Mimac-FastN - A directional fast neutron spectrometer
Fast neutron detection and their energy measurement is complex, because neutrons are electrically neutral particles, so they can’t be detected directly.
Mimac-FastN is a tight enclosure filled with a neutral gas at roughly the atmospheric pressure, with non-flammable and not regulated matters (so no 3He, no high pressure, no hydrogen, that limit operation in some industrial areas).
Neutrons can interact with the detector gas nucleii. This interaction results in a nuclear recoil : there is a partial energy transfer from the incident neutron to the gas nucleus.
The detector has a very fast sampling camera (40 MHz). Thanks to this camera, the detector provides 3D pictures of the nuclear recoils’ tracks in the gas.
At the same time, the energy deposited in ionization by the nuclear recoil in the gas is measured.
From these two information, tracks and ionization energy, we can calculate the energy of the incident neutron.
Hereafter a drawing of the detection principle :
Developments of Mimac-FastN result from 15 years of gaseous detectors know-how. Some specificities are listed below :
1/ A low noise and fast electronics, that opens the 3D detection field with a good resolution.
2/ The acquisition software, that controls physical events triggers.
3/ The ability of reconstructing the nuclear recoils kinetic energy from the measurement of their ionization energy. This reconstruction is specific to each gazeous mixture, and evolves with ionization energy. The higher the neutron energy is, the higher is the impact of this parameter on the kinetic energy calculation of the incident neutron.
4/ The data analysis software, that allows the selection of the events to consider for the neutron spectrum reconstruction or for the neutron source location.
Mimac-FastN differentiates from existing technologies with its performance that is not limited to neutron counting but also allows their energy measurement, with its mobility, with the 3D approach that gives access to the discrimination of all the physical contributions, and with its directionnal feature.
The proof of concept has been conducted in monoenergetic neutron fields, with a small mobile prototype, with data acquisitions of 1 hour.
Use cases are currently explored, for applications as diverse as detection of fissile matter in radioactive waste, characterization of atmospheric neutrons, or neutron dose measurements in industrial areas using neutron sources.
Reference : Article published in the NIM journal : https://doi.org/10.1016/j.nima.2020.163799
Nadine Sauzet : Scientific & technical responsible, simulations & data analysis
Olivier Guillaudin : Detector developments, micromegas & drift field cage
Marc Marton : 3D design, production & assembly
NEWS-G - New Experiment With Spheres-Gas
- Design, elaboration and tests of gaz detector prototypes for beam profile measurements in conformational radiotherapy
- Patent co-author
- High throughput data acquisition
On the LOHENGRIN experiment installed at ILL (Laue Langevin Institut), the SDI opearted on of a double small detector with neutrons manufacturing, with reading of current on the anodes XY wires composed of 4 cathode plans and of 8 anode plans (outside dimensions 75 mm × 38 mm), the useful window of detection of 20 mm by 20 mm. This activity, which took place in the year 2007, corresponds to :
- The manufacturing of 4 cathodes plans stuck, that is 4 times 2 frames FR4/Cu, 2 faces of 16/10 of mm of thickness. These two frames are in coincidence with, in the middle, a window of Mylar aluminised, 2 faces of 23 µm, with the HV supply contacts.
- The weaving of 2 wires plans (aluminum frames 250 × 140 × 10 mm). The wires are W/Au/Re of 30 µm, with a tension of 30 g, a tep of 1 mm, that is 115 wires/frame, for transfer on frames anodes.
- The transfer, the welds and the cuttings of the wires on the frames pads of XY anodes. There is 4 XY groups, that means 8 frames of FR4/Cu, two faces of 16/10 of thickness.
Martin Puplett Interferometer
For the CMB Survey (Cosmic Microwave Backgroung), the experiments have for objective the measurement of the polarization of the radiation.
On the other hand, the LPSC, in association with the Ultra low Température group at Louis Neel Institute (ex CRTBT), was responsible for the manufacturing project of the mechanical part of an Martin Puplett interferometer (MPI, photo), this device was dedicated to the tests of arrays in the millimetric and submillimétric length domain.
In 2004, the department participated actively in the sizing of the interferometer and in the specification of components. The department of study and mechanical realization of the LPSC then designed and realized all the parts of the Martin Puplett during year 2005. The final assembly and the installation at CRTBT took place in December, 2005 (collaboration of the SDI and the engineering workshop).
Contact : Myriam Migliore