The tagged neutron method makes it possible to perform non-destructive elemental analysis of matter at a distance.
MMN consists in irradiating the object of analysis with beams of fast neutrons with energy of 14.1 MeV, which are produced in the reaction of deuterium d collision with tritium 3H
d+3Н → 4He+n
This procedure is called neutron labeling. In this reaction, the neutron and the α-particle (4He nucleus) fly in almost opposite directions. Therefore, by recording the α-particle accompanying the neutron, the direction of departure of the neutron can be determined.
The labeled neutrons hitting the object of study induce inelastic scattering reactions
n+A → n’+A*, A*→ γ+A
Gamma-ray spectrum of apatite-nepheline ore sample
From the relationships between the lines, the concentrations of the various elements can be determined.
As a result of these reactions, the excitation of the nucleus is relieved by the emission of gamma quanta with an energy spectrum characteristic of each chemical element.
Samples in the measuring tray of the plant
Advantages of MMN
Analysis of samples of large size (up to 300 mm) and large mass (up to 10 kg)
The high penetrating power of fast neutrons combined with the emission of hard gamma quanta with energies of 1-8 MeV from samples allows efficient averaging of elemental composition over the entire sample volume. The great depth of FNM distinguishes it from the method of X-ray fluorescence analysis (XRF), which can analyze only the surface layer of the sample, no more than a few mm thick, at a single point.
No sample preparation
The sample is placed in the receiving tray of the unit as it was taken from the quarry. The moisture content of the sample does not affect the accuracy of the analysis.
Currently, MMN analyzers can determine concentrations of 24 elements:
Na, Mg, C, N, O, F, Al, Si, P, S, Cl, K, Ca, Ti, Cr, Mn, Fe, Ni, Cu, Zn, Zr, Pb, Sn, Bi
Sharp suppression of background from the environment
By using α-γ coincidence, the gamma ray spectrum is analyzed only for the sample region, resulting in a more than 200-fold improvement in signal-to-noise ratio. It becomes possible to correctly account for the background from sample activation.
Total elemental composition in a single measurement
The concentrations of all major elements of the sample are determined from the data collected in one measurement. For apatite-nepheline ore, the concentrations of 10 oxides are determined per measurement.
The possibility of determining the elemental composition of light elements - C, O, Na, K, F
MMN uses inelastic fast neutron scattering reactions, therefore it has a unique possibility to determine the elemental composition of light elements. This is its important advantage over XRF, X-ray radiometric methods, neutron activation analysis. MMN can analyze coal by direct determination of carbon content.
