For those needing portability, Rad Pro for Desktop works with Windows 8.1 tablets (just tested). Will not work with Surface tablets running Windows RT.
  
g U-234/g Total U Mass Fraction U-234 g U-235/g Sample Mass (Solid Matrix) U-235 g U-235/g Total U Mass Fraction U-235   g U-238/g Sample Mass (Solid Matrix) U-238   g U-234/g Sample Mass (Solid Matrix) U-234 Activity/Activity Ratios (Calculated from top panel entries.) g U-238/g Total U Mass Fraction U-238 Enrichment Uncertainty Range If Liquid, Enter Density g Total U/g Sample Mass (Solid Matrix) Total U ppm PPM of Total U in Solid Matrix   Mass/Mass Fractions (calculated from top panel entries.)   g/cc   Ci U-234 / Ci U-238 Sample Uranium Specific Activity    +/-Enter U-234 Activity+/-Enter U-238 ActivityU-235 Mass % EnrichmentCalculated Enrichment Select Activity Units Uranium Enrichment Calculations pCi/g Enter U-234 Uncertainty pCi/g Enter U-238 Uncertainty % Enrichment to Ci U-234/g U-234 Theoretical Specific Activity U-234 Ci U-235/g U-235 Theoretical Specific Activity U-235 Ci U-238/g U-238~~~~ You may enter your own values. Theoretical Specific Activity U-238 pCi U-234/g Sample Activity (Solid Matrix) U-234 pCi U-235/g Sample Activity (Solid Matrix) U-235 pCi U-238/g Sample Activity (Solid Matrix) U-238 pCi Total U/g Sample Activity (Solid Matrix) Total U Ci U/g U Activity Ratio U-234/U-238 Ci U-235 / Ci U-238 Activity Ratio U-235/U-238   
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Note: These formulas ignore the small presence of U-236 from recycled uranium.
Most of the time, samples with low levels of uranium such as soil or water return MDA values on U-235 and detectable values of U-234 and U-238 when sent to the laboratory for analysis. Since uranium enrichment is defined as the mass percent of U-235 in total uranium, a straight out percentage calculation cannot be performed from laboratory data. This calculator was developed for the purpose of calculating enrichment from U-234 and U-238 data. Specific activity formulas were developed from empirical data collected from US gaseous diffusion plants and other sources. The lab data ratios are compared to the formula ratios. Since enrichment always ends up on both sides of the equation, creative computer algorithms had to be developed to calculate enrichment. Additional useful calculations are performed for you such as mass and activity ratios, ppm, etc. This calculator is useful for proving that uranium found in soil and water samples are all naturally occurring as well as other situations. If enriched or depleted uranium were present, the enrichment would be higher or lower than normally found in soil and water. To see and read more about the formulas, read the white paper on this site available by clicking the "Documents/U Enrichment" button.