Hi Bill,
You're obviously much better at math than I am. I didn't derive
the formula I used for the plots I showed, but took them from a
report that I used when I was a grad student at SLAC. The report
is called "Studies in Penetration of Charged Particles in Matter"
and is by the National Academy of Sciences/National Research
Council and is dated 1964 (I'm dated prior to that...). It
basically uses Bethe's stopping power formalism and derives a
number of equations from it. Most of the calculations were done by
two guys (M.J.Berger and S.M.Seltzer) from the National Bureau of
Standards (I didn't check them...). It's interesting that they
give the data as tables printed out from what was clearly a
Fortran program (now I can relate to that...). Wikipedia tells me
that the CDC 6600 was just developed in 1964, so the calculation
probably wasn't done on one of those (although we had two of them
by the time I got to BNL). It was therefore probably done on a CDC
1604, which was one of the first solid state computers and the
fastest at its time. I bet you could run your Mathematica program
on your smart phone and not have to generate a box of paper
output. But then again, I bet your smart phone doesn't have a card
reader either....
Cheers,
Craig
On 7/8/2015 5:36 PM, W.A. Zajc wrote:
Hi Craig:
Something about your ‘old fashioned nuclear physics’
remark was rattling around in my brain and I finally remembered
I had done some really old fashioned nuclear physics when I was
teaching undergraduate lab more than 10 years ago. I’ve attached
a note I wrote to myself about the range of low-energy
electrons. Perhaps the form for the range I ‘derived’ is
well-known, but I had not seen it in any of the truly
old-fashioned references I consulted.
I put ‘derive’ in quotes, because it’s really only a
zero-th order integration of the leading term in the dE/dx
formula, but it works better than it has any right to.
Best regards,
Bill
P.S. Apologies for the funky formatting, converting
Mathematica notebooks to PDF is always an adventure...
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On Jun 30, 2015, at 6:18 PM, Craig Woody <woody AT bnl.gov> wrote:
Hi Bill,
You and Mike are are both right. Ru-106 is a better
source for high energy betas, but the problem is,
they're just not as available. At least we couldn't
find a suitable one here at BNL, probably for the
reason you mention, namely, that the half life is
rather short and you keep having to order new ones.
Also, in some cases, the gammas can be a problem,
particularly if you try and collimate the source, in
which case you can get a lot of soft Compton
background. The best collimator is actually a plastic
collimator if the gammas aren't a problem. Anyhow,
Sr90 works fine for most applications, as long as you
don't require deep penetration of the electrons. I
guess this is real old fashioned nuclear physics :-) .
Cheers,
Craig
On 6/30/2015 12:50 PM, W.A. Zajc wrote:
Hello all:
I was wondering about the same thing as
Mike. The endpoint is 3.5 MeV for a "Ru-106”, but
it’s actually from the Rh-106 decay (which I just
learned from Mike’s message):
Ru-106 —> Rh-106 + e^-(39 keV)
Rh-106 —> Pd-106
+ e^-(3540 keV)
Rh-106 also has two photons each ~ 0.5
MeV emitted at the 10-20% rate of the electron. Is
that the problem? Or perhaps more likely is it the
half-life ~ 1 year for Ru-106, which means you have
to keep somebody in business replenishing your
source?
Best regards,
Bill
—————————————
W.A. Zajc
I.I. Rabi Professor of Physics
Columbia University
New York, NY 10027
—————————————
On Jun 30, 2015, at 9:46 AM,
Michael J. Tannenbaum <mjt AT bnl.gov>
wrote:
Dear Craig et al,
If you use a
ruthenium-rhodium source, I think that the
end point is ~3 MeV and you can use a thin
scintillator as a trigger behind the
scintillator that you are testing.
Mike Tannenbaum
On Jun 30, 2015, at 9:00
AM, Craig Woody <woody AT bnl.gov>
wrote:
Hi All,
Following yesterday's discussion
about mapping the tiles, I thought
I would add a little information
and point out a few things to
watch out for when using a Sr90
source to measure scintillators.
The first thing to remember is
that the electrons coming from the
source are produced from beta
decay and have a broad spectrum.
While the end point of the
spectrum is 2.28 MeV, most of the
electrons are much lower energy
than this. The most energetic
electrons are actually the result
of Y90 decay which is part of the
decay sequence. I've attached a
few slides which give the decay
scheme and energy spectra of the
electrons. The average energy is
less than 1 MeV, and these range
out pretty quickly in plastic
scintillator. I've also included
some plots of the range-energy and
dE/dx curves for electrons in
plastic. In general, the electrons
from the source will range out in
a few millimeters. Generally this
is ok if you're just interested in
depositing energy in the
scintillator, but if you're trying
to study light collection,
especially with possible strong
surface effects, most of the
energy is going to be deposited
near the surface and it may give
some misleading results.
The other thing we heard about
was the trigger bias. In general,
as we all know, it's always better
to have your trigger be
independent from the thing you are
measuring. However, in this case,
there seemed to be an additional
problem in that the trigger was
very close to the noise. If the
light yield is indeed only ~ 10
pixels per MeV, and the average
energy is perhaps 0.5 MeV, that
means you're trying to trigger on
5 pixels firing, which is very
close to the single photoelectron
noise (and remember, this spectrum
extends to several photoelectrons
due to cross talk and
afterpulsing). This could make
getting an unbiased trigger very
tricky at best. A better way to
trigger would be to use an
independent trigger counter, which
has to be very thin (~ 0.5 mm) to
allow the electrons to pass
through, which is something we've
often used in the past with Sr90.
Another way would be to couple a
light guide on one long edge of
the tile (giving up the
reflectivity of one edge shouldn't
change the light collection
significantly) and trigger on the
direct light in the scintillator
with a PMT. This should give a
large signal and could also tell
you about any position dependence
of where the light is produced
without introducing any factors
due to the WLS fibers. I also
agree with Eric's suggestion that
measuring the tiles with cosmic
rays should be able to determine
whether there is any inherent
asymmetry in the tile from one end
to the other. At least you could
be sure then that light is being
produced uniformly throughout the
thickness of the scintillator.
Anyhow, I thought I would offer
this after hearing yesterday's
discussion. My personal feeling
from seeing the data was that
there was some asymmetry in the
light collection within the tile
which was over and above any of
the effects we've been talking
about. However, it certainly needs
further investigation.
Cheers,
Craig
On 6/25/2015 1:16 PM, John Lajoie
wrote:
Dear sPHENIX HCAL Folks:
This coming Monday, June 29th,
at 4PM BNL time we will kick off
the first bi-weekly HCAL meeting.
This meeting will alternate weeks
with the EMCal meeting chaired by
Anne, and is intended to be the
forum for the discussion of all
things HCAL. Any and all
interested parties are welcome.
This week we'll start off with
status reports from the tile
testing at Colorado and BNL. If
anyone would like to add a
contribution, by all means contact
me and we will work you into the
agenda.
An Indico agenda with
BlueJeans coordinates can be found
at:
https://indico.bnl.gov/conferenceDisplay.py?confId=1251
Regards,
John Lajoie
--
John Lajoie
PHENIX Deputy
Spokesperson
Professor of
Physics
Iowa State
University
(515) 294-6952
lajoie AT iastate.edu
Contact me:
john.lajoie
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