Research and Development tasks


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I. Monte Carlo simulation and detector design

 

Task Description

Review and validation of Monte Carlo simulation tools

Not every simulation tool is well designed for every task. It has been decided to adopt the following standard Monte Carlo codes for the working group simulations: GEANT4 (mainly for the TOF spectrometer) and MCNP(X) (mainly for the 4p detector). Even though both codes are tested and supported (MCNPx in particular for neutrons), one should not trust completely the results obtained. In particular, the built in physics models and transport methods. Thus, the capabilities and characteristics of each code should be described.

Validation of neutron cross section libraries for neutron detector design

The accuracy of the Monte Carlo results depends on the

It is necessary to upgrade (extend or replace the existing files) the cross section files in GEANT4 for a proper neutron transport treatment. There are two possible strategies:

a) Understand the GEANT4 cross section library format (tabulated point-wise cross sections, Doppler broadened?) and generate the appropriate files for all isotopes from the ENDFB7, JENDL 3.3 and JEFF 3.2. Write a simple tool to prepare an alternative library distribution (for the isotopes of interest)

b) Write an interface which allows GEANT4 to read standard ENDF formatted files

Correlated particle production physics models

Event generators and internal physics processes.

a) b-decay generator: gammas and conversion electrons

b) capture physics model with appropriate gamma correlations (conservation of energy) and realistic EM de-excitation patterns

c) fission generator for producing correlated gamma and neutron emission.

Scintillation process models (for scintillators)

Light production models for different ions: transform the dE/dx into dL/dx as a function of the ionising particle (protons, deuterons, He-3, alphas, Li-6, C-12...)

Light collection: simulate the light collection for a proper neutron detector cell design.

Response of gaseous detectors

Ionisation and border effects for a correct simulation of the detection efficiency with MNCP(X) and eventually GEANT4

Background suppression

a) flash from the Bremsstrahlung in the implantation setup.

b) coincident gamma background: from the decay itself and from neutron scattering in the active and passive materials (implantation setup, detector housing...)

c) natural room background.

d) cosmic radiation.

Tracking algorithms

TOF spectrometer

For cross talk rejection, multiplicity reconstruction, background rejection.

4p detector

Time/energy/space relation (with position sensitive detectors), pileup discrimination, neutron gamma separation

Analysis software

The Monte Carlo data can be used for definining appropriate analysis software tools to be applied in the real experiments.

Benchmarking with simple test experiments

All  Monte Carlo results should be validated with simple test experiments, ranging from the comparison of the individual cell response to a real beta decay experiment.

Design of the optimal detectors

TOF spectrometer

Dimensions and materials of the liquid scintillator cells. Diameter, thickness, size of the PMT, reflector materials.

4p detector

Dimensions of the inner hole, moderator, number of BF3 and 3He detector rings, need of position sensitivity, incident neutron energy reconstruction

Simulation of  complete experiments

Simulate the effect of all setups:

a) Implantation setup. Effect of the active and passive materials on the neutrons.

b) Ge array, Cross talk and combined neutron/gamma detection efficiency.

 

 

II. Neutron detector testing and construction

 

Task Description

Research and development on new solid/liquid scintillators.

With high intrinsic efficiency, good time and energy resolution, pulse shape discrimination capabilities, safer chemical properties (toxicity and flammability).

Characterisation of material properties

Scintillation modes: characterisation of the different light components with fast PMT and digital electronics.

Light yield: characterisation of the dL/dE (Erecoil) for different recoiling particles (electrons/positrons, protons, deuterons, tritons, 3He, alphas, 6Li, 12C, 16O...), including its proportionality, linearity and temperature dependence, Particle identification capabilities: lowest En and highest En.

Radiation hardness, chemical stability...

Solid and liquid scintillators

Signal readout, noise reduction, linearity, position sensitivity, light collection and optical coupling, detection efficiency, time and energy resolution.

Gas detectors

Position sensitivity, efficiency, optimal structural materials (Al, Cu, stainless steel?)

Detector geometry and electronics

TOF spectrometer

Definition of the cell dimensions, expansion volume, the structural materials (metallic or organic with low neutron interaction cross sections), optical contact (windows, light guides), fast or slow photomultiplier tubes, time and energy resolution, granularity of the array, recovery time after the "flash" saturation.

4p detector

Size of the detector, efficiency, time resolution (moderation time), geometry, moderator materials (polyethylene), efficiency and characteristics of the individual gas detectors, recovery time after the "flash" saturation.

General aspects

Neutron moderators and absorbers

Detector construction

It is still to be decided if the TOF spectrometer cells will be "home-made" or built in collaboration with a company. About 150 cell units will be necessary.

The supporting structure are not yet designed. They should be stable and made of neutron transparent materials: Al, carbon fiber, thin stainless steel plates?

Background suppression mechanisms

Neutron/gamma/particle discrimination, neutron shielding materials, cosmic rays.

 

 

III. Digital signal processing and analysis

 

Task Description

Definition of the needs and specifications

Dynamic ranges, time resolution, pulse height resolution, linearity, sampling rate and bandwith.

There are two philosophies under discussion:

a) have the digitiser board next to the detector (for reducing the noise and the use of long and costly low noise cables), perform the pulse shape analysis on the board on a DSP (data reduction) and send the few parameters for each event to a "event building" unit. Such a board should be capable of sending the digital "raw" data as well for testing or debugging purposes (oscilloscope mode).

b) connect the detectors via long cables to multi-channel digitiser modules coupled to a CPU (PCs, VME processors). Such a solution guarantees the upgrading of the CPUs on demand and is not limited by the on-board DSP.

Development of compact digitiser boards for its operation close to the detector

ADC + FPGA + DSP + data bus. Digitiser boards close the each detector.

Development of multi-channel digitiser modules a few meters away from the detector

ADC + FPGA + simple DSP + CPU (PC or equivalent) + data bus, noise pickup.

Development of associated front end electronics

Trigger and timestamp modules, event builders. Definition of the data bus from the board to the collector/processor unit and the bus on which the collector/processor is sitting (PCI, VME???)

Development and optimisation of pulse shape analysis and data reduction algorithms

Pileup reconstruction, particle identification, lossless compression. The capabilities of the algorithms will depend strongly on the solution adopted: small or large CPU capabilities.

 

 

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