Aug 31, 2023 03:55 PM
Photons Crash Into Each Other—on a Time Mirror
https://spectrum.ieee.org/time-crystal-f...me-mirrors
INTRO: Usually, electromagnetic waves pass through each other unseen and undisturbed. Getting light beams to notice each other is no easy task. Typically, scientists must coax them into interacting via complex materials.
Now, physicists at the City University of New York (CUNY) Advanced Science Research Center have designed a fundamentally new way to make light beams collide with each other—by reflecting them both on the same mirror in time. By controlling light with light, the team also showed off the beam-shaping capabilities of their technique, with possible applications in telecommunications and scientific measurement.
The team demonstrated their time-mirror technology back in March, but now they’ve shown that two opposing light pulses hitting the same time mirror can be made to collide with each other, much like massive objects.
Moreover, the researchers can exert control over the type of collision that occurs. The light pulses, the researchers report, can collide elastically, like two billiard balls bouncing off each other; inelastically, like two pieces of Silly Putty hitting each other and sticking together; or constructively, like two balls with spring-loaded mechanisms tripped by the collision, shooting apart faster than they came together...(MORE - details)
Rare oxygen isotope detected at last — and it defies expectations
https://www.nature.com/articles/d41586-023-02713-3
EXCERPTS: By combining a powerful set of instruments with some experimental savvy, physicists have for the first time detected oxygen-28 — an isotope of oxygen that has 12 extra neutrons packed into its nucleus. Scientists have long predicted that this isotope is unusually stable. But initial observations of the ^28O nucleus suggest that this isn’t the case: it disintegrates rapidly after creation, a team reports in Nature today. If the results can be replicated, physicists might need to update theories of how atomic nuclei are structured.
[...] Current theories state that atomic nuclei with certain numbers of protons and neutrons are inherently stable. This is because protons and neutrons fill up ‘shells’ in the nucleus. When a shell is filled with just the right number of protons or neutrons, it becomes massively difficult to add or take away particles. These are ‘magic’ numbers, and have been thought to include 2, 8, 20, 28, 50, 82 and 126 particles. If a nucleus has a magic number of both neutrons and protons, it becomes ‘doubly magic’ — and therefore even more stable.
The most abundant form of oxygen, ^16O, is doubly magic, because of its eight protons and eight neutrons. Oxygen-28, with 8 protons and 20 neutrons, has long been predicted to be doubly magic, too. But physicists have not been able to detect it before.
[...] Although the team wasn’t able to get an exact measurement of the lifetime of ^28O, Nakamura says that the isotope did not behave as if it were doubly magic — it fell apart almost as soon as it came into existence.
[...] This is not the first hint that nuclear physicists’ list of magic numbers is not universally applicable, says Rituparna Kanungo, a physicist at Saint Mary’s University in Halifax, Canada. She was part of a team of scientists that showed in 2009 that ^24O — contrary to the nuclear rulebook — has a nucleus that behaves as though it is doubly magic. Its 8 protons and 16 neutrons are strongly bound to one another, giving it a relatively long lifetime — it takes about 61 milliseconds for half of the ^24O to disappear through radioactive decay. This means that in some nuclei, if they are strongly bound, 16 could be a magic number, too.
“Magic numbers are not immutable,” Janssens says. For now, the confounding qualities of ^28O raise a whole host of questions about the forces that hold nuclei together... (MORE - missing details)
PAPER: https://www.nature.com/articles/d41586-023-02713-3
https://spectrum.ieee.org/time-crystal-f...me-mirrors
INTRO: Usually, electromagnetic waves pass through each other unseen and undisturbed. Getting light beams to notice each other is no easy task. Typically, scientists must coax them into interacting via complex materials.
Now, physicists at the City University of New York (CUNY) Advanced Science Research Center have designed a fundamentally new way to make light beams collide with each other—by reflecting them both on the same mirror in time. By controlling light with light, the team also showed off the beam-shaping capabilities of their technique, with possible applications in telecommunications and scientific measurement.
The team demonstrated their time-mirror technology back in March, but now they’ve shown that two opposing light pulses hitting the same time mirror can be made to collide with each other, much like massive objects.
Moreover, the researchers can exert control over the type of collision that occurs. The light pulses, the researchers report, can collide elastically, like two billiard balls bouncing off each other; inelastically, like two pieces of Silly Putty hitting each other and sticking together; or constructively, like two balls with spring-loaded mechanisms tripped by the collision, shooting apart faster than they came together...(MORE - details)
Rare oxygen isotope detected at last — and it defies expectations
https://www.nature.com/articles/d41586-023-02713-3
EXCERPTS: By combining a powerful set of instruments with some experimental savvy, physicists have for the first time detected oxygen-28 — an isotope of oxygen that has 12 extra neutrons packed into its nucleus. Scientists have long predicted that this isotope is unusually stable. But initial observations of the ^28O nucleus suggest that this isn’t the case: it disintegrates rapidly after creation, a team reports in Nature today. If the results can be replicated, physicists might need to update theories of how atomic nuclei are structured.
[...] Current theories state that atomic nuclei with certain numbers of protons and neutrons are inherently stable. This is because protons and neutrons fill up ‘shells’ in the nucleus. When a shell is filled with just the right number of protons or neutrons, it becomes massively difficult to add or take away particles. These are ‘magic’ numbers, and have been thought to include 2, 8, 20, 28, 50, 82 and 126 particles. If a nucleus has a magic number of both neutrons and protons, it becomes ‘doubly magic’ — and therefore even more stable.
The most abundant form of oxygen, ^16O, is doubly magic, because of its eight protons and eight neutrons. Oxygen-28, with 8 protons and 20 neutrons, has long been predicted to be doubly magic, too. But physicists have not been able to detect it before.
[...] Although the team wasn’t able to get an exact measurement of the lifetime of ^28O, Nakamura says that the isotope did not behave as if it were doubly magic — it fell apart almost as soon as it came into existence.
[...] This is not the first hint that nuclear physicists’ list of magic numbers is not universally applicable, says Rituparna Kanungo, a physicist at Saint Mary’s University in Halifax, Canada. She was part of a team of scientists that showed in 2009 that ^24O — contrary to the nuclear rulebook — has a nucleus that behaves as though it is doubly magic. Its 8 protons and 16 neutrons are strongly bound to one another, giving it a relatively long lifetime — it takes about 61 milliseconds for half of the ^24O to disappear through radioactive decay. This means that in some nuclei, if they are strongly bound, 16 could be a magic number, too.
“Magic numbers are not immutable,” Janssens says. For now, the confounding qualities of ^28O raise a whole host of questions about the forces that hold nuclei together... (MORE - missing details)
PAPER: https://www.nature.com/articles/d41586-023-02713-3