CALCIUM MOLYBDATE, CAMOO4: A PROMISING TARGET MATERIAL FOR 99MTC AND ITS POTENTIAL APPLICATIONS IN NUCLEAR MEDICINE AND NUCLEAR WASTE DISPOSITIONтезисы доклада
Дата последнего поиска статьи во внешних источниках: 3 июля 2019 г.
Аннотация:Calcium molybdate (CaMoO4) is a robust, inorganic material known for its favorable
physicochemical properties making it ideal for a wide scope of applications including optics (i.e.,
phosphors, scintillators, laser hosts, etc.) [1], nuclear waste encapsulation and disposal [2 – 5],
corrosion inhibition [6], etc. Calcium molybdate occurs in nature as the mineral powellite, and the
compound adopts the scheelite (CaWO4) structure-type with Mo fully oxidized in the +6-oxidation
state [7]. This Mo-containing mineral phase exhibits limited solubility in aqueous environments
and relative thermal stability at elevated temperatures. In the laboratory, CaMoO4 can be
synthesized straightforwardly from the stoichiometric solid-state reaction of MoO3 with the
respective calcium oxide or carbonate, e.g., CaO or CaCO3, at elevated temperatures, or
alternatively via co-precipitation, sol-gel, or mechanochemical methods [8 - 10]. Depending on
synthetic conditions, single phase nano-powders to monoliths can be generated and tailored for its
successive application. Likewise, the scheelite structure type can incorporate different doping
elements into the host lattice, such as Pb2+ or elements arising from the lanthanoid series, which
are used for phosphor applications [11-13].
On the periodic table, Mo (Z = 42) is located on the 5th row within the transition metals and
precedes the lightest, inherently radioactive element, technetium (Tc, Z = 43) [14]. Molybdenum
is characterized by an assortment of naturally occurring isotopes (i.e., 92Mo 14.53%, 94Mo 9.16%,
95Mo 15.84%, 96Mo 16.67%, 97Mo 9.60%, 98Mo 24.39%, and 100Mo 9.82%) making it a suitable
starting material for the transmutation to an array of different Tc isotopes depending on isotope
enrichment, particle beam type (e.g., proton, deuteron, electron, neutron, photon, etc.), and beam
energy. One of the most recognized Mo-Tc radionuclidic parent-daughter couples is 99Mo-99mTc,
where the daughter isotope 99mTc has been characterized as the workhorse of the nuclear diagnostic
imaging industry used worldwide in 30 to 40 million procedures annually, i.e., ~ 9,000 6-day Ci
at end of processing (EOP) per week [15]. As the international geopolitical attitude towards using
highly enriched uranium (HEU) for the production of 99Mo begins to shift, the use of non-fission
sources for the production of 99mTc is becoming increasingly more attractive, and new methods
for production and separation are desperately being sought. For example, the United States of
America currently has no domestic supply in place for the production of 99mTc, although it is
responsible for half of the world’s usage.
When considering both, the isotopic and physicochemical composition and properties of
Mo and CaMoO4, strong arguments can be made to pursue the better understanding of CaMoO4
and its relationship as a host material for direct transmutation of Mo → Tc and / or post-processing
integration of Tc at the atomistic level to weight percentages in its fundamental structure. In this
work, the synthesis and irradiation of CaMoO4 using a modular, fusion-based neutron source andits successive characterizations are reported. Further discussions are presented considering these
empirical data and their context with potential applications in the realms of nuclear medicine and
materials.
