Oxygen nucleus with twice as many neutrons as normal is shown to be surprisingly stable

Dec 07, 2012
The RIKEN Projectile fragment Separator (RIPS) (pictured) produces high-intensity beams of radioactive ions, which help scientists in the study of nuclear processes. Credit: 2012 Yoshiteru Sato, Seoul National University

The nucleus at the heart of an atom is held together by a subtle balance between the nuclear force that binds protons and neutrons and the electric repulsion that tries to fling the positively charged protons apart. Understanding how the number of nucleons—the collective term for protons and neutrons—affects this balance is crucial for predicting nuclear processes such as radioactive decay. RIKEN researchers, working as part of an international team, have now shown that 'heavy' oxygen nuclei with 16 neutrons form into a solid ball, which makes them unexpectedly stable.

More than 99% of the in the Earth's atmosphere is in its most stable form with eight and eight neutrons at the center. However, scientists can create neutron-heavy versions, or isotopes, in the laboratory to help them better understand what happens in a . Tohru Motobayashi from the RIKEN Nishina Center for Accelerator-Based Science, collaborating with Yoshinori Satou from the Seoul National University, Korea, Takashi Nakamura from the Tokyo Institute of Technology, Japan, and co-workers from France, Hungary and China have now performed the first spectroscopic study of oxygen nuclei with 16 neutrons using a technique known as proton inelastic scattering. They fired a beam of these oxygen-24 atoms at a liquid-hydrogen target, and then extracted the properties of the neutron-rich nuclei by tracking the direction and speed of the particles after the collision.

A nucleus has either a spherical or elliptical shape depending on the number of neutrons and protons. "The nucleus is more stable and solid when it is spherical," explains Motobayashi. "In our experiments we can hear the sound associated with this solidity, just as you can when you strike an everyday solid object."

An intriguing aspect of this result is that it runs contrary to the now well-established observation that nuclei are usually stable when the number of neutrons and protons corresponds to a so-called magic number: 2, 8, 20, 28, 50, 82 or 126. "We can now confirm that a neutron number of 16 is magic when proton and neutron numbers are largely unbalanced," says Motobayashi. "This supports other recent experiments on different nuclei."

This cutting edge experiment is another example of the importance of the steadily growing research collaboration between RIKEN, the Tokyo Institute of Technology and a number of Korean universities. "We next hope to explore more neutron-rich oxygen isotopes with 17, 18 or more to see if another stable oxygen nucleus exists," says Motobayashi.

Explore further: Physical constant is constant even in strong gravitational fields

More information: Tshoo, K., Satou, Y., Bhang, H., Choi, S., Nakamura, T., Kondo, Y., Deguchi, S., Kawada, Y., Kobayashi, N., Nakayama Y. et al. N = 16 spherical shell closure in 24O. Physical Review Letters 109, 022501 (2012). prl.aps.org/abstract/PRL/v109/i2/e022501

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PPihkala
5 / 5 (6) Dec 07, 2012
So what is the half-life of this 24 Oxygen?
ValeriaT
4 / 5 (2) Dec 07, 2012
The recent calculations found, the nuclei of 16 Oxygen are anomalously elongated, so there lotta place still exists for another neutrons, which could give it the spherical shape without violation of Aufbau principle of liquid droplet model of atom nuclei. The situation would be different, if the oxygen nuclei would be spherical already, because such shape is more sensitive to balance of volume, surface, coulomb, asymmetry and pairing interactions of nucleons within atom nuclei.
Silverhill
5 / 5 (3) Dec 07, 2012
So what is the half-life of this 24 Oxygen?
About 65 ms, decaying to F-23 or F-24.
http://en.wikiped...f_oxygen
Torbjorn_Larsson_OM
5 / 5 (2) Dec 07, 2012
ValeriaT, the team seems to have observed roundness by the experimental technique.

By the way, your ref are highly excited (rotating) nuclei. Not saying they don't happen or help predict sturdiness of the nuclei, only that it doesn't seem to be what is observed.
vacuum-mechanics
1 / 5 (5) Dec 08, 2012
The nucleus at the heart of an atom is held together by a subtle balance between the nuclear force that binds protons and neutrons and the electric repulsion that tries to fling the positively charged protons apart. Understanding how the number of nucleons—the collective term for protons and neutrons—affects this balance is crucial for predicting nuclear processes such as radioactive decay. …

Nowadays it seems that we know that 'strong force" in the nucleus override the repulsion force that tries to fling the positively charged protons apart, and also binds protons and neutrons together. But the problem is that we cannot understand how strong, weak and electromagnetic forces do their jobs. Maybe the physical view below could explain the mentioned mechanisms.
http://www.vacuum...=9〈=en
Spy Guy
not rated yet Dec 08, 2012
@ vacuum-mechanics

The paper you linked to, which I assume you wrote, is both poorly written and idiotic. In addition, your denial of time dilation and other effects regarding relativity are laughable. The crux of your arguments against relativity rely on some kind of "vacuum medium" that, assuming it exists in the first place, predicts things that are far from consistent with experimental results.

In short, you need to educate yourself before you post here. To anyone else reading this, please visit the home page of the link he provided. It'll make even the most depressed person laugh.
Infinum
1 / 5 (1) Dec 09, 2012
The http://physics.ap...28/st10, the nuclei of 16 Oxygen are anomalously elongated

It seems those are either bad calculations or bad theory they are based on. Nature says NO.
AlexDSP
not rated yet Dec 13, 2012
Accessable to everyone at http://arxiv.org/...5657.pdf but I couldn't find any explicit mention of the half life time.