"Alpha decay 2" joule = kilogram meter^2 / second^2 kilogram = "kilogram" meter = "meter" second = "second" alpha = 7.2973525643 10^(-3) c = 299792458.0 meter / second h = 6.62607015 10^(-34) joule second hbar = h / float(2 pi) -- mass of alpha particle m = 6.6446573450 * 10^(-27) kilogram C1 = sqrt(2 m) float(pi) alpha c C2 = 4 sqrt(m alpha c / hbar) M1 = 238.0507876 -- U238 M2 = 234.0435998 -- Th234 M3 = 4.002603254 -- helium (electron masses cancel) -- energy of alpha particle in MeV E = (M1 - M2 - M3) 931.49410372 "MeV" E -- energy of alpha particle in joules u = 1.66053906892 10^(-27) kilogram E = (M1 - M2 - M3) u c^2 -- fermi radius r0 = 1.2 10^(-15) meter A = 238.0 Z = 90.0 r1 = r0 A^(1/3) r1 gamma = C1 Z / sqrt(E) - C2 sqrt(Z r1) tau = 2 log(2.0) / 843 r1 / sqrt(E/m) exp(2 gamma) tau tau = tau / (365.25 24 60 60) "yr" / second tau Run