快猫短视频

THE first 鈥渄oubly magic鈥� nickel nuclei have popped into existence in France.
The nuclei can be used to test competing theories of nuclear forces and even set
the stage for detecting a new form of radioactivity.

Light atoms tend to break apart when there is an imbalance in the numbers of
protons and neutrons. But half a century ago, the German-American Nobel
prizewinner Maria Goeppert-Mayer showed that their stability depends on exactly
how many protons and neutrons they have. Quantum rules force protons and
neutrons into nested shells inside the nucleus, and when a shell has been filled
with its so-called 鈥渕agic number鈥� of protons or neutrons, it settles into a
stable shape
(快猫短视频, 2 October, p 38).

Some theories predict that because it has 28 protons and 20
neutrons鈥攂oth magic numbers鈥攏ickel-48 should have a just-detectable
lease on life, rather than flying apart the instant it forms. To test this,
Bertram Blank and his colleagues at the Centre for Nuclear Studies in
Bordeaux-Gradignan, France, bombarded a nickel target with nickel-58 nuclei.
After 17 days, they had detected two nuclei of nickel-48. 鈥淚t鈥檚 a highly
unstable nucleus with a half-life at best of a few milliseconds,鈥� says
Blank.

Now that his team can make and detect these proton-rich nuclei, Blank plans
to study how they fall apart. He suspects they鈥檒l emit two protons at the same
time鈥攁 type of radioactive decay quite distinct from the alpha and beta
forms familiar to scientists. Its existence was predicted nearly 40 years ago
but it has never been seen. 鈥淚t鈥檚 a new form of radioactivity,鈥� says Blank.

In 1991, Alex Brown of Michigan State University in East Lansing used a
nuclear shell model to predict that nickel-48 would decay after between 0.01 and
2 milliseconds. 鈥淭hat鈥檚 what the experiments will test,鈥� he says. He adds that
knowing how such magic nuclei behave could clarify what happens in supernova
explosions, where they may crop up all the time.