▶ Neutron Activation and Neutron Activation Analysis
▶ Neutron Activation Analysis Technology from Phoenix
▶ What Is Neutron Activation?
▶ What Is Neutron Activation Analysis?
▶ Neutron Activation Analysis for Materials Testing
▶ Neutron Activation Analysis for Radiotherapy
▶ Neutron Activation Analysis for Other Uses
▶ Phoenix Neutron Activation Case Studies
▶ Contact Us
Neutron activation is a physical phenomenon fundamental to nuclear technology. When we bombard material with neutron radiation, the material may become radioactive, emitting a unique signature of radiation depending on its chemical makeup (the elements present in the material). This phenomenon of neutron irradiation is the cornerstone of every nuclear fission reactor. It can also be used for neutron activation analysis (NAA), an extremely precise analytical method useful for nondestructive testing, destructive materials testing such as radiation survivability testing, analysis in other fields such as geology, archaeology, and agricultural science, and many other applications and analytical techniques.
Like neutron radiography, NAA can be a difficult tool to make use of due to a dearth of convenient neutron sources. While most forms of NAA can be done with far smaller neutron output than are required for useful neutron radiography, a higher output source of neutrons is still preferable for some applications of NAA.
Most neutron activation analysis is performed with fission reactors, isotope sources, or fusion neutron sources. Among these techniques, nuclear reactors produce the highest neutron output, but are very limited by their large size and high logistical overhead. Isotope sources rely on neutron emitting elements such as Californium-252, many of which are synthetic, have a relatively short half-life, and can be difficult to acquire. Fusion neutron sources, which produce neutrons by combining atoms of deuterium or tritium, run the gamut in both size and neutron output. For some purposes, such as oil well logging, a fusion neutron source small enough to fit on a benchtop is extremely useful for neutron activation analysis. However, for other needs, a more powerful source of neutrons with a larger neutron output is required.
Phoenix develops and builds the strongest deuterium-deuterium and deuterium-tritium neutron generators in the world. Our generators provide a convenient means to perform neutron activation analysis techniques that require higher neutron output than other fusion sources or isotope sources without the need for reliance on a nuclear reactor facility or other sources of neutrons such as neutron emitting isotopes like californium-252.
Neutron activation is a physical phenomenon that occurs when a neutron collides with an atom. Any given atom is made up of mostly empty space between the furthest edge of its electron cloud and its nucleus, which is tiny by comparison; because neutrons have no electrical charge, they cannot interact with electrons and instead can only interact with the nucleus, which itself contains other neutrons.
When a neutron collides with a nucleus, the nucleus can absorb the neutron. When an atom contains an extra neutron, it becomes an isotope with extra energy in a process called “neutron capture.” In many cases of neutron capture, an atom with an extra neutron will become an unstable isotope, or radioisotope. In order to return to a state of stability, it must expel the extra energy the neutron gave it.
Different atoms react with neutrons in different ways depending on their atomic makeup. One way unstable isotopes shed this energy is by releasing a short burst of gamma rays. Atoms can also expel this energy and return to a more stable state by releasing beta particles, alpha particles, neutrons, or smaller atoms (i.e. fission byproducts). For example, when fissile uranium is bombarded with neutrons, it releases more neutrons along with smaller elements. Specific nuclides, or atoms characterized by the number of protons and neutrons in their nuclei, are especially of interest when it comes to neutron irradiation.
In other words, when you bombard a material with neutrons, some of the atoms comprising the material will absorb some of the neutrons and become an unstable radionuclide. In order to return to a state of stability, the radionuclide must release radiation to expel the excess energy. As a result, the material will be, for a short period, somewhat radioactive. How radioactive it will be, and how long it will stay radioactive, depends on the nature of the radionuclides produced by neutron irradiation. The byproducts of neutron activation can remain radioactive for anywhere from a few fractions of a second to a few years.
Certain materials are more conducive to neutron activation than others. Some substances are very difficult to activate and will not react very much to neutrons. Other materials might react much, much more strongly and readily. How much a material might react to neutron irradiation is an extremely important fact to keep in mind when developing materials for use in high-radiation environments. Materials that are activated can undergo negative transformations due to the effects of radiation and become weaker or less suitable for their roles in critical components, resulting in complications and hazardous situations for personnel or for the environment.
Neutron activation isn’t always an undesirable event. Not only is it the cornerstone of the same nuclear fission reactions we rely on to produce energy, it is also actually a very useful tool for materials evaluation. When radionuclides expels excess energy in the form of, for example, gamma rays, how much energy they expel differs depending on the elements present.
Neutron Activation Analysis is a method used to determine the elemental composition of a material by analyzing the different energies produced during neutron activation.
Different radionuclides release different energies of gamma radiation, and by measuring the gamma ray energies produced by neutron activation, you can actually determine a material’s multi element composition – specifically, the amounts of each element it contains, including trace elements (as in trace element analysis). Neutron activation analysis is a very sensitive and precise method of materials analysis for detecting trace elements present in a material, especially useful considering trace elements can be tough to detect under certain thresholds using other means.
Neutron activation analysis can be done with both a thermal neutron source, which produces low energy neutrons, or with fast neutrons, or high energy neutrons. High energy neutrons interact with an element’s atomic nuclei in a slightly different way than low energy neutrons. Depending on the size and density of the material, either a thermal neutron source or fast neutrons can be better suited for neutron activation analysis.
Neutron activation analysis has a plethora of different use cases for non destructive testing. For example, RIKEN, a Japanese materials testing organization, has been developing a mobile neutron activation tool that can be used to scan the concrete used in bridges and highways for signs of saltwater erosion similar to our NEMESIS IED-detection system. Non destructive concrete inspection tools and methods are of critical importance for assessing our infrastructure and keeping people safe.
Other areas that often involve neutron activation in materials testing include radiation hardening and survivability testing, which is especially critical for electronics used in spacecraft, satellites, and defense systems as well as shielding used in nuclear reactors. Neutron irradiation is performed for these materials testing applications and is used to determine if neutron activation causes radioactive isotopes to produce gamma radiation or other unwanted forms of radiation. Whether irradiation produces long-lived or short-lived radioactive isotopes that will sooner or later decay back into stable isotopes is an important question to answer for many of these materials, since unwanted neutron activation in these situations can cause unforeseen damage.
Neutron activation is also used as a non destructive method to scan for defects in nuclear fuel rods and can be used to detect explosives, special nuclear material, and narcotics and other contraband.
Another application of neutron activation can be found in medicine.
In boron neutron capture therapy, medical professionals make use of boron’s neutron-absorbent properties to destroy cancer cells. A solution rich in the element boron that binds to cancer cells is introduced into a patient’s body and then a beam of neutrons is shot at the tumor. When a boron nuclide becomes an activated radionuclide, it releases alpha particles, which do not travel very far before they decay but will destroy the cells in their path.
By this process, neutron activation is used to destroy tumors without causing excessive damage to the surrounding healthy tissue. Neutron capture therapy is still an experimental form of radiotherapy, but recent testing has shown promising results.
Neutron activation is also used to create medical radioisotopes. Medical radioisotopes, which are potent enough to create detectable levels of radiation within the human body when ingested or injected, yet short-lived enough that they do not damage the patient, are used as contrast and tagging agents for medical scans. These isotopes are created through nuclear fission. When uranium is bombarded with neutron radiation, its activation causes it to split into other, smaller elements.
One of these specific medically vital radionuclides is the isotope Molybdenum-99, from which radioisotopes used daily for in lifesaving medical scans are derived.
Radiochemical neutron activation analysis and instrumental neutron activation analysis are used across many fields and disciplines as a tool for determining the chemical and elemental compositions of materials. Archaeologists have used radiochemical neutron activation analysis to inspect artifacts and determine the elements present without damaging them. Art historians have done the same with paintings.
Agricultural scientists studying soil composition and by geologists to research the formation of our planet’s crust also need to determine the multi element makeup of samples they collect, which is one common use of neutron activation analysis. Semiconductor manufacturers also use neutron activation analysis to detect impurities in semiconductors.
Forensic scientists have even used neutron activation analysis in criminal investigations, its first use being in the arrest of serial murderer John Norman Collins in 1969.
Applications of neutron activation analysis include:
At Phoenix, we use our high neutron flux neutron generators to induce neutron activation mainly for application in nondestructive testing, such as radiation effects testing, in which materials irradiated by neutron radiation for sustained periods in order to test how well they function in high-radiation environments and determine at which point radiation results in a loss of structural integrity or function.
By configuring our high neutron flux neutron generators to produced pulsed fusion output instead of sustained output, therefore releasing large amounts of neutron radiation in very short bursts, our systems can be used for other applications of neutron activation analysis as well.
In 2019, Phoenix installed a radiation effects testing system for a European defense agency, which will allow them to perform radiation survivability testing on the electronic components without the need for a nuclear reactor.
Neutron activation is a key component in Phoenix’s prototype standoff IED detection system, NEMESIS. NEMESIS is a prototype mobile deuterium-deuterium neutron generator specially configured for mobility, designed to be installed at the head of a military convoy and used to scan ahead for hidden IEDs by producing a pulsed neutron output and detecting the resulting gamma radiation.
IEDs, like most explosives, contain energetic chemicals rich in elements such as nitrogen and hydrogen, which give off characteristic gamma rays when bombarded with neutrons. When a beam of neutron radiation passes through a hidden IED, the energetic material releases gamma rays that can then be detected by an onboard detector. By analyzing the energies of the gamma rays, NEMESIS can not only detect IEDs, but also determine the composition of the explosive material itself.
Phoenix is also researching the use of neutron activation at border crossings and ports of entry to detect smuggled contraband such as special nuclear material and narcotics.
Phoenix and its sister company SHINE Medical Technologies also use fusion neutron sources to produce the element Molybdenum-99, a necessary medical isotope. By inducing fission in low-enriched uranium using Phoenix’s high-yield neutron generators, SHINE’s production facility will be able to produce large quantities of the isotope without the need for a nuclear reactor. When SHINE’s Janesville facility begins producing Molybdenum-99 in 2021, it will be able to meet the demand for half of the United States’ medical facilities, one-third of the global supply of the element in total.
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