Determination of uranium element concentration and235U isotope abundance by neutron activation analysis

A new neutron activation technique has been developed for the determination of uranium element concentration and²³⁵U isotope abundance in nuclear safeguards and reference material samples based on the activation of bare and cadmium-covered samples with different thermal to epithermal neutron flux ratios and on the combination of the two corre-sponding delayed-fission neutron measurements. The principle of the new technique can be applied also to improve multi-element neutron activation analysis.     

Syn-Anti Isomerism in a Mixed-Ligand Oxorhenium Complex, ReO[SN(R)S][S

The simultaneous action of the tridentate ligand (C(2)H(5))(2)NCH(2)CH(2)N(CH(2)CH(2)SH)(2) and the monodentate coligand HSC(6)H(4)OCH(3) on a suitable ReO(3+) precursor results in a mixture of syn- and anti-oxorhenium complexes, ReO[(C(2)H(5))(2)NCH(2)CH(2)N(CH(2)CH(2)S)(2)] [SC(6)H(4)OCH(3)], in a ratio of 25/1. The complexes are prepared by a ligand exchange reaction using ReO(eg)(2) (eg = ethylene glycol), ReOCl(3)(PPh(3))(2), or Re(V)-citrate as precursor. Both complexes have been characterized by elemental analysis, FT-IR, UV-vis, X-ray crystallography, and NMR spectroscopy. The syn isomer C(17)H(29)N(2)O(2)S(3)Re crystallizes in the monoclinic space group P2(1)/n, a = 14.109(4) ?, b = 7.518(2) ?, c = 20.900(5) ?, beta = 103.07(1) degrees, V = 2159.4(9) ?(3), Z = 4. The anti isomer C(17)H(29)N(2)O(2)S(3)Re crystallizes in P2(1)/n, a = 9.3850(7) ?, b = 27.979(2) ?, c = 8.3648(6) ?, beta = 99.86(1) degrees, V = 2163.9(3) ?(3), Z = 4. Complete NMR studies show that the orientation of the N substituent chain with respect to the Re=O core greatly influences the observed chemical shifts. Complexes were also prepared at the tracer ((186)Re) level by using (186)Re-citrate as precursor. Corroboration of the structure at tracer level was achieved by comparative HPLC studies.     

Neutron induced reactions at the Athens Tandem Accelerator NCSR “Demokritos”

The neutron facility at the 5.5 MV tandem T11/25 Accelerator of NCSR “Demokritos” can deliver monoenergetic neutron beams in the energy range from thermal to 450 keV, 4–11.5 MeV and 16–20.5 MeV via the ⁷Li(p,n), ²H(d,n) and ³H(d,n) reactions, respectively. The flux variation of the neutron beam is monitored by using a BF₃ counter and a liquid scintillator BC501A detector. The ²³²Th(n,2n)²³¹Th and ²⁴¹Am(n,2n)²⁴⁰Am as well as (n,2n), (n,p) and (n,α) reactions on natural Ge and Hf isotopes, have been investigated from threshold up to 11.5 MeV, by using the activation method. The cross section values have been determined relative to the ¹⁹⁷Au(n,2n)¹⁹⁶Au, ²⁷Al(n,α)²⁴Na and ⁹³Nb(n,2n) reference reaction cross sections.     

Reactions of derivatives of anthranilic acid with 3-chloropropyl isocyanate

The urea 1 obtained from anthranilonitrile and 3-chloropropyl isocyanate is converted into 3-(3-chloropropyl)-2,4(1H,3H)quinazolinedione ( 4 ) when heated with hydrochloric acid, whereas it undergoes a double cyclization to form 2,3,4,7-tetrahydro-6H-pyrimido[1,2-c]quinazolin-6-one ( 3 ) upon heating, or treatment with ammonia. On the other hand, the urea 5 formed from methyl anthranilate and 3-chloropropyl isocyanate cyclizes in three different ways, when treated with ammonia, potassium bicarbonate, or concentrated sulfuric acid, to yield compound 4 , 3,4-dihydro-2H,6H-[1,3]oxazino[2,3-b]quinazolin-6-one ( 9 ), or 2-[(3-chloropropyl)amino]-4H-3,1-benzoxazin-4-one ( 6 ), respectively. Acid-catalyzed reactions of compound 9 with nucleophilic reagents proceed with opening of the oxazine ring and readily yield various 3-substituted 2,4(1H,3H)-quinazolinediones.     

Synthesis and characterization of novel 99gTc(V) and Re(V) complexes with water-soluble tetraaza diamido dipyridino ligands: single-crystal X-ray structural investigations of mono- and dinuclear complexes

Rhenium and technetium are known for their useful applications in nuclear medicine with similar properties. In this study, new diamido dipyridino (N(4)) water-soluble ligands (2-C(5)H(4)NCH(2)NHCO)(2)CH(2), 1 (L(1)H2), (2-C(5)H(4)NNHNHCO)(2)CH(2), 2, and [2-C(5)H(4)N(+)(O)(-)CH(2)NHCO](2)CH(2), 3, were synthesized. Reaction of L(1)H2 with ReOCl(3)(PPh(3))(2) resulted in the novel six-coordinated rhenium(V) complex, trans-ReO(L(1))(OEt), 4. The complex was characterized by spectroscopic methods, and its X-ray crystallographic analysis revealed that rhenium is coordinated to four nitrogen atoms of the ligand and to two oxygen atoms from the deprotonated ethanol and the oxo group respectively in a distorted octahedral geometry. In solution, complex 4 was transformed to a new complex 5, which was proved to be the dinuclear complex mu-oxo [ReO(L(1))](2)O. Reaction of 1 with [n-Bu(4)N][ReOCl(4)] resulted in the neutral complex 6, trans-[ReO(L(1))]Cl. Similarly, when ligand 1 was reacted with [n-Bu(4)N][(99g)TcOCl(4)], the neutral trans-[(99)TcO(L(1))]Cl complex 7 was formed, which upon dissolution transformed into a cationic complex 8, trans-[(99)TcO(L(1))(OH(2))](+)Cl(-). The single-crystal X-ray structure of 8 reveals that the coordination sphere about technetium is a distorted octahedron with four nitrogen atoms in the equitorial plane, while doubly bonded oxygen and coordinated water occupy the apical positions. Further dissolution of 8 resulted in the formation of dinuclear mu-oxo [TcO(L(1))](2)O, 9. This study shows that Tc and Re have similar metal core structures in solution for diamido dipyridino systems, besides similarity in geometrical structure, proved by the X-ray structures on the same ligands.     

Determination of iron by catalytic oxidation of p-aminophenol by hydrogen peroxide

The oxidation reaction of p-aminophenol by hydrogen peroxide was studied in the presence of ferric ions, which catalyzes it. The corresponding rate constants were calculated and the activation energy was determined. A method for ultramicrodetermination of ferric ion was developed using the method of tangents. Determination of ferric ions from 0.5 × 10^?1 up to 4.5 × 10^?2 μg/ml is possible with a relative mean error of ± 1.55%. The influence of several ions was also investigated.     

Optimized automated activation analysis

A combination of special techniques has been developed for optimization of experimental conditions in order to improve the analytical capability, to facilitate automation and to broaden the applicability of instrumental neutron activation analysis. The techniques used are: (1) compensation for the rapid radioactive decay of short-lived nuclides with the increase of the counting efficiency by automatic source movement to the detector during the counting period, to minimize count rate variations and to prolong the counting period, (2) repeated cyclic and cumulative activation to improve the counting statistics, (3) instrumental correction of counting losses at high and varying count rates by a loss-free counting system and (4) differentiation of the reactor neutron spectrum to enhance the counts from the nuclides of interest by reducing matrix interferences. By optimized combination and automation of these techniques significant improvement of the capability of instrumental neutron activation analysis can be achieved.     

1,3-Dipolar cycloaddition reactions of nitrilimines with 1-aroyl-4,5-dihydro-3,4,4-trimethyl-5-methylene-1H-pyrazoles. Synthesis of 6-aroyl-8,9,9-trimethyl-1,2,6,7-tetrazaspiro[4.4]nona-2,7-dienes

From the 1,3-dipolar cycloaddition reactions of 5-methylene-1H-pyrazoles 3 with N-arylnitrilimines the novel spiro-cycloadducts 4 were isolated, in addition to the corresponding 5-(2-aroylhydrazono-1,1-dimethylpropyl)-1H-pyrazoles 5. These pyrazoles 5 were the only products from the reactions of 3 with N-methylnitrilimine 2d. The chemical behaviour of the spiro-cycloadducts 4 was also examined.