Minutes of DRAGON meeting of 3 December 2002
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Present: D. Gigliotti, P. Walden, J. D'Auria, A. Laird, J. Rogers,
S. Bishop, A. Olin, D. Hutcheon (recorder), S. Engel, A. Hussein,
L. Buchmann

1. Minutes of previous meeting -- corrections
	- 12C(a,g) report:  4th and 5th sentences should read:
	"An upper limit for the suppression factor was calculated to
	 be 10^-13.
	   It should be noted that the suppression factor is expected
	 to be much better for an (a,g) reaction compared to a (p,g)
	 reaction because of 10-20% difference in m/q for recoils to
	 beam compared to 4-5% for p,g."
	- Future plans to read: "Please be reminded that two new coop
	 students will arrive in January."

2. Run status and plan for the coming week of beam
	-JDA: we have seen resonance yield from the "6.051" level in
	 22Mg, looked for and seen ~0 yield from the "5.957" level.
	 Today they will check beam transmission from the Target Ion
	 Source through Mass Sep'r in parallel with tuning 21Ne through
	 accelerators to get to the 6.240 level.
	Possibible uses of rest of time (if nothing seen at 6.240):
	* SE: check charge state dist'n dependence on z (for broad
	resonances)
	* LB: go to the broad resonanaces seen by TUDA at higher energies
	* JR: repeat "212" with energy(ies) chosen to get <z> near centre
	at pressure ~4.5 Torr
	* AO: repeat "212" with reduced pressure and energy(ies) chosen to
	put resonance in upstream part of the target.  
	* LB: look for possible state at ~8 keV higher than the one we see
	at 204 keV.
	* DH: revisit the "822" elastic scattering with controlled small
	steps using gas pressure and Prague/MD1/Trf monitors.
	There was a spirited discussion of these options.  No concensus
	was reached, except that the Letter could be submitted with data
	already in hand.
 
3. Gamma array efficiency (DG)
	Results presented previously are suspect due to a "feature" when
	PAW does projections of 2-d spectra.  A separate 1-d histo has
	been formed to avoid this problem.
	The GEANT simulation of efficiency vs z of gamma ray creation for
	511 keV gammas looks reasonable, showing an asymmetry due to Pb
	shielding being upstream but not downstream of the target box.

	Various technical problems have delayed analysis of source data.
	The data from a 511 source mapping of full-energy peak yield vs
	z has, at present, a 15% uncertainty due to the uncertainty in
	source strength.  The z-shape of the 3 points analyzed to date
	is like the GEANT shape, but there is a ~25% discrepancy near 
	z=0 between GEANT and source estimates of efficiency.
	The 511 source was chosen because the peak is cleaner than for
	the higher-energy sources, but the dead times were large.
	There is a question about how the analysis software treats the
	double hits expected from the two 511's of positron decay.  
	Higher energy sources take longer to analyze, but don't have
	the large dead time correction and have absorption more like
	the gammas of interest in 21Na(p,g).
	Further results to be presented next meeting.

4. The ion chamber of the 8Li(a,n)11B proposal (PW)
	A concept for the target/ion chamber was shown.  It has a thin
	window separating the target gas (He) from the ion chamber gas
	(isobutane).  At lowest energies a windowless version with a
	He-isobutane 90:10 mixture may be necessary.  Could a windowless
	version run at all beam energies?  Probably not because at high
	beam energies a mixture rich in He needs high pressure to stop
	the 11B recoils.  Question of allowable window thickness for
	smallish-angle recoils is a key.
	Q: what about detection of neutrons?  A's: there is an efficiency
	problem unless neutrons are stopped in a large, surrounding volume
	of scintillator in which case ground state cannot be distinguished
	from excited states or cosmic-ray neutrons.