Minutes of DRAGON meeting, April 20th, 2004. -------------------------------------------- Present: CR, AO, MT, GR (recorder), JS, JP, ML, LB, CJ, DH, PM, DO 1. Correction to previous minutes --------------------------------- MT asks to provide always at least one plain text (ASCII) version of the minutes. MS-Word format is NOT suitable for the minutes web page. 2. Status of the Facility ------------------------- DH: Chris has started reviewing scaling instructions; AO: New scaling instructions have been posted on the DRAGON website. EPICS logging: AO: When you click on "EPICS variables" on the history page the 4 current integrators are available. (The new sensitive integrators were picked, but we have been using the original 'vsqx' version, so the initial histories are zeroes. This will be changed.) On a second page you can look at the EPICS history on-the-fly once you decide to start it. A description will be made (MT will work with AO.) MT: It seems that the simulation includes fringe fields on the entrance and exits of the EDs, but is it correct? DH and MT will investigate. 3. Status of Run (C12) LB ------------------------- LB: Running 1.22 MeV/u, where the counting rate is low and adequate statistics for gamma-ray angular distributions will take a very long time. Initial data analysis will be a several months' job. LB presented some digrams showing the tuning. The 1st diagram presents the normalized FCM2 current vs. tune at 1.45 MeV/u (forget the red points) - it is essentially flat. The 2nd shows the FCCH current vs. pressure. There are still some inconsistencies in the ratios of the FC currents. You normally have to wait a while until you read the currents. Charge-state equilibrium seems to be reached somewhere above 4 Torr. The 3rd figure shows the elastic monitors, Red=EM1, green=EM2, normalized to FCM2 and pressure and dead time. The resonances can be seen quite well. There are also points between 1.65 and 1.74 MeV/u but not presented here. 4th figure: ratio EM1/EM2: Only dependent on energy, pretty independent on any normalization. Should be 1:2. The 2+ and 0+ resonance can be well seen. In the 5th figure an excitation function of the total recoils normalized by FCM2 can be seen. Again, the 2+ (at 1.45 MeV/u) and 0+ resonance (at 1.63 MeV/u) can be seen very well. Summary by LB: We stop now for a while and analyse but the biggest problem remains the acceptance. So, we still need someone doing the analysis. Gštz will do this. LB and DH mentioned a NIM paper for 12C(a,g) measuremants with ERNA (Bochum) they found on their desks. Not sure about the parameters (pressure etc.) for the quoted suppression factors. 4. Report on Catania Detector ----------------------------- AO tested the Catania detector with attenuated 21Ne beam. All results are commented in his presentation (see attachment). A summary -------- While the dE resolution is better than expected, the E detector result is terrible: only 1/4 of the dE-energy (instead of double) and poor resolution. AO's interpretation: We are only collecting 1/4 of the charge due to a defect in the detector. The little peak at high energy in the E spectrum (see page 3) corresponds to less energy loss in the dE detector as can be seen in the correlation spectrum. (The zero peak in the dE Spectrum [page 3] emerges from particles triggering an event in a non-corresponding E segment). The four spectra on page 5 are with 0, 30V, 100V, 150V (normally) BIAS applied to the E side. The 30V diagram signals changed in amplitude sometime in the middle of the run. While testing det. 1 with an alpha source it stopped holding the BIAS. Shortly before the run det. 2 also lost the BIAS but det.1 mysteriously now holds BIAS. After the beam test det. 1 now no longer held BIAS and so on.... No explanation for this behaviour. The timing measurements show a strong dependence on the BIAS. Summary AO offers two explanations: Either incomplete charge collection due to defects, or large dead layer in the pads (which is inconsistent with the channel 420 peak.) AO recommends to order a new detector. Perhaps we got bad samples. 5. Plans for the IC ------------------- CR presents the schedule for 26Al run and IC testing. Although providing 26Al beam is in good progress, they are concerned about getting the voltage of the target ion source to 52 kV within this time (DH says this will be discussed in the ISAC meeting today). CR went through the steps of the (tight) schedule. (see attachment) The IC will be installed on 17th May. 18th May is for determining the beam contaminations. The expected contaminations are those Marik Dombsky gave on the ISAC forum. 26Mg content is unsure. A long discussion by DH, LB, AO and CR arose about how to measure the contaminations. LB: We can send the beam directly into the IC. DH: We have no attenuated beam, but we can select a high charge state. LB: You can use slits off the center of the beam. AO: In order to study the beam it is the best to look at decay curves; AO and DH discussed time constants of scalers to see 26Na and 26mAl. Short discussion of AO, DH, CR and CJ about the thickness of the 'German foils' for the ion chamber entrance. Have we enough electronics for MCP AND IC? CR and JP will check. MT: This is Joshua's last meeting. He will leave on Friday.