Predictive Formula for Electron Penetration Depth of Diverse Materials over Large Energy Ranges

An empirical model that predicts the approximate electron penetration depth—or range—of some common materials has been extended to predict the range for a broad assortment of other materials. The electron range of a material is the maximum distance electrons can travel through a material, before losing all of their incident kinetic energy. The original model used the Continuous Slow Down Approximation (CSDA) for energy deposition in a material to develop a composite analytical formula which estimated the range from10 MeV with an uncertainty of200 materials which have tabulated range and inelastic mean free path data in the NIST ESTAR and IMFP databases. Correlations of with key material constants (e.g., density, atomic number, atomic weight, and band gap) were established for this large set of materials. Somewhat different correlations were found for different sub-classes of materials (e.g., solids/liquids/gases, conductors/semi-conductors/insulators, elements/compounds/polymers/ composites). A predictive formula was developed to accurately determine for arbitrary materials

Predictive Formula for Electron Range over a Large Span of Energies

An empirical model developed by the Materials Research Group that predicts the approximate electron penetration depth—or range—of some common materials has been extended to predict the range for a broad assortment of other materials. The electron range of a material is the maximum distance electrons can travel through a material, before losing all of their incident kinetic energy. The original model used the Continuous-Slow-Down-Approximation for energy deposition in a material to develop a composite analytical formula which estimated the range from 10 MeV with an uncertainty of v, which describes the effective number of valence electrons. NV was empirically calculated for \u3e200 materials which have tabulated range and inelastic mean free path data in the NIST ESTAR and IMFP databases. Correlations of NV with key material constants (e.g., density, atomic number, atomic weight, and band gap) were established for this large set of materials. Somewhat different correlations were found for different sub-classes of materials (e.g., solids/liquids/gases, conductors/semiconductors/insulators, elements/compounds/polymers/composites). Values of the average energy lost per inelastic collision were related to band gap and plasmon energies for solids and first excitation energies for liquids and gases. Simulations were performed to test the sensitivity of NV and the range to materials parameters; these suggest that reasonably accurate results were achievable with modest precision of the parameters. These correlations have led to methods using only basic material properties to predict Nv and the range for additional untested materials which have no supporting range data. Estimates for both simple compounds (e.g., BN and AlN), composites, and complex biological materials (e.g., brain tissue and cortical bone tissue) are presented, along with tests of the validity and accuracy of the predictive formula. These calculations are of great value for studies involving high energy electron bombardment, such as electron spectroscopy, spacecraft charging, or electron beam therapy. Efforts are underway to create a user tool available to the scientific community to estimate the range of an arbitrary material with modest accuracy over an extended width of incident electron energies. *Supported through funding from NASA Goddard Space Flight Center and a USU URCO Fellowship

Of Mice and Materials: Payoffs of UNSGC Research Infrastructure Awards

A versatile test facility has been designed and built to study space environments effects on small satellites and system components. Testing for potentially environmental-induced modifications of small satellites is critical to avoid possible deleterious or catastrophic effects over the duration of space mission. This is increasingly more important as small satellite programs have longer mission lifetimes, expand to more harsh environments (such as polar or geosynchronous orbits), make more diverse and sensitive measurements, minimize shielding to reduce mass, and utilize more compact and sensitive electronics (often including untested off-the-shelf components). The vacuum chamber described here is particularly well suited for cost-effective, long-duration tests of modifications due to exposure to simulated space environment conditions for CubeSats, system components, and small scale materials samples of \u3e10 cm X 10 cm. The facility simulates critical environmental components including the neutral gas atmosphere, the FUV/UVMS/NIR solar spectrum, electron plasma fluxes, and temperature. The solar spectrum (-120 nm to 2500 nm) is simulated using an Solar Simulator and Kr resonance lamps at up to four Suns intensity. Low and intermediate electron flood guns and a Sr90 β radiation source provide uniform, stable, electron flux (~ 20 eV to 2.5 MeV) over the CubeSat surface at \u3e5X intensities of the geosynchronous spectrum. Stable temperatures from 100 K to 450 K are possible. An automated data acquisition system periodically monitors and records the environmental conditions, sample photographs, UVMS/NIR reflectivity, IR absorptivity/emissivity, and surface voltage over the CubeSat face and in situ calibration standards during the sample exposure cycle

Electron Penetration Range for Diverse Materials

The penetration range of energetic electrons into diverse materials can be modeled approximately with a simple fit. This fit is a function of a single parameter, Nv, which describes the effective number of valence electrons. Using the Continuous-Slow-Down-Approximation (CSDA) for energy deposition in a material, a composite analytical formula has been developed which estimates the range or maximum penetration depth of incident electrons for energies from10 MeV with an uncertainty o

Aperture effects on Star Formation Rate, Metallicity and Reddening

(Abridged) We use 101 galaxies selected from the Nearby Field Galaxy Survey (NFGS) to investigate the effect of aperture size on the star formation rate, metallicity and reddening determinations for galaxies. We compare the star formation rate, metallicity and reddening derived from nuclear spectra to those derived from integrated spectra. For apertures capturing <20% of the B(26) light, the differences between nuclear and global metallicity, extinction and star formation rate are substantial. We calculate an `expected' star formation rate using our nuclear spectra and apply the commonly-used aperture correction method. The expected star formation rate overestimates the global value for early type spirals, with large scatter for all Hubble types, particularly late types. The differences between the expected and global star formation rates probably result from the assumption that the distributions of the emission-line gas and the continuum are identical. We discuss the implications of these results for metallicity-luminosity relations and star formation history studies based on fiber spectra. To reduce systematic and random errors from aperture effects, we recommend selecting samples with fibers that capture >20% of the galaxy light. For the Sloan Digital Sky Survey and the 2dFGRS, redshifts z>0.04 and z>0.06 are required, respectively, to ensure a covering fraction >20% for galaxies similar to the average size, type, and luminosity observed in our sample. Higher luminosity samples and samples containing many late-type galaxies require a larger minimum redshift to ensure that >20% of the galaxy light is enclosed by the fiber.Comment: 19 pages, 11 figures, 5 tables. Accepted for publication in the PAS

Electron Penetration Range for Diverse Materials

The penetration range of energetic electrons into diverse materials can be modeled approximately with a simple fit. This fit is a function of a single parameter, Nv, which describes the effective number of valence electrons. Using the Continuous-Slow-Down-Approximation (CSDA) for energy deposition in a material, a composite analytic formula has been developed which estimates the range or maximum penetration depth of incident electrons for energies from \u3c10 eV to \u3e10 MeV with an uncertainty of \u3c20%. The fit also incorporates several common properties compiled for each material, including the mean atomic number, mean atomic weight, density, and band gap or Plasmon energy. The model has been fit to existing data for 247 materials collected from the ESTAR and IMFP databases compiled by NIST to determine Nv values. Comparison of Nv with the material\u27s properties from this large material database may lead to the prediction of Nv for materials which have no supporting data. These calculations are of great value for studies of high energy electron bombardment, such as electron spectroscopy, radiation damage or spacecraft charging. This research may also be applied in the medical field to uncharacterized complex biological materials, thereby improving physical selectivity in radiation therapy

Electron Penetration Range for Every Body

The penetration range of an electron into diverse materials can be estimated using an approximation fit as a function of a single parameter, N y, which describes the effective number of valence electrons. This fit is found using the Continuous-Slow Down-Approximation (CSDA), which simplifies the process of estimating an expected penetration range of a given material by applying some of the material’s key characteristics. Using the CSDA, a simple composite analytical formula is created which estimates the range or maximum penetration depth of incident electrons. This formula generates an approximation to the range using the parameter, Nv . The range of well-fit electrons encompasses energies from \u3c10 eV to \u3e10MeV with an accuracy of 20%. A list comprised of 247 materials has been compiled that greatly extends the applicability of this model. Several significant material constants were compiled for each material, including the atomic number, atomic weight, atomic density, and band gap. These materials were further separated into various subcategories including conductors, semiconductors, and insulators, and the material’s phase at room temperature. To determine Nv , the model was then fit to existing data for these materials collected from the ESTAR and IMFP databases compiled by NIST. Comparison of Nv with the material’s constants from this large database of materials will made. The resulting formula could possibly lead to the prediction of Nv for materials which have no supporting data. These calculations are of great value for studies of high electron bombardment, such as electron spectroscopy or spacecraft charging. This research may also be applied in the medical field, for instance, improving physical selectivity in radiation therapy

Small Satellite Space Environments Effects Test Facility

A versatile test facility has been designed and built to study space environments effects on small satellites and system components. Testing for potentially environmental-induced modifications of small satellites is critical to avoid possible deleterious or catastrophic effects over the duration of space mission. This is increasingly more important as small satellite programs have longer mission lifetimes, expand to more harsh environments (such as polar or geosynchronous orbits), make more diverse and sensitive measurements, minimize shielding to reduce mass, and utilize more compact and sensitive electronics (often including untested off-the-shelf components). The vacuum chamber described here is particularly well suited for cost-effective, long-duration tests of modifications due to exposure to simulated space environment conditions for CubeSats, system components, and small scale materials samples of \u3e10 cm X 10 cm. The facility simulates critical environmental components including the neutral gas atmosphere, the FUV/UV/VIS/NIR solar spectrum, electron plasma fluxes, and temperature. The solar spectrum (~120 nm to 2500 nm) is simulated using an Solar Simulator and Kr resonance lamps at up to four Suns intensity. Low and intermediate electron flood guns and a Sr90 β radiation source provide uniform, stable, electron flux (~20 eV to 2.5 MeV) over the CubeSat surface at \u3e5X intensities of the geosynchronous spectrum. Stable temperatures from 100 K to 450 K are possible. An automated data acquisition system periodically monitors and records the environmental conditions, sample photographs, UV/VIS/NIR reflectivity, IR absorptivity/emissivity, and surface voltage over the CubeSat face and in situ calibration standards during the sample exposure cycle