DRAGON Meeting Minutes     12 March 02

Present: S.Bishop, L.Buchmann, M.Chatterjee, A.Chen, D.Gigliotti,
D.Hutcheon, D.Lang, P.Machule, A.Olin, D.Ottewell, J.Rogers (recorder).
(G.Ball for part of the meeting)

1. Previous minutes were approved with minor corrections.

2. Business arising from the previous minutes:
LB said our width for the 822KeV/u 21Na(p,g) resonance is too big compared
to the TUDA value, and we must find out what we are doing wrong.

DH showed his joblist: BCM1 was fixed. MCP will need to use the DAQ computer
soon but exactly when is not yet known. DG said he needs two weeks of DAQ
time to complete his thesis data-taking of gamma efficiency vs z. DH
encouraged DG to go as fast as possible and try to get out of the way for
the test of of the new DAQ component, vxdragon, by the end of the month.


3. Dustin Lang's analysis of wobbler data:
He displayed tables of EMS transfer coefficients as measured with the wobbler
and as computed by GIOSP. The general trend was for good agreement except the
x|a coefficients were slightly non-zero at foci where they should be zero.
JR asked if the results helped solve the problem of the unexpectedly small
acceptance angle at the separator entrance. The answer was no, but DH added
that the new procedure of centering the beam on the EMS quads should help
avoid possible clipping of the acceptance cone at the entrance.

4. Shawn Bishop's thesis analysis of 212KeV/u 21Na(p,g) resonance data:
He distributed a 15 page report, 'A low statistics estimation of "212" keV/u
21Na(p,g)22Mg resonant reaction yield'. He has analyzed 18 runs covering
215,
220, and 225 KeV/u beam energy, acquired in Oct.-Nov. last year. Using a
Maximum Likelihood method of statistical analysis he showed that the 18 data
were statistically self-consistent. Possible sources of systematic errors
were also discussed, including unplugged detectors, tripping quads, beam
energy shifts, gamma ray efficiency variations, and varying separator
slit-settings. DH showed his computation of the log-error function computed
from summing the expected Poisson log-errors over the 18 data. This value
should agree with the Shawn's fitted value but DH's value is somewhat larger
than Shawn's indicating probable systematic errors from some source. DH
asked Shawn to try to explain this difference.

5. Plan for next month's run:
The discussion of Shawn's results led to a spirited discussion of what should
be done with the scheduled RIB time. After opinions were voiced 
 the consensus seemed to be that it would be
worthwhile to repeat one or two energies of the 212 KeV data set. LB stressed
the need to study also several other possible resonances above 212 KeV/u, to
obtain a good publication this year.

6. Art Olin's new GEANT simulation:
Art showed an improved simulation of the transport of beam, gamma rays, and
recoils through the target for the 822KeV/u 21Na beam. The gamma rate from
beam spill in the target apertures is predicted to be substantially larger
than earlier simulations. Most of the positron background comes from the 8mm
aperture at the downstream end of the target chamber. JR pointed out that
the spills in the upstream apertures before the target are especially
important for the functioning of the gamma array, because measurements
have indicated that shielding this region greatly reduces the gamma-array's
background rate.