2-7
c
Annihilation
When a
particle and its antiparticle meet, annihilation can occur, a
process
in which both particles are destroyed and a lot of energy is released,
according
to E=mc².
In some
cases, only the internal energy of the particles remains, which
was manifest as their mass (it is said that the entire mass is
converted into
energy). This energy then escapes in the form of electromagnetic
radiation.
For example, an electron-positron pair decays into two photons.
One gram
of matter with one gram of antimatter, when fully annihilated,
yields 1.8
× 1014 joules of energy, 43 kilotons of TNT, or the combustion
energy of
about 30,000 barrels of crude oil.
2-7
d
Antimatter in the Universe
In the
part of the universe studied by man, there is almost only ordinary
matter. This is remarkable given the above: from ‘nothing’,
matter and
antimatter would arise in equal quantities. There are various
hypotheses
about the cause.
During the Big Bang, approximately equal amounts of matter and
antimatter
were formed. However, there was slightly more matter than antimatter
and after a large-scale annihilation process, only some matter
remained.
This is the reason why today’s universe consists almost entirely
of matter
and why there is so much radiation in the universe (radiation
originating
from the annihilations).
Another hypothesis is that a large, distant (and as yet unobserved)
part of
the universe is composed entirely of antimatter. At the time of
its formation,
all matter would have ended up in one part and the antimatter
in another.
It should be noted that we observe celestial bodies primarily
through the
emission of photons, and a photon is equal to its antiparticle
(a photon is
the same as an antiphoton) so there is no difference to be seen.
In April 1997, it was discovered that positrons were formed in
the centre
of the galaxy. NASA’s Compton Gamma Ray Observatory discovered
clouds of positrons.
In July
2003, a team of researchers from NASA discovered that antimatter
is formed during giant explosions on the sun, known as solar flares.
The
researchers used NASA’s Reuven Ramaty High Energy Solar Spectroscopic
Imager (RHESSI) to study the high-energy X-rays and gamma rays.
In 2011, the Alpha Magnetic Spectrometer was transported to the
ISS with
the last flight of space shuttle Endeavour. It will remain there
for ten years,
conducting research into antimatter and dark matter.
At a height
of a few hundred kilometres, the Earth is surrounded by a belt
in which there are relatively many antiprotons. These are captured
by the
Earth’s magnetic field and remain in existence because there
is little nor64
mal matter at this altitude, so that annihilation does not occur.
Especially
in the South Atlantic Anomaly, high concentrations are measured
that
cannot be explained by normal decay. This conclusion was reached
by an
international team of physicists in 2011 based on measurements
from the
PAMELA experiment (Payload for Antimatter Matter Exploration and
Light-nuclei Astrophysics). This is a European satellite experiment
that
was launched five years ago. It is speculated that this antimatter
could be
used in an antimatter drive in the future.
