Experimental determination of synchrotron and Bremsstrahlung radiation contribution for a synchrotron radiation beam line

Full text: Indus-2 is a synchrotron radiation source (SRS) being commissioned at Raja Ramanna Centre for Advanced Technology, Indore, India. The SRS is a 2.5 GeV, 300 m A storage ring, 172 m in circumference which emits synchrotron radiation with a critical wavelength of 2 A0 . In the storage ring electrons area accelerated from injection energy (550 MeV, fed from a booster synchrotron) to 2.5 GeV and thereafter stored for several hours during which the emitted synchrotron radiation is exploited for scientific research. The ring has provision for 27 synchrotron radiation beam lines from bending dipole magnets and from insertion devices. The SR beam is transported to the SR beam line via. a front end in which several safety devices like safety shutter, water cooled shutter, collimators, gate valves etc. are installed. SR beam line users have started installing their beam lines and commissioning activities have begun. The radiation environment near a synchrotron beam line consists mainly of Synchrotron radiation (SR) and Bremsstrahlung radiation (BR). The SR emitted from the electrons traversing through the bending magnets has an energy range, 4 - 40 KeV. BR is produced either due to the interaction of the electrons with structural materials of the storage ring or the residual gas molecules within the vacuum chamber. They have a broad energy spectrum ranging up to the energy of the electron. It is very essential to quantify these radiations when the SR is brought out to the experimental hall for experiments. In the present work SR and BR contribution in an X-ray diffraction beam line, on Indus-2 is experimentally determined using an ion chamber detector. Measurement was carried out at the front-end exit just after a beryllium window, in the experimental hall, when the storage ring was operated at 2.0 GeV, ∼ 1 m A. Contribution due to SR was measured using a thin window ion chamber developed in house and the BR contribution was measured with different thickness of copper and aluminum absorbers in front of the ion chamber. Ion current from the chamber was measured for the determination of the contribution of both the radiations. The BR contribution is experimentally determined to be less than 1% in terms of the total ion current from all the measurements. It was found that a few millimeters thick Al or Cu absorbers eliminate the SR contribution. Absolute value of the SR and BR exposure rate and was then calculated from the ion current using measured sensitivity at 8 KeV and at Co-60 energy respectively. The exposure rate due to SR works out to be 105 R/h where as for BR it is about 20 R/h. The data is very useful in designing the shielding and other radiation protection requirements for SR beam lines in Indus-2. (author)