[ RadSafe ] Some Accelerator HP Stuff
JPreisig at aol.com
JPreisig at aol.com
Fri Dec 23 16:09:01 CST 2011
From: _jpreisig at aol.com_ (mailto:jpreisig at aol.com) .
Some thoughts about accelerator health physics follow. Guess I used
to work at the USA
particle accelerator that isn't too far from the closed Shoreham (Long
Island) nuclear plant.
One of the older HP super techs there used to kiddingly say that if you
weren't getting 5 rad a day, you weren't doing your job properly. Yuk yuk.
The old source calibration building at that lab was an old
military morgue, I think. It was a little creepy there on second shift
doing calibrations there.
I used to use a 0.5 Curie AmBe neutron source to do my calibration
work there. There was a larger
(ten times larger????!!!!) AmBe (or PuBe???) source there. but I usually
didn't use it. The old
calibration facility had neutron sources all over the place downstairs.
Try to keep clutter
(and extra sources) out of your calibration area during measurements. The
5 Ci AmBe or PuBe
source was kept in a large drum of parafin (or whatever) as shielding.
One definitely needs to
keep such a big source and shield away from the calibration area during
Hunt and Eisenhauer and Schwartz have written papers on how to do
properly. See their papers in Health Physics or other journals. See also
Accelerator Health Physics
by Patterson and Thomas (if you can actually find a copy of it) and the
Accelerator Book of Course
notes by Cossairt. A paper by Awschalom describes Bonner Multisphere
data analysis, unfolding etc.
Above 15 MeV or so, it is important to use a plastic scintillator
activation detector to get data
at energies the Bonner Multisphere Spectrometer doesn't measure. Analyze
Bonner data with
BON4/BON5, Louhi, Maxed or some other analysis code. The plastic
method/technique is described at the rear end of Patterson and Thomas'
(McCaslin). When using the Plastic Scintillator in a high energy
environment, be sure to carry
the scintillator in a shielded container (0.98 MeV positrons are created
upon activation) and also keep
the scintillator in a dark plastic bag, to keep light out. Usually the
plastic scintillator is counted
using a shielded photomultiplier tube, and mineral oil (or something like
it) is used to couple the
plastic scintillator to the photomultiplier tube. Yummy and messy.
An article in Health Physics right now describes the effects of
accelerator pulse structure on
counting losses. Read it???
The Health Physicist at a major particle physics accelerator usually
has a few or more varied
tasks. Do calibrations, run MCNP or MCNPX, Fluka, EGS, Lahet etc. The HP
should look out for
himself as far as personal dose equivalent is concerned. A dose
equivalent rate of only 1 mrem/hour
will build up over 10-15 weeks of accelerator work at 40 hours a week.
The plastic scintillator and
calibration work can contribute to overall dose equivalent. It's a good
idea to keep a Snoopy,
Anderson-Braun detector, remball or whatever on hand when doing
calibrations. Badges measure
some part of the neutron dose. Bubble dosimeters might have some
measuring capability at
At the accelerator near Shoreham, particle physics experiment crews
work in trailers
(yeah, Double wide, single wide etc.) on the accelerator floor. The main
accelerator is shielded with
iron and concrete blocks (and the beamlines also). Inside the shielding
people like Bob Casey have
made dose equivalent rate measurements using plastic or whatever --- see
information in Patterson and Thomas's book.
Things are probably different now at colliding beam accelerators
(CERN LHC and BNL RHIC).
I don't think anyone is sitting in a trailer near the beam collision points
when the accelerator
is running. Experiments may be run more remotely or perhaps from well
blockhouses --- I don't really know. Nobody is climbing over the
shielding when the accelerator
is on. Much of these accelerators is shielded with Earth mounds. Really.
Tour CERN LHC and/or
BNL RHIC to see what goes on.
Have a good holiday!!!!
Regards, Joseph R. (Joe) Preisig, PhD
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