Nuclear 101: the origins of the elements and nuclear vocabulary

 

MURR reactor

MURR (the University of Missouri Research Reactor) is the most powerful university research reactor.

By Molly Olmstead

Noted astronomer and science communicator Carl Sagan once famously said that we are made of “star stuff.” This was no metaphorical claim.

The elements that compose our bodies and the world that surrounds us did, for the most part, originate within the stars. Angela Speck, a professor of astrophysics at the University of Missouri, explained in a speech she gave over Skype titled “Nuclear processes in the cosmos” how a series of astral processes gave birth to these elements.

The speech kicked off the January 28-29 nuclear power workshop at MU for journalists as part of “Nuclear 101,” a panel session introducing attendees to the basic ideas of nuclear reactions and nuclear power.

The first elements – hydrogen and helium, the lightest two elements and, accordingly, the first two elements on the periodic table – were formed with the original expansion of the universe immediately after the Big Bang, Speck explained. A process of nuclear fusion created helium from hydrogen atoms, in an environment of so much energy that atoms slammed together to form something new.

The rest had to wait for the emergence of stars, which in their cores, with enough heat and density, could create newer and heavier elements by fusing hydrogen, helium, and the products of these elements together in a series of nuclear reactions. These reactions create energy, which fuels the star, and the newly created elements are eventually ejected from the star as it dies.  Our sun is relatively small, and it can’t efficiently produce the heavier elements. This is predominantly done by larger stars, some of which can create elements all the way up to iron, the 26th element. Another type of nuclear process called neutron capture creates the elements heavier than iron, either very slowly in the cores of regular stars, or rapidly in the blast of a supernova – the explosion of a dying star.

“That material goes off in space and forms the next generation of stars and planets,” Speck said. “Therefore, we are all stars.”

Bill Miller, emeritus professor of nuclear engineering and the second panel speaker, segued the conversation into a more concrete discussion of nuclear power and its specific jargon with his presentation, “Nuclear vocabulary 101.”

“The biggest problem with understanding someone else and what they’re talking about is the terms they use,” Miller said.  “I really decided over the years that it’s just a matter of vocabulary.”

Here are a few of the more prominent terms:

Alpha, beta and gamma radiation: These differ in their source, but for the average person the important difference is how strong they are. Alpha and beta particles are fairly weak and can generally be stopped outside your body. Gamma rays, on the other hand, can travel farther, and they’re the biggest source of radiation damage.

Radioactive: Radioactive materials emit radiation.  Something does not become radioactive simply from being hit by radiation. High concentrations of neutrons from a reactor or highly charged particles from an accelerator are needed to change a substance to make it radioactive.*

Scrammed or tripped: To scram or trip a reactor is to turn it off.

Critical and super-critical: A critical reactor is turned on and running, essentially, and a super-critical reactor’s power is increasing.

“I’m just struck by the fact we use so many unfortunate terms in this business,” Miller said.

Miller added that most radiation exposure is natural and comes from background radiation. The other largest source of exposure is medical tests such as X-rays and CT scans.

“I don’t want to in any way discourage you from having those procedures,” he said. “The benefit far outweighs any risk from radiation dose.”

CORRECTION: A previous version of this article incorrectly explained how materials become radioactive. High concentrations of neutrons or highly charged particles hitting a substance can make that substance radioactive.

 

 

 

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