Minutes from target meeting held September 28 2007 in 892-1-D20

These minutes are available also from:

http://wwwcompass.cern.ch/compass/detector/target/Minutes/2007/

a) Yuri: September 25 restart polarizing from +92.1 %, -79.8 % and +85.4 %.
In three days +94.3 %, -82.8 % and +89.4 % reached. Transverse data taking 
started from September 27 22:00 (0.63 T). 

b) Fabrice: repair magnetic field warning lights. One relay and lamp exchanged.
Problem in liquid helium distribution box isolation vacuum pump system control
unit.

c) Jaakko: program to calculate NMR signal second moment of protons in H2O 
molecule. The second moment about 500 kHz^2, which is very close to the value
of protons in NH3. This can be understood M2 ~ 1/r^6 and (1.710 A/1.515 A)^6 =
2.07, so the the extra proton in NH3 compensates the longer atomic distance of
1.710 A. Thus it is difficult to distinguish water signal from ammonia. The
natural abundance of oxygen-17 is only 0.038 % and it has broad NMR line due 
to quadrupole moment. Possible crystal structure for ice is Ic, which is formed
at temperatures 130 - 150 K and transforms to Ih above 200 K. 

d) Jaakko: program to iterate level populations in three proton system. For 
given proton polarization many solutions possible. Use Monte Carlo to simulate
possible solutions and make histogram of them. Use the median for the level 
population. For example with 80 % polarization the resulting NMR sublines have 
normalized intensities 0.024, 0.275 and 0.702. This gives a shoulder to the 
NMR-lineshape similar to the observed signals in polarized NH3. Above 85 % 
the shoulder disappears. Below 80 % the intensity histograms have large 
spread, which probably means that there is no stable solution to the problem.