Neutron Irradiation

TRIUMF makes use of three separate locations to perform neutron irradiations. The TNF facility offers energies from Thermal to 400 MeV at high intensity while at BL1B and BL2C, protons can be converted into neutrons yielding 1/E energy spectra up to 480 and 120 MeV, respectively. Each year, companies from around the world test many different types of devices, ranging from avionics to ground-based electronic systems such as network and power-distribution servers, or even the latest cell-phone chips. Neutron flux is monitored with BF₃ counters and dosimetry is regularly performed using activation foils of nickel, aluminum, carbon, and gold. The beam characteristics, sizes and intensities that are available at NIF are summarized below.

TNF Neutrons

The final beam stop on the high-intensity beam line BL1A produces neutrons from the spallation reaction of 100-150 µA of 400 to 450 MeV protons on an aluminum plate absorber surrounded by a water moderator. Neutron channels transport these neutrons through the shielding surrounding the TNF.  Initially thermal neutrons were used for a neutron scattering experiment on one of these channels. In 2002 the energy spectrum of these neutrons was measured to determine the greater than 1 MeV neutron component.

The flux of neutrons at the normal operating currents on BL1A is 6×10⁶ neutrons/cm²/s above 1 MeV, comparable with the neutron flux at the LANSCE neutron radiation-effect line, and has energies extending to about 400 MeV as shown in the neutron spectrum. Thermal neutrons are also present if desired; they can be easily removed using a cadmium shield. Beam specifications are available in this Table.

Access to this neutron beam is available for roughly 3000 hours per year as a symbiotic operation with BL1A. At TNF, the physical space for devices is limited: device size must be smaller than 15 cm thick and 25 cm wide.

The TNF plan view is shown below and gives the layout of the testing area.  There is also a separate counting room available to the users.  The neutron beam is accessed from 5 m above the beam through a vertical slot in the shielding.  Devices to be tested are mounted on a movable-trolley plate which is then lowered into the neutron beam on a cable.  The neutron-beam size obtained using radiochromic film is shown below in the neutron-beam picture.  There is no neutron-beam blocker.  The device is simply lowered into the beam and then raised out of the beam once the desired fluence is reached.

BL1B and BL2C

Neutrons can be produced in the present Proton Irradiation Facility (PIF) area by stopping energetic protons from either BL1B or BL2C on a fully absorbing beam stop and setting up downstream of the beam stop. The resulting neutron spectra have a 1/E falloff of flux with energies up to the proton energy.  Beam specifications are available in this Table.

The neutron flux and energy spectrum has been measured for different proton energies and a few geometries using a combination of Bonner spheres and carbon-foil activations. These neutrons have already been used to test various types of neutron dosimeters and to check for neutron radiation effects in sensitive electronics.

The sea-level neutron flux is approximated at 20 neutrons/cm²/hr above 10 MeV. The neutron flux produced by stopping 3 nA of 120 MeV protons on a lead absorber, at a location 1.4 m downstream, is about 5×10⁴ neutrons/cm²/s which is approximately 10⁷ times higher than the sea-level neutron flux, allowing rapid testing of electronic components or detectors.