This document summarizes the Simbol-X AntiCoïncidence detector, which is being developed by the APC Laboratory in Paris. The AntiCoïncidence detector consists of plastic scintillator plates read out by multi-anode photomultipliers via optical fibers. It aims to tag cosmic ray protons passing through the detector field of view in order to generate veto signals for the main detectors. The detector design includes upper and lower sections, with electronics to amplify and digitize signals above threshold from the photomultipliers. A muon telescope is being used to test performance of detector components and optimize the AntiCoïncidence concept prior to integration onto the Simbol-X payload.

1. 24. The Simbol-X AntiCoïncidence
J. Chabaud, P. Laurent, S. Colonges, J. Barbay, J.P. Baronick, M. Benallou,
P. Ferrando, M. Gilliot, J.J. Jaeger, M. Nicolas, E. Ollivier, J. Waisbard and
B. Yoffo
Laboratoire APC - AstroParticules & Cosmologie, Bâtiment Condorcet, 10 rue Alice Domon et
Léonie Duquet, 75205, Paris Cedex 13
Abstract. The Simbol-X telescope will be constitued by two satellites in formation flight. One will
host the mirror module and the other the detector payload. This payload will be built with two main
detectors able to measure the position, energy and arrival time of each focused photon, between
0.5 and 80 keV. The high sensitivity required by Simbol-X will necessitate low noise background
detectors. To achieve this goal, those detectors will be surrounded by a passive graded shield, aimed
to stop the out of field of view photons, and an active anticoïncidence system to tag the passing
particles. This anticoïncidence detector, whose conception, optimisation and realization are under
responsibility of th APC Laboratory, Paris, is based on plastic scintillator plates associated to multi-
anodes photo-multipliers via optical fibers. In this paper, we will present the present status of the
anticoïncidence system and its expected performances.
Keywords: Simbol-X, Anticoincidence, muon telescope
PACS: 95.55.Ka, 95.55.Vj, 95.85.Nv, 95.85.Ry
1. THE ANTI-COÏNCIDENCE DESCRIPTION
The Anti-Coïncidence (AC) has been conceived, optimised and will be realized by the
APC laboratory. The AC mainly aims to stop photons not coming from the telescope
field of view, and to detect protons passing through the Simbol-X focal plan assembly.
These protons, detected by a plastic scintillator, are tagged and a veto signal is generated
and sent to the low and high energy detectors. A passive shielding allows stopping high
energy photons and their resulting fluorescence.
FIGURE 1. AC description

2. 2. MECHANICAL ARCHITECTURE
The Anti-Coïncidence is divided into two parts: the upper and lower AC (see figure
1). Each part is composed by scintillator plates (five for the lower AC, and eight for the
upper ones), read by wavelenght shifting optical fibers. The plates will be packaged with
a special material in order to optimize the light output. The light collected by the fibers is
transported to a multi-anod photomultiplier Hamamatsu R7600-M16. Optical fibers are
grouped by four before to be read by a photomultiplier pixel. A tantalum passive shield,
1.5 mm thick, is implemented on each side of the scintillator plates, in order to stop the
out of field of view photons. The internal part, faced to the Simbol-X main detectors,
LED and HED, is protected by a graded shield, made of tin, copper, aluminium, and
carbon.
3. ELECTRONIC ARCHITECTURE
The multi-anodes photo-multipliers current will be amplified by the AC Front End
Electronics (ACFEE), placed just behind. This current is then compared to a threshold,
ajustable thanks to a DAC (Digital to Analog Converter), and the front end electronics
will send a trigger each time the photomultiplier output is greater than this threshold (see
figure 2). Another electronic box, the ACDE (AntiCoincidence Detector Electronics),
will generate a time tag corresponding to the ACFEE trigger and send it to the onboard
computer to search for coincidence with the low and high energy detectors.
FIGURE 2. ACFEE description

3. 4. MUON TELESCOPE
We need to build mock-ups in order to validate the AC concept, and study its sensitivity
to vibration and thermal load. In order to verify the performance of the anticoincidence at
each step of its conception, optimisation and validation, we have built a muon telescope,
working in triple coincidence (see figure 3 on the left). The energy deposed by a muon
is similar to the energy deposed by a cosmic proton. The tested sample will be placed
between the fifth and the third level of this telescope. Due to muon interactions with the
apparatus or room, we have a lot of unwanted particles that produce noise on the MAPM
signal. So, between the first and the third level, we have placed a lead plate stop all these
unwanted particles. The muons cross over this lead without any problem. The sample
test will be composed by a plastic scintillator (BC400), a R7600-M16 photomultiplier
and WLS fibers (Y11(200)MJ). The muon telescope is composed by hodoscopes made
of plastic scintillator (BC400), a light guide and a PM XP 3102 (see figure 3 on the right).
In this muon telescope, we will measure the number of photo-electrons produced by the
sample test, the WLS fibers performance when bent, the minimal radius of curvature
acceptable for these fibers, the performance of different gluing of the fibers to the
plastic scintillator, the dynamic signal of the MAPM, and the crosstalk of the signal
fiber arriving on the pixel of the MAPM.
FIGURE 3. On the left, µ-telescope description and on the right, hodoscope description
ACKNOWLEDGMENTS
I would like to thanks the conference organizers, the Simbol-X team and the APC
Laboratory, Paris.