Neutron elemental analysis

ANALYSER FEATURES

Unlike the nuclear isotope-based Analyzers developed in the 1980s the CNA uses an electrical neutron source. This new generation of analyzer offers major operational and analytical advantages:

Safety and liability have always been a major concern to the industrial community, it is a significant step forward in terms of user safety and handling to have an electrical neutron source which can be switched off on demand.

Further, the CNA has the ability to control the rate of neutron output reliably at a fixed level to ensure that analytical performance is stable and the calibration is long lasting. Neutron stability over time makes periodic and laborious on-site recalibration unnecessary.

Thanks to PFTNA abilities combined with a comprehensive in-factory calibration process, the CNA is non-material specific and highly robust in applications where highly variable chemistry with widely varying mineralogy exists. Its analytical performance is unaffected by varying belt loading, material origin and changing blend ratios from multiple sources with varying compositions.

The CNA’s on-off capability minimizes neutron and gamma shielding requirements without compromising personnel safety. The CNA can be equipped with the ARP (Automatic Radiation Protection) System, a safe system that automatically shuts off the source whenever a person is in the vicinity, reducing the requirement for heavy and voluminous solid shielding. Reduced size and weight simplify installation and lower cost, while supporting an easy relocation at a later date.

The CNA features a powerful diagnostics program that links the CNA with the EADS SODERN engineering team 24 hours a day for comprehensive remote diagnostics and maintenance services whenever needed. This ensures the highest possible system availability.

The CNA measures the elemental composition of the entire material moving on a conveyor belt in real-time. This makes the timely analytical information perfectly representative and extremely useful for high-speed process control.

EADS SODERN analyzer is operated from a user friendly Microsoft Windows TM based system. The operator interface is also an information gateway that can communicate with plant DCS and PLC networks. Powerful automation software can be combined with the elemental data stream to provide the highest process control benefit.

Highly Advanced Analytical Principle

Using high energy neutrons to determine the chemistry of materials is very useful for process control because the analysis is done instantaneously, allowing many control changes over short periods of time to achieve the target chemistry. The analysis is very representative since all the material on a belt from top-to-bottom and side-to-side is being analyzed.

Pulsed Fast Thermal Neutron Activation analysis involves “illuminating” the raw material with neutrons. By measuring the energy of each gamma ray induced by the interaction of neutron and nucleus of atoms, most elements contained in the raw material are identified and quantified. According to the range of neutron energy, different chemical elements are identified in the material.

The fast neutrons induce gamma rays that allow the measurement of carbon and oxygen and thermal and delayed neutrons induce gamma rays that measure Sulfur, Iron, Calcium, Sodium, Alumina, Silica, Chlorine, copper, nickel and many more elements besides.

The Safest Neutron Technology

Aside from better analytical performance, improving worker safety by using an electrical neutron source is a major benefit of EADS SODERN products. As a small particle accelerator EADS SODERN’s pulsed neutron generator is an ON/OFF electrical neutron source and the basis of PFTNA analysis. The typical lifetime of the existing tube is 8,000 working hours and EADS SODERN is working on the next generation of tube that will reach 15,000 working hours. So safety aside, the CNA is a very cost-effective process control product that is easily justified for a production facility where the process of quality control is critical.

EADS SODERN’s core technology is its sealed neutron tube, evolved from 40 years of experience in designing and manufacturing neutron generation products. Only EADS SODERN builds more than 200 tubes annually for a vast assortment of industrial, defense and security applications worldwide.

Gammas Spectrum Processing System

One of the keys to the quality of analysis by a EADS SODERN analyzer is the power of its data processing system. Built into the analyzer is the most advanced electronics commercially available that includes the fastest spectral processor ever developed specifically for the gamma-ray processing application. This system was fully developed and is manufactured in-house at EADS SODERN.

MORE ABOUT THE PFTNA ANALYSIS

The CNA uses PFTNA (Pulsed Fast Thermal Neutron Activation Analysis) to measure material composition. The physical principles that all these methods are based on have been established for a number of years, and have been extensively used by nuclear physicists and chemists for the investigation of nuclear structures.

Figure 1: Nuclear reactions initiated by thermal neutrons (capture reactions) and fast neutrons (inelastic scattering).

In principle, a neutron impinging on material can initiate one of several nuclear reactions with the chemical elements of the material is composed of (Figure 1). In most of these cases, as a result of these reactions, y-rays are emitted with characteristic and distinct energies. These y-rays are like the “fingerprints” of the elements contained in the material.

By counting the number of y-rays emitted with a specific energy (e.g. the y-rays of sulfur), we can deduce the amount of the element contained within bulk material.
Neutrons are highly penetrating particles. To a lesser extent, the outgoing y-rays are also very penetrating, easily exiting the inspected volume to be detected by an appropriate set of detectors placed outside the material. Thus, the method is non-intrusive (interrogation can take place from a distance of several centimeters) and non-destructive because of the very small amount of radiation absorbed by the interrogated material.

Depending on the chemical elements that we wish to measure, we might have to use neutrons having several energies. In many of the neutron-based applications currently in use, radioisotopic sources (Am-Be, 252Cf) are utilized for neutron production. These sources can excite a host of chemical elements (H, C, S, Fe, etc.) through neutron capture reactions.

However, there are other elements such as C and O needing neutron energies, several MeV higher than those available from the radioactive sources. To satisfy this, a neutron source must produce high energy neutrons for measuring elements such as C and O, and low energy (0.025 eV) for elements such as H and Cl. It has been shown, that such a task can be accomplished by using a pulsed neutron generator. This technique is called Pulsed Fast/Thermal Neutron Activation Analysis (PFTNA).

The basis of PFTNA is a pulsed neutron generator using the deuterium-tritium (D-T) reaction. The pulsed D-T neutron generator provides 14 MeV neutrons which in turn initiate several types of nuclear reactions ((n,n'y), (n,py), (n,y) etc.) on the object under scrutiny. The y-rays from these reactions are detected by a bismuth germanate (BGO) scintillator.
During the neutron pulse, the y-ray spectrum is primarily composed of y-rays from the (n,n’y) and (n,py) reactions on elements such as C and O, and is stored at a particular memory location within the data acquisition system. Between pulses, some of the fast neutrons that are still within the object lose energy by collisions with light elements composing the object. When the neutrons have an energy less than 1 eV, they are captured by such elements as H, N, and Fe through (n,y) reactions.

The y-rays from these reactions are detected by the same set of detectors, but stored at a different memory address within the data acquisition system. This procedure is repeated with a frequency of several kHz. After a predetermined number of pulses, there is a longer pause that allows the detection of y-rays emitted from elements that have been activated, such as Si and P. Therefore, by using fast neutron reactions, neutron capture reactions, and activation analysis, a large number of elements contained in an object can be identified in a continuous mode without sampling.