Indian Journal of Pure & Applied Physics Vol. 50, July 2012, pp. 462-464 Experimental determination of Bremsstrahlung dose rate due to accidental beam loss in Indus-1 storage ring G Haridas, D Verma, P K Sahani 1 , M K Nayak*, K K Thakkar 2 & P K Sarkar Health Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085, India 1 Indus Operation & Accelerator Physics Design Division, RRCAT, Indore 452 013, India 2 Ex-BARC, Health Physics Division, Bhabha Atomic Research Centre, Mumbai 400 085 E-mail: nayak@rracat.gov.in Received 20 April 1012; accepted 10 May 2012 During the operation of an electron storage ring where electron beam is stored for the production of synchrotron radiation, probability of accidental beam loss exists. In the present paper, Bremsstrahlung dose due to accidental beam loss in the storage ring Indus-1 has experimentally been measured. Stored electron beam current ranging from ~10 to 100 mA was killed using a beam viewer (destructive) and the Bremsstrahlung dose per event of killing in the forward direction was measured using an ion chamber, made in house, along with an electrometer. Measurement was carried out within the shielded enclosure of the storage ring. Measured dose per event showed linearity up to 99.3 mA. The dose per event of beam killing at 99.3 mA was found to be 5.69 mGy after applying high energy correction factor. The paper describes the experiment and discusses the results. Keywords: Synchrotron, Accidental loss, Bremsstrahlung, Radiation dose 1 Introduction In electron storage rings electrons are usually injected to accumulate the required number of electrons and made to circulate with the help of bending dipole magnets. During the process of circulation, when they pass through the dipole magnets, the electrons emit synchrotron radiation which is used for scientific research and other applications 1 . During the process of storage, users use the synchrotron beam which is transported to the experimental station through synchrotron radiation beam lines. Usually, these beam lines penetrate through the radiation shield placed around the ring. During the storage mode of operation if the stored beam accidentally gets lost at a single point, Bremsstrahlung radiation is generated due to these lost high energy electrons and may contribute to the dose to users. There are cases like tripping of dipole magnet power supply or the RF power etc where a distributed loss of beam over the entire ring may take place. The dose delivered will be maximum when the stored electron beam is accidentally lost at a single point. Therefore, an experimental investigation was carried out at the electron storage ring Indus-1 in order to assess the likely dose which will be received by a worker within or outside the shielded area surrounding the ring. Measurement of the exact dose delivered during the event of an accidental beam loss is practically difficult due to the following reasons: (a) An area monitor or a dose rate meter if used for the measurement, will give only the dose rate and hence, the dose delivered during the event of beam killing cannot be obtained. (b) If a passive dosimeter is placed within the shielded enclosure to measure the dose due to the event of accidental loss, contribution due to beam injection will pollute the dose due to accidental loss. In view of these difficulties a cylindrical ion chamber (17 cc) was developed in house with 5 mm thick Perspex wall, equivalent to Co-60 equilibrium wall thickness for the measurement. The ion chamber was used along with an electrometer for the measurement. The photograph of the ion chamber with electrometer (Dose1, iba Dosimetry, Germany) is shown in Fig. 1 The paper describes the experiments performed and discusses the results. 2 Characterization of the Detector The chamber was tested with a Co-60 source and found to be well saturated beyond 60 V. The chamber was then tested in the Bremsstrahlung radiation field of the storage ring, Indus-1 near the injection septum. For comparison purpose, radiation level data from a calibrated area monitor (ion chamber based) and a