The Periodic Table Helps Demonstrate PGNAA Detection Limits

The United Nations’ Educational, Scientific and Cultural Organization has declared 2019 the International Year of the Periodic Table (IYPT2019), celebrating the 150th anniversary of the year of discovery of the Periodic System by Dmitri Mendeleev. Mendeleev’s structure was based on similarities in chemical behavior. He used it to predict the properties of then-unknown elements in the gaps, a tradition many chemists followed. According to the UN web site, “The Periodic Table of Chemical Elements is one of the most significant achievements in science, capturing the essence not only of chemistry, but also of physics and biology. It is a unique tool, enabling scientist to predict the appearance and properties of matter on the Earth and in the rest of the Universe.”

An element is a pure chemical substance composed of only one type of atom. The elements in the Periodic Table are arranged in increasing order of their atomic weight, which is the number of protons in the nucleus of an atom. This is known as the Atomic Number and is different for each element. Electrons in shells closest to the nucleus are most strongly bound to the atom. Binding energy increases with atomic number. The higher the number, the higher the weight. If you look at the Periodic Table, you will also see that the number of electrons typically equals number of protons, so that the atom is neutral. The number of neutrons is variable and is what allows some atoms to have isotopes. Qualitative and quantitative techniques for determining the chemical and sometimes isotopic composition of a material can be termed elemental analysis and the Periodic Table can be used as a guide for the capabilities of different elemental analysis techniques.

Prompt gamma neutron activation analysis (PGNAA) and pulsed fast thermal neutron activation (PFTNA) are elemental analysis techniques. The Periodic Table of Elements can be used to help demonstrate PGNAA detection limit guidelines and assist in determining the applicability of this technique to a particular industry or process control strategy.

PGNAA and PFTNA are non-contact, non-destructive analytical techniques used in online analysis systems to determine the elemental composition of bulk raw materials. Both of these techniques are known collectively as neutron activation analysis and function by bombarding materials with neutrons.

The neutrons interact with elements in the materials, which then emit secondary, prompt gamma rays that can be measured. Similar to X-ray fluorescence (XRF), each element emits a characteristic energy signature as it returns to a stable state.

The emitted gamma-rays are detected and an energy spectrum generated which can then be analyzed for elemental composition.

PGNAA analyzers are situated directly on the conveyor belt and penetrate the entire raw material cross-section, providing minute-by-minute, uniform measurement of the entire material stream, not just a sample. Surface analysis technologies such as XRF, X-ray diffraction (XRD), and other spectral analysis technologies measure limited depths and surface areas that may not be representative of the entire amount of material on the belt. With PGNAA, sample errors are reduced, and the high-frequency of analysis helps reduce variation in material quality.

To learn more, visit the PGNAA/PFTNA Technology page.