Date of Award

8-2014

Degree Type

Thesis

Degree Name

Master of Science

Major

Nuclear Engineering

Major Professor

Lawrence H. Heilbronn

Committee Members

Howard L. Hall, Laurence F. Miller

Abstract

Actinium-225 is one of the more effective radioisotopes used in alpha radioimmunotherapy. Due to its ten-day half-life, it is more efficient to create its precursor, 229Th [Thorium-229] (t1/2[half-life] = 7932 ± 55 years). In this work, 229Th was produced via 40 MeV [Mega electron Volts] proton bombardment of a thick 232Th [Thorium-232] target. The irradiation took place at the Holifield Radioactive Ion Beam Facility (HRIBF) at Oak Ridge National Lab (ORNL). The target, consisting of 23 stacked natural thorium foils (137 mg/cm2 [milligrams per square centimeter] each), was irradiated with 50 nA [nanoamps] of protons from HRIBF’s 25 MV [Mega Volt] tandem electrostatic accelerator for approximately 143 discontinuous hours. After 215 days post bombardment, allowing for the decay of short-lived protactinium and actinium isotopes and fission products, the target was chemically purified by a series of ion chromatography techniques. Thorium-229 was measured directly by γ-ray [gamma-ray] spectroscopy immediately after separation of the thorium fraction from the decay daughters of 228Th [Thorium-228] (t1/2 = 1.9 years) and long long-lived fission products. The effective thick target cross section of 229Th is 205 ± 18 mb [millibarns] at a proton energy of 26.1 MeV. Variation of the effective cross-section as a function of proton energy is also reported.

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