From: Mohan Chatterjee Subject: Minutes of the DRAGON meeting held on June 17,2002 held at 3-30 p.m. Present: Mike Lamey,Chris,Joel,Alan,Art,Dave O.,Dario,Don,Ratchel,Sabine,Allison,Lothar,Anuj Parikh,Dale Bisser,Jeniffer, Shawn,Dave H.,Mohan,Cybelle Venue: ISAC Seminar Room Chaired by Dave Hutcheon Minutes of the previous meeting held on June 11,2002 were confirmed. Dave H. invited comments on the Data Analyses and Results obtained so far. Joel opened the discussion on Beam Energy determination from the TOF for the 822 KeV/u Resonance Runs. He presented the results showing linear relationship between Energy and time of Flight though there was some off- set between sets of Runs. The overall picture is consistent and satisfactory. He mentioned about one run where the energy was questionable. Dave H. mentioned and showed results of DSSD vs RF for beam pertaining to the Run 4786: dE/E obtained was 3.1x10-3. Possibly the MD1 (NMR) gives better estimate and TOF should be used as a check, he commented. Regarding the Beam intensity measurement Dave H stressed the beta monitor analyses he did. Joel showed data on the Faraday cup Normalizations. He maintained that those runs which gave good Elastic Spectra seem to be more reliable. FC4 current vs. Beta-monitor rate being a straight line shows that the beta monitor readings are quite consistent and can be relied upon in case there is discrepancy in the Faraday cup rdgs.The lowest energy run 6204 seem to be anomalous. Dave H. presented the elastic monitor counts normalised to beta monitor for the Nov. run at 215 KeV/u. He obtained a mean of 19.2 with sigma=1.5. The Nov. set of Runs show consistency. Joel stressed that for determination of absolute cross-section the beta counter normalizations should be relied upon. Discussion on efficiency and the question of cuts: Shawn showed the analyses of the Elastic energy spectra for the 4872/4878 Runs in Nov,2001. He could obtain the profile of protons by subtracting the average beta counts in the 21Na(p,gamma) run. Next he will try with time projections. So far no cut in the pulse height of DSSD has been used. Statistics was quite poor to look at the position distribution in DSSD for the 215 KeV/u runs. Joel felt that without any cut in the DSSD-it might be risky, since randoms may creep in. In the recoil spectrum in DSSD the resolution was about 6% and the events were scattered over energy. Sabine reported that for 822 Kev/u data putting cuts on the RF reduced the background by 50%. No coincidence event around the alpha-source energy was observed. Typical RF-spectra with various cuts to be circulated by Sabine. Dave H. showed the plots of Elastic yield vs. Beam Energy for the 822 KeV/u resonance runs in 21Na(p,gamma) normalised to the beta monitor. Joel has strong reservations about the redundant runs, where things did not function well should be thrown out. Joel questioned what is the guarantee that all electromagnetic elements/Valves etc. behaved all right when something palpably bad appears in the data. Dave H. commented that some consistent criterion needs to be evolved for rejecting the runs. On this issue there were lengthy discussions. Dave H. said there are still 4-5% random variations which are not understood well. Joel feels that criterion can be evolved when the goal is properly defined. At this moment the goal should be to obtain reliable omega-gamma values for the resonances. Dave H opened the discussion on the gas target density profile and the location of the resonance. He found Leff ~11 cm in the central plateu region and 6-10% of the gas in each pumping tube, in order to be consistent with the observed total Leff ~ 12.3 cm. At this point Sabine also presented the analysis with a different profile made up of 3 step functions assuming a linear drop at the tails and a central flat plateu of density. Joel discussed the extraction of width from the yield curves. Knowledge of the spatial profile of the gas target is necessary otherwise uncertainty due to the tail region would creep in. Art mentioned about the Geant Simulation he had made earlier for the gas target profile.Dario was asked to look into the gamma-array efficiency with source at the centre of the gas target and at the pumping tubes using the Geant simulation. Joel presented the gamma-HI coinc. yield curve versus energy for the 822 KeV/u resonance and commented that extraction of resonance width was seriously handicapped due to the beam energy spread and uncertainty. He could not get a good chi-square. How to account for the horizontal spread of the data points (viz. energy spread) was a big question. It was felt that the energy values depend on the goodness of tuning-as a result depends largely on the "human tuner"(both at the ISAC operator end and the DRAGON end) and thereby slightly varies from run to run. This has contribution to both energy spread and time spread. Also to be taken into account the angle offset of the incoming beam from the ISAC end. It was decided to work on the sources of undefined random errors to enhance the level of preciseness in the measurements. The guests from the Yale group reported their success in energy calibration with a split-pole Enge Spectrometer for the experiment on 24Mg(p,t)22Mg. They used two states in 24Mg(p,t) and 12C(p,d), 24Mg(p,alpha) peaks for calibration using a polynomial fit 5 th. order and got consistent results.