Studies of air pollution by biological indicators using 14 MeV neutron activation analysis

Neutron activation analysis, using a SAMES-T-400 neutron generator, producing 14 MeV neutrons via the T(d,n)4He reaction, was applied to the determination of polluting elements in moss, lichens and parks, in order to study the nature and the possible sources of air pollution in the regions of Rabat, Kenetra, Maamoura and Ifrane. The aim of this work was to study: 1/ the fixation and accumulation of air polluting elements by these species. 2/ the local fluctuation of results and the principal error sources in atmospheric pollution survey, by these bio-indicators. About 40 samples collected in 11 sites were activated in an intense neutron flux of about 5.109 neutrons/cm2.s, and analyzed by gamma spectrometry using HPGe detectors. The first analysis of spectra has shown the existence of the following elements: Si, Mg, Al, Cl, K, Ca, Ti, Fe, Zn, Rb, Sr, Ba and La. An experimental procedure is given for the correction of the 27Al(n,p)27Mg - 30Si(n,α)27Mg and 24Mg(n,p)24Na- 27Al(n,α)24Na interferences. Aluminum was determined using the 843,7 keV line, with the following corrections: 1) Subtraction of the contribution of the 846.8 keV line, deduced from the spectrum used to determine Fe. 2) Subtraction of the contribution of 27Mg produced by the 30Si(n,α)27Mg interfering reaction. For this last correction, a pure silicon sample has been activated and measured, in the same experimental conditions as the samples, to evaluate the ratio R(Si) of the 843.7 keV and 1779 keV lines. This ratio along with the 1779 keV peak area was used to calculate the contribution of the interfering reaction under the 843.7 keV line. For the determination of Mg, the 1368.5 keV line was used, after the subtraction of the contribution of 24Na produced by the 27Al(n,α)24Na interfering reaction. This contribution was calculated using the ratio RAl of the 1368.5 keV and 843.7 keV lines, emitted in the decay of 24Na and 27Mg produced by the reactions 27Al(n,α)24Na and 27Al(n,p)27Mg, in the standard containing Al2O3. Other analyses are in progress to search for other polluting elements and to make quantitative analysis. The results are compared with those obtained by X ray fluorescence analysis. (author)