Monte-Carlo Simulations of Radiation-Induced Activation in a Fast-Neutron and Gamma- Based Cargo Inspection System

An air cargo inspection system combining two nuclear reaction based techniques, namely Fast-Neutron Resonance Radiography and Dual-Discrete-Energy Gamma Radiography is currently being developed. This system is expected to allow detection of standard and improvised explosives as well as special nuclear materials. An important aspect for the applicability of nuclear techniques in an airport inspection facility is the inventory and lifetimes of radioactive isotopes produced by the neutron and gamma radiation inside the cargo, as well as the dose delivered by these isotopes to people in contact with the cargo during and following the interrogation procedure. Using MCNPX and CINDER90 we have calculated the activation levels for several typical inspection scenarios. One example is the activation of various metal samples embedded in a cotton-filled container. To validate the simulation results, a benchmark experiment was performed, in which metal samples were activated by fast-neutrons in a water-filled glass jar. The induced activity was determined by analyzing the gamma spectra. Based on the calculated radioactive inventory in the container, the dose levels due to the induced gamma radiation were calculated at several distances from the container and in relevant time windows after the irradiation, in order to evaluate the radiation exposure of the cargo handling staff, air crew and passengers during flight. The possibility of remanent long-lived radioactive inventory after cargo is delivered to the client is also of concern and was evaluated.Comment: Proceedings of FNDA 201

Fill factor limitations and non-ideal diode behaviour of Czochralski silicon solar cells due light-induced recombination centres Paper

The light-induced activation of the deep-level recombination centre specific to boron-doped, oxygen contaminated Czochralski (Cz) silicon leads to a shoulder in the current-voltage curve of solar cells fabricated on this material. This effect is demonstrated by means of numerical simulation and measurements on different types of high-efficiency Cz silicon solar cells. The physical reason for the non-ideal diode behaviour, characterised by a local ideality factor greater unity, is the strongly injection-level-dependent bulk lifetime produced by the characteristic recombination centre. The increased ideality factor causes a degradation in fill factor of up to 15% with the magnitude of degradation depending on the doping concentration of the Cz silicon. The optimal base resistivity for high-efficiency solar cells made on boron-doped Cz silicon is shown to be in the vicinity of 3 Wcm. The comparison of current voltage curves measured before and after degradation clearly shows that the reduction in fill factor is not due to device issues (i.e., series resistance, shunt, recombination in the space charge region), but is an inherent property of boron-doped, oxygen-contaminated Cz silicon as it is widely used in the production of solar cells.Available from: http://www.isfh.de/institut/publika/muenchen.htm / FIZ - Fachinformationszzentrum Karlsruhe / TIB - Technische InformationsbibliothekSIGLEDEGerman