Volume 104, Issue 9

Alpha particles exhibit three important characteristics: scattering, ionisation and activation. This article briefly discusses those properties and outlines their major applications. Among others, α -particles are used in elemental analysis, investigation and improvement of materials properties, nuclear reaction studies and medical radionuclide production. The latter two topics, dealing with activation of target materials, are treated in some detail in this paper. Measurements of excitation functions of α -particle induced reactions shed some light on their reaction mechanisms, and studies of isomeric cross sections reveal the probability of population of high-spin nuclear levels. Regarding medical radionuclides, an overview is presented of the isotopes commonly produced using α -particle beams. Consideration is also given to some routes which could be potentially useful for production of a few other radionuclides. The significance of α -particle induced reactions to produce a few high-spin isomeric states, decaying by emission of low-energy conversion or Auger electrons, which are of interest in localized internal radiotherapy, is outlined. The α -particle beam, thus broadens the scope of nuclear chemistry research related to development of non-standard positron emitters and therapeutic radionuclides.

90 Nb has an intermediate half-life of 14.6 h, a high positron branching of 53% and optimal β + emission energy of only E mean 0.35 MeV per decay. These favorable characteristics suggest it may be a potential candidate for application in immuno -PET. Our recent aim was to conduct studies on distribution coefficients for Zr IV and Nb V in mixtures of HCl/H 2 O 2 and HCl/oxalic acid for anion exchange resin (AG 1 × 8) and UTEVA resin to develop a “direct flow” separation strategy for 90 Nb. The direct flow concept refers to a separation accomplished using a single eluent on multiple columns, effectively streamlining the separation process and increasing the time efficiency. Finally, we also demonstrated that this separation strategy is applicable to the production of the positron emitter 90 Nb via the irradiation of molybdenum targets and isolation of 90 Nb from the irradiated molybdenum target.

In this study, for the first time ZnO nanoparticles and diatomite-supported ZnO nanocomposite have been utilized as adsorbent for the removal of Th(IV) ions from aqueous solutions under different experimental conditions. The Langmuir, Freundlich, Temkin and Dubinin– Radushkevich (D–R) isotherms were used to analyze the equilibrium data. The sorption equilibrium data were fitted well to the Langmuir isotherm with maximum sorption capacities values was found to be 1.105 mmol/g and 0.320 mmol/g for ZnO nanoparticles and diatomite supported ZnO nanocomposite, respectively. Pseudo-first and pseudo-second order equations, Intraparticle diffusion and Bangham’s models were considered to evaluate the rate parameters and sorption mechanism. Sorption kinetics were better reproduced by the pseudo-second order model ( R 2 > 0.999), with an activation energy ( E a ) of +99.74 kJ/mol and +62.95 kJ/mol for ZnO nanoparticles and diatomite-supported ZnO nanocomposite, respectively. In order to specify the type of sorption reaction, thermodynamic parameters were also determined. The evaluated Δ G * and Δ H * i ndicate the non-spontaneous and endothermic nature of the reactions. The results of this work suggest that both of the used materials are fast and effective adsorbents for removing Th(IV) from aqueous solutions and chemical sorption plays a role in controlling the sorption rate.

The influence of pH and reaction time on the formation of FeSe 2 by reductive precipitation of Se(IV) with nano-sized pyrite-greigite was investigated. Reductive precipitation is an effective method of attenuating the mobility of 79 Se, which is foreseen to be a dangerous radioisotope for the geological disposal of high-level radioactive waste (HLW). The results indicated that Se(0)was formed at pH <4.05, whereas, at pH > 6.07, considerable amount of FeSe 2 was formed along with Se(0). These observations are in agreement with the thermodynamic predictions reported in this work. Furthermore, the formation of FeSe 2 was found to continue by increasing the reaction time, indicating that the Se(0) formed in the early reaction stage is gradually transformed to FeSe 2 upon the depletion of aqueous Se(IV). Since FeSe 2 has a stronger reactivity than pyrite, it was proposed that greigite, rather than pyrite, was responsible for the formation of FeSe 2 . The findings in this study are of interest for key geochemical processes governing the mobility of toxic 79 Se in the environment in presence of iron sulfides.

An organomineral sorbent based on mixed nickel-potassium ferrocyanide and chitosan to be used in removal of Cs-137 radionuclide from highly mineralized media with high pH has been fabricated. The synthesized sorbent was applied to remove Cs-137 from model solutions under static and dynamic conditions. The effects of contact time, pH, and presence of sodium ions and complexing agents in the process of Cs-137 removal have been investigated. The sorbent is distinguished by increased stability to the impact of alkaline media containing complexing agents, whereas the sorbent capacity in solutions with pH 11 exceeds 1000 bed volumes with the Cs-137 removal efficiency higher than 95%.

Radiocarbon ( 14 C) is a top priority class radionuclide associated with the long-term safety of spent nuclear fuel disposal. Dissolved inorganic radiocarbon can be retained in bedrock via isotope exchange with calcite (CaCO 3 ) at solubility equilibrium with groundwater. In the present study, the rate of the isotope exchange process was investigated on synthetic calcite using batch experiments. Experiments were performed in solutions with a calcium concentration of 0.0002–0.1 M, including two synthetic reference groundwaters. The radiocarbon activity in the solutions decreased exponentially as a function of time, thus following first-order kinetics. The rate of isotope exchange was quantified from an exponential fit to the activity data over time. The rate of radiocarbon retention increased as a function of the calcium activity. The isotope exchange half-life was only 4.3 days at calcium ion activities over 0.01. This half-life is very much shorter than the half-life of 14 C or the time scale of groundwater movements; consequently calcite can effectively retain radiocarbon from brackish and saline groundwaters.

Naturally occurring radionuclides of the 226 Ra, 232 Th, and 40 K present in the lignite samples was measured by using a low-background Pb-shielded gamma spectroscopic counting assembly utilizing NaI(Tl) detector for the measurement and to evaluation the radiation hazard indices and excess life time cancer risk. The average values of specific activity concentrations in the investigated lignite samples was found to be 45.36 Bq kg −1 for 226 Ra, 21.42 Bq kg −1 for 232 Th, 40.51 Bq kg −1 for 40 K and 79.11 Bq kg −1 for Ra eq respectively. The average value excess life time cancer risk was found to be relatively higher than the world average. Moreover, the correlation analysis shows the strong dependence of excess lifetime cancer risk on measured dose and the radium equivalent activity.