Heavy-ion production of 77Br and 76Br

Abstract

Many radioisotopes with potential medical applications are difficult to produce routinely, especially those on the proton-rich side of the valley of stability. Current production methods typically use light-ion (protons or deuteron) reactions on materials of similar mass to the target radioisotope, which limits the elemental target material available and may require the use of targets with poor thermal properties (as is the case for the production of radiobromine). These reactions may also create significant amounts of proton-rich decay products which require chemical separation from the desired product in a highly radioactive environment. A promising alternative method using heavy-ion fusion-evaporation reactions for the production of the medically relevant bromine radioisotopes 76Br (t1/2 = 16.2 h) and 77Br (t1/2 = 57.0 h) is presented. Heavy-ion beams of 28Si and 16O were used to bombard natural chromium and copper targets just above the Coulomb barrier at the University of Notre Dame's Nuclear Science Laboratory to produce these bromine and precursor radioisotopes by fusion-evaporation reactions. Production yields for these reactions were measured and compared to PACE4 calculations. In addition to using more robust targets for irradiation, a simple physical–chemical separation method is proposed that will lead to very high radiopurity yields. A summary of accelerator facility requirements needed for routine production of these radioisotopes is also presented.

Radiochemistry: A Hot Field with Opportunities for Cool Chemistry

“…The diagnostic and therapeutic versions of the same radiopharmaceutical are chemically indistinguishable and thus have identical pharmacological properties. 38 This provides a significant advantage when designing, producing, evaluating, and approving novel theranostic compounds for clinical use. While the development of labeling methodologies specific to radiobromine has not received the attention afforded to the other radiohalogens, bromine chemistry is generally versatile and well-understood.…”

“…Positron emitting bromine-76 ( β + , t 1/2 = 16.2 h) and the auger electron emitter bromine-77 ( Auger e – , t 1/2 = 57 h) are well-suited as a “true theranostic pair” for the isotopic radiolabeling of small molecules against intracellular targets. The diagnostic and therapeutic versions of the same radiopharmaceutical are chemically indistinguishable and thus have identical pharmacological properties . This provides a significant advantage when designing, producing, evaluating, and approving novel theranostic compounds for clinical use.…”

“…Both radionuclides are typically produced from selenium targets via the 76/77 Se­(p,n) 76/77 Br nuclear reactions; however, the target physics and isotope isolation procedures (via thermal chromatographic distillation) pose significant challenges that limit production capacity. Selenium has poor electrical and thermal conductivity and high volatility, making it intolerant to even low-intensity proton bombardment . As such, it must be stabilized as an intermetallic alloy using other metals such as copper, nickel, zinc, or cobalt .…”

“…The number of sites capable of producing 76 Br and 77 Br is, therefore, currently limited; however, both isotopes have sufficiently long half-lives that allow them to be shipped moderate distances from centralized production sites. Higher-yielding production strategies have been proposed using heavy ion bombardment techniques, but the number of cyclotrons capable of performing these nuclear reactions is even more limited . Therefore, the development of new cyclotron targetry techniques and radionuclide isolation protocols to produce 76 Br and 77 Br are being actively investigated to meet the increasing preclinical and clinical demand .…”

Heavy-Ion Fusion Reaction Calculations: Establishing the Theoretical Frameworks for 111In Radionuclide over the Coupled Channel Model

“…These heavy-ion reactions also offer the possibility to produce excited nuclei. With the emergence of heavy-ion reactions, nuclear physics has taken on a new dimension [8][9][10]. To understand the inner structure and nuclear properties of the nucleus, many types of research have been, and continue to be, carried out in this field [11][12][13][14][15].…”