Volume 102, Issue 7

A new nuclear reaction for the production of 240 Am was experimentally investigated. Targets of 150 – 500  μ g/cm 2 242 Pu on 2  μ m Ti were produced through molecular deposition. Five irradiations, in which 242 Pu, nat Ti, and nat Ni targets were jointly activated with protons from the Lawrence Berkeley National Laboratory 88-Inch Cyclotron produced 240 Am, 48 V, and 57 Ni, respectively. The radioactive decay of these nuclides was monitored using high-purity Ge gamma ray detectors in the weeks following irradiation. A maximum 242 Pu( p , 3 n ) 240 Am nuclear reaction cross section was measured to be 45 ± 13 mb with 23 MeV protons. While this value is lower than theoretical predictions, it is high enough to be the most viable nuclear reaction for the large-scale production of 240 Am.

Accelerator production of 225 Ac addresses the global supply deficiency currently inhibiting clinical trials from establishing 225 Ac's therapeutic utility, provided that the accelerator product is of sufficient radionuclidic purity for patient use. Two proton activation experiments utilizing the stacked foil technique between 40 and 200 MeV were employed to study the likely co-formation of radionuclides expected to be especially challenging to separate from 225 Ac. Foils were assayed by nondestructive γ -spectroscopy and by α -spectroscopy of chemically processed target material. Nuclear formation cross sections for the radionuclides 226 Ac and 227 Ac as well as lower lanthanide radioisotopes 139 Ce, 141 Ce, 143 Ce, and 140 La whose elemental ionic radii closely match that of actinium were measured and are reported. The predictions of the latest MCNP6 event generators are compared with measured data, as they permit estimation of the formation rates of other radionuclides whose decay emissions are not clearly discerned in the complex spectra collected from 232 Th(p,x) fission product mixtures.

The neutron capture cross section for the 152 Sm( n ,   γ ) 153 Sm reaction at an energy of 0.0334 eV was measured for the first time using monochromatic neutrons of a powder diffractometer at the TRIGA Mark II nuclear reactor at Dhaka, Bangladesh. The 197 Au( n ,   γ ) 198 Au reaction was used to monitor the neutron beam intensity. The radioactivity of the products was determined via high resolution γ -ray spectrometry. The obtained cross section value is 184 ± 22 b, which is consistent with both the ENDF/B-VII and TENDL-2012 data libraries. The measured value at 0.0334 eV and the previous data at 0.0536 eV confirm the reliability of the data in the above libraries.

Extraction chromatographic resin prepared by impregnating CMPO-RTIL (C 8 mim + ·NTf 2 − ) on Chromosrob-W for the removal of trivalent actinides and lanthanides from aqueous solutions showed a significant improvement over the previously reported CMPO- n -dodecane resin. The resin was characterized by thermal analysis, for surface area by BET and for surface morphology by SEM. The K d value of Am(III) by CMPO-RTIL resin was found to be 5805 and 3.8E4 with 3 M and 0.01 M HNO 3 , respectively. The high K d values at lower acidity suggested metal ion uptake following a cation exchange mechanism usually seen with ionic liquid based solvents and use of 0.01 M EDTA resulted in a K d value of 0.11 which was subsequently used as the strippant. Uptake of other actinide ions such as UO 2 2+ , Pu 4+ , Np 4+ and fission product element ions such as Eu 3+ , Sr 2+ and Cs + was also studied. Column studies using a feed containing 1 g/L Eu(III) in 3 M HNO 3 suggested complete uptake of the metal ion up to passing 7 mL of the feed solution which corresponded to a column capacity of 7 mg of Eu. The loaded Eu(III) from the columns could be efficiently eluted with 0.01 M EDTA. The column capacity for Eu(III) was measured in the successive cycles of loading and elution and was found to be stable up to 60 d. The results suggested the possible application of the resins in the treatment of dilute laboratory radioactive waste.

A new approach, namely “Single-cycle method for partitioning of Minor Actinides using completely incinerable ReagenTs” (SMART), has been explored for the separation of Am(III) from Eu(III) present in nitric acid medium. The extraction behavior of Am(III) and Eu(III) in a solution of an unsymmetrical diglycolamide, N , N ,-didodecyl- N ′, N ′-dioctyl-3-oxapentane-1,5-diamide (D 3 DODGA), and an acidic extractant, N ,  N -di-2-ethylhexyl diglycolamic acid (HDEHDGA), in n -dodecane was studied. The distribution ratio of both these metal ions in D 3 DODGA-HDEHDGA/ n -dodecane initially decreased with increase in the concentration of nitric acid reached a minimum at 0.1 M nitric acid followed by increase. Synergic extraction of Am(III) and Eu(III) was observed at nitric acid concentrations above 0.1 M and antagonism at lower acidities. Contrasting behavior observed at different acidities was probed by the slope analysis of the extraction data. The study revealed the involvement of both D 3 DODGA and HDEHDGA during synergism and increased participation of HDEHDGA during antagonism. The stripping behavior of Am(III) and Eu(III) from the loaded organic phase was studied as a function of nitric acid, DTPA, and citric acid concentrations. The conditions needed for the mutual separation of Am(III) and Eu(III) from the loaded organic phase were optimized. Our studies revealed the possibility of separating trivalent actinides from HLLW using these completely incinerable reagents.

New unsymmetrical diglycolamides (UDGAs), N ,  N -di-butyl- N ′,  N ′-di-dodecyl-3-oxapentane-1,5-diamide (C 12 -C 4 ), N ,  N -di-dodecyl- N ′,  N ′-di-hexyl-3-oxapentane-1,5-diamide (C 12 -C 6 ), N ,  N -di-decyl- N ′,  N ′-di-dodecyl-3-oxapentane-1,5-diamide (C 12 -C 10 ) have been synthesized, and evaluated for the separation of americium(III) and europium(III) from nitric acid medium. The extraction behavior of Am(III), Eu(III), and Sr(II) in a solution of these UDGAs in n -dodecane was studied as a function of concentration of nitric acid in the aqueous phase. The distribution ratio of Am(III) and Eu(III) increased with increase in the concentration of nitric acid. The third phase formation behavior of nitric acid and neodymium(III) in 0.1 M UDGA/ n -dodecane was studied. The third phase formation was not observed in all these UDGAs in n -dodecane (0.1 M), when the concentration of Nd(III) was ∼ 500 mM in 3–4 M nitric acid. The stoichiometry of Am(III)-UDGA was determined from the slope analysis of the extraction data, which indicated the formation of 1:3 complex in all cases. Our studies revealed that the UDGA ligands with dodecyl group attached to one amidic nitrogen atom is inevitable for preventing third phase formation and the alkyl group at the other amidic nitrogen can be varied from butyl to decyl group for obtaining efficient extraction of trivalent actinides from high-level nuclear waste.

Batch extraction of U(VI) by 1.1 M solution of tri- iso -amyl phosphate (T i AP) in n -dodecane ( n -DD) from uranyl nitrate solutions in nitric acid media has been investigated as a function of metal loading and equilibrium aqueous phase acidity at 303 K. A method adopted for free acidity determination by using a mixture of potassium oxalate and sodium fluoride for complexing U(VI) has been validated by comparing the data generated in the present study with literature data available for tri- n -butyl phosphate (TBP) under identical conditions. Extraction and stripping behaviour of 1.1 M T i AP/ n -DD-U(VI)/HNO 3 and 1.1 M TBP/ n -DD-U(VI)/HNO 3 systems have been compared by carrying out extraction, scrubbing and a series of stripping in cross-current mode. Stripping behaviour of both the solvents loaded with U(VI) and HNO 3 has also been investigated as a function of time to understand the effects of nitric acid induced degradation on stripping.

In this work stability constants describing Pu(IV), Th(IV), and Np(V) binding to Leonardite humic acid (HA) were determined using a discrete pK a model. A hybrid ultra-filtration/equilibrium dialysis, ligand exchange technique was used to generate the partitioning data. Ethylenediaminetetraacetic acid (EDTA) was used as a reference ligand to allow the aqueous chemistry of the Pu(IV)-HA system to be examined over a range of pH values, while minimizing the possibility of precipitation of Pu(IV). The conditional stability constant for Pu(IV) complexation with HA determined as part of this work is log  β 112  = 6.76 ± 0.14 based on the equation: Pu 4+  + HL3 + 2H 2 O ↔ Pu(OH) 2 L3 +  + 3H + where HA is represented by HL3 (a binding site on the HA with a pK a value of 7). This value is three orders of magnitude higher than the Th(IV)-HA constant and between six and eight orders of magnitude higher than the Np(V)-HA complex. The magnitude of the stability constants and the general trend of increasing complexation strength with increasing pH is consistent with previous observations. The Pu(IV)-HA stability constants were used to model sorption of Pu(IV) to gibbsite in the presence of HA. Assuming only aqueous Pu-HA complexes and AlOH-Pu surface complexes, the model was unable to predict the observed data which exhibited greater sorption at pH 4 relative to pH 6; a phenomenon which does not occur in the absence of HA. Therefore, this study demonstrates that ternary Pu-HA-gibbsite complexes may form under low pH conditions and exhibit greater sorption than that observed in the absence of HA. Although the presence of HA may increase the solubility/aqueous concentrations of Pu in the absence of a solid phase, formation of ternary complexes may indeed retard the subsurface migration of Pu. The corollary to this finding is that increased mobility may occur if the ternary surface complex forms on a mobile colloid rather than part of the subsurface matrix

Soil samples from three forest soil pits were examined down to a depth of approximately three metres using 1 M ammonium acetate extraction and microwave-assisted extraction with concentrated nitric acid (HNO 3 ), to study the binding of cesium (Cs) at Olkiluoto Island, southern Finland. Ammonium acetate was used to extract the readily exchangeable Cs fractions roughly representing the Cs fraction in soil which is available for plants. Microwave-assisted HNO 3 extraction dissolves various minerals, e.g. carbonates, most sulphides, arsenides, selenides, phosphates, molybdates, sulphates, iron (Fe) and manganese (Mn) oxides and some silicates (olivine, biotite, zeolite), and reflects the total Cs concentrations. Cs was mostly found in the strongly bound fraction obtained through HNO 3 extraction. The average Cs concentrations found in this fraction were 3.53 ± 0.30 mg/kg (d.w.), 3.06 ± 1.86 mg/kg (d.w.) and 1.83 ± 0.42 mg/kg (d.w.) in the three soil pits, respectively. The average exchangeable Cs found in the ammonium acetate extraction in all three sampling pits was 0.015 ± 0.008 mg/kg (d.w.). In addition, Cs concentrations in the soil solution were determined and in situ distribution coefficients ( K d ) for Cs were calculated. Furthermore, the in situ K d data was compared with the Cs K d data obtained using the model batch experiments. The in situ K d values were observed to fairly well follow the trend of batch sorption data with respect to soil depth, but on average the batch distribution coefficients were almost an order of magnitude higher than the in situ K d data. In situ Cs sorption data could be satisfactory fitted with the Langmuir sorption isotherm, but the Freundlich isotherm failed to fit the data. Finally, distribution coefficients were calculated by an ion exchange approach using soil solution data, the cation exchange capacity (CEC) as well as Cs to sodium (Na) and Cs to potassium (K) ion exchange selectivity coefficients. The calculated distribution coefficients corresponded well with the in situ distribution coefficient values.

Radiolabeled porphyrins are potential tumor avid radiopharmaceuticals because of their behaviour in the human body, ability to complex various radionuclides, water solubility, low toxicity etc. , in this work radio ytterbium/samarium porphyrin complexes have been developed. 175 Yb and 153 Sm labeled 5,10,15,20-tetrakis(3,4-dimethoxyphenyl) porphyrins ([ 175 Yb]-TDMPP/[ 153 Sm]-TDMPP) were prepared using 5,10,15,20-tetrakis(3,4-dimethoxyphenyl) porphyrin (H 2 TDMPP) and [ 175 Yb]YbCl 3 or [ 153 Sm]SmCl 3 in 12–24 h at 60 ℃. Stability of the complexes were checked in final formulation and human serum for 24 h, followed by partition coefficient determination and biodistribution studies in wild type and breast carcinoma-bearing mice. The radiocomplexes were obtained with acceptable radiochemical purity (> 95% (paper chromatography) and > 96% (HPLC) for [ 175 Yb]-TDMPP and > 97% (paper chromatography) and >98% (HPLC) for [ 153 Sm]-TDMPP) with specific activities of 12–15 GBq/mmol and 278 GBq/mmol at the end of bombardment for [ 175 Yb]-TDMPP and [ 153 Sm]-TDMPP respectively. The partition coefficients were determined for [ 175 Yb]-TDMPP and [ 153 Sm]-TDMPP) (log  P  = 0.63 and log  P  = 0.96 respectively). The [ 175 Yb]-TDMPP complex is mostly washed out from the circulation through kidneys. Liver and spleen also demonstrated significant activity uptake in 72 h post injection. Also [ 153 Sm]-TDMPP, is mostly washed out from the circulation through kidneys, however lungs are the major accumulation sites. The [ 153 Sm]-TDMPP complex demonstrated significant targeted uptake in breast carcinoma xenografts with tumor: blood ratios of 10.67, 10.47 and 19.01 in 24, 48 and 72 h respectively. Also interesting tumor: kidney/liver ratios were obtained. 153 Sm-TDMPP properties suggest an efficient tumor targeting agent with high tumor-avidity. Further investigation on the therapeutic properties must be conducted.