II-9. Instrumentation

RIKEN Accel. Prog. Rep. 54 (2021)

RIKEN Accel. Prog. Rep. 54 (2021)

Radiation resistance of bus extender cable for sPHENIX-INTT

ratio

We are developing INTermidate Tracker (INTT),
which is a new tracking detector for the sPHENIX
experiment at RHIC in BNL, which is a successor ofPHENIX. The INTT needs to be designed to transmit approximately 14k signal lines through a very narrow space; therefore any commercial detector available in the market will not ﬁt to interconnect theINTT and the downstream readout controller board(ROC).1) Thus, we have been developing a long andhigh-density cable, which is called “bus extender” forthe last four years.
The bus extender cable is a multilayered ﬂexible
print cable. Liquid crystal polymer (LCP) and copper
foil layers are laminated using an epoxy glue, forming
a multilayered structure. The LCP and the glue are
made of macromolecule materials; therefore, there isconcern for their use under the radiation enviroment
because macromolecules are known to be weak against
a radiation dose, in geneanl. Thus, the cable needs todemonstrate radiation hardness. We list the following
two physical characteristics as indicators of the radiation hardness: 1) loss of ﬂexibility, 2) decrease in thepeel strength of the glue. The former can be quantitatively evaluated by measuring Young’s modulus. The

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Dose [kGy]Fig. 1. Ratio of Young’s modulus as function of radiation
dose.
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∗9RIKEN Nishina CenterPhysics Department, Brookhaven National Laboratory
National Central University
Department of Mathematical and Physical Science, Nara
Women’s University
Japan Atomic Energy Agency
Tokyo Metropolitan Industrial Technology Research InstituteDepartment of Physics and Astronomy, Purdue University
Department of Physics, National Taiwan University
Department of Physics, Rikkyo University- 112 -peeling strength [N/cm]

H. Imai,∗1,∗9 Y. Akiba,∗1 D. Cacace,∗2 K. Cheng,∗3 T. Hachiya,∗1,∗4 S. Hasegawa,∗5 D. Imagawa,∗9 T. Kondo,∗6C. Kuo,∗3 H. -S. Li,∗7 R. -S. Lu,∗8 E. Mannel,∗2 C. Miraval,∗2 M. Morita,∗4 I. Nakagawa,∗1 Y. Namimoto,∗4S. Nishimori,∗4 R. Nouicer,∗2 G. Nukazuka,∗1 R. Pisani,∗2 M. Shibata,∗4 C. Shih,∗3 M. Stojanovic,∗7
W. -C. Tang,∗3 and X. Wei∗72018161412108
6110102103

Dose [kGy]Fig. 2. Peeling strength as function of radiation dose.

latter was evaluated by a peel force measurement.
Dedicated test samples for the radiation test werefabricated, which have the same layer structure as thebus extender but a smaller size: 40 cm length and 2 cm
width each. These test samples are exposed to gamma
ray radiation from a 60 Co source at a facility in theNational Institute of Quantum and Radiological andTechnology.
The natural frequency method was employed tomeasure Young’s modulus. The natural frequency canbe related with Young’s modulus as deﬁned in Eq. (1)where, f is the natural frequency, E is Young’s modulus, I is the moment of second-order, A is a crosssection area, ρ is the density, l is the length, and λ isa constant. λ is approximately 1.8 for basic frequency.
√λ2EI(1)f=22πlρAFigure 1 shows the results of the measurement. The
vertical axis shows the ratio of the observed Young’smodulus of the samples with and without exposure.
The result is constant within the size of the error bars,and thus, there is no indication of loss of ﬂexibility.
Figure 2 shows the radiation dose dependence of theobserved peel strength. The peel strength is measured
using SHIMAZU MST-I. A clear degradation of thepeel strength is observed. However, the degradationis still moderate within the expected radiation dose∼5 kGy in three of sPHENIX operation. We conclude
that the bus extender demonstrates suﬃcient radiation
hardness to be used in the sPHENIX experiment.
Reference1) T. Hachiya et al., in this report.

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