CUP – a new high-flux irradiation position
at the ANITA neutron facility at TSL
A.V.
1The
1
Prokofiev ,
E.
1
Passoth ,
A.
2
Hjalmarsson ,
and M.
3
Majerle
Svedberg Laboratory, Uppsala University, Sweden. E-mail: [email protected]
2Department of Physics and Astronomy, Uppsala University, Sweden
3Nuclear Physics Institute of ASCR, Rež near Prague, Czech Republic
A new irradiation position has been constructed, characterized, and put into operation at the ANITA facility
for accelerated neutron SER testing. The neutron flux, ≈107 cm-2s-1, is the highest among facilities with
atmospheric-like spectrum.
Introduction
Characterization of the ANITA-CUP neutron field
One of the recent trends in SER testing is a growing need in intense fields of highenergy neutrons, which would allow one to observe less frequent events and to
accumulate sufficient statistics of events in shorter times. This need is addressed in the
present work, aimed at development of a new high-flux irradiation position at the ANITA
facility (Atmospheric-like Neutrons from thIck TArget) at The Svedberg Laboratory (TSL).
The new position is further referred as Close User Position (CUP).
The neutron field at the CUP has been characterized with regard to spectral neutron flux and
spatial profiles. Thermal neutron and γ-ray components have been characterized as well.
A schematic layout of the ANITA facility, together with the newly developed CUP, is
presented in Fig. 1. The proton beam from Gustaf Werner cyclotron, with the energy of
approximately 180 MeV, is guided to a 2.4-cm thick 99.8%-pure tungsten target, which
fully stops the incident protons. The target is situated inside a massive bending magnet
in a concrete cave. The neutron beam originates from nuclear reactions induced by
incident protons in the target.
The highest neutron flux at the conventional user area is available at the Standard User
Position (SUP), located at 250 cm distance downstream the ANITA target. The energyintegrated neutron flux above 10 MeV at SUP amounts to 106 cm-2·s-1 for the standard
incident proton beam current of 215 nA on the production target.
 Spectral neutron fluence at the CUP and at the SUP was calculated with the MCNPX code.
 A comparison of the CUP and SUP neutron spectra (see Fig. 4) shows that they are
very similar in the high-energy region, above ~10 MeV. Neutrons with energies below
10 MeV are more abundant in the CUP spectrum than in the SUP one.
 The CUP neutron field simulation has been verified in the following ways:
 We have calculated the ratio of fission event rates in a 238U target located at the CUP
and at the SUP. The calculated ratio (14.4) reproduces satisfactorily an experimental
result obtained using thin film breakdown counters (TFBC) (14.9±0.4).
 We have simulated a time-of-flight (ToF) spectrum of neutron-induced fission events in
a 238U target located at the CUP (see Fig. 5). Satisfactory agreement has been
achieved with experimental data obtained using TFBC.
Fig. 5. Experimental and simulated
ToF spectra of fission events in a
238U target at the CUP.
Fig. 4. The spectral neutron flux versus energy
at the ANITA-CUP in comparison with the
ANITA-SUP and other spallation neutron
facilities, in log-log scale (a) and as a “lethargy
plot” (b). The reference terrestrial neutron
flux, multiplied by 3 × 109, is plotted as well.
Fig.1 . A schematic layout of the ANITA facility with the newly developed Close User Position (CUP).
Description of the ANITA-CUP facility
 The in-beam position of the ANITA-CUP facility is located at the distance of 75 cm
downstream the target, between the bending magnet and the frontal wall (see Fig. 2).
 A vertical access shaft connects the in-beam position to the loading position, located
at the roof of the cave. A rail with a pulley system is installed in the shaft to allow a
DUT, mounted on a trolley sled, to be lowered to the in-beam position (see Fig. 3).
 Energy-integrated neutron flux above 10 MeV at the CUP amounts to 1.15 × 107 cm-2·s-1,
for the standard incident proton beam current of 215 nA on the production target. This is the
highest flux among facilities with atmospheric-like spectrum (e.g. jSUP = 1 × 106 cm-2·s-1).
 By relating this result to the reference terrestrial neutron flux above 10 MeV, an
acceleration factor of 3.2 × 109 has been obtained.
 Spatial profiles of the neutron beam have been measured using a TFBC with a 238U target.
 The neutron field has been found to be uniform within ±10% in the central area of the
beam, 20 cm × 20 cm (see Fig. 6).
 A user may perform testing/irradiation in parallel at the CUP and at the conventional
user area.
Fig. 6.
The spatial neutron beam
profile at the CUP. The
dashed lines represent the
limitations due to the
aperture of the bending
magnet upstream.
Fig. 2. A DUT at the
in-beam position
Fig. 3. A schematic layout of the trolley sled for
mounting of DUT (a). The DUT on its way from the
loading position to the in-beam position (b).
 Thermal neutron flux at the CUP amounts to 2.3*106 cm-2·s-1 (20% of the flux above 10
MeV). The measurement has been performed using a TFBC with a 235U target.
 Gamma dose rate at the CUP amounts to 17 rad/h. The measurement has been performed
with a conventional radiation survey instrument.
Conclusions
The ANITA-CUP neutron facility with atmospheric-like spectrum has been constructed, characterized, and put into regular operation for accelerated neutron SER testing. The
characterization measurements have confirmed the availability of the high neutron flux, the highest among the facilities in the same class. The space available at the CUP is
sufficient for testing of electronic components and smaller-scale systems.