Manufacturing Bits: Jan. 24

Trapping antimatter; antihydrogen atoms; neutron sources.


Trapping antimatter
Japan’s Riken has conducted measurements in order to discover the differences between matter and antimatter, namely in the complex field of antiprotons.

Antimatter is a material composed of antiparticles, according to Wikipedia. Antimatter has the same mass as particles of ordinary matter, but it has an opposite charge, according to Wikipedia.

Basically, neutrons and protons make up the nucleus of an atom. They reside at the center of the atom. Electrons orbit the nucleus. “A positron (the antiparticle of the electron) and an antiproton (the antiparticle of the proton) can form an antihydrogen atom,” according to Wikipedia. So, the antiproton, the antiparticle of the proton, is a stable but short-lived particle. It has a −1 electric charge.

In physics, matter and antimatter can come into contact with each other. When they do, they annihilate. It disappears in a flash of energy.

Researchers from Riken, meanwhile, used a technique that involves trapping individual particles in a magnetic device. In effect, they measured the magnetic moment where an antiproton is close to a proton–at an accuracy that is six times higher than before.

To perform the experiments, Riken took antiprotons generated by CERN’s Antiproton Decelerator, a machine that produces low-energy antiprotons. The machine produces antiproton beams and sends them to different experiments in the facility.

CERN's Antiproton Decelerator (Source: CERN)

CERN’s Antiproton Decelerator (Source: CERN)

After producing the antiprotons, Riken placed them into a magnetic device, dubbed a Penning trap. In this device, the particles can be stored for periods of more than a year. At certain periods, they took individual antiprotons from the containment trap and moved them into another trap, according to Riken.

Trapping individual particles in a magnetic device (Source: Riken)

Trapping individual particles in a magnetic device (Source: Riken)

Then, the particles were cooled to nearly absolute zero and placed into a magnetic field. This, in turn, allowed the group to measure the magnetic moment. Based on six measurements done using this method, the group found that the moment (g-factor) of the antiproton is 2.7928465(23), according to Riken. This compared to the previous measurement on record, which were 2.792847350(9), they said.

This puts the two measurements to within 0.8 parts per million of one another. “We see a deep contradiction between the standard model of particle physics, under which the proton and antiproton are identical mirror images of one another, and the fact that on cosmological scales, there is an enormous gap between the amount of matter and antimatter in the universe,” said Stefan Ulmer, a researcher from Riken.

“Our experiment has shown, based on a measurement six times more precise than any done before, that the standard model holds up, and that there seems in fact to be no difference in the proton/antiproton magnetic moments at the achieved measurement uncertainty. We did not find any evidence for CPT violation,” Ulmer said.

CPT is charge, parity, and time reversal symmetry. “The CPT theorem appeared for the first time, implicitly, in the work of Julian Schwinger in 1951 to prove the connection between spin and statistics,” according to Wikipedia.

Antihydrogen atoms
Researchers from CERN recently made the world’s first measurements on the optical spectrum of an antimatter atom.

Atoms are well understood, but antihydrogen atoms are not, according to CERN. Founded in 1954, the CERN laboratory is situated at the Franco-Swiss border near Geneva. The instruments used at CERN are purpose-built particle accelerators and detectors.

Antihydrogen atoms are made of antiprotons and positrons. They must be produced and assembled into atoms. This is so the antihydrogen spectrum can be measured. “It’s a painstaking process, but well worth the effort since any measurable difference between the spectra of hydrogen and antihydrogen would break basic principles of physics and possibly help understand the puzzle of the matter-antimatter imbalance in the Universe,” according to CERN.

To measure these particles, researchers used CERN’s Antiproton Decelerator facility. They were able to produce antihydrogen atoms and hold them in a specially-designed magnetic trap. “Moving and trapping antiprotons or positrons is easy because they are charged particles,” said Jeffrey Hangst, a researcher at CERN. “But when you combine the two you get neutral antihydrogen, which is far more difficult to trap, so we have designed a very special magnetic trap that relies on the fact that antihydrogen is a little bit magnetic.”

Neutron sources
The National Institute of Standards and Technology (NIST) is looking at a new way to calibrate its neutron source.

The source resides in NIST’s neutron source calibration facility. The facility provides calibration services for a range of systems, such as radioisotopic sources, as well as instruments that monitor radiation exposures and doses. The facility is also key for research programs in neutron metrology and scattering.

The neutron itself is a subatomic particle. It has no electric charge and a mass slightly larger than a proton. Neutrons and protons make up the nucleus of an atom.

Meanwhile, detectors and systems need to be tested for accuracy against a radiation standard. For this, the calibrations make use of NIST’s NBS-1, a spherical neutron source that is about the size of a golf ball.

The source contains one gram of radium-226 surrounded by beryllium. Radium-226 does not emit neutrons, but rather it emits other particles. Those strike adjacent beryllium-9 atoms, which emits neutrons, according to NIST.

Typically, calibrations are performed using the manganese bath technique. For this, a source or a system, which requires a calibration, is placed in a manganese bath. Researchers vary the concentration of the manganese. They measure the changes in gamma-ray emissions.

Basically, the source is compared to the emission rate of the NBS–1, according to NIST. With this, the emission rate of the NBS-1 has an uncertainty of about 0.85 %.

Recently, NIST began to look at new ways to calibrate the NBS-1. One method could reduce the uncertainties by a factor of three. The goal is to provide a separate reference neutron source from the NBS-1.

For this, NIST made use of a second and smaller spherical neutron source. This source will be placed in a different facility, dubbed the NIST Center for Neutron Research (NCNR).

The calibration, according to NIST, will take place in two stages. First, a neutron emitter will be placed in the center of the smaller sphere. Then, its emission rate will be measured via gamma rays. “The 0.85 percent uncertainty that we have now is pretty much a standard among the maybe 10 labs in the world that do this. If we could improve it by a factor of three, that would make us the most accurate in the world,” said Scott Dewey, a project scientist at NIST.

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witeken says:

“According to Wikipedia.” Haha, but nice to see these physics articles.

Mark LaPedus says:

Hi. Apologies for using Wikipedia. I am no expert in particle physics. I searched many sites to explain antimatter. Wikipedia provided a simple explanation (at least for me). Do you have any suggestions for other sites that can explain antimatter?

witeken says:

Not really, it’s probably too much for an article to go reading popular or scholar literature.

But basically, every fundamental particle in nature has a twin particle associated with it that is identical except for having the opposite charge, which is called the antiparticle (antimatter). This is because, as you can already see from math, there is not really anything that makes a positive charge more special or preferred than a negative charge (and vice versa).

So the fundamental laws of nature as we know them don’t distinguish between particles and antiparticles. So both have had be created during the big bang; for instance electron particles with negative as well as positive charges. So it is one of the unsolved mysteries of physics to understand why there is an asymmetry between matter and antimatter.

Now, the reason we don’t normally see ANY antimatter at all is because when a particle meets its antiparticle, they annihilate each other; they go out of existence. Per conservation of energy, of course, they release electromagnetic radiation. So all antiparticles are gone, and the leftover particles (which we only call matter by convention, just like if history had been different we might have postulated that the proton has a negative charge and the electron a positive charge, for there is no way to distinguish one from the other, they are just convention, the only thing that matters is whether they have the same or opposite charge) have remained.

If you have any other physics questions, feel free to ask. I have no formal physics education, but I have decent qualitative working memory from my interest in the field.

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