The Neutron Transmission Radiography (NEUTRA) Station at PSI

The neutron radiography (NR) facility of PSI, the Neutron Transmission Radiography (NEUTRA) station is under operation at the spallation source SINQ since 1997. The aim of NEUTRA is to provide a state-of-the-art tool for scientific and industrial NR-applications. It is designed as user facility for scientists from abroad too.
NEUTRA is located at a thermal beam port of SINQ and consists of the following elements:

• The collimator which is divided into a convergent and a divergent part separated by a Bi-filter. The convergent part limits the view from the collimator towards the neutron source, i.e. the moderator tank around the spallation target to an area of relatively homogenous flux. The Bi-filter reduces the gamma-ray contamination of the beam. Neutrons passing through the filter enter the divergent collimator through an initial circular aperture of 2 cm of diameter. The divergent collimator is 11 m long and consists of a divergent channel leading through the bulk shielding around the source and of a divergent evacuated tube, which continues the collimator outside the bulk shielding. It contains 5 additional circular blinds, which define the beam path. The beam can be shut off by turning 6 rotating iron drums inside the collimator.
  
  

• The shielded station in which the measurements are performed: the collimator ends at the position where objects will be observed, which is surrounded by concrete shielding and contains the object-positioning device, the detector-positioning device and a beam catcher where the beam ends. The positioning devices consist of modular sets of frames that can be adapted to a great diversity of objects and to different detectors. It can be moved remotely with the sample from outside the shielding. A special rotating desk is used for tomography experiments.
  
  

• The detector systems - four detector systems are available at NEUTRA presently: a track-etch film/converter device, a silver halide film / Gd- converter device, a imaging plate detector and an electronic detector based on the combination of a scintillator screen with a nitrogen-cooled CCD camera.
  
  

• A so-called "Local Access Control" system is protecting the users against the hazard of direct exposure of human body by a uncontrolled opening of shutter systems.
  
  

Position for experiments

Generally, three positions can be used inside the shielded area along the beam line for different purposes:

Position 1: close to the target wall - best suited for time resolved investigations where the demand for spatial resolution is not superior.

Position 2: at an interim position, where a thick iron shielding enables the inspection of highly activated samples.

Position 3: at the end of the beam line, where highest collimation and beam diameter enables the best spatial resolution and a large field of view.

The performance characteristics are presented in the following table:

A more detailed description of the design of the station can be found in

E. Lehmann, H. Pleinert and L. Wiezel:"Design of a neutron radiography facility at the spallation source SINQ", Nuclear Instruments and Methods A 377 (1996) 11-15.
and
E. Lehmann, P. Vontobel, L. Wiezel, Properties of the Radiography Facility NEUTRA at SINQ and its Potential for Use as European Reference Facility, Proc. 6th World Conference on Neutron Radiography, Osaka, 1999.