[ RadSafe ] Some Accelerator HP Stuff

[JPreisig at aol.com]

Dear Radsafe,
 
     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 
measurements.
 
     Hunt and Eisenhauer and Schwartz have written  papers on how to do 
neutron calibrations
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  
spectrometer
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  
scintillator activation
method/technique is described at the rear end of Patterson and Thomas'  
book.
(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
15 MeV????
 
     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  
the relevant
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  
shielded

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