Minutes of the n tof collaboration and Collaboration Board Meeting Lisbon, Portugal 13-15 December, 2011

Enrico Chiaveri, CERN (EC)

Roberto Losito, CERN (RL)

Vasilis Vlachoudis, CERN (VV)

Enrique Gonzales, CIEMAT (EG)

Daniel Cano Ott, CIEMAT (DCO)

Nicola Colonna, INFN (NC)

Marco Calviani, CERN (MC)

Carlos Guerrero, CIEMAT@CERN (CG)

Eric Berthomieux, CEA@CERN (EB)

Roza Vlastou, Un. Ath. (RV)

Laurent Tassan Got, IN2P3 (LTG)

Isabel Ferreira, ITN (IF)

Josef Andrzejewski, Un. of Lodz (JA)

Manuel Josè Quesada, Un. Sevilla (MJQ)

Vladimir Avrigeanu, IFIN (VA)

Helmut Leeb, Tech. Un. Vienna (HL)

Franz Kaeppeler, KIT (FK)

D. Bosnar, Univ. Of Zagreb (DB)

P. Schillebeeckx, IRMM (PS)

W. Mondelaers, IRMM (WM)

D. Schumann, PSI (DS)

C. Lederer, Univ. of Vienna (CL)

P. Milazzo, INFN-Trieste (PM)

P. Woods, Univ. of Edinburgh (PW)

J. Billows, Univ. of Manchester (JB)

EC and EG introduce the meeting, by thanking the ITN team for organizing the meeting. Isabel Goncalves and Pedro Vaz welcome all participants and give some more details on the organization.

EG proposes to approve the minutes of the last Collaboration and CB meeting. Apart for some minor correction, there are no objections, so the minutes are approved. EC asks NC to take the minutes of the present meeting, once more. He then invites FG to chair the first session, on the data analysis.

Status of data analysis

F. Belloni presents the latest results on the beam profile. The analysis has been refined, and the width of the beam is now given directly or as a result of a 2D Gaussian fit. From the width, the Beam Interception Factor has been determined. At present, the agreement between experimental results and simulations is still not satisfactory. In particular, the experimental results show an unexpected trend as a function of neutron energy. Several comments are made, but no final conclusion is drawn. Belloni will continue investigating the problem.

A. Tsinganis shows the results of the simulations on neutron fluence, beam profile and time-to-energy relation. He explains in details the geometry implemented in the simulations and the influence of various effects (gravity, collimator misalignment etc…) on the results. On the time-energy relation, he shows that a simple correction with a time offset, t₀ , works only up to a few hundred keV (with t₀ for the new target more than double that of n_TOF-Phase1). For high energy he suggests to use a correction taken directly from the simulations at each energy. This has been validated with the Al dip in the flux and with some fission data at higher energy. NC objects that the experimental validation is not as good as it was done in n_TOF-Phase1, and that at high energy the effect may not be so important. AT will make available the time-energy relation from simulations.

CG shows the results on the experimental determination of the neutron flux. All effects have now been taken into account, including attenuation in the material along the beam, and anisotropy effects in ¹⁰B. The agreement between various detectors is now very good, and also with simulations the agreement is not bad, except in some absorption dips. It is estimated that the uncertainty in the flux is typically 2-3% in most of the energy range. The results are final and they are available as Root file.

On the analysis of the ¹⁰B Micromegas, Maria Diakakis shows the results of some simulations she has performed in order to understand the effect of the discrimination between Li and alphas on the determination of the flux. She shows that the spectra relative to the two reaction products in some neutron energy regions overlap, and this makes difficult to estimate the flux from the a-particles only. One possibility she suggests is to take into account both Li and alpha in the analysls.

The next session is dedicated to test measurements performed at n_TOF in the course of 2011. Rogelio from Univ. of Sevilla reports on measurement on FBG dosimeters (optical fibers), whose response changes with the absorbed dose. The test was performed for a few days, in vacuum (FIC chamber), and it should continue in 2012. M. Calviani informs that there are other irradiation facilities at CERN where the test could be performed, on charged particles. Another test was performed by P. Woods, from Edinburgh, on Si detectors (mounted in the SiMon chamber) to check the feasibility of light-charged-particle detection at n_TOF. The aim would be to study the ²⁶Al(n,p) and (n,) reactions, of interest for astrophysics. The test was successful, and evidenced no particular noise problems, even connected with the -flash. The last test was proposed by the Kyushu Univ., to study the response of an E-E telescope made of plastic scintillators plus BGO, to be used for studying (n,d) and (n,) reactions at GeV neutron energy. Some data were collected, showing signals in correspondence of GeV neutrons, but to avoid the strong influence of the -flash, the detectors had to be moved far away from the beam direction. Before drawing conclusions on the feasibility of the measurement, more analysis is needed.

EC shows a list of samples that have been procured for the measurements so far, mostly from IRMM, and a list of many more samples that could be available from Univ. of Munich. Some of them are short-lived, and could be measured at the EAR-2. In any case, the n_TOF Collaboration is trying to establish contact with several Institutes and Organization, like IRMM, Univ. of Munich, ORELA, CACAO, PSI etc… for the production of high purity samples to be used in measurements at CERN. On this respect, three presentations follow: a very interesting possibility for the production of exotic target could be offered by the RadWasteAnalytic group of PSI, which has already been very helpful so far for the preparation of the ⁶³Ni sample. At PSI there are several sources of radionuclides, from accelerator waste, spallation neutron source, special irradiation, etc… She shows some instructive examples and describes the procedure used for the sample purification and preparation. At the end, a list of possibly interesting radionuclides is shown, among which is of particular interest the production of ⁷Be samples (for Big-Bang Nucleosynthesis experiments). DCO says a few words on the contacts ongoing with the Oak Ridge laboratory, for some specific samples. The reference group has been identified and work is in progress to finalize the framework for the sample procurement. A list of material of possible interest for n_TOF has been submitted to Oak Ridge, and he is optimistic that in the near future some samples could be obtained through them. As for CACAO, LA reports that things are progressing with authorization and preparation of the target laboratory, although some delay has to be expected. Nevertheless, some samples have already been prepared and characterized, such as ²³²Th.

A final measurement, for the characterization of a new Silicon detector under fast neutron irradiation is presented by Rogelio, Univ. of Sevilla. The test should be performed in the escape lane of n_TOF, in parasitic mode.

As for the proposal, EG suggests to add a few more figures in the final version, to show the full model of the various parts of the EAR-2, on which calculations are based.

AT presents a more detailed study, with simulations, of the -flash, in-beam -rays and effect of the collimator on EAR-1. This study is useful to provide a reference for the performance of EAR-2. One possibility is that in the so-called -flash there could also be a component of charged particles and -rays produced by interaction of high-energy neutrons in the second collimator. To be more realistic, AT has included in the geometry the detectors in EAR-1. The simulations clearly show that there are events with high energy deposition in the detectors, which are due to charged particles and -rays produced in the 2^nd collimator area which could be responsible for part of the observed -flash in the detectors. Clearly, such an effect could also affect the -flash in the EAR-2, and should be further investigated to optimize the collimator design and estimate the magnitude of the effect. Various questions arise on the fraction of the events that could be attributed to charged particles and -rays produced in the 2^nd collimator, on the directionality of the background, etc… All these effects need to be further investigated.

The last part of this session is dedicated to the work to be done in the near future to finalize the design of EAR-2 and to task assignment. There is a large amount of work to be done, if the proposal is approved, to complete the design and optimize the neutron beam optics, and people are needed to help with calculations of the background in the experimental area. It is important that the Collaboration starts already thinking about the detectors to be installed in the EAR-2 and the new acquisition system.

DCO mentions that at CIEMAT they have the intention of making some simulations to see if the performance of the facility could be further optimized with some minor modification of the design, They also plan to investigate possible alternative solutions for the detectors to be used for a new TAC. It is remarked that it is the time to start thinking about organization of the Collaboration for all work concerning experimental systems.

A general discussion takes place on the EAR-2. RL remarks that CERN management knows that Institutes right now are not in the position of commit for money, since the facility has not been approved. However, it is important that the Collaboration agrees that, once approved, all Institutes will make any effort to participate to the maximum of their possibilities to the manpower and financial request for the preparation of the EAR-2. EC ends with the road-map for the proposal: in February there will be the discussion within the INTC, and if approved, the proposal will be examined by the Research Board at the end of February. If approved at that point, it would be the official start of the EAR-2 project.

EG suggests to make clear that the Collaboration strongly supports the scientific case for EAR-2, and that there is very high interest towards this new facility for the opportunities of new research it would offer. It will be necessary, especially if and after EAR-2 is approved, to commit people from the Collaboration to continue the work. To his view, all Institutes should commit to participate to the effort at the best of their possibilities. EC remarks that the spirit of this new enterprise is to provide new results in conjuction, and not in competition, with other facilities that are now being proposed and built. It is also important to remark that in principle EAR-2 could start producing results in a reasonably short time, in a moment in which other facilities may be facing problems in being completed. In any case, the word to keep in mind is “complementarity” between the research activity to be done at n_TOF/EAR-2 and the one that could be carried out elsewhere.

Collaboration Board

The minutes of the last Collaboration Board are approved, with some minor changes on the participant list.

EB presents a status of the n_TOF facility (including EAR-1). In general, in 2011 there have not been major problems, and only a small maintenance on the target/cooling system and on the interlock for access is necessary. All this action will be performed during the shutdown. There will be also some intervention in the experimental area to understand and possibly cure the problem with the grounding, which is responsible for some noise observed in particular as oscillations after the -flash.

NC reports the status of the finance. In 2011 there have been few expenses, thanks to a bigger support from the CERN group in running the experiments. This has resulted in some funds saved, in view of the financial effort for the construction of EAR-2. The M&O contribution from the Institutes has been mostly collected. Apart for the Spanish Institutes, which will now follow a different procedure, only few Institutes have not yet complied with their obligations. Some of them have in fact never complied so far, and NC poses the question on whether they should be considered as part of the Collaboration. EC will contact these Institutes, one by one, to check if there is a possibility that they could start contributing, even with a different mean, to the Collaboration effort. A discussion takes place on the possibility for the Collaboration to contribute to the cost of EAR-2. According to the present budget and predictions for the next two years, it will be difficult, according to NC, to reach the level requested, especially if some funds will be also needed for building the detectors and acquisition systems. It may be necessary to ask the Institutes for an extra financial effort, but it is premature to foresee such additional contribution, given the difficult economic situation of almost all Institutes and the fact that the costs of EAR-2 have not been finalized. It is also hoped that a further negotiation with CERN will make things easier for the Collaboration.

EC presents some key points on the document to be sent to INTC for EAR-2. Some corrections are proposed to the phrasing, to make more clear the advantages of EAR-2. For example, it should be make clear the new feature of the facility, i.e. an instantaneous neutron rate 250 times higher than for EAR-1, “while maintaining the features already present in EAR-1, in particular the possibility to measure neutron induced reactions up to high neutron energy”. It should also be explicitly said that the new area is suited for low cross section measurements and (n,charged particle) reactions. Finally, on the last point, it should be mentioned that the irradiation facility is of interest for other applications, such as dosimetry, various material tests, devices, detector development etc….

A formal statement of suppot from the Collaboration is approved: “The n_TOF Collaboration Board in the meeting of Lisbon on December 15^th, 2011, strongly support the construction of a second experimental area at a shorted flight path, and is willing to participate in the effort, assuming that civil engineering and beam line contraction activities could be covered by extra contributions from CERN budget (see Appendix 1 on document “Proposal for n_TOF Experiment Area-2 (EAR-2)”.

The Collaboration supports the formulation of this sentence.

Planning of 2012

EC presents a tentative planning for experiments in 2012. The total request, including proposals to be submitted to INTC, is 1.9x10¹⁹ protons, to be compared to the expected number of 1.6 x10¹⁹. However, at present it is not necessary to rearrange the plan. If necessary, some measurements could be combined, some postponed and some shortened. A more realistic plan will be made in spring, on the basis of the situations of the various experiments. A tentative list of priorities is discussed, with the measurement on 87Sr assigned the lowest priority. FG mentions that there is a new PhD from INFN that is interested in analyzing the 238U data that will be collected in 2012 with C6D6 detectors. CG mentions that among the proposals to be submitted to INTC one should also consider ³³S(n,), which was originally sent as a letter of intent, but is now in the condition to ask for beam time. Most probably, the 2012 campaign will start with capture cross section measurements, and as usual we will switch to fission in the course of the year. DE and LTG strongly suggest this year to avoid switching at the last minute, since the experience of past years teaches that if there are problems with the beam at the end of the year it is not possible to recover. The fission program needs more data and effort should be made to make sure that they the requested statistics is collected.

EC mentions that three more Institutes are officially entering the Collaboration. One of them is IRMM, for which all legal aspects of their participation seem now to have been solved. NC remarks that IRMM is not a new Institute, but has always been collaborating with n_TOF, since the beginning, and that now such collaboration should only be strengthen. EC reminds that IRMM is providing some samples, but in the past some confusion has arisen from the n_TOF side. From now on, Peter Schillebeeckx is the contact person at IRMM for sample preparation.

R. Dessler for PSI presents the group and its activity and the interest in joining the collaboration. The main task of the group within n_TOF will be to support the Collaboration in the procurement, purification and preparation of some particular samples, on the example of what has already been done for 63Ni. EC on behalf of the whole collaboration states that this collaboration is important, since it can provide very valuable radioactive samples, and is willing to support the new PSI group to all extent.

The third Institute to join the n_TOF Collaboration is Univ. of Frankfurt. C. Lederer, which will soon join the group, shows a few slides on the composition and activity of that group. It is quite a large group, working mostly on Nuclear Astrophysics. It has several interests and making experiments in various facilities, like Los Alamos. It is also responsible for a future neutron facility, FRANZ, and is also working with radioactive beams. Finally, it is working on new detectors, in particular for neutrons.

CG presents a few slides on the activity of the analysis group. This has been operating in 2011, with periodic meetings organized to discuss on the progresses and find a common way to proceed. For 2012 the group will continue in the same way, with two dedicated meetings, in spring and fall, and perhaps another meeting during the general collaboration meeting in December.

A discussion takes place on the Editorial Board. In general only a few people of the EB seem active, providing comments and suggestions to the various papers. It is therefore suggested to add more people that could contribute more actively. The proposal is to add Carlos Guerrero and Peter Schilebeekx. The proposal is accepted.

At present there is some confusion on which author list should be used when preparing a new paper. There are lists for the first campaign, different lists for the phase-II, and each year the situation changes with the addition of new Institutes and of several PhD students. It is decided the a revision of the list year-by-year should be done, and that the EB should review such lists and decide on the authors. For the moment, the author lists should be maintained by Eric Berthoumieux.

EB gives a report on the shifts made by each Institute in 2011. After reminding the rule adopted, which seem to have avoided criticisms in covering the shifts in particular over night and in weekends, he shows a table with the percentage of shift completion for each individual Institutes. Many of them have provided more than 100% of their allocated shifts, while a few Institutes have done little or none. For 2012, the running period will be from March 19^th to Dec. 3^rd. Consequently, the number of shifts will be slightly larger than in 2011, with an average of 12 shifts per person instead of 11.5 of 2011. A tentative shift allocation for each Institute is then presented.