READOUT SYSTEM FOR ARRAYS OF FRISCH-RING CDZNTE DETECTORS. Page: 3 of 7
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Readout System for Arrays of Frisch-ring CdZnTe
Y. Cui, Member, IEEE, A. E. Bolotnikov, Member, IEEE, G. S. Camarda, G. De Geronimo, Member, IEEE, P.
O'Connor, Member, IEEE, R. B. James, Fellow, IEEE, A. Kargar, M. J. Harrison, and D. S. McGregor
Abstract - Frisch-ring CdZnTe detectors have demonstrated
good energy resolution for identifying isotopes, <1% FWHM at
662 keV, and good efficiency for detecting gamma rays. We will
fabricate and test at Brookhaven National Laboratory an
integrated module of a 64-element array of 6x6x12 mm3 Frisch-
ring detectors, coupled with a readout electronics system. It
supports 64 readout channels, and includes front-end electronics,
signal processing circuit, USB interface and high-voltage power
supply. The data-acquisition software is used to process the data
stream, which includes amplitude and timing information for
each detected event. This paper describes the design and
assembly of the detector modules, readout electronics, and a
conceptual prototype system. Some test results are also reported.
Keyword - CdZnTe, Data Acquisition System, Frisch-ring
C dZnTe (CZT) is very attractive material for room-
temperature semiconductor detectors due to its wide
bandgap and high atomic number . However, CZT
detectors are typically single-charge-carrier devices because
holes have poor mobility. Thus, to achieve high-energy
resolution, techniques for designing special detectors are
required, such as pixilated, co-planar grid, and virtual Frisch-
grid devices . Since the introduction of the first Frisch-ring
CZT detector , a variety of similar devices were designed
and tested. Our group in Brookhaven National Laboratory has
expended efforts in improving the performance of the Frisch-
ring CZT detectors; our most recent work focused on the non-
contacting Frisch-ring detector -. The unique features of
this configuration are its simplicity, yet outstanding spectral
performance . Its form allows us to build an inexpensive
large-volume detector array, which has high energy resolution
and a large effective area.
On the other hand, compact efficient radiation spectrometers
are needed in non-destructive detection, radiation imaging, and
homeland security (for example, non-proliferation safeguards,
custom inspection, and radiation field survey). Most of these
applications desire an instrument with compact size, room-
temperature operation, high gamma-ray energy resolution and
Manuscript received October 30 2006. This work was supported by the
U.S. Department of Energy under Grant No. DE-AC02-98CH1-886.
Y. Cui, A. E. Bolotnikov, G. S. Camarda, G. De Geronimo, P. O'Connor,
and R. B. James are with Brookhaven National Laboratory, Upton, NY 11973
USA (telephone: 631-344-5351, e-mail: email@example.com).
A. Kargar, M. J. Harrison, and D. S. McGregor are with Kansas State
University, Mahattan, KS 66506 USA (telephone: 785-532-5284, e-mail:.
absorption efficiency, and low cost. The devices presently
used for portable gamma ray spectroscopy include NaI(Tl)-
based detectors and portable high-purity germanium (HPGe)
detectors, yet neither of them fulfill the requirements.
Gamma-ray spectrometers based on CZT detectors have been
developed in the past; they either are very expensive or have
low gamma-ray absorption efficiency. Our improvements on
the Frisch-ring technique makes it possible to assemble a
detector array that meets the above requirements.
Recently, our group at Brookhaven National Laboratory
designed a 64-channel gamma-ray spectrometer utilizing the
non-contacting Frisch-ring detectors. Our goal is to
demonstrate the feasibility of employing such a detector in a
hand-held or portal systems. A detector module of Frisch-ring
detector array has been designed and assembled in our
laboratory. The readout electronics design is done. By using
the Multiple Input/Output System (MIOS) developed by
BNL's Instrumentation Division, a conceptual prototype
system has been built. In this paper, we describe the system
design and detail the assembly of the detector module. The
results from testing several detectors are reported, which help
us to characterize the performance and determine the structure
of our final compact spectrometer system.
II. DETECTOR MODULE
To install the system more easily, we divided 64 CZT
crystals into a series of detector modules, each consisting of a
A small printed circuit board (PCB board) served as the
substrate of the detector module. To reduce the parasitic
capacitance of the traces on this PCB board, the substrate was
made out of Rogers 4003 material. On one side of the
substrate, there is a 4x4 array of gold-plated square pads (3
mm x 3 mm) with a pitch between them of 5.5 mm. On the
other side, there are two mini connectors to the preamplifier
board. As shown in Fig. 1, manually wrapped Frisch-ring CZT
crystals were glued onto the pad using conductive epoxy resin.
To ensure a good connection between the crystal and the pad,
the pad side of the substrate was grooved so there were slots,
1.5 mm wide and 0.7 mm deep, between pads. On the top of
the crystal, high voltage is applied to the cathode through a
copper tap, which also is glued to the crystal using epoxy. All
the detector cathodes in the array share the same high voltage
supply, and all the copper shields are connected to the signal
ground of the system.
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CUI, Y.; BOLOTNIKOV, A.E.; CAMARDA, G.S.; DE GERONIMO, G.; O'CONNOR, P.; JAMES, R.B. et al. READOUT SYSTEM FOR ARRAYS OF FRISCH-RING CDZNTE DETECTORS., article, October 29, 2006; [Upton, New York]. (digital.library.unt.edu/ark:/67531/metadc882283/m1/3/: accessed April 19, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.