Energetic Particles
ˇˇ
What is Energetic Particles ?
Ions that stripped of their electrons , be in ~2 million degree plasma from the
free ions and electrons in plasma behave the same way. Knowing the temperature
of the high atmosphere of Earth, or that of the Sun, we can calculate energies
expected of ions and electrons found there. However, ions and electrons actually
observed in space are often much, much more energetic, and may move at a
respectable fraction of the velocity of light (300,000 km/sec or 186,000
miles/sec).
Low energy particles (E<100 MeV/nucleon) are present throughout the heliosphere
in different intensities and time scales. The source of most of these particles
in the heliosphere are the Sun, the planet's magnetospheres, and the
interplanetary shock waves. Spacecraft observations have established direct
evidence that particle acceleration occurs near all collisionless shocks found
in interplanetary space, including the Earth's bow shock, shocks triggered with
transient solar activity, and corotating shocks.
The "solar energetic particle"(SEP) events, a time limited increases of
low-energy particles, are often observed in the near earth space environment,
outside the magnetosphere and in the earth polar caps (where they were
discovered), but also observed everywhere in the interplanetary medium. In
recent years it has been widely accepted that there are two kinds of SEP events:
There is a convenient unit to measure such energies, the electron volt (ev). It
is the energy gained by an electron (or proton, same size of electric charge)
moving through a voltage difference of one volt. 0.03 ev
0.5 eV
0.67 ev
1000 -
15,000 ev 40,000
ev 50,000
ev Hold it! o 1,000
ev = 1 kev (kilo-electron-volt, pronounced kay-ee-vee) o
1,000,000 ev = 1 Mev (mega-electron volt or em-ee-vee) o
1,000,000,000 ev = 1 Gev (giga-electron-volt or gee-ee-vee) 4.2 Mev
10-100
Mev
10-15,000 Mev
1-100,000,000,000 Gev While
the theory of relativity allows no particle with mass to move with a velocity
exceeding (or even equaling) that of light, there is no limit on its energy.
Close to the speed of light, however, the addition of energy only slightly
increases the velocity. An ion accelerating from 0.9 to 0.99 times the speed of
light needs several times more energy than the amount it needed to reach 0.9
times in the first place, though its energy makes it considerably heavier. Why
and How ˇˇ ˇˇ Here you may see, as an example developed by B. Sanahuja*, A. Aran and D. Lario, Departament d'Astronomia i Meteorologia, Universitat de Barcelona. Spain
and Institut d'Estudis Espacials de Catalunya. Spain.
& **Applied Physics Laboratory. The John Hopkins University. USA
Sponsored by ESA/ESTEC, the DGCYT (MCyT) and NASA,
the aplication of the model for a limited set of choices. Just fill in or reply to the
following questions: Note: For longitude and transit
time, the closest values to the specified parameters will be selected from our
dataset. ˇˇ
Last upgrade
06/22/2004
1.) The gradual events have a duration of several days, they are proton rich
and they have, on average, the same element composition and ionization states as
those in the low-density ambient plasma of the high corona or solar wind. They
are associated with gradual X-ray flares, type II and type IV radioemission and
coronal mass ejections (CMEs). Such events are observed over a broad range of
heliolongitudes. 
2). The impulsive short-duration events are only observed from magnetically
well-connected locations on the Sun. They are electron-rich and they have an
strong association with impulsive H-alpha and X-rays flares, and type III radio
bursts. The high ion charge state indicates their origin in plasma heated by
flares.
Recent observations do challenge an strict separation of all SEP events in these
two types. There are large gradual events with abundances more like those of
impulsive events. It also seems that abundance variations are organized by the
heliolongitude of the parent solar activity.
The
Measurement ¨CElectron Volt
In the picture tube of a color TV, electrons are accelerated by about 30,000
volts, so that their energy when they hit the screen is about 30,000 ev. That is
actually quite a lot: those electrons move at about 1/3 the velocity of light.
Particle Energies in Nature
How
does nature compare?
ˇˇ
o The energy of a molecule of oxygen or nitrogen in the air we breathe. It moves
as fast as a speeding bullet, but is still rather low on the scale of energies.
ˇˇ
o An atom or molecule at the temperature of the Sun's surface.
ˇˇ
o The energy needed by a proton or neutron to escape the Earth's gravity.
ˇˇ
o Typical energy of an electron in the polar aurora.
ˇˇ
o Energy required by an electron to penetrate a thin-wall Geiger counter.
ˇˇ
o Typical energy of an ion in the ring current.
ˇˇ
ˇˇ
1.4 Mev
o The energy of electrons from radioactive potassium, a major source of the
Earth's internal heat.
o The energy of alpha particles from radioactive uranium 238, another source of
the Earth's heat (and of its helium as well--see positive ions, history).
ˇˇ
o Typical proton energies in the inner radiation belt.
ˇˇ
o Range of energies in solar outbursts (see Sun).
ˇˇ
o Range of energies among cosmic ray ions. However as their energy goes up,
their intensity goes way down, so that ions at the high energy end are quite
rare.
Note
on Relativity
ˇˇ
ˇˇ
Where do single electrons and ions acquire such high energies? Excellent
question. We guess magnetic and electric fields may be involved, and have
learned a great deal in that direction, but the exact processes (probably more
than one) remain to be nailed down. Acceleration takes place in solar flares and
CMEs (see Sun) but, like a clever conjuring trick, although it happens right in
front of our eyes, we still don't get it. 
Powerful shocks--abrupt discontinuities piled up in front of rapidly moving
gas--can also do it, and at least one interesting event of this sort was
observed in the Earth's magnetosphere. The most powerful shocks occur in the
envelope of gas expanding from the site of supernovas, and it is widely believed
that such shocks (which carry a great amount of energy) are the source of most
cosmic ray particles.