Minutes of DRAGON meeting, September 16th 2003

Present: Aaron Bebington (AB) - recorder, Alison Laird (AL), Art Olin 
(AO), Barry Davids (BD), Chris Ruiz (CR), Dario Gigliotti (DG), Dave 
Hutcheon (DH), Dave Ottewell (DO), John D'Auria (JDA), Joel Rogers 
(JR), Lothar Buchmann (LB), Mike Lamey (ML), Mike Trinczek (MT), Nicole 
Chorney (NC), Pete Machule (PM), Shawn Bishop (SB), Zihong Li (ZL)

1. Corrections to Previous Minutes: None. They were perfect.

2. Hardware
 2.1 Pumps (DO) [attachment 1]
The divider was taken out between pumps TP3 and TP1 because TP1 
was overheating and tripping off. By taking the divider out eased 
the pressure on TP1, and gives a linear response. TP1 and TP3 are 
now “happier”. However, limiting to a low speed (38000 to 
35000rpm) made the pumps “unhappy”.
AO – a bigger pump, maybe?
JR – look at the background and see how it changes with target 
pressure.
Running at 5Torr rather than the usual 10Torr means less stress 
on the pumps, but runs will be twice as long.
Solution: possibly another pump on top, downstream, next to TP3.
 2.2 ED1 (JDA)
PM has cleaned the old drivers and stacks. These are now the new 
drivers. So bad news is that we no longer have any backups. 
PM – they’ve all passed the test.
 2.3 Mass Slit Box (JDA) [attachment 2]
Hart has looked at the diagram and will modify the back end of 
the mass slit box. (Will be discussed more at a later meeting 
today at 1pm). 
AL – reminder that the current integrator needs to be put on FCM.
[2.4 Quick Comments (JDA)
a) the 5-year review went really well! 
b) there is problems with the beam time in the fall (to be 
discussed at a later date).]

3. Gamma Array Studies (DG) [attachment 3]
The following presentation was an attempt to explain progress 
thus far on the efficiency comparisons measurement to simulation 
for the DRAGON gamma array.
The efficiency of the DRAGON gamma array will be calculated for 
high energy gamma sources of unknown activity by calibrating them 
with a NaI detector of known efficiency. Once the activity of the 
source is known this becomes the denominator in the calculation 
of the efficiency of the array.  See Fig 1. NaI was the detector 
of choice as this crystal type has been thoroughly studied and 
efficiency for crystals of standard sizes are well known. These 
efficiencies are published in various places but have been 
compiled in Marion and Young's "Nuclear Reaction Analysis Graphs 
and Tables". These tables will be used in this work. It is to be 
noted that efficiencies above 3 MeV presented in these tables are 
calculations. As a test of these quoted efficiencies another 
calculation of the efficiency of NaI was produced using the GEANT 
simulation code. These two results agreed for low energy sources 
and have been presented earlier.
 Fig 4 represents a gamma spectrum from an AmBe source detected 
in a standard 3" x 3" NaI crystal. To extract the full energy of 
the 4.44 MeV gamma peak in this spectrum a fit was necessary. The 
fitting was done by producing a Monte Carlo (GEANT) spectrum of 
the response of this detector to 4.44 MeV monoenergetic gammas. 
The simulation includes all necessary physics except for 
resolution of the detector which will be a parameter in the 
fitting procedure. This spectrum is represented in Fig. 2. The 
fitting program (borrowed from Dan Melconian of the TRINAT group) 
uses this Monte Carlo spectrum as its base for a fitting 
function. On a suggestion by Peter Gumplinger it was decided by 
JR, AH (Ahmed Hussein) and DG that this was a good technique for 
fitting the spectra as this curve represents all necessary 
physics occurring in the detector. As was discussed before NaI 
has been thoroughly studied and it is assumed that the GEANT code 
does a good job in simulating this simple geometry. The fitting 
program takes as input the data file and the Monte Carlo spectra 
as inputs. It will then convolve each of the Monte Carlo spectra 
channels with a Gaussian of appropriate sigma which will, with 
the other fitting parameters, give the best fit to the data. 
Other fitting parameters include detector gain, zero offset, and 
overall normalization (the y-height of the fitting function) of 
the data. The result of the fitting for NaI is shown in Fig 3. 
The "yNorm" factor multiplied by the height of the single 
channel, Monte Carlo peak becomes the area under the curve of the 
full energy peak (ie. the number of 4.44 MeV gammas emitted by 
the source).
	The numerator of the array efficiencies comes from the full 
energy counts of each of the 30 detectors in the array. A typical 
spectrum of these detectors is shown in Fig 5. To find the area 
under the curve the fitting technique described above for the NaI 
was duplicated for each of the 30 detectors in the array. In 
addition to the Monte Carlo fitting function, a second linear 
function was also added to the fit to represent background. The 
result of the fit along with the fitting parameters is shown in 
Fig. 6. The number of 4.44 MeV gammas detected was found as for 
NaI.
	Figs 7 and 8 represent the detector by detector efficiency for 
each of the 30 detectors in the array. Measured efficiency is 
represented by two points. The squares represent BGO detector 
efficiency when the NaI detector is calibrated using GEANT. The 
diamonds represent the BGO efficiency when the NaI detector is 
calibrated by the tables of Marion and Young. Also plotted for 
each detector is the GEANT simulated efficiency of each of the 
detectors in the array. Fig 8 shows good agreement between 
measurement and simulation for the "east" side of the array. The 
west side shows good agreement in the relative detector to 
detector efficiency but also shows a systematic difference 
between data and simulation. This effect is being investigated. 
[On suggestion from JR the "crown" detectors of the array were 
removed and measurements were done after the DRAGON meeting of 
Sept 16/03. The analysis of the data showed the same systematic 
difference. Work is continuing.]
	Fig 9 shows the overall photopeak efficiency at 31.5 cm for the 
entire DRAGON gamma array. This number is calculated by adding up 
the individual efficiencies of each of the 30 detectors. 
Comparison to GEANT simulation shows agreement between "Marion 
calibrated" and "GEANT calibrated" of approximately 4%. This 
result shows that the GEANT simulation will provide a very good 
approximation of the array efficiency for high energy gammas when 
the systematic fluctuation of the west array is dealt with. 

4. Optics of DRAGON for 12C running (cont…) (JR) [attachment 4]
Summarized in the attached memo, GIOS input settings have been 
modified since last week, to only include transport up to the 
mass slits. Working on the lower 2+ resonance, 2nd order 
aberrations have been added (see 3rd column). Changing Q2 by -/+ 
5% gave new envelopes (columns 4 and 5 respectively). This +/- 5% 
was found by seeing where the rate drops off turning the knob for 
Q2. The other drop-off points can also be found similarly, by 
turning the other magnets’ knobs seven times. These seven pairs 
of numbers are found by looking at the count rate. With these 
seven pairs of numbers, a new tune can be determined by setting 
each magnet at the midpoint of its range.
The simulation maybe different in the real world. 
The envelope is the most sensitive to Q1.
JR will be ready to run next week.

5. 21Na results (DH) [attachment 5]
 5.1 733keV resonance (E_x = 6.25MeV)
We see a very small leaky beam, and the recoils well 
distinguished from it. We have a wg ~ 250meV, which with a spin 
of 4, gives a gamma-gamma of >= 220meV. The E_x = 6.35MeV, spin 
4, state of 22Ne, has a mean lifetime of 19fs, which gives a 
gamma-gamma of <= 35meV. These do not compare well.
 5.2 538keV resonance (E_x = 6.04MeV)
We can just distinguish the recoils from the leaky beam. We have 
a wg ~ 10meV. BD has proposed a spin of J = 1, which gives a 
gamma-gamma of ~ 30meV. This state may correspond to the E_x = 
6.69MeV state of 22Ne, but this state has a gamma-gamma value of 
2meV. Therefore these do not compare well.
 5.3 454keV resonance (E_x = 5.96MeV)
After a whole weekend of running, only 13 counts were seen above 
the background. This gave a wg ~ 1meV. BD has proposed a spin of 
J = 0, which gives a gamma-gamma of ~ 8meV. The E_x = 5.96MeV, 
spin 0, state of 22Ne, has a gamma-gamma of ~ (1-7)meV.
 5.4 Stellar Rate
The 206keV resonance state that we published is the dashed line 
under the solid line, until we get to 0.8GK. This graph shows 
that only the 206keV resonance matters for nova temperatures. 
Above 1GK, the 733keV and the 822keV resonance become dominate. 
The 454keV and 538keV resonance are never more than 10% of the 
total. 

6. 26Al(p,g)27Si proposal (CR) [attachment 6]
This reaction is important for two reasons. 1) 26Al is 
galactically observed 2) the 26Al/27Al ratio can be measured from 
meteorites. An 26Al beam will contain both the isomeric state 
(0+) and ground state (5+), which have to be separated. (Isomeric 
state = a long lived excited state that does not decay to the 
ground state). The ground state of 26Al will beta-decay to an 
excited state of 26Mg, and the isomeric state will beta-decay 
straight to the ground state of 26Mg (which cannot be observed as 
no gammas are given off). The ground state of 26Al has been 
looked at a lot previously, unlike the isomeric state. For the 
ground state (p,g) reaction, the 188keV resonance dominates. It’s 
also possible that there maybe some unknown states in that 
region. The 226 resonance has only been seen once but could be 
important. The levels highlighted in orange are the ones listed 
in the NACRE table. For the isomeric (p,g) reaction, there are 
several observed resonances which could contribute, but their 
spins are unknown. A suggested TUDA experiment would be to 
determine the spins of these states, either doing a (p,p’) 
reaction or a (3He,p) reaction. This would be a 2 phase 
experiment. In a 26Al ion beam, the ground state is thought to be 
two orders of magnitude more than the isomeric state. A changing 
beam intensity, perhaps? The only problem is that the yields will 
be very small.
JDA – this is a very important astrophysical reaction (probably 
more so than the 21Na experiment). A possibility of 4 PhDs within 
this. Will this be two proposals to the EEC?

7. Operation “ISDAQ04 cleanup” (AB) [attachment 7]
With all .mid files backup on DLT tapes (found in the control 
room, by the isdaq04 machine), and all duplicate .mid files 
deleted, the /data disk is now down from 100% used to 72% used. 
The /data1 disk is now down from 80% used to 75% used, and the 
/data2 disk is now down from 22% used to 18% used.  
All softlinks for every .mid file and every .odb file are found  
under /data1/dragon/datalinks in folders in divisions of 100. 
/home/dragon is currently 73% used and could also use a clean up. 
This needs everyone in the group to take a look at /home/dragon 
and see if any of the things on there are theirs, and if so, do 
they still need to be there.

8. Gains (NC) [attachment 8]
Following up on last weeks 12C meeting, the gain stability of the 
BGOs was looked into. Looking at runs 8217 and 8439, and plotting 
their peak bin number, for each detector, versus one another, you 
see that there is a ~7% shift for detectors 5 and 6 in gain. This 
shows that we need to pay more attention to the gain shift. Cause 
of gain shift is uncertain. 

9. 11C(p,g)12N proposal (ZL) [attachment 9]
From the wobbler studies results, the recoil acceptance of DRAGON 
is to be found. The ellipse in the first diagram covers all the 
wobbler measurements. The maximum recoil angles and the maximum 
relative energy difference, both as a function of the centre of 
mass energy for 11C(p,g)12N, show similar curves. The increase 
after 0.6Mev E_cm is due to a small Q value. The 11C(p,g)12N 
reaction is maximum at 0.2MeV, which is no problem for DRAGON, as 
this is well within the wobbler ellipse measurements, of DRAGON’s 
acceptance.
AL & CR – This reaction is being done at Louvain-La-Neuve. Their 
data will be presented at next week’s ‘Radioactive Nuclear Beam 
6’ conference in Chicago by Carmen Angulo.
JDA – We’ll invite Carmen to DRAGON to help us with this.  

10. AOB (JDA)
      All students should be attending astrophysical seminars.