ROSPEC - A SIMPLE RELIABLE HIGH-RESOLUTION NEUTRON SPECTROMETER

A first prototype of ROSPEC (Rotating Spectrometer) was constructed ov er 10 years ago with the aim of achieving a high resolution neutron sp ectrometer for radiation protection applications around sources of fis sion neutrons. Studies have confirmed that the main contribution to do se equivalent from such neutrons involve those over the energy range 5 0 keV to 4.5 MeV. Thus, a neutron spectrometer spanning this energy ra nge would be adequate for the intended purpose. The selected sensors f or ROSPEC were four spherical gas counters filled with different press ures of hydrogenous gas. The pressures were selected to cover four sep arate energy segments within 50 keV to 4.5 MeV with generous overlap b etween adjacent energy segments. The sensors rely on hydrogen recoil f rom elastic neutron scattering. Low energy recoil protons whose pulse heights were contaminated with gamma-induced signals were not used. La rge signals from recoil protons whose ranges were comparable to the de tector size were also rejected because of distortion of the theoretica l response function. The first ROSPEC prototype was successfully used to determine the neutron spectra for several radiation fields of dosim etric interest. However, the analyses of the data required spectroscop ic expertise. In recent years, the enormous advances in electronic min iaturisation and computer power has allowed the re-design of the proto type spectrometer into a compact reliable, user-friendly instrument. D ata acquisition and spectral unfolding can now be done with simple com puter commands, transforming ROSPEC from a specialist tool to an every day routine instrument for radiation protection. Typically, a reliable spectral measurement can be done over periods of hours, e.g. overnigh t Over the past few years, several ROSPECs have been built for various groups who have used them to measure an enormous number of neutron sp ectra of interest to military and nuclear power applications. These sp ectra are providing a detailed understanding of important neutron inte raction processes and a scientific basis for choosing personal neutron dosemeters for a variety of radiation environments. ROSPEC has alread y been accepted as the reference neutron spectrometer for NATO experim ental studies. It is now rapidly being adopted as a reference secondar y standard for neutron dosimetry in nuclear institutions.