Fast Neutron Beam Facility

Experiment set up in fast neutron beam to test Si based solar cells response to radiation
Experiment set up in fast neutron beam to test Si based solar cells response to radiation

The OSURR fast neutron beam facility is able to deliver a reactor-spectrum neutron beam with a diameter of 1.25” (32 mm) and relatively high flux (~ 2E7 nv) that can be used for both thermal and fast neutron radiography and tomography.

The facility is particularly useful for researchers interested in the fields of neutron imaging and its applications such as imaging water flow in fuel cells, mapping hydrogen in metal hydride, lithium distribution in Li-ion batteries, defects in additive manufacturing process, and the general non-destructive testing (NDT) and non-destructive evaluation (NDE). It can also be used to evaluate neutron sensors, rad-hard electronics, and for other neutron sensitive studies.

A 5”-thick bismuth plug is included in the collimator to greatly reduce the gamma dose in the beam, and different external thermal neutron filters can be used to greatly reduce thermal neutrons in the beam. However, when thermal neutron filter is not applied, this beam also provides a high flux of thermal neutrons for research.

A moveable backstop for the facility allows for a maximum experiment setup depth of 2 feet from the collimator exit, with approximately 3 feet of working space from side to side.

Beam facility characteristics

Table listing the characteristics of the fast beam (this is a draft of alt text that needs to be updated later)

Accessories:

A rotating neutron chopper is available with a rotation speed up to approximately 1200 rpm that can produce a train of neutron pulses with a minimum duration of approximately 1 ms.

In addition, a fast neutron tomography setup is available. This automated neutron computed tomography (CT) system has a mobile imaging station which provides researchers with flexibility, efficiency, and reduced imaging time, as well as repeatable experimental setups and runs with online focusing. The imaging apparatus is composed of a water-cooled EMCCD camera, a front-surface mirror, and a high energy neutron-sensitive PVT scintillator, with a customized mobile design and a special on-line focusing feature. A total of 5 motion stages are built into the system to give XYZ and rotational freedoms for sample positioning, and there is another linear stage to fine tune the distance between the camera and the mirror. A customized Python code and user-friendly GUI provides a fully automated imaging acquisition not requiring user interaction but that allows tracking of progress. A complete fast neutron tomography dataset with 360° projections can be acquired in less than 2 hours, with 20 seconds per projection. The on-line focusing is accomplished with a dielectrically actuated liquid lens. The focusing algorithm is written into the code to search for the best spatial resolution by adjusting the applied voltage to the lens. While a spatial resolution of ~ 500 mm has been achieved for fast nCT, our thermal nCT has a resolution around 150 mm.

Beam control and Beam-stop

The beam shutter is a cylindrical drum with lead shot to shield against gamma radiation when the beam is not in use. The majority of the neutron radiation is attenuated by the beam-stop shielding external to the shutter.

The longer segment of the collimator, closest to the reactor core is 42" long and contains graphite, borated cement, MetamicTM, and lead apertures along with a 4" thick bismuth plug to reduce gamma radiation in the beam.

A shorter segment of the collimator has a larger diameter (~7” O.D.) and is situated inside the tube shutter box.

Diagram of Fast Beam Setup
animation of an object turning

 

 

 

 

 

 

 

 

 

The total neutron flux at the beam exit of the fast beam facility without using a thermal neutron filter at a reactor power of 450 kW is 2.3E+07 n/cm2/s. The unfiltered flux is composed of 36% thermal neutrons (En<0.5 eV, 0.8E+07 nv) and 64% epi-cadmium neutrons (En>0.5 eV, 1.5E+07 nv).

This upgraded beam port infrastructure was funded through a Reactor Upgrade Award from DOE NEUP received by the Ohio State University Research Reactor (OSURR). The automated neutron imaging station was built by Mr. Matt Bisbee who is a DOE NEUP Fellow and was partially supported by Lawrence Livermore National Laboratory.

What is fast neutron radiography?

  • Form of non-destructive evaluation (NDE) largely to evaluate interior structures
  • Think X-ray image but with fast neutrons as the source

Why fast neutrons?

  • Highly penetrative of High Z materials but interact  more with low Z materials
  • Higher scatter cross sections, and lower absorption; therefore less activation

What is tomography?

  • 3-D reconstruction from group of 2-D radiographs
  • Improves ability to detect features within sample

Fast neutron imaging is a non-destructive evaluation method that provides contrast in the images based on the elastic scattering cross sections differences of the materials. It has a higher penetration and less activation compared to thermal neutron imaging, which has a potential for spent fuel and dry cast storage canister evaluation.