Measurements of the thermal neutron cross-sections and resonance integrals for 186W (n,γ) 187W and 98Mo (n,γ) 99Mo reactions

Adsorption behavior of Mo(VI) from aqueous solutions using tungstate-modified magnetic nanoparticle

A new magnetic nanoparticle modified with sodium tungstate (Mnp-Si-W) was synthesized and employed for the sorption of molybdenum from aqueous solutions. The prepared nanoparticles (Mnp-Si-W) were characterized by different advanced techniques. Different parameters that influenced the adsorption percent of Mo(VI) were investigated using a batch process. Based on a systematic investigation of the adsorption isotherms and kinetics models, Mo(VI) adsorption follows the Langmuir model and pseudo-second-order kinetics. According to the Langmuir isotherm model, the Mnp-Si-W nanoparticles exhibited a maximum adsorption capacity of 182.03 mg g-1 for Mo(VI) at pH 2.0. The effect of competing ions showed that the prepared nanoparticles have a high selectivity for the sorption of molybdenum. Moreover, the effect of some interfering anions on Mo(VI) ion sorption is found in the following order: phosphate < sulfate < chromate. Finally, the nanoparticle (Mnp-Si-W) can be successfully reused five times.

Measurement of neutron capture cross section of 187W for production of 188W

Tungsten-188 (t_1/2 = 69.4 d) is routinely produced by double neutron capture using highly enriched ¹⁸⁶W target, ¹⁸⁶W(n,γ)¹⁸⁷W(n,γ)¹⁸⁸W reaction, at the ORNL 85 MWt High Flux Isotope Reactor. While the thermal neutron cross section for the first reaction, ¹⁸⁶W(n,γ)¹⁸⁷W, is well known, the single reported 64 b cross-section for the second reaction, ¹⁸⁷W(n,γ)¹⁸⁸W, cannot be validated by experimental results that yield lower than expected activities of ¹⁸⁸W. In this study, we report a new value for the thermal neutron capture cross section of ¹⁸⁷W. After confirming the neutron capture cross section of ¹⁸⁶W (σ⁰ = 37.8 ± 1.8 b for thermal and I⁰ = 476 ± 25 b for resonance integrals with σ⁰/I⁰ = 12.6 ± 0.4) in two short irradiations, longer irradiations (1-10 d) were performed to obtain a value of 6.5 ± 0.8 b for the σ⁰ of ¹⁸⁷W, which is lower than the adopted value by a factor of 10. Due to the short half-life of ¹⁸⁷W (t_1/2 = 23.7 d), the σ⁰ for ¹⁸⁷W was obtained empirically by comparing the ¹⁸⁸W experimental yields with the theoretical yields generated by code IsoChain and varying the ¹⁸⁷W cross section while keeping all other parameters constant.

Calcium molybdate nanoparticles formation in egg phosphatidyl choline based liposome caused by liposome fusion

In order to achieve the highly efficient ^99mTc production from ¹⁰⁰MoO₃ by the ¹⁰⁰Mo(n, 2n)⁹⁹Mo reaction, we have developed a new protocol to synthesize nano-sized Mo particles, of which the size was controlled by the inner space of the liposomes. Calcium and molybdate ions were encapsulated into ∼100 nm size liposomes. The liposome suspensions were then mixed and heated to promote the membrane fusion. As a result, the insoluble CaMoO₄ nanoparticles precipitated inside the liposomes. The median particle diameter of 168 nm and average diameter of 169 ± 56 nm (n = 109) were obtained from an SEM image, and the particles have a powellite-structure. The formation process of the particles was then examined. The formation of nano-sized CaMoO₄ was observed by the high resolution TEM image and TEM image of negative-stained liposome. At the room temperature, the fusion of liposome did not occur significantly. These results suggest that nanocrystals of the CaMoO₄ were likely formed in the liposomes because of the liposome fusion and aggregated during the drying processes of reaction solution.

Neutron capture cross section measurements and theoretical calculation for the 186W(n,γ)187W reaction

Neutron capture cross section (σ 0) and resonance integral (I 0) of the reaction 186W(n,γ)187W were measured experimentally using the research reactor (ETRR-2) and an Am–Be neutron source, also calculated using TALYS-1.6 code. The present results of σ 0 are (39.08±2.6, 38.75±0.98 and 38.33 barn) and I 0 are (418.5±74, 439.3±36 and 445.5 barn) by using the reactor, neutron source and TALYS-1.6, respectively. The present results are in acceptable agreement with most of the previous experimental and evaluated data as well as the theoretical calculations.

Estimation of 99Mo production rates from natural molybdenum in research reactors

Molybdenum-99 is one of the most important radionuclides for medical diagnostics. In 2015, the International Atomic Energy Agency organized a round-robin exercise where the participants measured and calculated specific saturation activities achievable for the ⁹⁸Mo(n,γ)⁹⁹Mo reaction. This reaction is of interest as a means to locally, and on a small scale, produce ⁹⁹Mo from natural molybdenum. The current paper summarises a set of experimental results and reviews the methodology for calculating the corresponding saturation activities. Activation by epithermal neutrons and also epithermal neutron self-shielding are found to be of high importance in this case.