July 29th, 2003 DRAGON Minutes

Present: Dave Hutcheon (DAH), Mike Lamey (ML), Aaron Bebington (AB), 
Mike Anderson (MA), Uwe Greife (UG), Chris Ruiz (CR), Zhihong Li (ZL), 
Cassi Galt (CG), Alison Laird (AL), Lothar Buchmann (LB), 
Anthony Olivieri (ATO), Dario Gigliotti (DG), Cybele Jewett (CJ), 
Joel Rogers (JR), Ahmed Hussein (AH), John D’Auria (JDA), Sabine Enges (SE),
 Peter Machule (PM), James Kennedy (JK)


Corrections to Previous Minutes:

Spelling and grammatical errors, and Sean Bishop's name should be removed
from the list of people doing 21Na(p,g)22Mg. So far, only Sabine has done 
this analysis.


Hardware Status:

DH	- The solid target ladder is hard to mount, due to the O-ring, but
	is ready to go.
	- An order has been put in for a pumping tube with a new aperture.

UG	- Stopping power measurements have been completed, using helium on 
	helium and helium on hydrogen. The helium on helium results agreed 
	with previously published results. A potential difference in
	effective length was seen for different apertures. The previous 
	number was believed to be 12.4 cm. Now UG has found 12.9 cm and 
	DH 13.5 cm. The exact number will be calculated later. 

ML	- We have some 10- and 20- mg/cm^2 carbon foils for the solid target. 
	- MCP has been tested, using 20Ne at 400KeV/u to check the timing 
	between the MCP and DSSSD. There used to be two timing peaks, but 
	after removing an inverter only one peak was seen. The hardware, 
	amplifiers and cables, should be modified to improve the timing. 
	The MCP will be further tested over the next couple of weeks. 


12C(a,g)16O acceptance problems:

JR	- GIOS is being used to check the standard tune of the separator, 
	to see if moving the charge focus downstream might soften the 
	acceptance problem. Using GIOS, the size of the beam can be found 
	after each component, and checked against the actual beampipe size. 
	For the defining reaction, 15O(a,g)19Ne, the beam is uncomfortably 
	large at ED1. The beam gets larger at this point for the 12C(a,g)16O. 
	Using the algorithm that created the standard tune, but with the 
	12C(a,g) reaction, creates a different standard tune, with a more
	comfortable envelope at ED1. The next step is moving the charge focus 
	downstream and seeing the effect on the beam size at all the 
	components, including in the second stage. 

CR	- GEANT has been modified further, with more beampipes and collimators 
	added. A reaction specific file has been added, so that the simulation 
	can be easily changed over to a different reaction. The next step will 
	be to run high statistic simulations, to look for asymmetries and 
	where recoils are being lost in the separator.


BGO efficiency:

DG	- An AmBe source has been used to measure the BGO efficiency, and 
	check a simulation of the BGO array. The source was placed on top of 
	the target box, and the BGO array pulled back 30cm. The photopeaks 
	were measured, corrected for the source strength according to two 
	sources: –Marion and Yuone, and a GEANT simulation previously
	tested.  These corrected photopeak efficiency measurements were then 
	compared against the array simulation with identical geometry. The 
	average results seem to agree well, but systematic errors seem to be 
	present. In the east array, detectors 12-30 show consistently low
	efficiencies, with an odd pattern. In the west array, all the
	calculated efficiencies are too high. The simulation will be
	further checked, and other sources will be used to test this again. 

CJ	- The 160 data has been analyzed using NOVA, to obtain a number for 
	the BGO array efficiency. The coincident recoil spectra was used to 
	find energy cuts that are then applied to the singles spectra, and 
	the ratio of good gammas to good recoils was used to get an estimate 
	of the BGO efficiency. The numbers seem a little low. It's
	possible that a broad resonance of unknown strength may be
	interfering with the low energy data. It is also possible the 
	threshold settings could have an effect. Going further with this 
	analysis could give another measured value against whick to check
	the gamma array simulation. Further analysis will be conducted, in
	PAW as well as NOVA.