ANS is committed to advancing, fostering, and promoting the development and application of nuclear sciences and technologies to benefit society.
Explore the many uses for nuclear science and its impact on energy, the environment, healthcare, food, and more.
Division Spotlight
Radiation Protection & Shielding
The Radiation Protection and Shielding Division is developing and promoting radiation protection and shielding aspects of nuclear science and technology — including interaction of nuclear radiation with materials and biological systems, instruments and techniques for the measurement of nuclear radiation fields, and radiation shield design and evaluation.
Meeting Spotlight
2021 ANS Winter Meeting and Technology Expo
November 30–December 3, 2021
Washington, DC|Washington Hilton
Standards Program
The Standards Committee is responsible for the development and maintenance of voluntary consensus standards that address the design, analysis, and operation of components, systems, and facilities related to the application of nuclear science and technology. Find out What’s New, check out the Standards Store, or Get Involved today!
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Sep 2021
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Nuclear Science and Engineering
October 2021
Nuclear Technology
Fusion Science and Technology
August 2021
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Matthew Denman: On Probabilistic Risk Assessment
Matthew Denman
Probabilistic risk assessment is a systematic methodology for evaluating risks associated with a complex engineered technology such as nuclear energy. PRA risk is defined in terms of possible detrimental outcomes of an activity or action, and as such, risk is characterized by three quantities: what can go wrong, the likelihood of the problem, and the resulting consequences of the problem.
Matthew Denman is principal engineer for reliability engineering at Kairos Power and the chair of the American Nuclear Society and American Society of Mechanical Engineers Joint Committee on Nuclear Risk Management’s Subcommittee of Standards Development. As a college student at the University of Florida, Denman took a course on PRA but didn’t enjoy it, because he did not see its connection to the nuclear power industry. Later, during his Ph.D. study at the Massachusetts Institute of Technology, his advisor was Neil Todreas, a well-known thermal hydraulics expert. Todreas was working on a project with George Apostolakis, who would leave MIT to become a commissioner of the Nuclear Regulatory Commission. The project, “Risk Informing the Design of the Sodium-Cooled Fast Reactor,” was a multi-university effort funded through a Department of Energy Nuclear Energy Research Initiative (NERI) grant. Todreas and Apostolakis were joined in this project by a who’s who of nuclear academia, including Andy Kadak (MIT, ANS past president [1999–2000]), Mike Driscoll (MIT), Mike Golay (MIT), Mike Lineberry (Idaho State University, former ANS treasurer), Rich Denning (Ohio State University), and Tunc Aldemir (Ohio State University).
Nuclear science is far-reaching in the fabric of modern life. It can help explain the origins of the universe or how x-rays reveal the bones in your body. In fact, nuclear science is at the heart of so many of the technologies that improve our lives, that it’s easy to take for granted how those technologies came to be. But behind every innovation and discovery in the nuclear fields, is a scientist or engineer researching the atomic nucleus and how to use it to improve our lives.
Scientists used to think there was nothing smaller than an atom.
Today, we know the atom is made of smaller particles, and those are made of even smaller particles.
The nucleus is made of protons and neutrons; each has the same mass: 1 amu (atomic mass unit).
Protons and neutrons aren’t exactly alike, though; protons have a positive charge while neutrons don’t have a charge.
Electrons are so small that they have nearly no mass at all. A single electron has only 1/1836 amu. Electrons are also negatively charged.
All of the known elements are organized on the periodic table of the elements. They are arranged by atomic number, from smallest to largest, and labeled with their element symbol, atomic number, and atomic mass.
To easily communicate information about the elements, scientists use standard nuclear notation.
Nuclear notation is formed by writing an elemental symbol preceded by a subscript indicating its atomic number—the number of protons—and a superscript indicating its mass number—the number of protons and neutrons combined.
For example: Carbon has 6 protons, so it’s atomic number is 6.
Carbon's mass number is 12. How many neutrons does it have?
The mass number of an element is a round number; the atomic mass usually isn't. Atomic mass is an average mass of all of the isotopes of an element. We use the mass number, which is always a round number, to make calculations easier.
Think about clover. Clovers can have three, four, or even more leaves. The four-leaved clovers are rare, but they are still clovers. In a similar way, two atoms of an element can have different numbers of neutrons. Because they still have the same number of protons, though, they are the same element. These “varieties” of the same element are called isotopes.
Learn more about radioactivity
Last modified April 5, 2021, 2:24pm CDT
