BRIKEN Workshop, 30-31 July, 2013 Meeting Minutes

BRIKEN Workshop
RIKEN Nishina Center, 30-31 July, 2013
*** Meeting Minutes ***

Draft Version 2

Participants (28):

J. Agramunt, A. Algora, H. Baba, R. Caballero-Folch, D. Cano-Ott[1], G. Cortes-Rossell, T. Davinson, F. Delaunay, I. Dillmann1, C. Domingo-Pardo, P. Doornenbal, A. Estrade1, J. Gibelin, H. Koura, S. Kubono, T. Kubo, S. Leblond, G. Lorusso, H. Makii, M. Marta, K. Matsui, F. Montes, M. Niikura, S.Nishimura, K. Nishio, B. Rubio, K. Rykaczewski, H. Sakurai, P. Shury, E. Sokol, P.A. Söderström, J.L. Taín1 and P. Woods.

Event webpage:

The EURICA – BRIKEN connection:

After the Welcome by G.Lorusso, S.Nishimura made an introduction to the RIKEN Nishina center, summarizing production yields, measuring devices, location for decay experiments, and beam-time at RIBF. Regarding the production rates, although intensities higher than 10pnA have been achieved for U-238 beams, it was agreed that for proposal preparation we will count with 10pnA. The present decay experiments focus on the EURICA set-up, which is foreseen to return to GSI by December of 2014. Then the plan is to carry-on with an experimental campaign using high-efficiency beta-delayed neutron detection (BRIKEN) and afterwards a beta-gamma-neutron campaign including fast-timing, neutron TOF detectors, LaBr3 and HPGe detectors. The most reasonable locations for the BRIKEN set-up seem to be, at this time, either F12, which is empty, or F11, which is presently occupied by EURICA. A summary of the main results obtained with EURICA was presented. It is important to emphasize that most of the physics cases which are proposed within BRIKEN correspond to the same regions of the nuclear chart that have been (are being) explored with EURICA. Thus, the experimental production rates measured in the EURICA campaign, as well as other technical aspects such as separation, resolution, etc, should be used for the preparation of the BRIKEN proposals. Each BRIKEN spokesperson has to contact the corresponding spokespersons of the EURICA proposals in order to collaborate or get such information.

Summary and status of the BRIKEN project

C.Domingomade a summary of the 1st BRIKEN workshop at Valencia, and the current status of the BRIKEN project. The main scientific areas covered by BRIKEN are astrophysics, nuclear structure and reactor technology. In particular, BRIKEN aims at the detection of the most exotic nuclei (reason for coming to RIKEN) in combination with the largest neutron detection efficiency (reason to combine detectors from several institutions worldwide). Right now, BRIKEN comprises 20 research institutions and more than 50 scientists. The BRIKEN collaboration philosophy and aims have been specified in a letter of “Scientific Collaboration Agreement”. Thanks to the collaborating institutions, at present the BRIKEN setup counts with the sophisticated AIDA array for the detection of both implants and beta-decays, and with 172 He-3 tubes and the related electronics (three times more than the number of tubes available at the time of the previous workshop). Such contribution will allow for very large neutron detection efficiencies[for quantities see below MC-presentations], both for one- and for multiple-neutron detection. This also opens the possibility to set-up an hybrid configuration for the detection of both neutrons and gamma-rays (see also below MC-section).

Experience with previous neutron detectors: NERO, 3HEN and BELEN

F.Montes gave an overview presentation on previous measurements made with NERO at NSCL-MSU, with focus on the r-process astrophysics applications. A highlight was a new implant-beta detection system based on a planar segmented Ge-detector, with a beta-detection efficiency of around 85%. He offered the possibility to consider future experiments with this detector within the BRIKEN project. Interested people should contact FM about this.

K.Rykaczewskipresented a summary on the activities carried out at the Holifield Radioactive Ion Beam Facility of ORNL with a setup combining HPGe clover detectors with 3Hen detectors for n-emission channel selection. Recent nuclear structure results in the region beyond Ni-78 were presented by Rykaczewski, covering a systematic study of the neutron branching evolution from Cu-76 up to Ga-85. The latter are also of relevance for reactor studies.Rykaczewski reported also on multiple neutron emission measurements with 3Henin the region around Ga-86 and discrepancies between theoretical models in the 2n emission predictions.

R.Caballero made a summary of the measurements made with BELEN at JYFL and at GSI. At the ISOL facility of JYFL (Finland), Ge-85, As-85,86 and Br-91 were measured, which are of relevance both for nuclear structure and reactor technology. At the fragmentation facility of GSI, two experiments were made with BELEN, one around N=82 (128Pd-region), and a second one beyond N=126 in the Hg-Tl-Bi region. Detector calibration measurements at PTB-Braunschweig (Germany) as well as underground neutron-background measurements at LSC-Canfranc (Spain) were also summarized.

Neutron Background Measurements at RIKEN-BigRIPS

K.Matsui presented results from neutron background measurements made at the F11 focal plane of BigRIPS using 3 He-3 tubes, each counter inserted inside a block of HD-PE of 10x10x40 cm3. All the results, regardless of the exact location of the He-3 tube, indicated a very low neutron background at F11, with an average value of just 1 neutron/minute detected in each tube while the beam was on.

Conceptual design of the BRIKEN Neutron detector: MC simulations

Simulations by RIKEN/Tokyo Group:

K.Matsui showed results obtained with MCNP5 employing the different types of counters available. A preliminary configuration of 4 rings shows an average efficiency of about 73% up to 1 MeV. See Fig.1.

Fig. 1 Preliminary BRIKEN configuration proposed by KMatsui. Ring radii are 8 cm, 13.5 cm, 20.5 cm and 27.0 cm.

Simulations by UPC Group:

GCortés presented results using MCNPX for several configurations aiming at flattest possible efficiency curve up to maximum neutron energies of 1 MeV, 3 MeV and 5 MeV. The flatness of the efficiency curve (F) is evaluated as the ratio of the maximum between the minimum efficiencies, always in the energy interval from 10 keV up to the maximum energy for which the configuration has been optimized.

Fig. 2 shows the MCNPX results for the 3 MeV case, yielding 64% average efficiency and F=1.09.

Fig. 2 Preliminary BRIKEN configuration proposed by GCortés aiming at flat efficiency up to 3 MeV.

Fig. 3 shows the results for the 5 MeV case, showing 61% average efficiency up to 5 MeV, with F = 1.15.

Fig. 3 Preliminary BRIKEN Configuration with 149 tubes proposed by GCortés aiming at flat efficiency up to 5 MeV.

Simulations by IFIC Group:

J.L.Tain presented results obtained with Geant4 and validated with MCNPX. The aim was at largest possible and rather flat efficiency up to neutron energies of 2-3 MeV. An efficiency of 84.4% @ 500 keV and 73% @ 2.5 MeV was achieved.

Fig. 4 Preliminary BRIKEN configuration proposed by JLTainusing 153 tubes, aiming at largest possible efficiency up to 2-3 MeV. The efficiency curve with red down-pointing triangles corresponds to the squared geometry shown on the left hand side.

J.L.Tain presented results also for hybrid configuration of He3-tubes combined with two EXOGAM Clover detectors, and with four EXOGAM Clover detectors. For the2xHPGe Clover detectors shown in Fig.5, the neutron efficiency was 75.6% (66.5%) at 500 keV (2.5 MeV), while a g-ray efficiency of 3% is obtained at E=1MeV.

Fig. 5 Preliminary BRIKEN-Hybrid configuration proposed by JLTain. In the transversal view of the middle, AIDA is inserted from the right hand side.

Simulations by ORNL-LSU Group:

K.Rykaczewski presented results obtained with Geant4 by B.C. Rasco (LSU). Simulations were made for HD-PE moderators of 32 cm and 45 cm radius. Fig. 6 shows the results for the 45 cm case, which are slighly better than for the 32 cm configuration. The latter however, would allow us to use already existing mounting structures and Cd-HD-PE shields.

In summary, an average efficiency of about 85% is obtained in the energy range up to 1 MeV.

Fig. 6 Preliminary BRIKEN configuration analyzed by B.C. Rasco (LSU) and presented by KRykaczewskiis using 144 He-3 tubes.

Future simulation work:

Although all the presented geometries were already very elaborated, they are preliminary in the sense that there may be still some room for improvement. Some general aspects have to be considered for future simulation work:

The square hole seems to provide higher efficiencies, so one should better go for a squared hole rather than cylindrical. The size to accommodate AIDA inside must be 11x11 cm2.
For technical reasons, one has to make sure that tubes are separated at least by 4mm of PE. Otherwise the matrix may not be mechanically stable.
We all have to use the same PE composition: CH2, 0.95 g/cm2.
One can count with 20 He-3 tubes from JINR, and a total number of 67 2-inch tubes from ORNL (instead of 58).
There might be the possibility of having more 30cm tubes from MSU, particularly if simulations show that more tubes would contribute significantly.
One has to make sure that we use the same data-base for neutron cross sections in the codes.
When using Geant4, one has to fix a bug in the code (see link in JLT presentation, or ask him directly). Otherwise, the efficiency may be overestimated.
In any case, the final efficiency values should be obtained with MCNPX, which has been found to be more realistic than Geant4.
It was agreed to fix at least half of the moderator matrix length to 45cm, to make sure that AIDA (as it is) will fit from that side. The other half of the moderator matrix may be longer.

Data acquisition:

H.Baba presented the data acquisition system of the RIKEN RIBF, and how the EURICA MBS data acquisition system, which uses its own individual trigger, was integrated within the existing system. In summary, there was the request of using the RIBF-DAQ, i.e. to no build any dedicated system for the BRIKEN campaign. As there are already two existing DAQ systems (one for the neutron detector, another for AIDA) there is the possibility of time-stamping with clock synchronization. The analysis can be ROOT-based with an offline (nearline) event building.

J.Agramunt presented the self-triggered digital data acquisition system (DDAS) that is foreseen for the BRIKEN neutron detector. It is based on the Struck digitizers (SIS3302) which record time and energy of all incoming events. A total of 192 channels are available (to be compared with 172 He-3 tubes), which leaves 20 channels for back-up, synchronization signals or storage of signals from another ancillary detectors. The module readout and acquisition system is based on the GasificTL modular software, which has been fully developed by the IFIC group.

There was a dedicated extra meeting by H.Baba, T.Davinson and J.Agramunt to discuss the integration of the three daqs: BigRIPS + AIDA + BRIKEN-DDAS. It was agreed that T.Davinson will write a document with the conclusions and the integration strategy as well as how to merge data from all three systems for near-line/off-line analysis.

The Advanced Implantation Detector Array (AIDA)

T.Davinson presented the status of AIDA, which is a multi-plane Si-DSSDs array, with 1 mm wafer thickness and 8x8cm2 size (128x128 strips). Results from a commissioning run made at GSI with a Bi-209 beam at 250 MeV/u were presented. The current status is that 4 prototypes (8x8cm2) have been delivered. Another 12 prototypes are being produced or have been ordered. Front End Electronics, time-stamp distribution system and mechanical infrastructure is all available.

The SLOWRI facility

P.Schury presented an alternative approach for experiments with ultra-pure low-energy beams. The so-called SLOWRI facility will operate in parasitic mode, sitting on the shadow of the slits at the middle focal plane of BigRIPS, thus being able to select and provide ions, which otherwise would be lost in the slits. This may represent a good opportunity for those isotopes which are not very exotic, i.e. nuclear reactor technology proposals, and which need good statistical accuracy.

Physics Proposals

A total number of 12 physics proposals were presented at the workshop. Some of them show overlap in the isotopes. Other proposals can be combined within one proposal, as they cover two neighboring regions of the nuclear chart. They are summarized in the table below. It is up to the spokespersons to contact each other and join efforts.

ID / Spokesperson / Topic / Region / Notes
1 / S. Nishimura / 2nd r-process peak / A=110-125
112Zr-129Pd / Check overlap with (8)
2 / F. Montes / 2nd r-process peak / 139Sb / Check overlap with (7)
3 / C. Domingo Pardo / Rare Earth Peak in r-process / A=150-170
151La-177Tb / Check overlap/synergy with (10)
4 / M. Marta / Multiple n-emitters / 78Ni
(76Co-81Cu)
132Sn (134Sn-133Cd) / Check overlap with (5,6)
5 / K.Rykaczewski / Multiple n-emitters / 78Ni-81Ga
81Cu-85Se
82Cu-86Se
84Zn-87Se
91As,92As
134,135In / Check overlap with (4)
Close to region (11)
6 / R. Grzywacz / Multiple n-emitters / 48Cl-64V
67Cr-69Fe
74Co-77Zn
76Co-79Zn / Check overlap with (4)
7 / G. Lorusso / 2nd r-process peak / 129Ag-142Te
133-134Cd
Pd-chain
In-chain / Check overlap with (2,7,9)
8 / A. Algora / Deformation / 106Zr-114Mo / Check overlap with (1)
9 / B. Rubio / Full b-strength function (TAS+N) / N>82
130Ag-138Sb / Check overlap with (7)
10 / A. Estrade / Masses + neutrons / Several
153Ce region / Check overlap with SLOWRI.
Check overlap/synergy with (3)
11 / J.L. Tain / 1st r-process peak. / 85Ge-97Br / No overlap.
Close to region (5)
12 / D. Cano-Ott / Reactor Technology / 86Ge-86As
96Rb-100Rb, 98mYm,131Cd,137Sb137 / Check possibilities with SLOWRI.
Check synergy with (10) for tof-calibration.

Final discussionand tasks:

Some aspects have been included already in the section above, otherwise:

Shipping costs:

UPC+GSI tubes: the price to ship the tubes to RIKEN was quantified as 1kE. G.Cortés to check the procedure and cost of shipping the tubes back.
ORNL-Tubes: to be checked. In principle seems no problem. K.Rykaczewski and S.Nishimura to prepare a “material transfer agreement”.K. Rykaczewski is working on shipping certificates and formalities following an experience from an attempt to transfer 3He tubes to TRIUMF, Canada.
JINR tubes: E.Sokolto check the shipping price, estimated cost 1kE. A protocol with RIKENwill be needed for formalities.
AIDA: 15 kP + 12 kP
Note that EURICA was also a similar situation, which was solved by doing a very detailed custom declaration.

PE Matrix + Holding Structures:

If there is no-one assuming this cost, the cost will be shared between all the collaborating institutions. (In the meanwhile I.Dillmann has expressed the wish to contribute to the PE-matrix).
Manufacture in Japan. Apparently, the cost of drilling the holes in the PE-blocks seems to be very expensive, according to a quotation requested by G.Lorusso at some local workshop.G.Lorusso/K.Matsui will check again at another place.Alternatively, G.Cortés will check for the cost of producing it in Spain and shipping it to Japan.
S.Nishimura will check the availability of a table to support the BRIKEN neutron detector.

Grants and funding for students. G.Lorusso will gather information about this and distribute it to the collaborators.

H.Sakurai proposed to present first (in the next winter NP-PAC) a DetectorConstruction Proposal. This will define the collaboration and it will allow us to get beam-time for commissioning (and experiments) plus some resources.

Scientific Collaboration Agreement:

Add a synopsis of the project highlighting the most relevant physics cases: introduction, discovery nuclei, physics highlights, amount of new neutron branchings to be gained in this campaign, etc.
Everyone should check that there is no-one missing in the list of collaborators and institutions.

Sign this document before the presentation of the construction proposal.(It will be a Material Transfer Agreement for ORNL collaborators)

Proposals preparation:

The construction proposal will be presented at the next Winter NP-PAC. The physics and nuclear technology proposals will be presented at the next NP-PAC in June 2014, within the “BRIKEN” Umbrella.
The people with overlap in their proposals or with topics that can be better covered within one single proposal, should discuss among themselves to find a solution.
A local expert from RIKEN will check the feasibility of the different proposals in terms of CS and LISE++ calculations. S.Nishimura to find the proper person for this.Toshi Kubo, Naoki Fukuda, Naohito Inabe and R. Grzywacz provided the analysis for BigRIPS setting and rates from Rykaczewski’s proposal presentation.
Data from previous EURICA experiments (production rates) should be preferably used for the preparation of new proposals. It is up to each spokesperson to check the overlap with the EURICA experiments, and contact the corresponding spokesperson to get production rates, LISE++ files, etc.
After the construction proposal, we should prepare a “guide” for proposals preparation, where we fix the set-up and efficiency that can be used for detection rates estimates, etc./what’s about the common data base – Nishimura ?/

NP-PAC 13-14 December 2013, with deadline October 28th:

General presentation of the project (Construction Proposal), set-up or set-ups, efficiencies, institutions, main physics cases, etc.

This document wasoriginally written by C. Domingo-Pardo and includes corrections from:

Michele Marta
Jose Luis Taín
Krzystof Rykaczewski

[1] Participted in the Workshop via Video-Conference.