The first three experiments performed with the Microball were:
In those experiments the detectors of the Microball were wrapped with 0.290 mg/cm2 aluminized Mylar and protective absorbers of Pb and Sn60/Pb40 were used.
The beam currents employed in these experiments were typically 3 pnA on about 0.3 mg/cm2 targets. The linear amplifier shaping constants were adjusted to have peaking times at 4.5 microseconds with the energy and PID gates at 4.0 and 14.0 microseconds (gate widths 1.2 and 0.050 microseconds), respectively. In all these cases a common E and a PID gate (early and late) was applied to all 96 channels of FERA ADCs. Under these conditions, the rates per detector were approximately 2,000 c/s for Experiment 1 and 3,000 c/s for Experiments 2 and 3. The pileup rates were typically 1-3% depending on experiment and detector angle and rate.
The proton detection efficiency for Exp. 1 was measured to be 0.89.
The early reports from this work
is given in the references below.
The improvement to the Microball signal processing was to shorten the time constants in all the 96 shapers to a peaking time of 3.2 microseconds. This allowed the PID gate to be moved to 9.0 microseconds. In this way the counting rates could be increased to about 4,000 c/s per detector, while the beam currents were increased to 4-6 pnA. As before a common E and a PID gate was employed for all 96 detectors.
Although the particle identification resolution was nearly as good as in Experiments 1-3, with the increased beam intensity, we experienced a major difficulty due to periodic sparking and base line deterioration after the linear shapers and base line restorers. This was associated with the increased beam intensities. Interestingly, we found that about 300 nA of negative current (due to electrons from atomic collisions of the beam with the target) was hitting any one of the detectors. A temporary solution was implemented by grounding each ring of the Microball detectors to the chamber with Al foil.
Here a new technique for PID was employed. This time it was possible to store the cyclotron RF and thus use it as a time reference for the Microball constant fraction signals. These times provide an additional method for doing the particle identification. Thus the new feature is that we can use for the pulse shape (early to late ratio) and the crossing time and get a dual identification procedure. It was thus found that for the detectors for which the sparking was absent the ratio method gave superior PID resolution. When the sparking affected the base line, then the crossing time provided better PID resolution which was just adequate to separate protons and alphas.
The proton detection efficiency for experiments 4 and 5 was measured after the experiments were completed and found to be 0.78-0.83. This was disturbingly low and its origin was not understood until a year later (see following section).
Another difficulty associated with the on line monitoring of the performance of the Microball was the presence of two misplaced groups of particles in the E vs. PID maps that appeared to have the wrong timing relative to the prompt coincidences. Most of these could be rejected in the off-line analysis, but again their origin was not clearly identified until the next set of experiments were carried out.
Early reports from these experiments
have been presented in the Gammasphere dedication conference and
at the Argonne International Conference.
A major advance was that now thick or backed target experiments can now be done by reducing the beam only by a factor of 2 relative to a thin target.
The measured proton detection efficiency for the overall Microball now is 89-92%. For tricks to get the efficiency that high contact D. G. Sarantites at dgs@wuchem.wustl.edu. The overall alpha-particle detection efficiency depends more on the reaction at hand. For reactions with normal kinematics in the mass 160 region it is the same as for protons. For light systems it may be a few percent lower due to losses for the lowest energy alpha particles at the backward angles.
At the end of each group of experiments the leakage current for photodiode is measured at the operating applied voltage. The current values for rings 3 and 4 (worse case) are about 10 times higher than the original values. When they become leaky enough that full depletion cannot be maintained, the photodiodes will have to be replaced. Of course the reactions that produce the most neutrons are those that cause the most damage both to the Ge detectors and the photodiodes.
In preparing for the runs in July 1996, we made another major improvement in the preamplifiers. We shortened considerably the decay time of the signal. This resulted in a further shortening of the peaking time of the shaped signals, that in turn allows for faster counting. In addition the pole-zero adjustment now works a lot better, allowing for the correct adjustment for all the detector channels.
During the test run in July, 1996 we adjusted carefully all the pole-zeros. This required beam on target and placing the signal processing modules on a double extender board to provide access to the adjustment pots on the side of the boards internal to the modules. As a result of this fine tuning the linearity of the PID signal with energy (Slow vs. Fast ratio) improved considerably and the amount of pile-up for at least 10 detectors was reduced considerably.
In July, 1996 five additional experiments were performed:
In January and February 1997 nine (9) additional experiments were performed:
During the group of experiments (GS-87 through GS-95) the detector No 17 (in bank 2-0) was functioning intermittently (most of the time it was Ok). The problem was an internal connection that was fixed only at the end of the runs.
In the interval between runs a new preamplifier power box was completed and is currently being tested. It is more modular and much more convenient if repairs are needed. It will be used in the next set of experiments.
We have also made external attenuators that conveniently allow changing the time range of the CsI FTCs. We are planning to extend the range to cover 1 ms, which matches the time range of the Ge detectors.
The last group of approved experiments, while Gammasphere was still at LBNL, were carried out in May and June 1997. For these experiments, the Microball absorbers for the first few front rings were changed and made thinner.
These experiments were:
The ANL personnel are thanked for the superb assistance and willingness to help the users. The Gammasphere operation still has some rough spots due to to trip from LBNL, but it is getting there. For example: what happened to the Ge detector absorbers (Ta + Cu)., why are the EFFs crush every 20 - 120 minutes, why are the tape routers and distributors not functioning for all EFFs? The EFF problem seems to have been fixed , Thanks to Torben. The Tapers are not totally out of the woods yet.
Anyway, the first round of Microball experiments were completed and the Microball is safe at home. The experiments completed are:
These three completed experiments and calibration are:
Prior to experiment MB-41, the Microball base lines for all banks were adjusted to ~ -(1.5±0.5) mV. Then the pedestals were measured by downloading 0 for each channel and then measuring the all simultaneously. The acquisition did not crash!!! Thanks Torben, keep up the good work. The pedestals were calculated with LaFosse's little program and then checked. Great job. Interestingly, the pedestals for the PID (tail) was also sharp, indicating good baseline stability. This was indeed seen in experiment MB-41 where, for the first time, the noise level at the back detectors was at the same level as the front ones (3-5 mV, RMS values). What happened to the electron noise that plagued MB-36 and many other runs ???
The Microball parameters for this
group of experiments is the same as for the MB-36 through MB-40. Here are
the current Parameters
for experiments MB-41, MB-42, MB-43 and
MB-44. The a-particle
calibration of the Microball for the above experiments and
all future ones is available here: Microball Alpha
calibration coefficients
for all future experiments. Only the alpha coefficients are given for this
group of experiments. The proton energies that are needed were determined
in experiment MB-42. The data were analyzed by J.W. The proton
energy calibration coefficients were calculated by DGS and are given here:
Proton
coefficients file. The slopes and intercepts
in MeV/channel (2048 full scale) and MeV, respectively, are tabulated.
For your proton energies use these. For the alphas, get the proton
energy in MeV and insert it in the expression(s) for the non-linear alpha
response given above.
For the 40Ca + 92Mo
run we had 7-8 pnA of beam on a 0.7 mg/cm2 target. The front
Ge were counting at 9-10 kHz, while the Microball operated at 4200 c/s
per detector with excellent resolution for alphas and protons.
The proton efficiency of the Microball
for MB-43 was measured to be 88%, while that for alphas was 72%. Higher
efficiencies, particularly for a's, should be
obtained for MB-44. In that run a 3-pnA of 58Ni beam was
used which was focussed through a 2 mm aperture to 1 mm diameter.
It was burning a hole in the 0.54 mg/cm254Fe target!
The Microball is now (July 2, 1998)
back home.
The parameter file for the above
experiments can be found here: Parameters
for experiments MB-45 to MB-47
, or GSFMA-39 to GSFMA-42. The calibration coefficients from the MB-47A
experiment that apply to MB-45, MB-46 and MB-47 are available here : Proton
coefficients file. In this file the slopes
and intercepts in MeV/channel (2048 full scale) and MeV, respectively,
are tabulated. For your proton energies use these. The proton coefficients
for MB-48A will become available shortly, please, be patient.
The parameter file for the Microball
for experiment MB-48 is the same as the MB-47 but with the first 28 CsI
detectors removed and the target position empty in detector 62.
Important Extra Help from the Washington U. group: The alpha calibration now is at hand. So from the proton coefficients it is possible to calculate externally all the particle relevant quantities for each experiment. DGS wrote a program to compute the following quantities for each type of particle (protons and alphas) and each detector as a function of the raw channel number (0 to 2047) :
For further information ask : dgs@wuchem.wustl.edu.
Parameters
for experiments MB-49 and MB-50 here
the cables for banks 5 and 6 were switched by mistake during setup and
were left switched. We did not find out about this until the proton calibration
did not make sense. Elastic scattering at 170 degrees still works!
Parameters
for experiments MB-51 and MB-52.
The Microball calibration files for MB-49 (GSFMA64), MB-50 (GSFMA65), MB-51(GSFMA66) and MB-52(GSFMA67) are ready. They contain the following information for both protons and alphas:
In this setup detector 15 is missing (broken cable again) and detector 17 was moved to the target position 62.
The first group of experiments performed with the Neutron Shell and the Microball was:
The Neutron detector gain matching was done approximately with the 2615 keV gamma from a 228Th source. The edge of that gamma was placed at approximately channel 1900 in the high gain energy spectra. It corresponds to about 6 MeV in neutron energy.
The setup had 78 Ge detectors in Gammasphere, 30 Neutron detectors and 94 out of 95 working detectors in the Microball. In experiment MB-56 the detector 14 fixed "itself". From then on all 95 out 95 detectors in the Microball work.
Parameters for experiments MB-53 to MB-60, or GSFMA-73 to GSFMA-79 . Parameters for experiment MB-62, or GSFMA-83 Since the rings 2 and 4 of the Microball were removed and the rings 1 and 3 were moved back to make room for the Si cube, the angles for the detectors in rings 1 and 3 must be recalculated.
The configuration file for the Neutron Shell contains angles and positions of the neutron detectors in Gammasphere. Configuration file for the Neutron Shell.
Microball Calibration files for the MB-53 (GSFMA73), MB-54, MB-55, and MB-57 (GSFMA76) experiments are available by request to DGS by sending email to dgs@wuchem.wustl.edu.
These two experiment are:
February 18th marks the last group of experiments with the Microball at ATLAS, just before Gammasphere is moved back to LBNL. Now the Microball is back to its home at Washington University for a rest and for a small face lift. The absorbers in the the first two rings will be replaced. They collected a lot of evaporation residues over the last two years from all the experiments at ATLAS.
Experiments in February 2001 !
The Microball and neutron array did not run experiments
for about one year. Three months were taken to move Gammasphere back to
LBNL and the wisdom of the PAC did not approve enough experiments to be
worthwhile to schedule!
So in February 2002, we run 4 experiments.
The Parameters for the experiments MB-66 through MB-68 or GS2k017-GS2k019 can be found here.(NS-8, GS2k016) excitation function 32S + 40Ca, LEPS + Neutron Shell + Gammasphere, D. Jenkins et al. (MB-66, NS-9, GS2k017) 130 MeV and 125 MeV 32S + 28Si, Gammasphere + Microball + Neutron Shell, D. Rudolph, D.G. Sarantites et al. (MB-67, GS2k018) xxx 58Ni + 58Ni () (MB-68, GS2k019) xxx MeV 40Ca + 40Ca, Gammasphere + Microball, C. Svensson et al. (MB-69, GS2k019A) 12.0 MeV 1H + 12C, Microball calibration, D.G. Sarantites and C. Svensson.
Experiments in October 2001
The Microball was installed in the Gammasphere at LBNL on October 28, 2001. There were 101 Ge detectors operating. The Microball had all 95 detectors working with the following changes/problems. The detector cable in Bank 1-4 was moved to the target position 62 because of a broken cable during shipment. One detector in ring 2 has its time partly of scale. However here the ratio completely identifies the protons and alphas for all reactions in this group. In addition detector in position 96 has no time.
( Click here for summary of all Experiments )(MB-70, GS2k039) 24Mg + 24Mg/Ta(backing) at 94 MeV, Gammasphere + Microball, D.G. Sarantites et al. (completed succesfully) (MB-71, GS2k040) 40Ca + 58Ni/Au(backing) at 185 MeV, Gammasphere + Microball, B. Cederwall et al. (completed succesfully) (MB-72, GS2k041) 1H + 12C, at 13 MeV, Microball standalone, D. Sarantites, A. Macchiavelli. (completed succesfully) (MB-73, GS2k042) 58Ni + 96Ru at 250 MeV, Gammasphere + Microball, Andreas Gorgen et al.
Microball Calibration files are also available. Please send email to DGS at dgs@wuchem.wustl.edu.
The Microball configuration file for runs MB-70 through MB-73 is here as MBALL_A_10_14_01.txt.
Summary of All Microball experiments
Below you can find a List of the
Microball based experiments with Gammasphere. In addition, Published referreed
papers in Major Journals and those in Proceedings of Major Conferences
that resulted from this work are listed. B.A.P.S. abstracts are not included.
When I wrote this I knew that there
will be errors and offending omissions. If you find such errors and omissions,
please bring them to my attention and I promise to correct them.
Please, send mail to: dgs@wuchem.wustl.edu.
(The publications in the table below
needs revising, since they have been renumbered)
| MB-GS Run#, Date | Reaction | C.N. | Spokesperson | Publ. # in Mball List of Publ. |
| MB-1, 3/94 | 230 MeV 51V+100Mo | 151Tb* | D.G. Sarantites | 2-(4,8,9,18), 3-(5) |
| MB-2, 3/94 | 130 MeV 29Si+58Ni | 87Mo* | C. Baktash | 2-(1,2,3,21), 3-(1,2,3,11,13) |
| MB-3, 3/94 | 135 MeV 32S+58Ni | 90Ru* | C. Gross | 2-(3,7,13,15,23), 3-(2,4,10,11,13) |
| MB-4, 7/95 | 230 MeV 51V+100Mo | 151Tb* | D.G. Sarantites | 2-(8,9) |
| MB-5, 7/95 | 130 MeV 28Si+58Ni | 86Mo* | C. Baktash | 2-(11,14,24,28,39,55), 3-(7,9,11,12,13) |
| MB-6, 7/95 | 150 MeV 48Ca+100Mo | 148Sm* | C. Baktash | - |
| MB-7, 8/95 | 150 MeV 27Al+132Te | 159Tb* | B. Cederwall | - |
| MB-8, 8/95 | 180 MeV 35Cl+105Pd | 143Eu* | M. Riley | 2-(10,12,22,31,33,34,41,46), 3-(6,14,16,25) |
| MB-9, 8/95 | 230 MeV 51V+98Mo | 149Tb* | P. Fallon | |
| MB-10, 3/96 | 157 MeV 29Si+124Sn | 153Gd* | S. Flibotte | Cancelled |
| MB-11, 3/96 | 250 MeV 54Fe+94Mo | 148Er* | J. Wilson | 2-(8) |
| MB-12, 3/96 | 134 MeV 31P+58Ni | 89Tc* | D.G. Sarantites | 2-(26) |
| MB-13, 4/96 | 145 MeV 36Ar+40Ca | 76Sr* | D. Balamuth | - |
| MB-14, 4/96 | 160 MeV 40Ca+40Ca | 80Zr* | M. Leddy | - |
| MB-15, 4/96 | 143 MeV 36Ar+28Si | 64Ge* | C. Baktash | 2-(17,29,32,38,44,45,49), 3-(26,27) |
| MB-16, GS61, 7/96 | 230 MeV 51V+100Mo | 151Tb* | D.G. Sarantites | 2-(8,9,18), 3-(5) |
| MB-17, GS62, 7/96 | 185 MeV 40Ca+58Ni | 98Cd* | B. Cederwall | 2-(40,48,50), 3-(18) |
| MB-18, GS63, 7/96 | 180 MeV 36Ar+58Ni | 94Pd* | D.R. LaFosse | |
| MB-19, GS64, 7/96 | 158 MeV 29Si+124Sn | 153Gd* | S. Flibotte | 2-(25,30,35) |
| MB-20, GS65, 7/96 | 180 MeV 40Ca+94Mo | 134Sm* | L. Riedinger | 2-(51,54,61), 3-(28) |
| MB-21, 1/97 | 6.1-12.0 MeV +232Th | - | Wash. U. | Calibration |
| MB-22, GS88, 1/97 | 250 MeV 58Ni+50Cr | 108Te* | S. Freeman | - |
| MB-23, GS89, 1/97 | 250 MeV 58Ni+58Ni | 116Ba* | J. Smith | 2-(57), 3-(15,17,18,20,29,30,31) |
| MB-24, GS90, 2/97 | 125 MeV 28Si+40Ca | 68Se* | C. Baktash | 2-(19,27,36), 3-(24,32) |
| MB-26, GS91, 2/97 | 157 MeV 48Ca+26Mg | 74Ge* | M. Devlin | 2-(42), 3-(19) |
| MB-27, GS92, 2/97 | 135 MeV 32S+58Ni | 90Ru* | S. Tabor | - |
| MB-28, GS93, 2/97 | 310 MeV 76Ge+96Zr | 172Hf* | B. Herskind/I.Y. Lee | - |
| MB-29, GS94, 2/97 | 350 MeV 78Kr+103Rh | 181Tl* | M. Carpenter | - |
| MB-30, GS95, 2/97 | 173 MeV 35Cl+105Pd | 145Eu* | M. Riley | 2-(41,46), 3-(16,25) |
| MB-31, GS108, 5/97 | 230 MeV 60Ni+100Mo | 160Yb* | L.G. Sobotka | - |
| MB-32, GS109, 5/97 | 160 MeV 40Ca+58Ni | 98Cd* | A.O. Macchiavelli | - |
| MB-33, GS110, 5/97 | 130 MeV 28Si+58Ni(Au) | 86Mo* | F. Lerma | 2-(37,47), 3-(21) |
| MB-34, GS111, 6/97 | 130 MeV 29Si+58Ni(Au) | 87Mo* | F. Lerma | 2-(37,47), 3-(21) |
| MB-35, GS112, 6/97 | 128 MeV 29Si+40Ca | 69Se* | C. Baktash | 2-(22,23,33) |
| MB-36, GSFMA6A, 2/98 | 260 MeV 64Zn+64Zn | 128Gd* | J. Smith | - |
| MB-37, GSFMA6B, 2/98 | 265 MeV 64Zn+58Ni | 122Nd* | J. Smith | - |
| MB-38, GSFMA7, 2/98 | 12-48 MeV 4He+232Th | - | Wash. U. | Calibration |
| MB-39, GSFMA8, 2/98 | 84 MeV 20Ne+28Si | 48Cr* | D.G. Sarantites | - |
| MB-40, GSFMA9, 2/98 | 135 MeV 32S+40Ca, | 72Kr* | C. Svensson | 3-(32) |
| MB-41, GSFMA19, 6/98 | 160 MeV 40Ca+40Ca | 80Zr* | D. Balamuth | - |
| MB-42, 6/98 | 11.96 MeV 1H+12C | - | Wash. U. | Calibration |
| MB-43, GSFMA21, 6/98 | 238 MeV 58Ni+54Fe | 112Xe* | R.M. Clark | 2-(58) |
| MB-44, GSFMA22, 6/98 | 184 MeV 40Ca+92Mo | 132Sm* | L. Riedinger | 3-(28) |
| MB-45, GSFMA39, 11/98 | 257 MeV 60Ni+50Cr | 110Te* | S. Freeman | - |
| MB-46, GSFMA40, 11/98 | 185 MeV 40Ca+58Ni | 98Cd* | B. Cederwall | Cancelled |
| MB-47, GSFMA41, 11/98 | 215 MeV 58Ni+46Ti | 104Sn* | R. Clark | 2-(53) |
| MB-47A, 11/98 | 12 MeV p+12C, | - | Wash. U. | Calibration |
| MB-48, GSFMA42, 12/98 | 141 MeV 36Ar+28Si | 64Ge* |
|
- |
| MB-48A, 12/98 | 12 MeV p+12C | - | Wash. U. | Calibration |
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Back to the Milestones
Back
to the Home Page
For more details send mail to D.G.
Sarantites at: dgs@wuchem.wustl.edu.
For comments and corrections send mail to: dgs@wuchem.wustl.edu.