chest wall thickness of human voxel phantom for the purpose of numerical efficiency calibration of lung counters. This method was based on two basic mathematical morphology operations (dilation and erosion) and combined with proper structure elements. The voxel model of LLNL torso phantom was used as a reference to validate the modification process. The chest wall was mathematically modified from the starting phantom with no overlay plate to the target with an overlay plate of 24-mm thickness. The influences of different structure elements on detection efficiency were discussed. When diamond or square structure elements were used, the calculated efficiency was overestimated or underestimated by ∼40 % for 17.5-keV photons, compared with that of target phantom. In contrast, it was shown a good agreement with a deviation of <3 % when the hybrid structure elements were adopted. A similar adjustment method can be used for 3D modification of human voxel phantom to keep the bodys anatomical geometry without distortion during the adjustment process.

Probabilistic Safety Analysis about the Radiation Risk for the Driver in a Fast-Scan Container/Vehicle Inspection System

A new Container/Vehicle Inspection System called fast-scan inspection system has been developed and used in some countries, which has a special advantage in scanning efficiency of 200~00 containers per hour. However, for its unique scanning mode, the fast-scan inspection system causes some worries about the radiation risk for the truck drivers, who will drive the container truck to pass through the scanning tunnel and might be exposed by the radiation beam in accidents. A PSA analysis, which has been widely used to evaluate the safety of nuclear power plant in the past, is presented here to estimate the probability of accidental exposure to the driver and evaluate the health risk. The fault tree and event tree analysis show that the probability of accidental exposure to the driver is pretty low and the main failure contributions are human errors and scanning control devices failures, which provides some recommendations for the further improvement about this product. Furthermore, on the basic of ICRP No.60 and 76 reports, the health risk to the truck driver is only about 4.0×10-14/a. Compared with the exempt level of 5×10-7/a, it can be concluded that the fast-scan system is safe enough for the truck driver.