Scientists Gain Initial Insight into the Elusive Nitrogen-9 Isotope

Scientists are thought to have detected the elusive, ephemeral nucleus of nitrogen-9 for the first time. This unique atomic nucleus, made up of seven protons and two neutrons, pushes boundaries as to what is considered a nucleus.

The possible presence of nitrogen-9 has been identified in previously-collected data from experiments seeking another different nucleus, as revealed in an article in the Oct. 27 Physical Review Letters.

If further studies validate this detection, nitrogen-9 will notably become the first nucleus observed to have five protons more than it can stably hold, expanding the previous limit of four.

Andreas Heinz, a nuclear physicist at Chalmers University of Technology in Gothenburg, Sweden, and not part of the study, asked "What are the limits of nuclear existence?" This is the question that the study's authors and physicists are trying to answer.

Nuclear particles, including protons and neutrons, are essentially bound together by the strong nuclear force. However, this force is unable to keep together nuclei with extremely skewed ratios of protons to neutrons. If there are too many of either one of these particles - especially protons which repel each other due to their positive charge - the nucleus begins to overflow.

Particles cannot be fully bound by nuclei that reach this overflow point, dubbed the "drip line" by physicists.

According to Marek Płoszajczak, a nuclear physicist at the Grand Accélérateur National d’Ions Lourds in Caen, France, who is not associated with the study, the "drip line" signifies the existence limits of nuclei.

Yet nuclei do still exist beyond the drip line, albeit in an ephemeral state. The minimum existence of a nucleus, Heinz explains, is approximately 10-22 seconds which, despite being a very brief time, is still longer than the duration that fits in the age of the universe.

Those probing for nuclei beyond the drip line are examining these definitions. Robert Charity, a nuclear scientist at Washington University in St. Louis, is intrigued as to how far it is possible to go before it is no longer feasible to identify these clusters as new nuclei.

Nitrogen-9— five protons past the drip line — surprised even Charity's team. Previously, only isotopes a maximum of four protons beyond the drip line had been discovered.

In the experiment, scientists attempted to find an oxygen isotope by directing high-powered beams of oxygen-13 nuclei at beryllium targets to measure the decay of short-lived nuclei produced by the collision. The researchers found decay products in the data that appeared to have come from decaying nitrogen-9 nuclei.

The consistency of the evidence for nitrogen-9 is on the borderline of what scientists categorize as a discovery. According to Heinz, there is "strong evidence" for the existence of nitrogen-9, which he considers "really convincing".

Płoszajczak believes this outcome should help them enhance their models of nuclei beyond the drip line. He stated that these experiments demonstrate that the lifespan of a nucleus is far longer than the drip line.

Nitrogen-9 was first discovered through experimentation, before theories. Updated theories could allow for the purposeful search for "drippy" nuclei, which in return could make it easier to validate theories. Płoszajczak notes that this could lead to a "discussion" with nature and could revolutionize the entire field.

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