Minutes of DRAGON meeting August 27, 2002 Present: J.D'Auria, L.Buchmann, C.Jewett, J.Rogers, M.Lamey, A.Olin, D.Hutcheon (recorder), D.Ottewell, C.Wrede, A.Hussein, P.Machule 1. Minutes of previous meeting and business arising still at 'draft' stage; figures not distributed 2. Hardware status and studies * MCP/cooled-detector tests (CW,AH) The DSSSD has be re-installed, an alpha source mounted upstream of the F slits. and yesterday the system was pumped down. First goal is to understand and get rid of the double peak that has appeared in the MCP timing spectrum. JR suggested it was due to inappropriate values in the table of timing offsets for the individual strips of the DSSSD. A problem: the supposed strong Gd source gives only a very low count rate (~400/day) when positioned upstream of the MCP foil. * a suggestion to make a new Si detector box (CW) will be deferred until after we know the results of tests with the cooled detector. * Ion chamber data (CJ) Range-energy curves have been calculated using SRIM for 21Ne and 22Na, for comparison vs data from the recent run. There is a puzzle in that the R-E plot shows 22Na with greater range than the 21Ne -- this should be double-checked. Yields of "Recoil" and "Beam" peaks have been obtained for each anode. The peaks are distinct in anodes 1 and 3-5, but unresoled in anode 2. * Turbo cooling There was an e-mail message from Igor, regarding Varian's recommendation concerning turbo cooling. We do not understand what it means for DRAGON. DO will get more information. * MD power supplies (DH) Another water leak had to be fixed on the old SX4 power supply. Its replacement P/S and 3 other air-cooled P/S's were ordered 10 days ago. The new supplies for MD1,MD2 should be delivered within a month. Installation will have to be coordinated with any stable beam runs. 3. Stable beam request JDA has circulated suggestions for measurements and had some comments. This will be discussed as a major agenda item next meeting. 4. Analysis of 21Na(p,g) 822 keV data (JR) [see attachments] * The Elastic monitor r.f. time centroid is a sensitive measure of beam energy, and can be extracted for old runs from data that do not require transcription by people (as MD1 fields do). * The good Elastic monitor time resolution of Nov/01 was not available for the Spring/02 runs (bad replacement Si det'r?) * the plot of beam energy from Prague magnet readings vs Elastic monitor r.f. time centroids has points falling with little scatter on 2 lines: one line for runs in the 4700 series and one line for the 4800 series. They are separated by 6.5 keV/u at the lowest data point, 4 keV/u at the highest energy. AO questioned the validity of a calibration which had different slopes for the two lines -- are there too few points for reliable slopes? * the Nov. 8 logbook entry about change in tables refers to the DTL, not the Prague magnet as originally believed. However, this may be related to the observed shift in E(Prague) vs T(rf) calibration. * the plot of E(Prague) vs E(MD1) shows more scatter: the 4700 series fall on a straight line of slope 1 to within 1 keV/u, but the 4800 series deviate from this line by 4,2, and 5 keV/u. A much bigger difference is seen between the "4700 series" line and the 6200 series of runs (spring 2002): most runs are shifted by 6 keV/u (in the opposite sense to the 4800 series) and there is a run shifted by 9 keV/u, another by 11 keV/u. The change between 2001 and 2002 is ascribed to a change in Prague magnet calibration. * from the 7 runs with Elastic monitor and coincidence capture data, excitation curves for capture and elastic yields were formed by assigning to both the 4700 and 4800 runs a beam energy computed from Elastic monitor time, using the "4800" line of the E(Prague) vs Trf plot. * the capture yields should be enough to get omega-gamma. The 7 points have FWHM = 18 keV/u, which should give a Gamma in rough agreement with TUDA's 8 keV. Subtracting 6 keV/u from the position of the elastic resonance gives 861 keV/u, in good agreement with TUDA's 863 +- 10. * fits to these points (LB): fits to capture data are consistent with TUDA's Gamma=7.2 keV; free fit prefers Gamma=16 keV. Elastic data can't be fit with TUDA's Gamma or any other Gamma. The latest analysis of 21Ne resonances by TUDA (C.Ruiz) has lead to a downward revision of beam energies compared to initial estimates. Q (DH): are rf time centroids available in TUDA data? A (LB): yes, but they are not yet analyzed. * rf time vs MD1 energy for BGO's (DH) Using JR's analysis of BGO-rf for coinc. events allows checks of the MD1 settings for 6200 series; BGO agrees with Elastic timing when both are available, within statistics; the 621x runs are shifted with respect to the other series, even after correcting for the phase shift by 1 RFQ period; upward shifts by 3, 2.5 and 2 keV/u from the MD1 values are proposed for runs 6211, 6284 and 4797, respectively, and no shift for 11 other runs. 5. Facilities paper An animated/heated discussion centred on the question of what we can/should claim to have shown. Exec. summary of discussion: JR: there is nothing in present version that demonstrates we can measure broad resonances; 7-point capture analysis of 21Na(p,g) [presented above] proposed. AO: we should present omega-gamma and beam energy calibration results from stable beams in the facilities paper. JDA/DH: go with present version and give these other results in a follow-up. Action: JR and AO will write their versions of modification to present wording.