Gallego Díaz, Eduardo; Amgarou, Khalil; Bedogni, Roberto; Lorente, Alfredo; Mendez, Roberto; Vega Carrillo, Héctor René
Resumen:
An automated panoramic irradiator with a 3 Ci 241Am-Be neutron source is installed in a bunker-type large room
at the Universidad Politécnica de Madrid (UPM). It was recently modified and a neutron spectrometry campaign
was organized to characterize the neutron fields in different measurement points along the irradiation bench.
Four research groups working with different Bonner Sphere Spectrometers (BSS) and using different spectral
unfolding codes took part to this exercise.
INFN–LNF used a BSS formed by 9 spheres plus bare detector, with cylindrical, almost point like, 6LiI(Eu)
scintillator (4 mm x 4 mm, from Ludlum); UAZ-UPM employed a similar system but with only 6 spheres plus
bare detector; UAB worked with a 3He filled proportional counter at 8kPa filling pressure, cylindrical 9 mm x
10 mm (05NH1 from Eurisys) with 11 spheres configuration; and CIEMAT used 12 spheres with an spherical
3He SP9 counter (Centronic Ltd., UK) with very high sensitivity due to the large diameter (3.2 cm) and the
filling pressure of the order of 228 kPa.
Each group applied a different spectral unfolding method: INFN and UAB worked with FRUIT ver. 3.0 with
their own response matrixes; UAZ-UPM used the BUNKIUT unfolding code with the response matrix UTA4
and CIEMAT employed the GRAVEL-MAXED-IQU package with their own response matrix.
The paper shows the main results obtained in terms of neutron spectra at fixed distances from the source as well
as total neutron fluence rate and ambient dose equivalent rate H*(10) determined from the spectra. The latter are
compared with the readings of a common active survey-meter (LB 6411). The small differences in the results of
the various groups are discussed.