PFTNA v/s PGNAA: Frequently Asked Questions

1. How is the PFTNA different from PGNAA?

The basic difference lies in the ‘neutron source’ or the method of generating neutrons. While the PGNAA deploys hazardous radioactive isotopes (viz. Cf252, Am241, Cs137, Am241-Be etc.), the PFTNA based system generates neutrons electrically in a pulsed manner, allowing the detector(s) to differentiate between the 3 neutron-nucleus interactions. High frequency pulsing can only be achieved with an electric neutron source.

2. How do they compare in terms of safety?

Being electrically operated, highest level of safety is assured in the PFTNA. It is easy to configure variety of protection levels with electrical interlocks. To name a few – No or low Sample on the belt, Conveyor belt OFF, Forced entry in the analyser premises, unauthorised intrusion, Motion sensing etc. However, the same is not true for the PGNAA. Unlike as in the PFTNA, neutron emission cannot be stopped or switched off. This exposes those servicing the analyser hardware or maintaining the conveyor belt near the analyser to unhealthy neutron and gamma radiation. Some analysers include a shielding block that reduces the radiation when the analyser is not in use. This minimises but does not eliminate the problem.

3. How does the PFTNA compare with PGNAA in terms of analytical performance?

The neutrons generated by the PFTNA generators bear high energy of 14 MeV as compared to that of mere 2.5 MeV in the PGNAA emanating from Cf252 which is ~ 5.6x weaker. The higher energy of neutron brings in a host of analytical advantages. The most important one being ability to analyse Carbon and Oxygen. This makes analysis of coal easy by enabling direct measurement and computation of Calorific Value & Moisture. Thus making a PFTNA based system a ‘complete’ Coal analyser capable of full proximate and ultimate analysis. Higher neutron energy also results in an overall enhancement in sensitivity and performance.

4. What are the other benefits of 14 MeV PFTNA neutrons as compared to the PGNAA?

Ability to handle wide ranging mass variation on the conveyor belt and immunity towards particle size are some added advantages. Typically, a PFTNA based analyser can handle mass variation from 50% to 200% of the rated conveyor capacity with no limitation on particle size. This is far superior performance as compared with the PGNAA based analysers that operate within a very narrow tolerance of ±10% in belt load and particle size ≤40mm

5. Isn’t the PFTNA with14 MeV neutron energy more dangerous as compared to the PGNAA?

No. Higher energy of neutrons in no manner means more danger. What actually matters is the level of radiation measured around such analysers while they are in operation and during ‘Power Off’. The analysers conforming to ALARA and other International / European Safety norms have their radiation emission well within prescribed safe limits. Typically it could be < 8 μ-Sieverts/hour during operation and 0 μ-Sieverts/hour when ‘Power Off’. It all depends on the shielding and protection interlocks (uniquely possible only in the PFTNA systems). The higher energy neutrons necessitate different shielding techniques, but as with Cf252 units, they can be adequately shielded during operation. The difference is when the analyser is off. Since the PFTNA analyser can be turned off, often less shielding is used and a simple fence and switch provides unmatched safety.

6. Does that mean PFTNA analysers are bulkier, heavier and come with extra shielding?

No. The PFTNA based analysers are as lighter as their PGNAA counterparts. In fact the PFTNA based analysers are much more compact and easier to install with no need for any additional air-conditioned rooms for housing the operator console. Since the analyser can be turned off, often less shielding is used. Also the analysers can be installed on any terrain be it on the flat ground level or inclined elevations.

7. The PFTNA analysers are expensive to own and operate as compare to PGNAA systems

Not true. The PGNAA analysers using hazardous radioactive isotopes with finite half-life (viz. 2.6 years for the Cf252) need to be compulsively replenished or topped-up periodically. This is irrespective of the analyser operation and usage time. Whether the analyser works 8 hours/day, round the clock or may be defunct and waiting for fixing of some conveyor belt breakdown – the loss of neutrons and decay of radioactive source (Cf252) is imminent. The PFTNA on the other hand with its unique On-Off technology has neutron on-demand. Given the prevailing life span of 18000 – 20000 working hours, the neutron tube in a PFTNA analyser can typically last up to 6 years for 8 hour of daily operations. For a 24/7 operation, the Cf252 based analysers WERE more economical. However, increasing tube life and rising costs of Cf252 have eliminated that advantage.

8. What are the various applications of PFTNA based Online analysers?

Worldwide, hundreds of PFTNA based analysers are successfully performing and serving in the Cement (for limestone stockpile and raw mix applications), Coal, Iron Ore, Copper and Nickel Ore applications.

9. How easy it is to maintain such analysers?

The maintenance needs for a PFTNA based analysers are minimal as compared to the PGNAA systems that need periodic recalibration once in 3 months (Cf252 based) to compensate for 5% drop in intensity owing to its 2.6 year half life. The PFTNA generator voltage is continuously adjusted as the tube ages providing constant neutron flux. The decaying Cf252 sources provide a constantly decreasing neutron flux which reduces precision and necessitates recalibration. The Neutron Tube can be easily replaced by the user himself without any special “Radiation Protection” gears and training.

Remember - NO RADIATION when Power OFF!!