Scientists have demonstrated for the first time the nuclear excitation by electron capture (NEEC), an effect that is believed to be crucial in the evolution of certain stars and that allows these objects to produce elements heavier than iron.
NEEC happens when an atomic nucleus captures a free electron and gets to a higher energy state. When this happens, the decay of the isotope is accelerated through a specific excitation pathway and the emission of gamma rays. The research, published in Nature, looked at the exotic isotope molybdenum-93, with the international team able to witness the signature of the NEEC process for the first time.
Molybdenum-93 doesn’t occur naturally and, unlike almost all the other versions of the element (with more or less atoms), is unstable. Its half-life, the time it takes half of a sample to decay, is usually in the order of 4,000 years. However, when the nucleus undergoes NEEC, it reduces this to about seven hours. This could be used to estimate the survival rate of certain elements inside stars, and it could preferentially reduce the abundance of certain atoms instead of others.
“The NEEC phenomenon modifies the nucleus lifetime so that it survives for a shorter amount of time in a star,” co-author Dr Greg Lane, from the ANU Research School of Physics and Engineering, said in a statement. “The abundance of the different elements in a star depends primarily on the structure and behavior of atomic nuclei.”
The discovery was possible thanks to the Heavy Ion Accelerator Facility at the Australia National University, where free electrons collided with the atoms. It was a collaboration between researchers and institutions from Australia, the United States, Russia, and Poland.
The project leader was the US Army Research Laboratory, and the rational for investigating this phenomenon is the potential use of NEEC – which was first proposed in 1976 – as an energy source. The phenomenon can lead to an energy density 100,000 times greater than chemical batteries.
“Our study demonstrated a new way to release the energy stored in a long-lived nuclear state, which the US Army Research Laboratory is interested to explore further,” he said.
This is clearly interesting for both theoretical and technical applications, but don’t expect NEEC batteries any time soon.