Research for Radiation Damage of CCD Vertex Detector

Research Project

Project/Area Number	11640247
Research Category	Grant-in-Aid for Scientific Research (C)
Allocation Type	Single-year Grants
Section	一般
Research Field	素粒子・核・宇宙線
Research Institution	Tohoku University
Principal Investigator	ABE Koya Tohoku University, Faculty of Science, Prof., 大学院・理学研究科, 教授 (60004412)
Co-Investigator(Kenkyū-buntansha)	KAWAMURA Nobuaki Aomori University, Faculty of Engineering, Prof., 工学部, 教授 (30004352) NAGAMINE Tadashi Tohoku University, Faculty of Science, Associate researcher., 大学院・理学研究科, 助手 (30212111)
Project Period (FY)	1999 – 2000
Project Status	Completed (Fiscal Year 2000)
Budget Amount *help	¥2,800,000 (Direct Cost: ¥2,800,000) Fiscal Year 2000: ¥1,000,000 (Direct Cost: ¥1,000,000) Fiscal Year 1999: ¥1,800,000 (Direct Cost: ¥1,800,000)
Keywords	CCD / Radiation damage / e^+e^- linear collider / Vertex detector / Surface damage / 電子線型加速器 / 短寿命重粒子 / 電子線形加速器
Research Abstract	Two subjects were studied for an application of CCD's as vertex detector at nearby room temperature in future e^+e^- linear collider JLC. 1) Noise hits should be suppressed to less than 10^<-5> for total number of pixels more than 10^8 for the vertex detector. As dark currents strongly depend on an operating temperature, can we obtain enough S/N ratio at the room temperature? A dependence of the dark current on accumulation time and S/N using ^<55>Fe X-ray (5.89 keV) source were measured in order to verify the applicability. Four CCS's with pixel size of 12×12, 24×24, and 48×48 μm^2, which are commercially available, were used in the study. A mode of Multi-Pinned-Phase (MPP) were adapted to reduce the dark current. We concluded that the enough S/N could be obtained with the CCD of pixel size smaller than 24×24 μm^2 and a faster driver circuit of CCDs with charge transfer speed more than 5 MHz. 2) Radiation of 150 krad is expected for 10 year operation of JLC.Can CCD has sufficient radiation hardness in the environment near collision point of JLC? Negative driving voltage V^<MPP>_<cc> at which CCD is converted to MPP mode and Charge Transfer Inefficiency (CTI) were measured before and after irradiation of ^<60>Co γ-ray of about 200 Ci. After irradiation of 27 krad V^<MPP>_<cc> moved from -6.5 V to -9.8 V and CTI increased from 1.0×10^<-6> to 3.5×10^<-6>. After an additional exposure of 18 krad the operation of the CCD became difficult. This means that this type of CCDs tested now can not be used to operation of JLC for more than two years. We conclude that enough S/N can be obtained for the operation of CCDs at the room temperature. However we need more extensive R＆D to get adequate radiation hardness for the operation of JLC over ten years.