Neutron Beam Ports
Numerous beam ports penetrate the reactor's shield, graphite reflector, and heavy-water reflector as shown below. These ports provide a high-quality neutron flux for such endeavors as neutron scattering, neutron imaging and tomography, neutron physics, and neutron transmutation doping (NTD). Currently, port 4DH1 is equipped with a neutron chopper facility and time-of-flight neutron spectrometer with remote access capability, used for a number of educational programs, while port 4DH4 is equipped with a neutron diffractometer.
Cutaway view of the MITR showing the radial beam ports.
A thermal neutron beam from a 4” port is used for neutron tomography and radiography. A range of apertures is used to achieve the necessary spatial resolution. L/D ratio of up to 520 has been used. Neutron flux at the sample position is about 2x106 n/cm2/s at L/D = 320. A standard scintillator-based detector is used. It is equipped with a commercial scintillator of 3.75”x 3.75” size, a lens, and a CCD. The sample can be installed on a rotation stage for tomography. A spatial resolution of 30 µm can be achieved. Fig. 1 shows a photograph of the detector and a sample (coin-cell batteries) during recent tomographic measurements. Fig. 2 shows an example of tomographic imaging of a 3-D printed stainless-steel object. Other previous projects included imaging of irradiated hydride fuel rodlets, in-situ radiography of electrolyzer cells, and dynamical imaging of water boiling.
MIT utilizes the 4TH and 6TH horizontal through ports for neutron transmutation doping (NTD) of single crystal silicon. These through ports are tangent to the D2O reflector tank as shown below. The 4TH port can accommodate 4 inch OD samples and the 6TH port can accommodate up to 6 inch OD samples. Automatic conveyer, neutron detectors, and control systems were installed for routine NTD silicon crystal doping as shown in below. These through ports offer high-quality thermal neutron flux and can be used to accommodate larger sample irradiations. There are also two 3” also shown below. These thimbles offer a uniform, thermal flux for an active height of about 24” and are suitable for medium and long-term irradiations.
Cutaway view of the MITR showing the horizontal through ports and the location of the 3GV vertical irradiation facilities in the graphite reflector region.