No abstract

Compared to conventional hardware GPS receivers (GPSR), software GPS receivers are more suitable for research and development. Software GPS receivers can be dynamically programmed in software to reconfigure the characteristics of GPS receiver and new algorithms can easily be integrated without changing the design of the hardware. However, the most important issue for this approach is the computational load. It can be solved by using the high performance state-of-art digital signal processor. The harshness of space environment, such as Total Ionizing Dosage (TID), Single Event Effect (SEE), always cast certain thread to GPS receiver intended for space applications. Common resolution to cope with this thread is the robustness of space grade EEE parts toward those effects along with the protection of circuit design. Nevertheless, the most of the state-of-art EEE parts are not space qualified. In this study, certain Commercial Off The Shelf (COTS) parts such as COTS level RF Front-End (RFFE) and Digital SignalProcessor (DSP) along with single event effect (SEE) mitigation circuit design, are considered in the proposed GPSR design for their advantages, such as availability, performance, size, weight and lead time, over regular space qualified ones.

Purpose: A scanning proton beam is a highly desired option in new proton facilities. However, the patient specific brass aperture used to shape the beam is one of the major sources of secondary neutrons, which contribute to whole body dose. Thus, minimizing neutron yield from the aperture is a critical criteria for optimization of scanning parameters. In this study we investigated this neutron yield, and the concurrent generation of the neutrons inside the patient, in a uniform scanning proton beam using Monte Carlo simulation. Materials and Methods: The general purpose Monte Carlo code FLUKA was used to simulate the interaction of a 204.8 MeV uniform scanning beam with brass apertures between 2 and 10 cm in diameter using a 10 cm shout. A water phantom 5 cm from the aperture surface was used to simulate a homogeneous absorbing medium. The neutron fluence, spectrum and dose equivalent in the phantom was acquired for various scanning patterns. Results: Neutrons generated in the brass aperture affect the ambient dose equivalent H*(10) near the surface of the phantom. However, neutrons generated inside the phantom have a dominant contribution to the ambient dose equivalent H*(10) close to isocenter. Their contribution ranges from 50% to 90% to the total neutron H*(10), corresponding to a dose equivalent of 2.5 to 5.5 mSv/Gy for the different apertures used in this study. The H*(10) values 30 cm from the beam axes are one order of magnitude less than at the isocenter. Conclusions: The neutrons produced in the aperture are the major contributor to secondary dose only in the superficial region. However, neutrons generated inside the patient are the most important factor contributing to the total body dose in proton therapy.