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Accelerators
Name: Leah
Status: N/A
Age: 20s
Location: N/A
Country: N/A
Date: 1999
Question:
I actually have a few questions about particle
accelerators (I hope you don't mind!). The first is: are particle
accelerators noisy (i.e.: would you need ear-plugs while working near an
accelerator)? The second is: how much radiation is produced by the
acceleration of particles? Is it enough to be of danger to humans? The
last question is: considering the amount of force in an explosion caused
by the collision of mater and antimater, what keeps the accelerator from
being damaged?
Replies:
You don't generally need earplugs around most particle accelerators,
but the noise does get tiring after a while. Most of the noise is from
things like fans, water pipes, and cryogenic equipment. The actual
particles are absolutely silent, even when they slam into the beamstop.
The amount of radiation produced varies widely depending on the type of
particles and the energies to which they are accelerated, but only very
low-energy machines (e.g., ion implanters) are safe to stand next to
while they are running. Relatively little radiation is produced in the
acceleration process; nearly all of it is produced when the particles
are decelerated, e.g., by hitting stray molecules of air in the nearly
perfect vacuum through which the particles pass, by hitting the walls
of the pipes, or by hitting the beamstop. In powerful accelerators,
these events produce lots of radiation and the shielding that reduces
this radiation to normal background levels is several feet thick. One
nice thing about particle accelerators is that when you turn them off
they stop producing radiation. Some parts do become activated by the
radiation hitting them, and heavy particle accelerators generally
become more activated than light particle accelerators. The radiation
from these activated parts would be dangerous to someone standing
near them.
Antimatter is not a significant product of most particle accelerators,
and even accelerators designed to produce antimatter produce such
unbelievably small quantities of it that the total energy produced by
matter/antimatter collisions is not enough to measure without very
sensitive equipment. For example, the synchrotron light source at
Argonne was originally designed to produce a 100 milliamp beam of
positrons (antielectrons). It sounds like there might be a noticeable
amount of antimatter involved until you realize it's the same positrons
going around and around the storage ring 3 million times per second
that add up to this current. If you only counted each positron once,
the current would be 30 billionths of an amp. If all the positrons in
this beam met electrons and annihilated at the same time, there'd be
lots of x rays around for maybe a microsecond, but the total energy
released wouldn't wake up a mouse.
Tim Mooney
This is not my area, but in case you don't get a reply from a
particle person:
(1) The acceleration itself is noiseless, since there are no ``moving
parts,'' but the ancillary machinery, such as pumps, air conditioners,
generators, and so forth would be as noisy as such things normally
are. I expect it's about the same as working in a machine shop, and
doubt earplugs are indicated.
(2) ``Synchotron radiation'' is produced by the acceleration of
charged particles, and its frequency varies with how hard they are
being accelerated. This is light ranging from the far infrared
through the visible and on into the near X-ray region. It is
exceedingly valuable for research, because the wavelength can be
precisely controlled and the beam is tightly collimated (narrowly
focussed) and bright. Indeed, the National Light Source at Brookhaven
is a facility where particles are accelerated specifically for the
purpose of providing this valuable light.
Is it enough to be of danger to humans? Well, of course. If you
stand in the way of an X-ray beam, you're going to be hurt, just as
much as if you stand in the way of a falling piano. However, strict
rules ensure that the only persons found near an operating accelerator
are adult human beings with enough common sense to come in out of the rain.
Perhaps you mean radioactivity? In that case, the answer is no, an
accelerator per se does not produce radioactivity.
(3) The amount of energy (not force) released by the collision of
matter and antimatter is enormous on a per weight basis, but in an
absolute sense is quite undetectable to human senses. That is simply
because we are talking about accelerating only about 100 atoms at at
time and smacking them into another 100 atoms. Do you realize how
small an amount of matter this is? If you took 100 atoms of water
every second from a single raindrop, it would take you 300 billion
years to use up the entire raindrop. So even if the amount of energy
released PER WEIGHT of water is enormous, you are simply not going to
notice the amount of energy released PER COLLISION. Indeed, it takes
exceedingly sophisticated instruments to detect the fact that anything
at all has happened when matter and antimatter collided in an
accelerator. Damage to the accelerator is out of the question.
Incidentally, the fastest particles available, that is the particles
that have been accelerated the hardest, are not found in accelerators
but in the atmosphere. They are accelerated by natural processes in
outer space and come smashing down to the Earth, where they collide
with atoms in the atmosphere. These are called ``cosmic rays'' and
the results of their collisions is a constant shower of ``cosmic
radiation'' here on the ground. Most of the ionizing (dangerous)
radiation an average person is exposed to in their daily life comes
from this source, as well as ionizing radiation emitted by normal rock
and soil. You can get away from cosmic radiation (partially) by
living at low altitude, or completely by living underwater or in a
cave, but you can't escape radiation from earth and rock.
Grayce
I work in a place where we use an linear accelerator (LINAC), but I do not
work directly with that part of the job (I work on where the protons come
out). However, I can tell you from experience that yes they are noisy, but
not from the point of view you think. First of all, large magnets are used
to accelerate and align the proton as it goes down the LINAC. These magnets
hum due to the large amounts of electricity flowing through the copper
windings. These magnets are what help prevent the protons from touching
things to cause damage. A proton is going to have an electrical charge and
hence a magnetic moment. You can computer control the magnets to make sure
the proton stays on course. There is radiation created by this system, and
you don't want to stand in its way. We are shielded from direct exposure to
the beam. The main problem we have is EMF noise generated by the large
amounts of electricity running through the magnets as it trys to align and
move the proton. This EMF shows up as noise on our data aquisition systems,
so we have to account for it when we are taking data. You don't really need
earplugs if you are passing by it. It sounds more like really loud light
bulbs humming. Due to the radiation, the only time you can be near it is
when it is shut off and not humming.
Hope this helped.
Chris Murphy
The noise around particle accelerators is mainly from motors and vacuum pumps,
and just the normal building ventilation. Its like being at any factory, you
can easily have a conversation at normal level of talking.
harmful radiation is often produced. The idea is to keep people away from
this part of the accelerator. There are often thick walls, buried underground
etc. You don't go into the accelerator's immediate area when it is "turned
on". So doing these obvious precautions, there is no danger at all to
people. Very often tho your radiation dose is monitored with special badges,
just to see if you ever get anything at all harmful. It would be a big deal
if you did , and this is very very rare. Lots of safety systems.
Lots of energy can be released per collistion as you say, its just that there
really are not very many of these. Its like you have a few very hot, very
energetic particles, but really not much in the way of mass.
Ross
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