Preliminary study on the effect of cosmic-ray induced neutrons on DRAM at aircraft’s altitude using MCNP simulation

Abstract

The Galactic Cosmic Rays (GCRs) interacts with the atmosphere to produce the secondary particles (e.g., neutrons, alpha particles, heavier nuclei, muons, and pions). These secondary particles can interact with semiconductor devices that frequently transported via an aircraft and may affect their performance. Considering the stopping power of all the particles, the impact of neutrons on these devices is significant as compared to others. This effect can minimized by enclosing the devices inside a radiation shielding material. In this thesis, the entire scenario is simulated using Monte-Carlo N-Particle (MCNP6) transport code. The geometry is modelled in such a way that cosmic rays source is simulated at a height of 65 km and a shielding box is placed inside the aircraft. Various kinds of shielding materials i.e., normal polyethylene, borated lead-polyethylene, 30% borated polyethylene, and Bismuth loaded polyethylene have been considered to reduce the neutron fluence inside the shielded box where semi-conductor devices are supposed to be placed. The results show that the normal polyethylene is the most effective shielding material against neutrons. As it has the finest neutron moderation properties considering hydrogen to carbon ratio being around 66.67% to 33.33% by atom fraction. Furthermore, these neutrons after passing through the packaging box may collide with the DRAM devices and deposit energy on DRAM’s material i.e. silicon. Due to Energy deposition by Heavy charged Particle and emission of e-hole pairs, DRAM devices show up failure. These failures are of two kinds, soft errors and hard errors, depending on the location of the strike on the DRAM devices. Quantifying the e-hole pairs in the silicon substrate by the neutron spectrum inside the packaging box can lead to account for failure in DRAM devices.