Summary of the meeting 18/10/1999

Meeting on Monte Carlo simulation inside the nTOF collaboration

Geneva 18-10-1999

List of participants:

"Frank Gunsing" <> CEA/SPhN
"Alfred Lepretre"  <>  CEA/SPhN
"Samuel Andriamonje"  <>  CERN
"Paolo Cennini"  <>  CERN
"Alfredo Ferrari"  <>  CERN
"Ilias Goulas"  <>  CERN
"Yacine Kadi"  <>  CERN
"Ernst Radermacher"  <>  CERN
"Vassilis Vlachoudis"  <>  CERN
"Daniel Cano-Ott"  <>  CIEMAT
"Enrique Gonzalez" <>  CIEMAT
"Robert Meunier"  <>  CSNSM
"Michael Heil"  <>  FZK
"Franz Kaeppeler" <> FZK
"Rene Reifarth" <> FZK
"Jose Luis Tain" <> IFIC
"Nicola Colonna" <> INFN-BA
"Mario De Poli" <> INFN-LNL
"Pierefrancesco Mastinu" <> INFN-LNL
"Paolo Molazzo" <> INFN-TS
"Paule Baumann" <> IRES
"Aleksandra Kelic" <> IRES
"Gerard Rudolf" <> IRES
"Vitaly Chepel"  <> LIP-Coimbra 
"Isabel Lopes"  <> LIP-Coimbra
"Noulis Pavlopoulos"  <> UNI-BASEL


A. Structure of the simulation group

The main purpose of the meeting was to define the structure, objectives, tasks and priorities of the nTOF Monte Carlo simulation group (TOFMC). E. Gonzalez proposed that the simulation work can be done in a distributed way at the home institute of every TOFMC participant. However, all the relevant information should be concentrated in one place of easy access (email, WEB). The group at CIEMAT offered to perform the co-ordination of the simulation activities and also to provide the concentration, distribution and archiving of the TOFMC data including:

B. Simulation strategy

  1. Different types of simulations are involved in the MC for the nTOF:
  2. Global simulation is a problem to be solved in several steps: Usually, the output of one step becomes the input for the next one. Several codes can (should if possible) be applied at each step. The transport of high energy neutrons (En > 20 MeV) can be done for example with Fluka (one of the best available codes) down to En = 20 MeV. The tracking of such neutrons is then continued either by MCNP or EAMC (Energy Amplifier Monte Carlo). The tracking of photons (produced by capture, bremsstrahlung or other processes) can be done with MCNP, Fluka, GEANT or EGS. The simulations of the g-detectors can be done independently with any of the codes well suited for it (Fluka, GEANT, EGS). In addition, GEANT has been used for some neutron transport problems. Extra codes will be needed in order to compute the input of one phase from the output of the previous one (for example, the cascades of g following the capture processes computed with MCNP which can be simulated with the same or a different code like GEANT). A remark was made on the need to converge to the same versions of the codes. Additionally, any modification of them should be properly documented. 
  3. The strategy of using more than one point of view for each simulation is recommended. In this sense, some limited duplication with more than one group studying the same problem will be encouraged.

The list of specific topics concerning simulations were divided into five blocks:

  1. Simulation of the nTOF facility:

  2. Simulation of the TOF detectors:

  3. Simulation of the specific run 2000 experiments:

  4. New phases of the facility:

  5. Design of future detectors and measurements:


C. New layout of the facility

The new layout of the facility was presented by E. Radermacher. With respect to the previous design, the lead target has been moved 30 m inside the tunnel. This makes possible (but delicate due to activation) to have access to it if needed. The tube length is now 200 m, and the pipe has been divided in three sections: an approx. 70 m long tube of 80 cm diameter, an approx. 70 m long tube of 60 cm diameter and finally an approx. 60 m tube of 40 cm diameter. The geometry of the tube at the end of the pipe as well as the shielding elements along the neutron flight path have to be defined. The most urgent thing is to specify the first shielding element at about 70 from the lead target (at the 1st reduction of the tube diameter), since the pipe will be finished up to this point by middle of November. An important point is that the shielding can not be a wall: safety reasons force to allow a free path through all the parts of the tunnel. The drawings of the facility can be found in the copy of the presented transparencies attached to this document. The shielding after the 2nd reduction of the tube diameter should be done before middle of December. Several participants expressed their concerns about the chicane design of the walls at the pipe diameter reduction locations and its effect on the neutron background.

A comment was also made on the possibility of having a counting station at 30 meters. There exists the possibility of installing a device which permits to insert/remove fission detectors inside the vacuum. However, the reduced space inside the pipe (80 cm diameter) makes difficult to insert g-detectors for capture measurements. For the second phase of facility, the installation of a second pipe of 30 m length coming directly from the lead target was discussed as a possible near capture measurements station.

Another difficulty is coming from the activation of the target. Some calculations done by the CERN group indicate that g-radiation will be too high there. Even at the end of the tube at 200 m, it will be necessary to shield the g's coming from the target whenever some work is needed there. A report of this calculation was requested.

Another topic of discussion was the carbon window at the beginning of the pipe (80 cm diameter). It was stated that calculations made at CERN reveal no influence of the window on the time/energy relation of the neutrons. A report on the results of these simulations was also requested.

Since the design of the facility has been modified, a new overall simulation is required in order to have the proper definition of the neutron source (intensity spatial profile and angular and energy distributions) for the new conditions. This task will be done by the CERN group: a DST (data summary tape) containing all the important parameters related to the neutron source at a certain position will be provided in the next weeks. The details of the DST have still to be specified, and this must be done very soon.

D. Descriptions of the facility and the detectors

The inputs needed for the simulations were separated in three groups, even if those are strongly linked.  

  1. The facility: full geometrical description of the facility. Technical drawings including dimensions and detailed descriptions of the material compositions of all the elements are required. The contact person is:

    Ernst Radermacher
  2. The detectors: the complete description of the geometry, composition and surrounding materials have to be provided. Additionally, the people constructing a detector should be involved in the Monte Carlo simulation group. The contact persons for detectors:

    PPAC fission detectors

    Samuel Andriamonje

    HP Ge for (n,xn) measurements (Si ?)

    Gerard Rudolf

    C6D6 detectors for capture 

    Frank Gunsing

    BaF2 detectors for capture 

    Franz Kaeppeler

    Moxon-Rae detector for capture measurements

    Franz Kaeppeler

    Liquid Noble gas detectors for capture measurements

    Vitaly Chepel

    Monitoring detectors

    N. Pavlopoulos

  3. The samples: in order to define the beam parameters, some initial information on the samples to be used is urgently needed. It was noticed that the beam parameters also influence the geometry of the samples.

    1. Samples for capture measurements

      Two different approaches seem to be possible. The Saclay group pointed out that the samples used in their experiments at Geel have the same dimensions as the beam pipe (8 cm) and variable thickness (0.1 mm for Au and 1g/cm2 for 237Np). On the other hand, the group at Karlsruhe mentioned that their samples have much smaller surface (1-8 cm) and larger thickness.

    2. Samples for fission measurements

      The samples used in fission experiments can not be thicker than few times 100 mm for a proper release of the fission fragments. Their diameter can be typically of 1-3 cm.

    3. Samples for (n,xn) measurements

      Usually there are two kind of samples: small surface and thick samples are used when the g-radiation has to be detected, while large surface and thin samples are needed when looking at the conversion electrons.

    The contact persons for the samples are:

    Noulis Pavlopoulos

    Robert Meunier


    E. Priorities for the year 2000 experiments

    1. Fission cross section measurements of 235U, 237Np, 238U and 239Pu with PPAC detectors.
    2. Capture cross sections of 197Au, 27Al, 19F and natAg with C6D6 detectors and/or Moxon-Rae detectors.
    3. Capture cross sections of fissiles: 235U and 238 U (simultaneuosly with FF-detectors).
    4. Test of g-detectors: 1p BaF2 and HPGe detectors.

F. Simulation of the C6D6 detectors for the year 2000

F. Gunsing presented a first layout of the C6D6 detectors for the year 2000 experiments. The analysis of the capture x-section measurements with C6D6 detectors needs an accurate determination of its response functions, and this should be attempted by Monte Carlo simulation. As commented by J.L. Tain, this seems to be a delicate problem and related to the materials surrounding the detector. A complete geometrical description will be distributed as soon as possible.

On the other hand, some general comments on the C6D6 setup were made by F. Gunsing:

G. Other business

N. Pavlopoulos commented on the possibility of creating a PC-farm running Linux for the computing needs of the collaboration. The farm would be maintained by the CERN computing division. Also mentioned was the need for CPU requests to CERN for the PS213.

H. Concluding remarks

I. Actions to be taken


Talk by E. Gonzalez

(simulation group)

Slide 1

Slide 2

Slide 3

Slide 4

Slide 5

Slide 6


Talk by E. Radermacher

Slide 1

Slide 2 PDF2

Slide 3 PDF3

Slide 4 PDF4

Slide 5 PDF5



Talk by F. Gunsing

Slide 1

Slide 2

Slide 3


Talk by E. Gonzalez

(year 2000 experiments)

Slide 1

Slide 2

Slide 3




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