Milestones of the Microball

Last update: Thursday, November 15, 2001


The Spectroscopy Microball-A (the thin one)

The Microball had its maiden set of experiments in March 1994 with the early implementation of Gammasphere. In order to make these experiments possible a special acquisition system based on the MSU 4p acquisition was implemented, thanks to Skip Vanden Mollen, in order to allow a rapid FERA ECL bus readout.

The first three experiments performed with the Microball were:

  • (MB-1) 230 MeV 51V + 100Mo
  • (MB-2) 130 MeV 29Si + 58Ni
  • (MB-3) 135 MeV 32S + 58Ni

with 36 Ge detectors in Gammasphere.

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.


Experiments in 1995 - Final Gammasphere Configuration

The second set of experiments of the Microball with Gammasphere had to wait nearly 14 months for the completion of the VXI interface module that permits readout of the external FERA ADC's. The following experiments were performed in July and August of 1995.

  • (MB-4) 230 MeV 51V + 100Mo
  • (MB-5) 130 MeV 28Si + 58Ni
  • (MB-6) 150 MeV 48Ca + 100Mo
  • (MB-7) 150 MeV 27Al + 132Te
  • (MB-8) 180 MeV 35Cl + 105Pd
  • (MB-9) 230 MeV 51V + 98Mo

In this round of experiments the Gammasphere had 57 Ge detectors. Encouraged by the previous success, we wanted to increase the counting rates in the Microball and at the same time retain the small pile up rates that we had before.

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.


Experiments in 1996

This year the first group of experiments took place in March and April. The following experiments were run:

  • (MB-10) 157 MeV 29Si + 124Sn (Microball and Gammasphere, S. Flibotte et al.)
  • (MB-11) 250 MeV 54Fe + 94Mo (Microball and Gammasphere, J. Wilson et al.)
  • (MB-12) 134 MeV 31P + 58Ni (Microball and Gammasphere, GS-51, D.G. Sarantites et al.)
  • (MB-13) 145 MeV 36Ar + 40Ca (Microball + Neutron detectors and Gammasphere, D. Balamuth et al.)
  • (MB-14) 160 MeV 40Ca + 40Ca (Microball + Neutron detectors and Gammasphere, M. Leddy et al.)
  • (MB-15) 143 MeV 36Ar + 28Si (Microball + Neutron detectors and Gammasphere, C. Baktash et al.)

Prior to these experiments we carefully measured the leakage current in each Si photodiode. We found a definite correlation of increased leakage current with angle (actually it is the product of photodiode solid angle and the neutron flux angular distribution). Two major modifications of the Microball arrangement were made.

  1. The light reflector in the CsI(Tl) detectors was changed from aluminized Mylar to Al leaf. This was done by unpacking the Microball, disconnecting all cables, removing all detector elements from there supporting rings, removing the aluminized Mylar, and using Al leaf as reflector inside the new Sn or Pb absorbers. After re-wrapping the Microball was assembled cabled up and then each absorber was grounded by conductively epoxying thin grounding wires to the Al support structure. The latter is grounded to the scattering chamber.
  2. The gating procedure for the FERAs was changed from a single gate for all 6 banks (96 detectors) to individual bank gating for each type of FERA (common gate to 16 detectors). The E and tail gates were set at 2 microseconds and 9.2 microseconds respectively.

As a result of these changes the performance of the Microball improved considerably. Thus maximum counting rates of ~4,000 c/sec per detector were achieved with beam intensities up to ~5 pnA with NO Sparking !

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@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:

  • (MB-16) Microball Adjustment Run, GS-61
  • (MB-17) 185 MeV 40Ca + 58Ni (GS-62, B. Cederwall et al.)
  • (MB-18) 180 MeV 36Ar + 58Ni (GS-63, D.R. LaFosse et al.)
  • (MB-19) 158 MeV 29Si + 124Sn (GS-64, S. Flibotte et al.)
  • (MB-20) 180 MeV 40Ca + 94Mo (GS-65, L. Riedinger et al.)

Here are the Parameters for experiments MB-16 through MB-20, or GS-62 through GS65.

 


Experiments in 1997

Prior to the next set of experiments some of the Microball Sn absorbers were replaced with equal thickness of SnPb ones and the Microball was tested for reliable performance at Washington University.

In January and February 1997 nine (9) additional experiments were performed:

  • (MB-21, GS-87) Light output measurements of the Microball detectors using Elab/A = 12.0, 10.0, 8.0, 6.1 MeV protons and alpha particles on 232Th (, D.G. Sarantites et al. ).
  • (MB-22, GS-88) 250 MeV 58Ni + 50Cr (Microball, Neutron det. and Gammasphere,  S. Freeman et al.).
  • (MB-23, GS-89) 250 MeV 58Ni + 58Ni (Microball, Neutron det. and Gammasphere,  J. Smith et al.).
  • (MB-24, GS-90) 125 MeV 28Si + 40Ca (Microball, Neutron det. and Gammasphere, C. Baktash et al. ).
  • (MB-26, GS-91) 157 MeV 48Ca + 26Mg (Microball and Gammasphere, M. Devlin et al.).
  • (MB-27, GS-92) 135 MeV 32S + 58Ni on Ta (Microball and Gammasphere, S. Tabor et al.).
  • (MB-28, GS-93) 310 MeV 76Ge + 96Zr (Microball and Gammasphere, B. Herskind/I.Y. Lee, et al.).
  • (MB-29, GS-94) 350 MeV 78Kr + 103Rh (Microball and Gammasphere, M. Carpenter et al.).
  • (MB-30, GS-95) 173 MeV 35Cl + 105Pd on Au (Microball and Gammasphere, M. Riley et al. ).

Here you can find the Parameters for experiments MB-21 through MB-30 or GS-87 through GS-95.

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:

  • (MB-31, GS-108) 230 MeV 60Ni + 100Mo (X-ray Detectors, Microball and Gammasphere , L.G. Sobotka et al.).
  • (MB-32, GS-109) 160 MeV 40Ca + 58Ni (Microball and Gammasphere, A.O. Macchiavelli et al.).
  • (MB-33, GS-110) 130 MeV 28Si + 58Ni(Au) (Microball and Gammasphere, D.R. LaFosse, F. Lerma et al.).
  • (MB-34, GS-111), 130 MeV 29Si + 58Ni(Au) (Microball and Gammasphere, D.R. LaFosse, F. Lerma et al.).
  • (MB-35, GS-112) 128 MeV 29Si + 40Ca (Microball and Gammasphere, C. Baktash et al.).

They were all quite successful. You can find the Microball parameters for the above group of experiments here: Parameters for experiments MB-31 through MB-35 or GS-108 through GS-112.


Experiments in 1998

First group at ATLAS ( Feb.  24 - March 13, 1998)

Now the Gammasphere is at ATLAS at the Argonne National Laboratory. The Microball was installed in the Gammasphere on the 14th of February. New procedures for aligning it in its chamber and in front of the FMA had to be devised. The ribbon cables for the Microball signals were strung by the Washington University personnel. There were the usual problems with CAMAC crates and failing FERA ADC's. Finally these were solved and the first group of experiments at ATLAS with the Gammasphere having 100 Ge detectors installed, the Microball and the FMA began.

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:

  • (MB-36, GSFMA-6A)  260 MeV 64Zn + 64Zn, (Gammasphere, Microball, FMA, PPAC, Ionization chamber; J. Smith et al.).
  • (MB-37, GSFMA-6B) 265 MeV 64Zn + 58Ni, (Gammasphere, Microball, FMA, PPAC, Ionization chamber;   J. Smith et al.).
  • (MB-38, GSFMA-7,) 12-48 MeV 4He + 232Th, (Microball standalone; D.G. Sarantites et al.)
  • (MB-39, GSFMA-8) 84 MeV 20Ne + 28Si, (Gammasphere, Microball, FMA, Channel plates (one only), Ionization chamber;   D.G.    Sarantites, J. Wilson et al.).
  • (MB-40, GSFMA-9) 135 MeV 32S + 40Ca, (Gammasphere, Microball, FMA, Channel plates (one only), Ionization chamber; C. Svensson et al.).

The Microball parameters for this group of experiments can be found here: Parameters for experiments   MB-36 through M-40   or GSFMA-6A through GSFMA-9. The results of the Microball calibration for the above experiments are available here Microballcalibration from MB-38. For further information ask here dgs@wustl.edu.

Experiments in June 1998 (ATLAS)

The Microball was set up in June 4 for the next three approved experiments at ATLAS.    As usual,  all 95  of the 95 Microball detectors are working. More important, however, is that all 18 of the FERA ADCs are by "magic" now operating in one CAMAC crate, as they always did at LBNL!!

These three completed experiments and calibration are:

  • (MB-41, GSFMA-19) 160 MeV 40Ca + 40Ca (Microball + Neutrons + FMA with PPAC + I.C. and Gammasphere, D. Balamuth,  et al.).
  • (MB-42, GSFMA-20) 11.96 MeV 1H + 12C. (Microball self triggered for energy calibration of this group of experiments. Please contact DGS below for details, Completed and analyzed (see table below).
  • (MB-43, GSFMA-21) 238 MeV 58Ni + 54Fe (Microball + FMA with PPAC, DSSD and Gammasphere, R.M. Clark, et al.).
  • (MB-44, GSFMA-22) 184 MeV 40Ca + 92Mo (Microball + FMA + PPAC and Gammasphere, L.L. Riedinger, et al.).

For the good news read below.

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.

Experiments in November 1998 (ATLAS)

On November 2 the Microball was setup again at ATLAS in Gammasphere for the next group of four experiments. One bad cable was identified for detector 2-00. That detector was connected to the spare cable (Target position) as detector 62 instead of 17.  The detector in Bank 1-6 is flaky and noisy.

The new experiments are:

  • (MB-45, GSFMA-39) 257 MeV 60Ni + 50Cr (Microball + Neutrons + FMA with Channel plates + I.C. and Gammasphere, S. Freeman,  et al.).  Completed.
  • (MB-46,GSFMA-40) 185 MeV 40Ca + 58Ni (Microball + Neutrons + FMA with Channel plates + I.C. and Gammasphere, B. Cederwall, et al. ). It ran for less than a day and then cancelled due to Gammasphere acquisistion failure. It will be rescheduled later.
  • (MB-47,GSFMA-41) 215 MeV 58Ni + 46Ti (Microball + Neutrons + FMA with Channel plates + I.C. and Gammasphere, R. Clark, et al.). Completed succesfully.
  • (MB-47A,GSFMA-41A) 12 MeV p + 12C (Microball stand-alone, Washington U. group).
  • (MB-48,GSFMA-42) 141 MeV 36Ar + 28Si (Silicon Microstrip Wall, Microball, Neutron detectors, Gammasphere and No FMA, D. Rudolph et al.). Completed succesfully.
  • (MB-48A,GSFMA-42A) 12 MeV p + 12C (Si Microstrip Wall and Microball, stand-alone, Washington U. group). Completed succesfully. The calibration of the Si Wall with protons worked very well. The alpha calibration of the DE detectors showed superb energy resolution (better than 40 keV FWHM at 5.8 MeV).

The Threshold and Gain Files that are used in the Microball Control Panel in the IBM PC that controls the Microball for this group of experiments are: MB-45.dat through MB-48.dat, respectively.

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) :

  • The Center-of-Mass Angle
  • The Center-of-Mass Energy
  • The Laboratory Frame Energy
  • The Jacobian (sC.M./sLab).

Eight files can be made available containing the above quantities, 4 for protons and 4 for alpha particles.

So for a given channel number for a proton or an alpha, the above quantities are available in table look-up form. Thus, the lab energy calibrations of the CsI, the multilayer absorber corrections, and CoM conversions for your reaction will all be included. Please send email to DGS to obtain these files. You may request these setup files for the MB-46 and MB-47 experiments by contacting Demetrios Sarantites at Please have the reaction, the target thickness and orientation, and the beam energy at mid-target available when you inquire.

This is guaranteed to save you a lot of time in your data analysis.

You may request these setup files for the MB-46 and MB-47 experiments by contacting Demetrios Sarantites at dgs@wustl.edu.

The setup files needed for these calculations are there also for your information. Enjoy.

For further information ask : dgs@wustl.edu

Experiments in July 6 1999 (ATLAS)

On July 6, 1999 the Microball was setup again at ATLAS in Gammasphere for yet another group of four experiments. One bad cable was identified for detector 1-13 (or det 14). Experiment MB-49 is done with that detector missing.

  • (MB-49, GSFMA-64) 75 MeV 16O + 24Mg (Microball and Gammasphere, No FMA, C.Baktash, A. Macchiavelli, and D.G. Sarantites,   et al.).
  • (MB-50, GSFMA-65) 165 MeV 48Ca + 30Si (Microball and Gammasphere, No FMA, M. Devlin,   et al.).
  • (MB-50A, GSFMA-65A) 12 MeV protons on 12C (Microball standalone calibration; D.G. Sarantites et al.).
  • (MB-51, GSFMA-66) 122 MeV 28Si + 40Ca (Microball and Gammasphere, No FMA, C. Svensson, et al.)
  • (MB-52, GSFMA-67) 180 MeV 40Ca + 94Mo (Microball and Gammasphere, No FMA, D. Hartley et al.)

All 4 experiments above were done succesfully.

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:

  • The Center-of-Mass Angle
  • The Center-of-Mass Energy
  • The Laboratory Frame Energy
  • The Jacobian (sC.M./sLab).

Eight files are available containing the above quantities, 4 for protons and 4 for alpha particles.

So for a given channel number for a proton or an alpha, the above quantities are available in table look-up form. For a given channel number of the particle of interest simply look up the appropriate quantity in the proper table. The laboratory frame energy calibrations of the CsI, the multilayer absorber corrections, and CoM conversions for your reaction are all be included.

This is guaranteed to save you a lot of time in your data analysis.

You may find (download) these files for the MB- 49 (GSFMA64), MB-50 (GSFMA65), MB-51 (GSFMA66), and MB-51(GSFMA67) experiments by requesting them from Demetrios Sarantites: dgs@wustl.edu.

The Calibration files for these experiments (MB-49, MB-50, and MB-51) are available from dgs on request. Please send email for instructions to:  dgs@wustl.edu.

Experiments in September 27, 1999 (ATLAS)

On September 24, the Microball and the Neutron Shell were installed in Gammasphere for another group of 8 experiments. For the Neutron Shell these were the first experiments.

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:

  • (MB-53, NS-1, GSFMA-73) 130 MeV 32S + 28Si (Gammasphere, Neutron shell, Microball, D.G. Sarantites et al.) Completed succesfully.
  • (MB-54, NS-2, GSFMA-74) 100 MeV 32S + 40Ca (Gammasphere, Neutron shell, Microball, FMA) P. Fallon et al. Completed succesfully.
  • (MB-55, NS-3, GSFMA-74) 145 MeV 36Ar + 40Ca (Gammasphere, Microball, Neutron shell, FMA) P.Fallon et al. Completed succesfully.
  • (MB-56, GSFMA-75) 12 MeV p + 12C (Microball, stand- alone, Washington U. group).
  • (MB-57, NS-4, GSFMA-76) 185 MeV 40Ca + 58Ni, Gammasphere, Microball, Neutron Shell, FMA, B. Cederwall et al. Completed succesfully.
  • (MB-58, NS-5, GSFMA-77) 125 MeV 40Ca + 40Ca, Gammasphere, Microball, Neutron Shell, S. Paul et al.. Postponed (operations lost the Ca in the source.)
  • (MB-59, NS-6, GSFMA-78)Beam 225 MeV 58Ni + 50Cr, Gammasphere, Microball, Neutron Shell, no FMA, C. Baktash et al. Completed succesfully.
  • (MB-58A, NS-5A, GSFMA-77) 125 MeV 40Ca + 40Ca, Gammasphere, Microball, Neutron Shell, no FMA, S. Paul et al. Repeated and done succesfully.
  • (MB-59, NS-7, GSFMA-79) 260 MeV 64Zn + 64Zn, Gammasphere, Microball, Neutron Shell, and FMA, D. LaFosse et al.. Completed succesfully.
  • (MB-60, GSFMA-80) 235 MeV 58Ni + 58Ni, D. Seweryniak et al.(Microball, Neutron Shell, Si detectors) Succesfully attempted.
  • (MB-61, GSFMA-81) 12 MeV p + 12C (Microball, stand- alone, Washington U. group). Completed
  • (MB-62, GSFMA-82) 207 MeV 54Fe + 58Ni, D. G. Sarantites et al.(Microball, Neutron Shell, Si cube) Completed. Lots of accelerator trouble, lost quite a bit of beam time (not recovered).

This marks the first and last Microball + Neutron shell experiments with Gammasphere at ATLAS.

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@wustl.edu.

Experiments in February 3, 2000 (Last group at ATLAS)

The last two Microball + Gammasphere experiments at ATLAS began on February 3, 2000. In about five weeks from the begining of these experments Gammasphere will be dismantled and moved back to LBNL where it will resume operation. The Miocroball will be available for experiments at LBNL at that time.

Since the previous group of experiments, the Microball underwent a small but probably important improvement. The RTV potting of the cables inside the chamber was removed and modified. The 34 pin connectors have now been encased in Al housings that support the PC 50-Ohm boards better. This will reduce the breakage of the thin cables from handling them during assembly. A better grounding was also provided in this modification.

These two experiment are:

  • (MB-63, GSFMA-92) 230 MeV 58Ni + 58Ni (Gammasphere, Microball, and FMA), J. Smith et al., completed succesfully.
  • (MB-64, GSFMA-93) 80 MeV 20Ne + 24Mg (Gammasphere + Microball, No FMA), C. Svensson et al., Completed succesfully.
  • (MB-65, GSFMA-94) 12.0 MeV 1H + 12C (Microball, stand-alone, Washington U. group, calibration for MB-63 and MB-64), (completed succesfully).

One detector in bank 4 (number 4-02 or detector 51) was not working during the MB-63 experiment. After that experiment we openned the chamber and found that detector 51 was not even connected! That's an easy fix. Lucky Carl and sorry John...
The Parameters for the experiments MB-63 or GSFMA-92 and MB-64 can be found here.

The Microball seems to be very stable with excellent PID resolution even at the back angles. Note that the angles of the detectors in the first ring of the Microball have now been rotated by 30 degrees. So do not use an old parameter file.

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.

  • ( 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.

The Parameters for the experiments MB-66 through MB-68 or GS2k017-GS2k019 can be found here.

Notice that detector 32 was moved to the target position 62.

Microball Calibration files are also available. Please send email to DGS at dgs@wustl.edu

Recent News

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.

  • (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@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@wustl.edu

(The publications in the table below needs revising, since they have been renumbered)
 

MB-GS Run#,  Date ReactionC.N.SpokespersonPubl. # in Mball List of Publ.
MB-1, 3/94 230 MeV 51V+100Mo151Tb*D.G. Sarantites2-(4,8,9,18), 3-(5)
MB-2, 3/94 130 MeV 29Si+58Ni87Mo*C. Baktash2-(1,2,3,21), 3-(1,2,3,11,13) 
MB-3, 3/94 135 MeV 32S+58Ni90Ru*C. Gross2-(3,7,13,15,23), 3-(2,4,10,11,13)
MB-4, 7/95230 MeV 51V+100Mo151Tb*D.G. Sarantites2-(8,9)
MB-5, 7/95130 MeV 28Si+58Ni86Mo*C. Baktash2-(11,14,24,28,39,55), 3-(7,9,11,12,13)
MB-6, 7/95 150 MeV 48Ca+100Mo148Sm*C. Baktash-
MB-7, 8/95150 MeV 27Al+132Te159Tb*B. Cederwall
MB-8, 8/95180 MeV 35Cl+105Pd143Eu*M. Riley2-(10,12,22,31,33,34,41,46), 3-(6,14,16,25)
MB-9, 8/95230 MeV 51V+98Mo149Tb*P. Fallon 
MB-10, 3/96157 MeV 29Si+124Sn153Gd*S. FlibotteCancelled
MB-11, 3/96250 MeV 54Fe+94Mo148Er*J. Wilson2-(8)
MB-12, 3/96134 MeV 31P+58Ni89Tc*D.G. Sarantites2-(26)
MB-13, 4/96145 MeV 36Ar+40Ca 76Sr*D. Balamuth
MB-14, 4/96160 MeV 40Ca+40Ca 80Zr*M. Leddy-
MB-15, 4/96143 MeV 36Ar+28Si64Ge*C. Baktash2-(17,29,32,38,44,45,49), 3-(26,27)
MB-16, GS61, 7/96230 MeV 51V+100Mo151Tb*D.G. Sarantites2-(8,9,18), 3-(5)
MB-17, GS62, 7/96185 MeV 40Ca+58Ni 98Cd*B. Cederwall2-(40,48,50), 3-(18)
MB-18, GS63, 7/96180 MeV 36Ar+58Ni 94Pd*D.R. LaFosse 
MB-19, GS64, 7/96158 MeV 29Si+124Sn 153Gd*S. Flibotte2-(25,30,35)
MB-20, GS65, 7/96180 MeV 40Ca+94Mo134Sm*L. Riedinger2-(51,54,61), 3-(28)
MB-21, 1/976.1-12.0 MeV +232Th-Wash. U.Calibration
MB-22, GS88, 1/97250 MeV 58Ni+50Cr108Te*S. Freeman
MB-23, GS89, 1/97250 MeV 58Ni+58Ni 116Ba*J. Smith2-(57), 3-(15,17,18,20,29,30,31)
MB-24, GS90, 2/97125 MeV 28Si+40Ca 68Se*C. Baktash2-(19,27,36), 3-(24,32)
MB-26, GS91, 2/97157 MeV 48Ca+26Mg 74Ge*M. Devlin2-(42), 3-(19)
MB-27, GS92, 2/97135 MeV 32S+58Ni90Ru*S. Tabor
MB-28, GS93, 2/97310 MeV 76Ge+96Zr172Hf*B. Herskind/I.Y. Lee
MB-29, GS94, 2/97350 MeV 78Kr+103Rh181Tl*M. Carpenter -
MB-30, GS95, 2/97173 MeV 35Cl+105Pd 145Eu*M. Riley2-(41,46), 3-(16,25)
MB-31, GS108, 5/97230 MeV 60Ni+100Mo160Yb*L.G. Sobotka -
MB-32, GS109, 5/97160 MeV 40Ca+58Ni98Cd*A.O. Macchiavelli -
MB-33, GS110, 5/97130 MeV 28Si+58Ni(Au)86Mo*F. Lerma2-(37,47), 3-(21)
MB-34, GS111, 6/97130 MeV 29Si+58Ni(Au)87Mo*F. Lerma2-(37,47), 3-(21)
MB-35, GS112, 6/97128 MeV 29Si+40Ca69Se*C. Baktash2-(22,23,33)
MB-36, GSFMA6A, 2/98260 MeV 64Zn+64Zn128Gd*J. Smith -
MB-37, GSFMA6B, 2/98265 MeV 64Zn+58Ni122Nd*J. Smith -
MB-38, GSFMA7, 2/9812-48 MeV 4He+232Th-Wash. U.Calibration
MB-39, GSFMA8, 2/9884 MeV 20Ne+28Si48Cr*D.G. Sarantites -
MB-40, GSFMA9, 2/98135 MeV 32S+40Ca,72Kr*C. Svensson3-(32)
MB-41, GSFMA19, 6/98160 MeV 40Ca+40Ca 80Zr*D. Balamuth -
MB-42, 6/9811.96 MeV 1H+12C-Wash. U.Calibration
MB-43, GSFMA21, 6/98238 MeV 58Ni+54Fe 112Xe*R.M. Clark2-(58) 
MB-44, GSFMA22, 6/98184 MeV 40Ca+92Mo132Sm*L. Riedinger3-(28) 
MB-45, GSFMA39, 11/98257 MeV 60Ni+50Cr110Te*S. Freeman
MB-46, GSFMA40, 11/98185 MeV 40Ca+58Ni98Cd*B. CederwallCancelled
MB-47, GSFMA41, 11/98215 MeV 58Ni+46Ti 104Sn*R. Clark2-(53) 
MB-47A, 11/9812 MeV p+12C, -Wash. U.Calibration
MB-48, GSFMA42, 12/98141 MeV 36Ar+28Si64Ge*D. Rudolph/D. Sarantites -
MB-48A, 12/9812 MeV p+12C-Wash. U.Calibration
MB-49, GSFMA64, 7/9975 MeV 16O+24Mg40Ca*C. Baktash, A. Macchiavelli, D.G. Sarantites2-(60)
MB-50, GSFMA-65 165 MeV 48Ca+30Si78SeM. Devlin, et al.  -
MB-50A, GSFMA-65A12 MeV p+12C-Wash. U.Calibration
MB-51, GSFMA-66122 MeV 28Si+40Ca68Se*C. Svensson, et al. -
MB-52, GSFMA-67180 MeV 40Ca+94Mo134Sm*D. Hartley et al. -
MB-53, NS-1, GSFMA-73130 MeV 32S + 28Si60Zn*D.G. Sarantites et al. -
MB-54, NS-2, GSFMA-74100 MeV 32S + 40Ca72Kr*P. Fallon et al. -
MB-55, NS-3, GSFMA-74145 MeV 36Ar + 40Ca72Kr*P.Fallon et al. -
MB-56, GSFMA-7512 MeV p + 12C -Washington U.  
MB-57, NS-4, GSFMA-76185 MeV 40Ca + 58Ni98Cd*B. Cederwall et al. 
MB-58, NS-5, GSFMA-77125 MeV 40Ca+40Ca80Zr*S. Paul et al. 
MB-59, NS-6, GSFMA-78225 MeV 58Ni+50Cr108Te*C. Baktash et al. 
MB-59, NS-7, GSFMA-79260 MeV 64Zn + 64Zn128Nd*D. LaFosse et al. 
MB-60, GSFMA-80235 MeV 58Ni + 58Ni116Ba*D. Seweryniak et al. 
MB-61, GSFMA-8112 MeV p + 12C -Washington U. group 
MB-62, GSFMA-82207 MeV 54Fe + 58Ni112Xe*D. G. Sarantites et al. 
MB-63, GSFMA-92230 MeV 58Ni + 58Ni116Ba*J. Smith et al. 
MB-64, GSFMA-9380 MeV 20Ne + 24Mg44Ti*C. Svensson et al. 
MB-65, GSFMA-9412 MeV p + 12C -Washington U. 

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For more details send mail to D.G. Sarantites at: dgs@wustl.edu.


 

Experiments done with Microball-B (the thick one)

Three series of experiments have been done with the Reactions Microball - The fat brother of the Spectroscopy Microball A. These were carried out at the Michigan State University Superconducting Cyclotron facility and at the ATLAS facility at the Argonne National Laboratory. Briefly these are:

 

  1. 86Kr + 197Au at Elab/A = 35 MeV. In this experiment the Microball was inserted in the chamber of the University of Rochester and it was used in conjunction with Si telescopes and the U. of Rochester Superball neutron detector.
  2. 64Ni + 100Mo at Elab/A = 5.0, 6.7, 9.0, and 10.0 MeV;
  3. 16O + 148Sm at Elab/A = 8.6 and 13.4 MeV. In the last two experiments the Microball was used at ATLAS in conjunction with an external segmented annular parallel-plate avalanche counter (PPAC) to count the evaporation residues.
  4. 60Ni + 100Mo at Elab/A = 9.17 MeV;
  5. 60Ni + 92Mo at Elab/A = 9.17 MeV. In the last two experiments the Microball was used at ATLAS in conjunction with the FMA which provided the q/A of the associated evaporation residues. In addition, two Si strip position sensitive detectors backed with thick CsI(Tl) detectors, external to the Microball, were used to count isotopes of light-charged particles and intermediate mass fragments.

For comments and corrections send mail to D.G. Sarantites at: dgs@wustl.edu.

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