A. J. Kestelman

Heavy metals in the vicinity of a chlor-alkali factory in the Upper Negro River ecosystem, Northern Patagonia, Argentina.

A study on heavy metal contents was performed in sediments and biota of the Upper Negro River (Alto Valle) aquatic system, Northern Patagonia, Argentina. The irrigation system of the Neuquén and Negro Rivers runs alongside these rivers for 150 km, supporting intensive agricultural and economical activities, mainly related to fruit production. A mercury cell chlor-alkali factory operated between 1951 and 1995. Close attention was given to the surroundings of the plant, located next to the Main Irrigation Channel, and to the PII drainage channel which received the plants effluents between 1951 and 1979. From 1979 until its closure, the effluents were pumped above a ravine to a series of evaporation and decantation pools. Mercury and other heavy metals and metalloids (Ag, As, Ba, Co, Cr, Cs, Ni, Sb, Se, U and Zn) contents were measured for bottom sediments of the river and irrigation and drainage channels, for two widespread species of macrophytes (Potamogeton pectinatus and Myriophyllum brasiliensi), and for liver and muscle of native fish Odontesthes microlepidotus. River bed sediments show no evidence of heavy metal accumulation, however, biota might indicate that contaminants are entering the rivers. Mercury was the only element accumulated in the Main Irrigation channel sediments, the highest contents occurring in the surroundings of the nowadays shut-down chlor-alkali plant, returning to background values approximately 40 km downstream the plant. At the plant site, sediments from the center of the channel showed a decrease in Hg content in the upper 10 cm layer, ranging from 0.8 to 3.4 microg g(-1), and from 2.8 to 13.7 microg g(-1) in the next 10 cm lower layer. Conversely, the PII drainage channel sediments showed accumulation of Hg (2-4 microg g(-1)), distributed uniformly at different depths and along the channel, until its mouth at Negro river. Mercury contents of macrophytes downstream the chlor-alkali plant are higher than the baseline for the area, and macrophytes and fish liver from the PII drainage channel present the highest content in this element. The drainage channel system showed different degrees of impact, those channels flowing through densely populated areas being the most affected.

Neutron Activation Analysis of Soils and Loess Deposits, for the Investigation of the Origin of the Natural Arsenic-Contamination in the Argentine Pampa

By M. A. Arribere,1. M. Cohen, L. H. Ferpozzi, A. J. Kestelman, V. A. Casa and S. Ribeiro Guevara 1 Laboratorio de Anälisis por Activation Neutronica, Centra Atomico Bariloche e Institute Balseiro, Comision National de Energia Atomica y Universidad Nacional de Cuyo, 8400 Bariloche, Argentina 2 Comision Nacional de Energia Atomica, Centra Atomico Ezeiza, Consejo de Direction Agencia Minipost, 1842 Buenos Aires, Argentina 3 Direction Nacional de Servicio Geologico, Avda. Julio a. Roca 651, 1322 Buenos Aires, Argentina 4 Comision Nacional de Energia Atomica, Centra Atomico Constituyentes, Gestion de la Calidad, Avda. del Libertador 8250,1429 Buenos Aires, Argentina

Determination of nuclear constants of reactions induced on zinc by short irradiations with the epithermal and fast components of a reactor neutron spectrum

Summary Cross sections, averaged over a 235U fission neutron spectrum, of some threshold reactions induced on zinc after short irradiations, have been measured. The studied reactions and the corresponding values are: 64Zn(n, p) 64Cu, (37.4 ± 1.4) mb; 64Zn(n, 2n) 63Zn, (23.4 ± 2.0) μb; 66Zn(n, p) 66Cu, (0.775 ± 0.079) mb; 68Zn(n, p)68mCu, (5.32 ± 0.65) μb; and 68Zn(n, α) 65Ni, (52.1 ± 2.3) μb, all referred to the cross section of the 27Al(n, p) 27Mg standard reaction, (3.84 ± 0.18) mb. Working values for the resonance integrals of the reactions 70Zn(n, γ) 71Zn and 70Zn(n, γ)71mZn, referred to the tabulated value for the resonance integral of the 68Zn(n, γ)69mZn reaction, (0.24 ± 0.03) b, were also obtained. The results were (0.1350 ± 0.0093) b and (0.157 ± 0.029) b, respectively.

Use of the Absolute Parametric Method to Evaluate the Analytical Significance of Threshold Reactions on P, Si, Al and Mg by NAA

We investigated the use of threshold reactions on magnesium, aluminum, silicon and phosphorus to determine elemental concentrations and also to correct analytical interferences, using the parametric method. The reactor neutron spectrum averaged cross sections of the threshold reactions on these elements were referred to the (111±3) mb value for the 58Ni(n,p)58g+mCo reaction cross section. The results of the cross section measurements are: 25Mg(n,p)25Na, 1.57±0.12 mb; 28Si(n,p)28Al, 5.68±0.25 mb; 29Si(n,p)29Al, 3.02±0.15 mb; 30Si(n,α)27Mg, 0.1346±0.0090 mb; and 31P(n,α)28Al, 1.912±0.083 mb. The values for the cross sections of the following reactions: 24Mg(n,p)24Na, 1.441±0.092 mb; 27Al(n,p)27Mg, 3.84±0.18 mb; and 27Al(n,α)24Na 0.721±0.028 mb were re-measured to check the methodology. We present the application of these values to the analysis of some reference materials.

Determination of the 54Fe(n, 2n)53gFe and 54Fe(n, 2n)53mFe cross sections averaged over a 235U fission neutron spectrum

The reaction cross sections averaged over a 235U fission neutron spectrum have been measured for the 54Fe(n, 2n)53gFe and 54Fe(n, 2n)53mFe threshold reactions. The values found are, respectively: (1.14±0.13) mb, and (0.52±0.16) mb. The measured cross sections are referred to the (111±3) mb standard cross section of the 58Ni(n, p)58m+gCo reaction. The (81.7±2.2) mb standard cross section value for the 54Fe(n, p)54Mn reaction, was also used as a monitor to check the results obtained with the Ni standard, leading to an excellent agreement.

Determination of the fission averaged cross sections of some threshold reactions induced on chlorine, potassium, and calcium, and their role in the development of self-validated methods of neutron activation analysis

The feasibility of validating data obtained in the determination of chlorine, potassium, and calcium by neutron capture activation analysis, through their determination using threshold reactions has been studied. To this purpose the authors experimentally determined the following fission neutron spectrum averaged cross sections (in mb):37Cl(n,p)37S, 0.234±0.015;41K(n,α)38Cl, 0.740±0.044;42Ca(n,p)42K, 3.09±0.22;43Ca(n,p)43K, 2.27±0.12;44Ca(n,p)44K, 0.074±0.013. The application of these values to the analysis of some reference materials are presented. Also, the problem of mutual interferences has been addressed for the following pairs:36S(n,Γ)37S and37Cl(n,p)37S;37Cl(n,Γ)38Cl and41K(n,α)38Cl;41K(n,ψ)42K and42Ca(n,p)42K.

Measurement of the50Ti(n,α)47Ca reaction cross section averaged over a235U fission neutron spectrum

The235U fission neutron spectrum averaged cross section for the50Ti(n,α)47Ca reaction was experimentally determined by irradiation of titanium with reactor neutrons. A value of (9.7±1.1) μb was found for this cross section, using (307±11) μb for the48Ti(n,p)48Sc spectrum-averaged cross section that was used as a standard. The50Ti(n,α)47Ca spectrum-averaged cross section was also semiempirically evaluated by numerically integrating, through the ENDF/B-V representation of the235U fission neutron spectrum, the available experimental differential cross section data.

Determination of the fission-neutron averaged cross sections of some high-energy threshold reactions of interest for reactor dosimetry

For three high threshold reactions, we have measured the cross sections averaged over a 235U fission neutron spectrum. The measured reactions, and corresponding averaged cross sections found, are: 127I(n,2n)126I, (1.36±0.12) mb; 90Zr(n,2n)89mZr, (13.86±0.83) mb; and 58Ni(n,d+np+pn)57Co, (274±15) μ b; all referred to the well known standard of (111±3) mb for the 58Ni(n,p)58m+gCo averaged cross section. The measured cross sections are of interest in nuclear engineering for the characterization of the fast neutron component in the energy distribution of reactor neutrons.

Threshold reaction cross sections of nickel isotopes, averaged over a 235U fission neutron spectrum

Abstract We have measured, for nickel isotopes, several threshold reaction cross sections averaged over a 235U fission neutron spectrum. The measured reactions, and corresponding averaged cross sections found, are the following: 60Ni(n,p)60mCo, 1.499 ± 0.083 mb; 61Ni(n,p)61Co, 1.632 ± 0.096 mb; 58Ni(n,2n)57Ni, 4.72 ± 0.26 μb; 58Ni(n, d+np+pn)57Co, 275 ± 15 μb; 58Ni(n,p)58gCo, 74.8 ± 2.3 mb; and 58Ni(n,p)58mCo, 36.6 ± 1.2 mb; all referred to the well-known standard of 111 ± 3 mb for the 58Ni(n,p)58m+gCo-averaged cross section. The measured cross sections are of interest in nuclear engineering for the characterization of the fast neutron component in the energy distribution of reactor neutrons.