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The Van de Graaff laboratory

The high intensity quasi mono-energetic neutron source at IRMM is driven by a vertical 7 MV Van de Graaff accelerator producing either continuous or pulsed ion beams. The installation has two pulsing systems:

  1. a fast beam pulsing generating a minimum ion beam pulse width of 2 ns and pulse repetition rates of 2.5, 1.25 or 0.625 MHz, and

  2. a slow pulsing system giving a minimum pulsing width of 10 μs at an adjustable frequency up to 5 kHz.

The neutron fields that have well defined energies are produced by the nuclear reactions Li(p,n), T(p,n), D(d,n) or T(d,n) giving neutrons within the energy regions 0.3 – 10.0 MeV and 14.5 - 24 MeV.

The IRMM Van de Graaff facility houses six experimental set-ups in two large laboratory halls. The accelerator is operated 24 hours a day and seven days a week and it provides a stable neutron field for more than a week without interruption. Neutron fluxes and neutron energy spectra are monitored and characterised with high precision by long counters, proportional counters, BF 3 counters, Bonner spheres, time-of-flight systems, fission chambers and activation foils. Absolute neutron fluencies are measured using a calibrated recoil proton telescope. Several shadow cones are available for measurements of possible neutron scattering.

Characteristic neutron fluence rate

EnergySet calculator[595Kb] - EnergySet is a program developed by IRMM that calculates neutron energy spectra and fluencies for the most commonly used nuclear reactions for production of quasi mono-energetic neutron fields. The program uses kinematics for real-time neutron spectrum calculations as a function of ion energy, neutron emission angle, reaction target thickness, measurement distance and ion beam current. Also related accelerator parameters are calculated. All files needed to run the program are in this .zip file, which you can download for your personal use.

NeuSDesc calculator[1041Kb] - NeuSDesc is an extended version of the EnergySet program including the option of creating an MCNP input file containing the description of the neutron field at an arbitrary surface in space. NeuSDesc does not, however, provide any accelerator parameters. NeuSDesc requires SRIM-2008 installed on the PC to be fully operational.

Typical spectra[140Kb]

Experimental hall

Latest update 1 March, 2006

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