The ORELA is a powerful electron accelerator-based neutron source located in the Physics Division of Oak Ridge National Laboratory. It produces intense, nanosecond bursts of neutrons, each burst containing neutrons with energies from 10e-03 to 10e08 eV. ORELA is operated about 1200 hours per year and is an ORNL User Facility open to university, national laboratory and industrial scientists. The mission of ORELA has changed from a recent focus on applied research to nuclear astrophysics. This is an area in which ORELA has historically been very productive: most of the measurements of neutron capture cross sections necessary for understanding heavy element nucleosynthesis through the slow neutron capture process (s-process) have been made at ORELA.

Measurement Capabilities

Many types of neutron cross section measurements (total, capture, fission, elastic, scattering, and gamma ray and neutron production) can be made at this facility with extremely good energy resolution. The time-of-flight method is used to determine the energy of the interacting neutron. Detector calibrations and measurements of detector responses to neutrons are also performed, and with a flux peaked around 1 MeV neutron energy, ORELA is ideal for many types of radiation damage and activation studies.

The Facility

The facility consists of a 180-MeV electron accelerator, neutron producing targets, buried and evacuated flight tubes up to 200 m long leading to underground detector locations, a wide variety of sophisticated detectors, and data acquisition and analysis systems. Neutrons are produced by bremsstrahlung from a tantalum radiator. Moderated or unmoderated neutrons are available, and further tailoring of the spectral shape is done with movable filters. Pulse widths from 4 - 30 nanoseconds are available at a repetition rates from 12 - 1000 pulses per second. There is one remaining facility in the world similar to ORELA, located in Belgium.

Facility Details

    Electron energy               180 MeV maximum
    Peak Current                  20 amps maximum
    Power on target               60 kW maximum
    Electron beam diameter        1 cm
    Neutron targets               Ta with H2O moderator
                                  Be block (En > 1 MeV)

    Neutron production            10e11 neutrons/pulse
         (Ta target)              10e14 n/sec at 50 kW
                                  5 X 10e18 n/sec (peak)

    Neutron spectrum              4 X 10e13 n/MeV/sec at 1 MeV
         (Ta target)              4 X 10e10 n/MeV/sec at 14 MeV

    Number of flight paths        10
    Number of flight stations     18
    Flight path lengths           9 to 200 m

P. E. Koehler
Bldg 6010, MS-6354
Oak Ridge National Laboratory
Oak Ridge, TN 37831-6354
Phone: (865) 574-6133
FAX: (865) 576-8746
Internet: koehlerpe@ornl.gov

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