The Bonner sphere spectrometer
serves to determine the neutron fluence
as well as the energy distribution of
neutrons. The spectrometer of the PTB
consists of a set of 12 Bonner spheres
of polyethylene 7.62 cm (3") to
45.72 cm (18") in diameter. In its
centre there are spherical proportional
counters which are filled with
3He gas
and thus are very sensitive to thermalized neutrons. In addition to these, there are four spheres in which lead or copper shells are embedded in the polyethylene; as a result,
the
response of the spectrometer at high neutron energies (>20 MeV) is considerably raised. NEMUS serves as a reference system for the
spectrometry and dosimetry of unknown neutron fields in the wide energy range of thermal neutrons up to about 400 MeV.
The total neutron fluence can be determined by suitable deconvolution methods with uncertainties of 5%. With the aid of recommended conversion coefficients,
dose equivalent quantities (e.g. the ambient dose equivalent, H*(10)) ecan be determined from the neutron spectrum, the uncertainties being normally up to 15%.
The spectrometer was used, among other things, for the measurement at workplaces in nuclear industry and aircraft as well as for the investigation of the neutron component of cosmic radiation on the ground.
Literature:
B. Wiegel, A.V. Alevra and B.R.L. Siebert: Calculations of the Response Functions of Bonner Spheres with a Spherical 3He Proportional Counter Using a Realistic Detector Model, PTB-Bericht PTB-N-21, ISBN 3-89429-563-5 (1994).
B. Wiegel and A.V. Alevra: NEMUS - The PTB Neutron Multisphere Spectrometer: Bonner Spheres and More, Beitrag "International Workshop on Neutron Field Spectrometry in Science, Technology and Radiation Protection", 5.-8. Juni 2000; Nucl. Instrum. Meth. A 476, (2002) 36-41.
http://dx.doi.org/10.1016/S0168-9002(01)01385-7
Contact
Dr. Burkhard Wiegel
Phone: +49 (0) 531-592-6531
e-mail: Burkhard.Wiegel@ptb.de
