title: Thorotrast: analysis of the time evolution of its α activity concentration, in the 70 years following the chemical purification of Thorium.
abstract: We simulate the α-activity of the Thorium series elements present in the contrast medium named Thorotrast, used until 1960 and cause of certified deaths until today. Assuming, as active components at t=0, (232)Th and (228)Th in the same relative concentration they have in nature, α-activity oscillates for some decades before reaching a stationary value that in absence of biological depletion would be AST =24000Bq/g. Our Montecarlo code generates the nuclear decays of the Thorium series with and without in-vivo biological depletion, arriving to three kinds of results for the activity: 1) Theoretical activity concentration (no biological depletion). Our result is fitted by: A(t)=A(ST).{[1-exp(-t/10)]+[exp(-t/tB)(1-0.8exp(-t/tA))]}, with t in years, tA=1.07.10(-2) years, and tB=2.38 years. 2) Weak biological depletion (228Ra/232 Th equilibrium activity ratio 0.6, 224Ra/228Ra e.a.r 0.9, 10% excretion for 220Rn). The ratio of the activity concentration to the theoretical activity concentration is fitted by: A weak (t)/A(t)=0.61+0.29 exp[-(t/15)2] (t in years). 3) Strong biological depletion (228Ra/232Th e.a.r 0.4, 224Ra/228Ra e.a.r. 0.8, 10% excretion for 220Rn). The ratio of the activity concentration to the theoretical activity concentration is fitted by A(strong)(t)/A(t)=0.44+0.4 exp[-(t/13)2](t in years). We also report fluctuation calculation for two cases where standard statistical behavior is not expected.
authors: Dipartimento di Ingegneria Informatica dell'Università degli Studi di Brescia, via Branze 6 I-25123 Brescia, Italy. bianconi@bs.infn.it
authors: A
authors: A
authors: Bianconi
authors: M
authors: M
authors: Corradini
authors: M
authors: M
authors: Leali
authors: E
authors: E
authors: Lodi Rizzini
authors: L
authors: L
authors: Venturelli
authors: N
authors: N
authors: Zurlo
mesh_terms: D000512:Alpha Particles; D008962:Models, Theoretical; D011854:Radiochemistry; D013910:Thorium / Q000737:chemistry* / Q000302:isolation & purification; D013911:Thorium Dioxide / Q000737:chemistry; D013997:Time Factors
chemical_list: D013910:Thorium; D013911:Thorium Dioxide
keywords: Analytical fit; Monte Carlo simulation; Thorium series activity; Thorotrast