Radiation effects on the mechanical properties of the material for the BESIII beam pipe supporting flange

The supporting flanges were designed and made to support the Beijing Spectrometer (BESIII) beam pipe in Beijing Electron Positron Collider (BEPCII). They will be irradiated to neutron and gamma in their 10 years design life in BESIII. As one kind of excellent insulating materials, G10 epoxy glass cloth-laminated sheets (G10) was selected as the candidate material, and some experiments have to be performed to obtain information on the changes of mechanical properties after irradiation. According to the requirements of BESIII experiment, samples were irradiated by a 60Co-source up to 104 Gy and in a reactor to a slow neutron fluence of 4.1×1018 m−2 (E=0.625 eV) sequently. The results show that the shear strength declines from 79.8 to 70.7 MPa. Since the established standards for tensile strength measurements involve sample sizes, which are far too large for the existing irradiation facilities, small size samples were designed to investigate the influence of the sample geometry on the tensile strength, based on which the tensile strength of G10 was deduced to decrease from 324.8 to 317.1 MPa after the same irradiation. The results indicate that G10 can well meet the requirements of the supporting flanges. Moreover, the shear and tensile fractures were observed by SEM to explain the experiment data. Now the supporting flanges made of G10 has been used in BEPCII supporting the BESIII beam pipe.