Detection of diamonds using the tagged neutron method

Current technologies for the detection and extraction of diamonds involve the repeti tive mechanical crushing of kimberlite ore, resulting in the damage of real diamonds.

In particular, the breakage of large diamonds into smaller constituents decreases

their value drastically, resulting in huge financial losses to mining companies. This

dissertation focuses on testing a newly developed technology for the detection of di amonds in the kimberlite ore prior to crushing processes, thus preventing breakage

and retaining their value. This technology is based on the tagged neutron method

which involves the irradiation of the ore by fast neutrons of 14.1 MeV and the detection of characteristic gamma rays from the inelastic scattering of neutrons. The

criterion for diamond detection is the presence of increased carbon concentration

within a certain area of the kimberlite sample.

This dissertation presents the results of the testing of the pilot prototype called

Diamant-1000 where the neutron source is a portable neutron generator with inbuilt

256 channel alpha-detector from gallium arsenide. The characteristic gamma-rays

are detected by a system of 22 bismuth germanium oxide detectors in coincidence

with signals from the alpha detector. The Diamant-1000 prototype was tested

on kimberlite ore from the Archangelsk mine in Russia and the Letseng mine in

Lesotho. Diamond imitators ranging from 8 to 20 mm are inserted in the kim berlite stones ranging from 30 to 150 mm, which are placed in trays and passed

through the neutron module. The minimum size of the diamond imitator detected

was 8 mm (5 carats). The prototype had a throughput of about 1 ton/hour (1060

kg/hr) with false alarms rate of 3%. The probability to detect diamonds hidden in

kimberlite ore of the range -150 + 100 mm is 95%, whereas for the kimberlite ore

within the range of -90 + 40 mm the probability is 97%. The electric consumption

of prototype is 0.6 kW/ ton of ore.

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The study demonstrates that the tagged neutron method has the potential to be

of significant benefit to mining industries in terms of profits, minimum waste and

minimal impact on the environment. This method is especially valuable for pre venting damages of large diamond