Talk with Georgio Gratta, Feb. 17

I am out at Stanford for the next few weeks. I spoke with Georgio today.
Notes from talk with Georgio Gratta, Feb. 17.

1. He suggests that we look into isotopically separated Gd (perhaps
Russia cheapest for this). Only one isotope is useful for us and
using it can shorten capture times, etc. For theta_W measurement
which was recently suggested as a side result of the theta13 experiment,
n capture on p is a background and the better Gd is especially important
for this.
2. He suggests that we look into other scintillators than pseudo-cumen.
Palo Verde used 40% pseudo-cumen, 60% oil
Kamland used 20% , 80% for flashpoint limits.
The gain in signal size is small going to pure scintillator, but the gain
in distinguishing pulse length is large. For instance, alphas which
saturate, give a long pulse and e-like things shorter pulses. If the
pseudo-cumen is diluted the distinction is much less clear. Also, if
you dilute, you can put in less Gd (linear).
The Germans like something called pxe, and
Georgio likes something called din (di-isopropyl-napthalene, I think).
It is non-flammable, non-poisonous, non-smelly. However it does
have phosphorescence states, but it seems possible to get attenuation
lengths of more than 5 m.

By the way, Georgio found the Gd to be reasonably stable in his Palo Verde
experiment (after the first try). The transparency changed somewhat over
the first year but then remained steady and tests with samples some 8 years
later show essentially the same fraction still there. (The transparency
is the most sensitive thing.)

I think I mentioned before his recommendations on the muon background, but
since we rediscussed it, I'll outline it here. He thinks that Fluka works
well for the neutrons produced by muons. He notes that it is VERY important
to take into account the secondary production of neutrons.
This multiplies the total by more than a factor of 2. Some of the graphs
in his paper PRD 64 013012 (2001) are very instructive (look at neutron
multiplicities in Fig. 6.

Recipe:
Use muon spectra from the L3-cosmic results (Jon Link has the paper)
Use Fluka for the neutrons--he has parameterized the Fluka results in
formulas 6-12 in the above work

Activation of various materials in the experiment is done by hand, looking
up the cross-sections for each material. Note that some of the
radioactive isotopes produced have lifetimes of the order of minutes!

                              Byron

-- 
Byron Roe (byronroe@umich.edu)
Office: 355 W. Hall   (734)764-4441
Mailing Address:  Department of Physics, Randall Laboratory
University of Michigan, Ann Arbor, MI 48109