Volume 89, Issue 6 -

The available experimental data on the most common route for the production of 18 F, viz. 18 O( p , n ) 18 F reaction, obtained both via neutron spectral studies and activation measurements, were critically reviewed. In some energy regions the cross section database was found to be rather weak or discrepant. In order to fill the gaps and to clear some of the discrepancies, the excitation function was remeasured from threshold up to 30 MeV using different solid and gas targets containing highly enriched 18 O. For this purpose a van de Graaff machine ( E p <4 MeV) and several cyclotrons ( E p = 4-30 MeV) were utilized. The new experimental data help to prepare a recommended data set. At E p = 14 MeV the integral yield of 18 F calculated from the new excitation curve is slightly higher than that from the hitherto accepted data set; at E p > 14 MeV the yields reported here are new.

Organoberkelium and organocalifornium ions were produced for the first time by laser ablation of 249 Bk 2O_{3 } and 249 Cf 2O_{3 } dispersions in polyimide, followed by analysis with time-of flight mass spectrometry. The primary products formed were: BkCH 3 + , BkC 2 + , AnC 2 H + , AnCN + , AnC 4 H + , An(OH)(CN) + , AnOCN + , AnOH + , An(OH) 2 + and AnO + (where An=Bk or Cf). Several of these complexes represent the first organoactindes in which Bk and Cf are directly bonded to carbon. The compositions and abundance distributions of the products are effectively evaluated in the context of a bonding model which requires one or two non-5 f valence electrons at the An + center for participation in direct An + -C bonding to form the monovalent or divalent complexes. Both Bk and Cf exhibit a propensity to form "monovalent" organoactinides in which the metal center forms a single σ-type bond to the organic moiety. Most earlier actinides form "divalent" complexes having two An + -C bonds. A few small oxide cluster ions, An m O n + ( m =2 or 3) were identified, demonstrating the feasibility of preparing clusters for the heavy actinides. The energetics underlying the present results are discussed with an emphasis on the evidently pivotal position of Bk in the actinide series.

The plutonium activities ( 238 Pu and 239,240 Pu) of soil samples from the village of Dolon, located close to the Semipalatinsk Nuclear Test Site in Kazakhstan, were measured and compared with the 90 Sr and 137 Cs activities. Depth profiles of 239,240 Pu were determined for four of the nine sampling sites. The 239,240 Pu areal deposition at the nine sites is in the range of 140 to 9700 Bq m -2 . For all samples, the 239,240 Pu yield after destruction of the soil matrix is significantly higher than after extracting with 8 M HNO 3 indicating that 239,240 Pu originates mainly from local fallout. The fraction of 239,240 Pu not leached with 8 M HNO 3 is assumed to be associated with fused silicates.

The interactions between Pu(IV) and Pu(VI), respectively, and some synthetic water-soluble polymers were investigated by absorption spectroscopy and ultrafiltration. Depending on the type of polymer plutonium can be bound by different mechanisms. Poly(acrylic acid) binds Pu(IV) and Pu(VI) by stepwise complexation, which can be observed by absorption spectroscopy. Due to chelation, some of the formation constants are greater than those from corresponding complexes with low-molecular carboxylic acids. By poly(styrenesulfonic acid) and poly(vinylesulfonic acid), Pu(IV) is bound via counterion condensation. In nitrate and chloride media, anionic Pu(IV) complexes may be bound by quaternary ammonium polymers like poly(diallydimethylammonium chloride) and permethylated poly(ethyleneimine).

The influence of humic substances on the migration of radionuclides 237 Np, 238 Pu and 241 Am in a weak loess aquifer was investigated in situ with bisectional experimental columns. The experimental columns were constructed by connecting two undisturbed aquifer medium columns together, and inserted into the aquifer horizontally through holes pre-prepared in the wall of a vertical Experimental Shaft in an Underground Research Facility at the CIRP´s field test site. Quartz containing radionuclides 3 H, 237 Np, 238 Pu and 241 Am was introduced as point source and plane source at the central parts of the experimental columns, respectively. Outflow water of the experimental columns were collected and 3 H in the outflows were analyzed for calculating the water flow velocity in the experimental columns. When the experiment was completed, the experimental columns were dismounted and cut into slices and the activities of 237 Np, 238 Pu and 241 Am in the sliced samples were determined. The water flow velocity in the point source experimental column and in the plane source experimental column was calculated as 1.15±0.05 cm/d and 1.06±0.05 cm/d, respectively. The concentration distribution of 237 Np, 238 Pu and 241 Am in the experimental columns indicate that, adjacent to the source, the concentration of each radionuclide is very large and decreases abruptly as the distance increases. In addition, some other high concentration regions/points were observed. This phenomenon may suggest that multiple species of these radionuclides with different mobility may exist in the in-situ aquifer condition. The calculated apparent distribution coefficients ( K d , ml/g) of the main specie of these radionuclides with and without additional humic substances are 8.90×10 1 and 8.90×10 2 for 237 Np, 1.93×10 2 and 9.48×10 2 for 238 Pu, 7.60×10 2 and 9.79×10 2 for 241 Am, respectively. These data suggest that the introduction of additional humic substances into the aquifer may enhance the mobility of 237 Np and 238 Pu, while it has no obvious influence on the migration of 241 Am.

The complexation of Th(IV) and Eu(III) by α-isosaccharinic acid (ISA) has been studied in the pH range from 10.7 to 13.3 by batch sorption experiments, and the influence of Ca on the complexation was investigated. Sixteen data sets – each determined at variable ISA concentrations – are used to determine the stoichiometry of the complexation reactions and the stability constants. Based on best-fit analysis of the sorption data, it is postulated that 1:1 Th:ISA complexes are formed in the absence of Ca according to the complexation reaction: Th+ISA↔(ThISA) -4H +4H with log K =-10.1 at I =0.3 M. In the presence of Ca, the sorption data can be interpreted best by a mixed-metal complex, according to the complexation reaction: Th+2ISA+Ca↔(Th(ISA) 2 Ca) -4H +4H with log K Ca =-3.6 at I =0.3 M. There are no indications that Ca participates in complexes of ISA with Eu. The sorption data suggest that 1:1 Eu:ISA complexes are dominant in the pH range from 10.7 to 13.3 according to the complexation reaction: Eu+ISA↔(EuISA) -4H +4H with log K =-30.6 at I = 0.3 M. It is important to note that the stoichiometric numbers and stability constants proposed here are not independent of the hydrolysis reactions of the two metal cations. Thus, the same hydrolysis data as used here have to be applied in speciation calculations with the ISA complexation data for Eu(III) and Th(IV).

A five-year cooperative research project between China Institute for Radiation Protection (CIRP) and Japan Atomic Energy Research Institute JAERI) on establishment of methodology for safety assessment of shallow land disposal of low-level radioactive wastes (LLRW) had been conducted since 1988. This paper describes the simulation of the migration of 85 Sr in Chinese Loess under artificial rainfall condition at the CIRP's field test site by NESOR, a numerical model considering nonequilibrium sorption. FEMWASTE was used to verify the simulation results of NESOR. The results show that the sorption at the surface of loess media may be controlled by a nonequilibrium sorption.

Technetium-99, in the form of Tc(VII), is one of major problems in the management and disposal of nuclear waste in view of its long half-life in combination with high geochemical mobility. Solvent extraction is an important separation technique to remove 99 Tc from liquid nuclear waste streams. 2-nitrophenyl octyl ether (NPOE) shows high extraction ability for Tc(VII) from water and NaOH solutions (>99.5%) in spite of the lack of donating atoms. Upon extraction from alkaline solutions, TcO 4 - associates with NPOE molecules in 1:1 stoichiometry where the co-extracted cation is expected to play an important role in the extraction mechanism. At pH > 4 the Tc(VII) distribution is relatively insensitive towards changes in pH, while at decreasing pH (<4) the distribution ratio decreases sharply. The strong dependency of the Tc(VII) distribution on the acidity is very useful for developing efficient extraction-stripping systems. This study showed that NPOE is an excellent compound for the removal of technetium from alkaline nuclear wastes.

Some features of a novel 90 Sr- 90 Y generator which employs supported liquid membrane (SLM) to separate carrier-free 90 Y from 90 Sr present in the high level waste of the spent fuel of reactor are described. After ascertaining the purity of 90 Y particularly with respect to 90 Sr breakthrough, its complexation was studied with a few oxo/aza donor ligands, such as DTPA, EDTMP, DOTA, TETA and a cyclic phosphonate, CTMP. These studies were primarily carried out to adjudge the quality of the 90 Y obtained from a novel 90 Sr- 90 Y generator and ascertain its usability for labelling biomolecules such as antibodies and peptides. The DOTA complexes are most stable at 37 C in human serum; they appear to be ideal bifunctional chelating agent for use in radioimmunotherapy with 90 Y.