siliconchip.com.au Australia’s electronics magazine July 2019 15
Opposite: an artist’s concept of the
NASA Lunar IceCube spacecraft to be
launched in 2020. It is a 6U CubeSat
that uses a Space Micro Proton400K
radiation-hardened single board
computer (Fig.1; inset).
Image credit: Recentcontributor2000.
R
adiation effects on electron-
ics are primarily of concern in
aerospace and military appli-
cations, although not exclusively so.
Ground-based computers also suffer
from radiation-based errors regularly.
This problem has been exacerbated
by the continuous reduction in transis-
tor sizes as higher computing speeds
and lower manufacturing costs are
required; smaller transistors are more
susceptible to radiation effects.
Space is one environment where
environmental radiation is a major
problem for electronics. The types of
radiation encountered in space vary
enormously with time and locality.
Even if a spacecraft remains within
a certain area, eg, the surface of the
moon, low earth orbit or geosynchro-
nous orbit, the radiation it is exposed
to can vary greatly.
This is influenced by factors such
as solar radiation, which varies all the
time, and “space weather” in general.
It is not just the intensity or energy
of radiation that changes but also the
types of radiation particles that are
encountered.
And these, in turn, affect both the
likelihood and severity of effects on
electronic components.
Radiation can cause a variety of im-
pacts to electronics devices, including
long term degradation of devices like
solar cells, loss or alteration of comput-
er memory contents, halting (“crash-
ing”) of computer systems (possibly
requiring a reset) or causing computers
to issue incorrect instructions.
In severe cases, the entire electron-
ics system or subsystem can burn out,
rendering a system permanently in-
operative.
Electronics may be irradiated by
particles such as electrons, protons,
neutrons and ions as well as pho-
tonic radiation such as gamma rays
and x-rays.
Electromagnetic pulses (EMPs) can
also cause problems. These can arise
from nuclear explosions, lightning or
other events which cause an electric
or magnetic field or an induced elec-
tric current.
Apart from the space environment,
electronics may be subject to radiation
in applications such as nuclear reac-
tors (eg, control systems), particle ac-
celerators, high-altitude aircraft, high-
altitude balloons, x-ray machines, food
irradiation machines (for preservation)and radiotherapy machines for medi-
cal applications.Sources of radiation
Some potential sources of radiation,
the particles produced, and the effects
they have are:- Cosmic rays – these are very fast
particles which come from all direc-
tions in the universe. They consist of
about 85% protons, 14% alpha parti-
cles (helium nuclei), 1% heavy ions
as well as x-rays and gamma rays.
Most of these are filtered by the
atmosphere and therefore mostly
spacecraft are affected; however,
collisions between cosmic rays and
particles in the Earth’s atmosphere
can also generate secondary radia-
tion which can reach the surface. - The Van Allen radiation belts sur-
rounding the Earth contain electrons
and protons, mostly from the Sun,
which are trapped by the Earth’s
magnetic field. The strength of the
radiation in these belts varies enor-
mously. Spacecraft are affected by
them, and they are also hazardous
to astronauts. (Fig.2) - Solar flares eject particles such as
protons and heavy ions as well as
x-rays, some of which reach the
Earth’s atmosphere. These can be
associated with solar storms or geo-
magnetic storms.
Fig.2: the Van Allen
radiation belts comprise
two or three regions of
energetic charged particles
(eg, electrons and protons),
mostly from the Sun, which
are trapped in Earth’s
magnetic field. This diagram
shows the location of the inner
belt, the outer belt and the
position of various satellites.
There is a so-called “safe zone”
between the inner and out belts which
Image credit: NASA. is relatively low in radiation.