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Thermal Neutron Detectors with Discrete
Anode Pad Readout
B. Yu, N. A. Schaknowski, G.C. Smith, Senior Member, IEEE G. De Geronimo, E.O. Vernon, L.G. Clonts,
C L. Britton, Member, IEEE, and S.S. Frank.Abstracr-A new two-dimensiona] thermal neutron detector
concept that is capable of very high rates is being developed. It is
based on neutron conversion in 3H1 in an ionization chamber
(unity gas gain) that uses only a cathode and anode plane; there
is no additional electrode such as a Frisch grid., The cathode is
simply the entrance window, and the anode plane is composed of
discrete pads, each with their own readout electronics
implemented via application specific integrated circuits. The aim
is to provide a new generation of detectors with key
characteristics that are superior to existing techniques, such as
higher count rate capability, better stability, lower sensitivity to
background radiation, and more flexible geometries. Such
capabilities will improve the performance of neutron scattering
instruments at major neutron user facilities. In this paper, we
report on progress with the development of a prototype device
that has 48 x 48 anode pads and a sensitive area of 24cm x 24cm.
I. INTRODUCTION
Several new user facilities, with an order of magnitude more
neutron flux than previously available, are being built or
have been recently commissioned, e.g. J-PARC in Japan, the
Spallation Neutron Source (SNS) at Oak Ridge National
Laboratory, and the OPAL research reactor at the Australian
Nuclear Science and Technology Organization. The beam-
lines at these facilities will ultimately require detectors with
much higher rate capability than presently achievable [1], with
Manuscript received November 20, 2008. This work was supported by the
Ofce of Basic Energy Sciences of the U.S. Department of Energy (DOE) and
also by U.S. DOE: Contract No. DE-AC02-98CH10886 at Brookhaven and
U.S. DOE: Contract No: DE-AC05-000R22725 at Oak Ridge.
B. Yu is with the Instrumentation Division, Brookhaven National
Laboratory, Upton, NY 11973-5000 (tel: 631 344 5184, e-mail: yu@bnl.gov).
N.A. Schaknowski is with the Instrumentation Division, Brookhaven
National Laboratory, Upton, NY 11973-50000 (tel: 631 344 4261, e-mail:
neildbnl.gov).
G.C. Smith is with the Instrumentation Division, Brookhaven National
Laboratory, Upton, NY 11973-5000 (tel: 631 344 4253, e-mail:
gsmithfbnl.gov).
0. De Geronimo is with the Instrumentation Division, Brookhaven
National Laboratory, Upton, NY 11973-5000 (tel: 631 344 5336, c-mail:
degeronimocbnl gov).
E.O. Vemon is with the Instrumentation Division, Brookhaven National
Laboratory, Upton, NY 11973-5000 (tel: 631 344 2416, e-mail:
cvemondbnl.gov).
L.G. Clonts is with the Engineering, Science and Technology Division,
Oak Ridge National Laboratory, Oak Ridge, TN 37831-6475 (tel: 865 576
4421, e-mail: clontslg@ornl.gov).
C.L. Britton is with the Engineering, Science and Technology Division,
Oak Ridge National Laboratory, Oak Ridge, TN 37831-6006 (tel: 865 576
28 13, e-maiu: brittoncl@oml.gov).
S.S. Frank is with the Engineering, Science and Technology Division, Oak
Ridge National Laboratory, Oak Ridge, TN 37831-6006 (tel: 865 574 7660, e-
mail: frankss~aornl.gov).also an emphasis on dynamic studies over wide time-slice
scales.
II. ANODE PAD READOUT
Our group has broad experience with development of 3He
filled wire chambers for position-sensitive thermal neutron
detection [2]. In general, these existing instruments begin to
exhibit dead-time losses at global rates above 10' s-. Some
approaches to improving upon this would be a much higher
degree of parallelism in the readout, and ensuring the physics
of the signal development will permit high local rates. A
highly segmented anode plane and operation of the chamber
with unity gas gain are suitable approaches; our initial studies
of small ionization chambers with pad readout [3,4] have been
successful. The basic features are described below.
Fig. I illustrates the detector geometry, the anode taking the
fonm of independent pads (all connected to their own
preamplifier), with spacing a. The separation of the anode
plane from the cathode (or window), d, defines the depth of
the neutron conversion region. With the orange pad denoted
as the sensing electrode (pad), the weighting field concept [5]
determines the equipotential lines shown in blue. A uniform
field (typically 1kV/cm) is applied across the conversion
region, and an electron cloud drifting at constant velocity from
the window will therefore induce the majority of its charge
only as it closely approaches the sensing pad.Sno ' Pae
/
-1l/
4/
N/t
N -
-- -Fig. 1. The blue lines represent the weighting potential inside the detector
for the sensing electrode (pad) denoted in orange. An electron cloud drifting
in the unifonn electric field from the window to the orange pad induces most
of its charge on the sensing pad only as it closely approaches that pad.
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Yu,B. & Schaknowski, N.A., Smith, G.C., DeGeronimo, G., Vernon, E.O. Thermal Neutron Detectors with Discrete Anode Pad Readout, article, October 19, 2008; United States. (https://digital.library.unt.edu/ark:/67531/metadc926623/m1/3/: accessed April 17, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.