From: Dick Hahn (hahn1@bnl.gov)
Date: Wed Apr 13 2005 - 11:10:47 CDT
Ed,
I have a doctor's appointment scheduled for tomorrow morning. If I get out
by 1030, depending where I will be, I'll phone in, either from my cell phone
or from my office. I haven't seen Minfang yet this morning. Assuming that he
can be available for the call, he can represent BNL.
Concerning the Gd concentration, changing from 0.1% to 0.2% will not be a
major perturbation in the chemical preparation of the scintillator, since
our approach is to make Gd-LS with 1% concentration and then dilute it with
pure scintillator. The questions of course involve issues such as (1) What
is the variation of the delay time for n-capture with Gd concentration? What
is the delay time for 0.1% and 0.2% Gd? Certainly the delta-t decreases as
Gd concentration increases. How large a benefit in reducing backgrounds is
produced by decreasing the time delay? (2) How large is the benefit of
increasing the Gd concentration, i.e., what is the magnitude of the neutron
signal at 0.2% Gd vs. 0.1% Gd? (3) Our chemical purification steps will in
general be done on the Gd BEFORE the Gd-loaded scintillator is prepared. So
the concentrations of any U, Th or other impurities in the Gd will be
proportional to the Gd concentration in the scintillator. In principle,
doubling the Gd concentration will double the impurity levels. There will
then be a trade-off between the improvement caused by the shorter delay time
and the higher background caused by the radioactive impurities (and any
optical effects that might be due to chemical impurities). Can we
quantitatively evaluate the magnitude of the trade-off?
Dick
-----Original Message-----
From: Ed Blucher [mailto:blucher@hep.uchicago.edu]
Sent: Wednesday, April 13, 2005 10:01 AM
To: braidwood@hep.uchicago.edu
Subject: Thursday Braidwood phone meeting
Dear Colleagues,
We will have the first of two phone meetings this Thursday at 10:30 EDT.
To connect to the meeting, dial 1-510-883-7860; at the prompt enter
826763 follwed by the # sign.
To prepare for the upcoming (but still unscheduled) NUSAG review, we need
to refine and make more specific many aspects of our Engineering/R&D
proposal. We believe updating several sections of the document will be
a useful way to organize the new information. To facilitate the
discussion at Thursday's phone meeting, it would be helpful if primary
authors for different sections of the proposal reread their sections. Some
possible additions/refinements to the proposal are listed below.
Thursday's meeting will begin with brief reports from the working groups.
We will then discuss our goals for the next few weeks.
Ed and Mike
Updates to the proposal should include the following.
Revisions/refinements of the baseline design:
- Gd concentration. Should we change baseline concentration to 0.2%?
- Real design for veto system.
- Calibration momvement system design
- Improved design of underground areas
- Refined vessel support, neck design (if available)
- Rough surface design (if available)
- Final depth in mwe (using bore hole data)
Additions/improvements to proposal text
Clearer discussion of sensitivity. We should provide a more detailed
table of systematic errors. We must
provide justification for the acceptance systematic error (e.g., what is our
strategy for measuring volumes, etc.)
Backgrounds:
We need to provide a complete discussion of backgrounds,
describing the role of the veto system in reducing and measuring
backgrounds,
and giving estimates of remaining background levels (both levels and
estimated uncertainties on each background source).
The in-situ monitor section needs to be quantitative, and we should explain
how these measurements affect overall background uncertainties.
Calibration:
- Include strawman calibration system design (mentioned above)
- Is source calibration necessary in buffer region?
- Expand discussion of dissolved sources.
Cross checks:
- Add possibility of using isotope production from cosmic muons
to measure fiducial mass.
- Improve detector movement section to make role of this cross-check
clearer.
Incorporate discussion of bore hole information in civil
engineering section.
Incorporate any available updates to mechanical engineering discussion.
Elastic scattering measurement. Incorporate results of several recent
studies in writeup. We need to understand additional costs and requirements
required by this measurement. (The elastic scattering measurement will be
discussed in detail at the second phone meeting.)
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