Insoo Jun

Proton nonionizing energy loss (NIEL) for device applications

The proton-induced nonionizing energy loss (NIEL) for representative device materials are presented for the energy range between the displacement damage threshold to 1 GeV. All interaction mechanisms (Coulomb and nuclear elastic/nonelastic) are fully accounted for in the present NIEL calculations. For Coulomb interactions, the Ziegler-Biersack-Littmark (ZBL) screened potential was used in the lower energy range (<50 MeV) and the relativistic formulation was used in the higher energy range (/spl ges/50 MeV). A charged particle transport code, MCNPX, was used to compute the NIEL due to nuclear interactions.

NIEL for heavy ions: an analytical approach

We describe an analytical model for calculating nonionizing energy loss (NIEL) for heavy ions based on screened Coulomb potentials in the nonrelativistic limit. The model applies to any incident ion on any target material where the Coulomb interaction is primarily responsible for atomic displacement. Results are compared with previous methods of extracting NIEL from Monte Carlo SRIM runs. Examples of NIEL calculations are given for incident ions having energies ranging from the threshold for atomic displacement to 1 GeV. The incident ions include H, He, B, Si, Fe, Xe, and Au. Example targets include Si, GaAs, InP, and SiC.

Effects of secondary particles on the total dose and the displacement damage in space proton environments

MCNPX, a powerful Monte Carlo charged particle transport code, is introduced in this paper for space-radiation effect applications. By using MCNPX version 2.1.5, the enhancement of the total dose and the displacement damage due to secondary particles generated by the protons in the typical space radiation environments was assessed, then the results were compared to those obtained by the continuous slowing down approximation (CSDA) method. The comparison showed that the effects of the secondary particles were up to +7% for the total dose and up to +25% for the displacement damage when compared to the respective CSDA results in heavy shielding applications where trapped and solar protons dominate. Also presented in this paper is a method to compute the neutron/proton displacement cross sections by using MCNPX. The cross sections obtained show an excellent agreement with previously published values.

Electron Nonionizing Energy Loss for Device Applications

The electron induced nonionizing energy loss (NIEL) for representative device and detector materials are presented here. The electron NIELs are computed analytically using the Mott differential cross section. As for the partition function, which describes the portion of energy deposited into displacing lattice atoms, the expression recently developed by Akkerman was used that better fits for the low recoil energy.

Proton energy dependence of the light output in gallium nitride light-emitting diodes

Gallium nitride (GaN)-based blue-emitting diodes (CREE Model C430-DH85) were irradiated at room temperature with protons in the energy range 2 to 115 MeV at fluences varying from 1/spl times/10/sup 11/ to 1/spl times/10/sup 15/ cm/sup -2/. Light output degradation curves were obtained for each energy and the damage constant (A) associated with these curves was determined according to the theory of Rose and Barnes. For proton energies less than 10 MeV, A varies inversely with the proton energy (E). At higher energies, A is consistently above the 1/E relationship. The change in nature of the energy dependence is attributed to nuclear interactions. Nonionizing energy loss calculations for the case of protons on GaN are presented. Good agreement between theory and experiment is obtained.

Monte Carlo simulations of the Galileo energetic particle detector

Abstract Monte Carlo radiation transport studies have been performed for the Galileo spacecraft energetic particle detector (EPD) in order to study its response to energetic electrons and protons. Three-dimensional Monte Carlo radiation transport codes, MCNP version 4B (for electrons) and MCNPX version 2.2.3 (for protons), were used throughout the study. The results are presented in the form of “geometric factors” for the high-energy channels studied in this paper: B1, DC2, and DC3 for electrons and B0, DC0, and DC1 for protons. The geometric factor is the energy-dependent detector response function that relates the incident particle fluxes to instrument count rates. The trend of actual data measured by the EPD was successfully reproduced using the geometric factors obtained in this study.

Water and chlorine content in the Martian soil along the first 1900 m of the Curiosity rover traverse as estimated by the DAN instrument

The presence of hydrated phases in the soil and near-surface bedrock of Gale Crater is thought to be direct evidence for water-rock interaction in the crater in the ancient past. Layered sediments over the Gale Crater floor are thought to have formed in past epochs due to sediment transport, accumulation, and cementation through interaction with fluids, and the observed strata of water-bearing minerals record the history of these episodes. The first data analysis of the Dynamic Albedo of Neutrons (DAN) investigation on board the Curiosity rover is presented for 154 individual points of active mode measurements along 1900 m of the traverse over the first 361 Martian solar days in Gale crater. It is found that a model of constant water content within subsurface should be rejected for practically all tested points, whereas a two-layer model with different water contents in each layer is supported by the data. A so-called direct two-layer model (water content increasing with depth) yields acceptable fits for odometry ranges between 0 and 455 m and beyond 638 m. The mean water (H2O) abundances of the top and bottom layers vary from 1.5 to 1.7 wt % and from 2.2 to 3.3 wt %, respectively, while at some tested spots the water content is estimated to be as high as ~5 wt %. The data for odometry range 455–638 m support an inverse two-layer model (water content decreasing with depth), with an estimated mean water abundance of 2.1 ± 0.1 wt % and 1.4 ± 0.04 wt % in the top and bottom layers, respectively.

Review of an Internal Charging Code, NUMIT

An internal charging code, which is called NUMerical InTegration, has been used on many occasions to study the charging and discharging characteristics of dielectrics in space. The capabilities and limitations of the code are reviewed in this paper. In particular, the basic assumptions of the model are briefly discussed, and an example for the internal charging in the Juno environment is presented.

Diagenetic silica enrichment and late‐stage groundwater activity in Gale crater, Mars

Diagenetic silica enrichment in fracture-associated halos that crosscut lacustrine and unconformably overlying aeolian sedimentary bedrock is observed on the lower north slope of Aeolis Mons in Gale crater, Mars. The diagenetic silica enrichment is colocated with detrital silica enrichment observed in the lacustrine bedrock yet extends into a considerably younger, unconformably draping aeolian sandstone, implying that diagenetic silica enrichment postdates the detrital silica enrichment. A causal connection between the detrital and diagenetic silica enrichment implies that water was present in the subsurface of Gale crater long after deposition of the lacustrine sediments and that it mobilized detrital amorphous silica and precipitated it along fractures in the overlying bedrock. Although absolute timing is uncertain, the observed diagenesis likely represents some of the most recent groundwater activity in Gale crater and suggests that the timescale of potential habitability extended considerably beyond the time that the lacustrine sediments of Aeolis Mons were deposited.

High-energy trapped particle environments at Jupiter: an update

The particle data measured by the energetic particle detector (EPD) and heavy ion counter (HIC) on board Galileo were used to update the radiation environments at Jupiter: EPD data for trapped electrons and HIC data for trapped carbon, oxygen, and sulfur ions. The models developed in this study were successfully used to generate the total dose and single event effect environments for a sample mission to Europa.