LIBS vs PGNNA FAQs
1. How is the LIBS different from the PGNAA?
Fundamental difference is in the source of energy, used to excite the substance to perform remote elemental analysis. While PGNAA uses hazardous radioactive isotopes (viz. Cf252, Am241, Cs137, Am241-Be etc.), LIBS-based system deploys high intencity laser beam.
2. How do they compare in terms of safety?
There is obvious safety factor when looking at PGNAA technology – the need to handle radioactive material. This is an ongoing problem with PGNAA machines, due to the half-life decay of the source they require regular restocking with radioactive Californium-252. That restocking creates its own safety hazard every time it is required.
With LIBS, there is no radioactive source involved. In addition, it is easy to configure variety of protection levels with electrical interlocks. To name a few: No or low substance level on conveyor belt, conveyor belt OFF, unauthorised entry in the analyser premises, unauthorised intrusion, motion sensing, etc.
However, the same is not true for the PGNAA. Neutron emission cannot be stopped or switched off. This exposes those servicing the analyser hardware or maintaining the conveyor belt near the analyser to 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 LIBS compare with PGNAA in terms of analytical performance?
LIBS delivers much more energy, between 20–100 mJ/pulse and this results in a higher energy output for analysis, 14 MeV for LIBS compared to PGNAA of around 2.5 MeV. The higher energy of laser brings in analytical advantages. The most important one being ability to accurately analyse Carbon and Oxygen. This makes analysis of coal easy by enabling direct measurement and computation of Calorific Value & Moisture.
Higher energy also results in an overall enhancement in sensitivity and performance. PGNAA analysers suffer from relatively low sensitivity compared to a LIBS machine. The minimal signal accumulation time for PGNAA is typically 1–2 min, but for LIBS technology, the information is received in every single laser pulse – as little as, 20–30 sec. For PGNAA means a slower rate of analysis, and a need for a much higher volume of material to obtain results.
4. Are LIBS analysers expensive to own and operate as compare to PGNAA systems?
Not true. The PGNAA analysers, using hazardous radioactive isotopes with finite half-life (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. The LIBS analyser on the other hand provides energy on-demand. The laser in a LIBS analyser can typically last up to 10 years for 8-hour daily operation. A lot of customers find that costs of using LIBS technology are about 20% lower, compared to that of PGNAA.
5. Is there any issue with LIBS compared to PGNAA?
LIBS is a surface method. This laser-based technology can only affect the surface of material on the conveyor belt. PGNAA radiation is absorbed throughout the mass of the material. This means that with LIBS technology there is a need to ensure that material surface represents the whole volume of material for accurate measurement – the substance needs to be homogenous. Usually, it is simply a question of installation point. In mining, bulk materials usually arrive at the conveyor after explosive and crushing processes that universally considered to be producing a homogeneous mix. However, if that is not the case, to make the material ready for real-time analysis by LIBS system, adding a simple and inexpensive mixing device on the conveyor belt prior to the online analyser solves the issue.
6. What are the various applications of LIBS based online analysers?
Worldwide, LIBS based analysers are successfully performing and serving in the Phosphates, Potash, Refractories and Iron Ore applications.
7. How easy is the maintenance of LIBS analysers?
The maintenance needs for a LIBS based analysers are minimal as compared to the PGNAA systems that need periodic recalibration once in a few months to compensate for 5% to 10% drop in neutron intensity because of source decay. LIBS systems require only periodic air filter and laser lamp change – can be performed by user personnel without any special gear and training.