Meeting minutes Tuesday 12th August 2003

Present: 	 Aaron Bebington (AB), Ahmed Hussein (AH), Art Olin (AO), Anthony Olivieri (AOli), Barry
 	Davids (BD), Cassi Galt (CG) RECORDER, Cybele Jewett (CJ), Chris Ruiz (CR), Dario Gigliotti (DG), John D'Auria 	
	(JDA), Joel Rogers (JR), Mike Anderson (MA), Mike Lamey (ML), Marcello Pavid (MP), Peter 	
	Machule (PM), Zhihong Li (ZL) 

1.  Minutes of previous meeting and business arising

ML	Corrections to previous minutes:	
		Hardware status - carbon foil thickness is 10-20 ug/cm^2.  
		BGO efficiency - correct source is Marion and Young 	

JDA	Remember that the effective length of the target must still be calculated.

CJ	Further analysis in PAW of gamma spectra has come to a dead end; have switched to 21Na analysis.

JDA	Sabine did analysis with Nova; Shawn will use the n-tuple/PAW program.  We must look for 	
	agreement between the results.  

2.  Hardware status and plans

JDA	The solid target holder doesn't fit because of the gamma array support structure.  Hart and Heinz 
        are making mods to gamma array support structure and should be ready in a few days. 

ML	Have new, shorter cables for the MCP; will compare signals obtained with these shorter cables to 	
	those obtained with the long cables.   

JDA	Are there new ultracam detectors for the elastics in gas target?  The current detector is not 
        very effective.

JR	We have at least one spare, maybe two; it is possible that the current one is bad.  Tests are 	
	recommended; Anthony can help with this.

AH	Has a new delta E / E detector system and needs someone to assist to work on electronics for it.

3.  Optics of DRAGON

JR	Has been working with GIOS to better understand DRAGON optics and acceptance loss of 16O 	
	recoils.  Such a loss was expected because the recoil cone is larger than that of the flagship 	
	experiment (21Na) for which DRAGON was designed.  The accepted tune works well for 21Na, but 	
	not for 16O.  Progress so far includes development of a tune that works well for 16O in the first 	
	stage, and looks promising for the second stage.  Following the completion of the optics 	
	calculation, an excitation function can be produced for 16O at the lowest possible resonance 	
	(about 0.8 MeV/u).  This will verify that the separator works.  

	It is possible that modifications to the front end will be required to go to the lowest energies.

JD	If changes are required, must draft an NSERC grant for them in the next weeks.  


4.  Simulation Calculations

MA	Presents results of 12C analysis.  The control simulation, done with the standard tune, illustrates 	
	the known acceptance loss and shows that events are lost primarily at the mass slits and charge 	
	slits.  Changing the energy tune by +1% makes things worse.  Low energy acceptance decreases, 	
	with a large increase in the number of events lost at the charge slits.  Changing the energy tune by 	
	-0.5% has the opposite effect - acceptance improves, with fewer events lost at the charge slits.     

	Before Dave Hutcheon left, he suggested a new tune to try.  This was done, and the results were 	
	not good.

CR	Shows a plot of recoil cone angle vs recoil energy immediately after the reaction, and identifies 	
	three important energies:  the high energy peak, the low energy peak, and the median energy.  Goal 	
	is to identify what is special about the low energy gammas that prevents them getting through the 	
	separator.  Chart of transmission of recoils through QSLIT shows only one set of conditions that 	
	corresponds to no transmission.  The conclusion is that accepatance loss is more a property of a 	
	broad resonance than of something wrong with the tune.  A tune must be designed with 	
	reasonable acceptance for broad resonances.  

	Next step:  Aaron can take over simulations.

AO	In the long run, must determine if our optics simulations accurately represent reality. 

5.  12C(a,g)16O Data Analysis

CG	Updates status of 12C(a,g)16O gamma spectra fitting.  Summarizes method used to fit spectra and 	
	obtain branching ratios (see attached slides).  Shows two examples of completed fits.  The first, 	
	done for beam energy 1.280 MeV/u (off resonance), has a reasonable chi-squared value and shows 	
	contributions from the ground state and the 7.117, 6.917, 6.130, and 6.059 MeV states.  The second, 	
	for beam energy 1.067 MeV/u (on resonance), is not so encouraging.  The chi-squared is 	unacceptably large.  
	The tails are fit in favor of the peaks, suggesting that the tail representation in 	
	the response functions is inaccurate.  The fit shows a 63 +/- 4 % contribution from the 6.917 MeV 	
	state, and a 35 +/- 3 % contribution from the 7.117 MeV state.  However, the literature shows that, 	
	on this resonance, decay occurs solely through the 6.917 MeV state.  

	The conclusion is that knowledge of detector gains is not sufficient to resolve the 6.917 MeV and 	
	7.117 MeV states using this method.  The variation in detector gain will be investigated at the four 	
	resonances for which data exists.  

6. AOB

AO	Will discuss ROOT project next week.

AOli	Has procedure for opening new safe for radiation sources.  AB will put this on the web page.