PGNAA ve PFTNA
Prompt gamma neutron activation analysis (PGNAA) and pulsed fast thermal neutron activation (PFTNA) are non-contact, non-destructive analytical techniques used in online analysis systems to determine the basic composition of bulk raw materials. Both of these techniques are collectively known as neutron activation analysis and function by bombarding materials with neutrons.
Neutrons interact with elements in materials and then secondary emitting gamma rays can be measured. Similar to X-ray fluorescence (XRF), each element emits a characteristic energy as it returns to a steady state.
PGNAA and PFTNA Overview
Instantaneous gamma neutron activation analysis and pulsed rapid thermal neutron activation are based on the subatomic reaction between a low energy neutron and the nucleus of an atom. When a neutron of thermal or lower energy (<0.025 eV) comes close enough to the nucleus of an atom or collides with it, an interaction occurs between the neutron and the nucleus. Energy from the neutron is transferred to the nucleus and temporarily elevates it to an excited energy state. Energy is then released almost instantaneously in the form of a gamma ray. The gamma ray delivered has a different energy associated with the atom from which it is released. In fact, the emitted gamma ray is like the "fingerprint" of the element. The emitted gamma rays are detected and an energy spectrum is created that can then be analyzed for the basic composition.
PGNAA and PFTNA online analyzers detect gamma rays using scintillation detectors. These detectors consist of a high purity crystalline structure that when exposed to gamma rays produces photons that generate energy proportional to the energy of the gamma rays entering the crystal. A photomultiplier tube connected to the crystal converts the light pulses into electrical signals that are energy-proportional to the photon. Advanced high-speed electronic circuits then amplify and process electrical pulses to form a composite energy spectrum. The spectrum is analyzed to determine information about certain elements.
Each element has a different tendency to interact with neutrons; those with high propensity can be measured. In addition, there must be enough elements to interact with neutrons. What is recorded as the "detection threshold" for an element is a function of the amount of material analyzed, the percentage of the element in that sample, and the tendency of that element to interact with neutrons.
