Band 102, Heft 1-2

Nuclear analytical techniques are a family of modern analytical methods that are based on nuclear reactions, nuclear effects, nuclear radiations, nuclear spectroscopy, nuclear parameters, and nuclear facilities. Because of their combined characteristics of sensitivity and selectivity, they are widely used in projects ranging from life sciences to deep-space exploration.In this review article, new nuclear facilities and their analytical applications in China are selectively reviewed, covering the following aspects: large scientific facilities, national demands, and key scientific issues with the emphasis on the new achievements.

The advances in computational actinide chemistry made in China are reviewed. Several areas relevant to chemistry of actinides in gas, liquid, and solid phases have been explored. However, we limit the scope to selected contributions in the chemistry of molecular actinide systems in gas and liquid phases. These studies may be classified into two categories: treatment of relativistic effects, which cover the development of two- and four-component Hamiltonians and the optimization of relativistic pseudopotentials, and the applications of theoretical methods in actinide chemistry. The applications include (1) the electronic structures of actinocene, noble gas complexes, An-C multiple bonding compounds, uranyl and its isoelectronic species, fluorides and oxides, molecular systems with metal-metal bonding in their isolated forms (U 2 , Pu 2 ) and in fullerene (U 2 @C 60 ), and the excited states of actinide complexes; (2) chemical reactions, including oxidation, hydrolysis of UF 6 , ligand exchange, reactivities of thorium oxo and sulfido metallocenes, CO 2 /CS 2 functionalization promoted by trivalent uranium complex; and (3) migration of actinides in the environment. A future outlook is discussed.

Uranium is very important in nuclear energy industry; however, uranium and its alloys corrode seriously in various atmospheres because of their chemical reactivities. In China, continuous investigations focused on surface chemistry have been carried out for a thorough understanding of uranium in order to provide technical support for its engineering applications. Oxidation kinetics of uranium and its alloys in oxidizing atmospheres are in good agreement with those in the literature. In addition to the traditional techniques, non-traditional methods have been applied for oxidation kinetics of uranium, and it has been verified that spectroscopic ellipsometry and X-ray diffraction are effective and nondestructive tools for in situ kinetic studies. The inhibition efficiency of oxidizing gas impurities on uranium hydrogenation is found to follow the order CO 2 > CO > O 2 , and the broadening of XPS shoulders with temperature in depth profile of hydrogenated uranium surface is discussed, which is not mentioned in the literature. Significant progress on surface chemistry of alloyed uranium (U-Nb and U-Ti) in hydrogen atmosphere is reported, and it is revealed that the hydrating nucleation and subsequent growth of alloyed uranium are closely connected with the surface states, underlying metal matrix, and it is microstructure-dependent. In this review, the recent advances in uranium surface chemistry in China, published so far mostly in Chinese language, are briefly summarized. Suggestions for further study are made.

In the last decades, the separation of actinides was widely and continuously studied in China. A few kinds of salt-free reductants to adjust Pu and Np valences have been investigated. N ,  N -dimethylhydroxylamine is a good reductant with high reduction rate constants for the co-reduction of Pu(IV) and Np(VI), and monomethylhydrazine is a simple compound for the individual reduction of Np(VI). A dvanced P UREX based on O rganic R eductants (APOR) was proposed. Trialkylphosphine oxide (TRPO) with a single functional group was found to possess strong affinity to tri- , tetra- and hexa -valent actinides. TRPO process has been first explored in China for actinides partitioning from high level waste and the good partitioning performance was demonstrated by the hot test. High extraction selectivity for trivalent actinides over lanthanides by dialkyldithiophosphinic acids was originally found in China. A separation process based on purified Cyanex 301 for the separation of Am from lanthanides was presented and successfully tested in a battery of miniature centrifugal contactors.

The review provides an overview of the current status of radiopharmaceuticals in China for in vivo clinical use and also describes some important advances in the past three decades. Development of the diagnostic and therapeutic radiopharmaceuticals as well as basic research on radiopharmaceutical chemistry are being introduced. The radiotracers developed in China include: (1) Brain perfusion imaging agents and CNS radiotracers for β -amyloid plaques, σ 1 receptors, and dopamine D 2 or D 4 receptors; (2) 99m Tc- and 18 F-labeled myocardial perfusion imaging agents; (3) tumor imaging agents including integrin-targeting radiotracer, novel sentinel lymph node imaging agents, hypoxia imaging agents, 99m Tc-labeled glucose derivatives, σ 2 receptor imaging agents, folate receptor imaging agents, and potential radiotracers for imaging of human telomerase reverse transcriptase expression; (4) Potential infection imaging agents; (5) Potential asialoglycoprotein receptor imaging agents; (6) Other imaging agents. Moreover, some prospects of research and development of radiopharmaceuticals in the near future are discussed.

Metal carbonyl complexes were used for studying the gas-phase chemical behavior of Mo, Ru, W and Os isotopes with an on-line low temperature isothermal gas chromatography apparatus. Short-lived Mo and Ru isotopes were produced by a  252 Cf spontaneous fission source. Short-lived nuclides of W and Os were produced using the heavy ion reactions 19 F + 159 Tb and 165 Ho, respectively. Short-lived products were thermalized in a recoil chamber filled with a gas mixture of helium and carbon monoxide. The carbonyls formed were then transported through capillaries to an isothermal chromatography column for study of the adsorption behavior as a function of temperature. On-line isothermal chromatography (IC) experiments on Teflon (PTFE) and quartz surfaces showed that short-lived isotopes of the listed elements can form carbonyl complexes which are very volatile and interact most likely in physical sorption processes. Deduced adsorption enthalpies of Mo and Ru carbonyls were − 38 ± 2 kJ/mol and − 36 ± 2 kJ/mol, respectively. These values are in good agreement with literature data, partly obtained with different chromatographic techniques. A validation of the applied Monte Carlo model to deduce adsorption enthalpies with Mo isotopes of different half-lives proved the validity of the underlying adsorption model. The investigations using a gas-jet system coupled to a heavy ion accelerator without any preseparator clearly showed the limitations of the approach. The He and CO gas mixture, which was directly added into the chamber, will result in decomposition of CO gas and produce some aerosol particles. After the experiment of 173 W and 179 Os in the heavy ion experiments, the Teflon column was covered by a yellowish deposit; the adsorption enthalpy of W and Os carbonyls could therefore not be properly deduced using Monte Carlo simulations.

The extraction complexes of Pu(IV) with n -octyl(phenyl)-N,N-diisobutyl-methylcarbamoyl phosphine oxide (CMPO) and diphenyl-N,N-diisobutyl carbamoyl phosphine oxide (Ph 2 CMPO) have been studied by using density functional theory (DFT) combined with relativistic small-core pseudopotentials. For most complexes, the CMPO and Ph 2 CMPO molecules are coordinated as bidentate chelating ligands through the carbonyl oxygen and phosphoric oxygen atoms. The metal-ligand bonding is mainly ionic for all of these complexes. The neutral PuL(NO 3 ) 4 and PuL 2 (NO 3 ) 4 complexes are predicted to be the most thermodynamically stable molecules according to the metal-ligand complexation reactions. In addition, hydration energies may also play a significant role in the extractability of CMPO and Ph 2 CMPO for the plutonium cations. In most cases, the complexes with CMPO possess qualitatively similar geometries and electron structures to those with Ph 2 CMPO, and they also have comparable metal-ligand binding energies. Thus, replacement of alkyl groups by phenyl groups at the phosphorus atom of CMPO seems to have no obvious influence on the extraction of Pu(IV).

Room-temperature ionic liquids (RTILs) have recently received increasing attention as solvent alternatives for possible application in spent fuel reprocessing, particularly in the extraction of metal ions from high-level radioactive aqueous waste, due to their unique physical and chemical properties. Herein, the solvent extraction of the uranyl ions (UO 2 2+ ) was performed using N , N ′-diethyl- N , N ′-di(para)tolyl-dipicolinamide (Et (p) TDPA) as the extractant in a commonly used ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([C 4 mim][PF 6 ]). The effects of vortexing time, phase ratio and the concentration dependence of Et (p) TDPA, nitric acid and sodium nitrate on the extraction were studied in detail. The extraction mechanism was deduced based on the slope analysis and UV-vis measurement. The distribution ratio of U from 3 mol/L nitric acid by 0.3 mol/L EtTDPA/C 4 mimPF 6 is found to be almost 100. Conventional log-log plot analysis of the extraction equilibrium data suggests that the ions are extracted as a complex in 2:3 ratio of UO 2 2+ to extractant, and the extraction most likely occurs by a cation-exchange mode since the concentration of C 4 mim + in the aqueous phase increases linearly with the percent extraction of UO 2 2+ evidenced by UV-vis measurement. This work promises to provide new efficient media based on RTILs for separation of uranium from the radioactive aqueous waste.

To separate the long-lived minor actinides (MA = Am, Cm) from high level liquid waste (HLLW), we have been studying a partitioning technology named “MAREC” (Minor Actinides Recovery from HLLW by Extraction Chromatography) process which consists of two separation columns packed with silica-based adsorbents. In this work, we prepared the silica-based 2,6-bis(5,6-di iso hexyl-1,2,4-triazin-3-yl)pyridine ( iso hexyl-BTP/SiO 2 -P) adsorbent used in the second column (0.01 ∼ 0.1 mol dm – 3 HNO 3 ) in the MAREC process for the separation of trivalent minor actinides (MA(III)) from trivalent rare earth elements (RE(III)) which are contained in HLLW. The content of extracting agent iso hexyl-BTP in iso hexyl-BTP/SiO 2 -P was as high as 33.3% of the total mass of the adsorbent. The adsorbent exhibited high affinity and selectivity for Am(III) over RE(III) not only in nitric acid solution but also in nitrate solution. Investigation showed that only a small part of iso hexyl-BTP molecules inside iso hexyl-BTP/SiO 2 -P leaked into 0.01 mol dm – 3 HNO 3 with or without γ -irradiation. The adsorption performance of iso hexyl-BTP/SiO 2 -P did not evidently change after 120 d of contact with 0.01 mol dm – 3 nitric acid. Furthermore, after γ -irradiated in 0.01 mol dm – 3 HNO 3 under the experimental conditions, iso hexyl-BTP/SiO 2 -P exhibited higher adsorption for RE(III) than before γ -irradiation.

Density functional theory was used to study the coordination of Cm 3+ and Ce 4+ with pridine (Py), water (H 2 O) and chloride anion (Cl − ). The competitive coordination of Cl − and Py was investigated to simulate the ligand exchange between Cl − and Py at high concentration of hydrochloric acid (HCl), where Cm 3+ and Ce 4+ may exist in the form of [CmCl 6 ] 3− and [CeCl 6 ] 2− , while that of water and Py to simulate the process at low concentration or without the presence of Cl − . The calculations show that Ce 4+ has higher affinity to Py than Cm 3+ in the absence of Cl − , while it binds much more weakly at high concentration of HCl. This is consistent with experimental data that at high concentration of HCl, Ce 4+ has much shorter retention time than Cm 3+ using tertiary pyridine resin (TPR). In view of the strengthening of M-Cl and the weakening of M-OW at bonds upon the coordination of Py, we conclude that the distinct coordination abilities of the three ligands to Ce 4+ and Cm 3+ are due to different strengths of the inner-shell electrostatic interaction between the ligands and the central metal ions.

The chemical behavior of Np is influenced by many factors, such as U(IV), hydrazine, Pu and Tc, which coexist in U/Pu separation stage of PUREX process. Firstly, the reduction of Np(V) to Np(IV) by Tc(IV) was studied in nitric acid media, and the rate equation could be expressed as − d[Np(V)]/d t  =  k [Np(V)][Tc(IV)] 0.8 [HNO 3 ] 1.2 , k  = 28.5 ± 0.9 (L/mol) 2 /min at 25 ℃, the activation energy was E a  = 70.0 kJ/mol. Thereafter, the chemical behavior of Np was investigated in aqueous nitric acid solution containing Tc(VII), U(IV) and N 2 H 4 . Np(V) was reduced to Np(IV) quickly, Tc(VII) was reduced to Tc(IV) and U(IV) was oxidized to U(VI) at the same time. Thereafter Np(IV) was entirely reoxidized to Np(V) when U(IV) and hydrazine were completely consumed. The fast reduction of Np(V) was mainly ascribed to Tc(IV). In addition, Tc(VII) and nitric acid had little influence on the fast oxidation of Np(IV).

A low-waste technology for the reprocessing of spent nuclear fuel (SNF) has been developed recently, which involves the conversion of actinide and lanthanide oxides with liquid N 2 O 4 into their nitrates followed by supercritical fluid extraction of the nitrates. The possibility of the reprocessing of SNF from high-temperature gas-cooled reactors (HTGRs) with nitrate conversion and supercritical fluid extraction is a current area of research in China. Here, a UO 2 -CeO 2 solid solution was prepared as a surrogate for a UO 2 -PuO 2 solid solution, and the recovery of U and Ce from the UO 2 -CeO 2 solid solution with liquid N 2 O 4 and supercritical CO 2 containing tri-n-butyl phosphate (TBP) was investigated. The UO 2 -CeO 2 solid solution prepared by electrolytic reduction-coprecipitation method had square plate microstructures. The solid solution after heat treatment was completely converted into nitrates with liquid N 2 O 4 . The XRD pattern of the nitrates was similar to that of UO 2 (NO 3 ) 2  ·3H 2 O. After 120 min of online extraction at 25 MPa and 50 ℃, 99.98% of the U and 98.74% of the Ce were recovered from the nitrates with supercritical CO 2 containing TBP. The results suggest a promising potential technology for the reprocessing of SNF from HTGRs.

An advanced plutonium and uranium recovery process has been established based on two organic reductants, N , N -dimethylhydroxylamine (DMHAN) and methylhydrazine (MH), as U/Pu separation reagents. This Advanced Purex process based on Organic Reductants (APOR) is composed of three cycles, including U/Pu co-decontamination/separation cycle, uranium purification cycle and plutonium purification cycle. Using DMHAN and MH as plutonium stripping reagents in the U/Pu co-decontamination/separation cycle and plutonium purification cycle, the APOR process exhibits high performance with following highlights: 1) the process is much simpler because of the elimination of Tc scrubbing operation and the supplement extraction operation, 2) high efficiency of U/Pu separation can be achieved in the first cycle, 3) plutonium product solution of high concentration can be obtained in the Pu purification cycle with a simple extraction operation instead of circumfluent extraction or evaporation of the plutonium solution.

A new macrocyclic supramolecular recognition agent, 1,3-di(1-decyloxy)-2,4-crown-6-calix[4]arene (DecylCalix[4]C6), was synthesized by a multistep reaction through separation and purification by column chromatography packed with silica gel. The extraction behavior of some representative fission and non-fission products such as La(III), Y(III), Cs(I), Rb(I), Pd(II), Mo(VI), Zr(IV), Sr(II), Ba(II), Ru(III), Na(I), and K(I), which were contained in highly active liquid waste (HLW), with DecylCalix[4]C6/1-octanol in HNO 3 medium was investigated, in particular by examining the impact of contact time, the HNO 3 concentration in the range of 0.4 to 5.0 M, and the temperature. DecylCalix[4]C6 showed excellent extraction ability and high selectivity for Cs(I) over the tested metals except for Rb(I). It was attributed to the effective recognition and complxation of DecylCalix[4]C6 for Cs(I). The optimum HNO 3 concentration for the Cs(I) extraction was 3.0 M. The composition of the extracted species of Cs(I) with DecylCalix[4]C6 was determined to be (CsDecylCalix [4]C6)NO 3 . It is valuable for the effective partitioning of Cs(I) from highly active liquid waste with DecylCalix[4]C6 by liquid-liquid solvent extraction.

In this study, the interactions among Eu(III), humic acid (HA) and γ -Al 2 O 3 as a function of pH and ionic strength were investigated by batch technique and extended X-ray absorption fine structure (EXAFS) analysis. For binary γ -Al 2 O 3 /Eu(III) systems, the pH-dependent and ionic strength-independent sorption behavior was indicative of an inner-sphere complexation mechanism. The EXAFS spectra analysis showed that Eu(III) sorption mechanisms at pH 5.0, 6.5 and 8.0 could be attributed to the formation of edge-shared and corner-shared surface complexes. In contrast, surface precipitation and/or surface polymerization tended to be the predominant sorption mechanism at pH 10.0. The spectra analysis results suggested no difference between the proportions of edge-shared and corner-shared complexes formed at different ionic strengths. For ternary γ -Al 2 O 3 /HA/Eu(III) systems, the sorption percentage of Eu(III) increased with increasing ionic strength. The EXAFS-derived structural parameters pointed to the formation of binary surface complexes ( i.e. , edge-shared mode and corner-shared mode) at low ionic strength and ligand-bridging ternary complexes at high ionic strength. In addition, the stoichiometry of ternary complexes showed a trend from 1:1 form ( i.e. , γ -Al 2 O 3 /L/Eu(III), L represents HA sites) to 1:2 form ( i.e. , γ -Al 2 O 3 /L 2 /Eu(III), L represents HA sites) with increasing ionic strength. The experimental findings in this study can provide an important theoretical basis for further predicting the fate of trivalent radionuclides in aquatic systems.

The batch experiment and high resolution EXAFS technique with bent crystal analyzer were combined to study Eu(III) retention mechanisms on β -MnO 2 as a function of various environmental factors. The results indicated that the sorption of Eu(III) onto β -MnO 2 was obviously dependent on pH but independent of ionic strength, suggesting the formation of inner-sphere surface complexes. Results of high resolution EXAFS analysis showed that Eu was surrounded by 8 ± 1 O atoms in the first shell at R Eu−O  ≈ 2.40 Å for all sorption samples. A second shell of Mn atoms at R Eu−Mn  ≈ 3.78 Å was observed for all sorption samples, which was associated with the formation of a bidendate inner-sphere complex with chemical bonding via edge sharing to MnO 6 -octahedron. This study shows the utility of high resolution EXAFS technique with bent crystal analyzer to discriminate the fluorescence peak of Eu(III) from that of manganese hydroxides, whose fluorescence peaks are too close in energy to be discriminated by the conventional EXAFS technique with a low resolving solid-state detector. Both the macroscopic interaction data and the molecular level evidence of Eu(III) surface speciation at the oxide-water interface should be factored into better evaluation of Eu(III) and related radionuclide mobility in the natural environment.

The method of 227 Ac extraction and purification from high-grade uranium ore and the test results of solid 219 Rn source made from 227 Ac are reported in this paper. With five years of follow-up monitoring, radiochemical purity of 227 Ac and the emanation power of solid 219 Rn source has been checked by emanation method and γ -spectrometry, the results showed that 228 Th, 231 Pa and 226 Ra have been effectively removed and the emanation power of 219 Rn source is about 80%. The long-term test results also showed that the 219 Rn emanation rate remains stable in a wide air humidity range (40% ∼ 90%). Though the 219 Rn source has not been accurately calibrated yet, it has been applied in the research for delay coincidence measurement of 223 Ra.

In order to understand the impact of microorganisms on the fate of thorium in soils, we investigated the thorium biosorption behavior and the corresponding mechanisms by the cells of Geotrichum sp. dwc-1, one of the dominant species of fungal group isolated from 3.5 m depth soil layer in Southwest China. It was observed that fast thorium adsorption onto cells of G . sp. dwc-1 could take place, with a high distribution coefficient K d (0.93 mL/mg) obtained, when Geotrichum sp. dwc-1and thorium concentrations were 5 g/L and 10 mg/L, respectively. The thorium biosorption behavior was dependent on the pH value, and the lower pH could disrupt cell membrane of G . sp. dwc-1. At pH 1, thorium was accumulated in the cytoplasmic region of the cells. When pH was higher than 1, thorium was adsorbed on the cell surface of G . sp. dwc-1, like in periplasmic region or in the outer membrane. FTIR study combined with biosorption experiments further indicated that the thorium distribution and binding behavior on cell surface were associated with amino, hydroxyl groups and phosphate or sulphur functional groups, and might also be governed by electrostatic interaction. Moreover, PIXE and EPBS showed that ion-exchange mechanism contributed to the thorium biosorption process, in which the tetravalent thorium ions replaced smaller counter-ions (K + , Ca 2+ and Fe 3+ ) occuring on the cell surface.

Four stilbene derivatives from natural products were screened as novel β -amyloid (A β ) imaging ligands. In vitro binding assay showed that the methylated ligand, (E)-1-methoxy-4-styrylbenzene ( 8 ) displayed high binding affinity to A β 1−42 aggregates ( K i  = 19.5 nM). Moreover, the 11 C-labeled ligand, [ 11 C] 8 was prepared through an O -methylation reaction using [ 11 C]CH 3 OTf. In vitro autoradiography with sections of transgenic mouse brain also confirmed the high and specific binding of [ 11 C] 8 to A β plaques. In vivo biodistribution experiments in normal mice indicated that [ 11 C] 8 displayed high initial uptake (9.41 ± 0.51% ID/g at 5 min post-injection) into and rapid washout from the brain, with a brain 5   min /brain 30   min ratio of 6.63. These preliminary results suggest that [ 11 C] 8 may be served as a novel A β imaging probe for PET.

Hypoxia, as a common phenomenon in solid tumors, is of interest for its relationship with resistance to tumor therapies and malignant progression of tumor. The noninvasive nuclear medical imaging technique using hypoxia markers is an important method for the detection of tumor hypoxia. The aim of current study is designing tumor hypoxia markers with hypoxia selectivity and improved properties. Two MAG 3 -based bisnitroimidazole compounds were synthesized and purified by semi-preparative HPLC. Both the MAG 3 derivatives were labeled with 99m Tc-oxo-technetium core via stannous tartrate exchange method in high yields (> 95%). The 99m Tc-MAG 3 complexes were stable at 37 ℃, 4 h after preparation, and were more hydrophilic than 99m Tc-MAMA complexes. As biodistribution results showed, clearances of background activity for both the complexes were fast and they were excreted mainly through the hepatobiliary tract and part of renal tract. Although tumor uptakes of 99m Tc-MAG 3 -B2NIL were lower than those of 99m Tc-MAG 3 -B4NIL, tumor-to-blood ratios of 99m Tc-MAG 3 -B2NIL showed an increasing trend and were better than those of 99m Tc-MAG 3 -B4NIL after 2 h due to their different blood clearances. Tumor-to-muscle ratios of 99m Tc-MAG 3 -B2NIL and 99m Tc-MAG 3 -B4NIL were similar. Comparing with 99m Tc-MAMA complexes, 99m Tc-MAG 3 -B2NIL with better tumor-to-blood ratios exhibits improved feature for hypoxia imaging, though it has lower tumor uptake than 99m Tc-MAMA complexes.

γ -radiation effect on dicyclohexano-18-crown-6 (DCH18C6) aqueous solution in the presence of metal cations, such as K + and Sr 2+ , was investigated, and some pale yellow precipitates were obtained at doses above 100 kGy. It was found that the complexation interaction of metal cations could accelerate the conversion of DCH18C6 into oligomers and the formation of precipitates, but it did not affect the formation mechanism of precipitates. Furthermore, the salting-out effect of metal cations played an important role in the precipitation. In order to inhibit the radiation-induced precipitation of DCH18C6 in water phase, nitric acid with a concentration of more than 1 M could be added to the system. The methods and results for analyzing radiation-induced products reported in this work are useful to understand the radiation chemistry behavior of DCH18C6 which is used as the extractant in the separation of long half-life radionuclides from spent nuclear fuel.