During the various phases of operation of Indus-1, intense bemsstrahlung X-rays and photo-neutrons are emitted.  In order to protect the working personnel from these ionizing radiation adequate shielding is needed. Pre-injector  & Booster synchrotron is located in a zone fully enclosed with 1000mm thick concrete walls & modular roof (300 mm). Storage ring is located in the main hall of the building. After commissioning of Indus-1 synchrotron radiation facility in May 1999, bulk shielding around the storage ring was required to be modified for the installation of SR beam lines.

2.0 Design Philosophy/ Features:

Flexibility (for accommodating future beam-lines), compactness and accessibility (multiple entry for SR components) are some of the important design features of the shielding arrangements. After few iterations, a final layout of modified shielding arrangement with above features was prepared. The evolved design is a combination of Hybrid structures (lead + MS) and Multiple mazes (concrete).  Hybrid shielding structure was intended to be installed across and near the beam-lines for compactness and interlocking concrete blocks of 500 mm thickness were used for making labyrinths/maze. (a) Hybrid Shielding: Hybrid shielding and lead was conceived to fulfil the requirements of compactness & flexibility. MS plates are used in these structures to reduce photo-neutrons production, whereas lead blocks provide compactness. As bemsstrahlung radiation has angular distribution with a peak value at beam plane, hybrid-shielding structure was also designed such that it provides maximum Tenth Value Layer (TVL) value around centre plane (2.5 TVL) and lower value (0.8 & 1.6 TVL) above and below this. Each structure has 4 x 40 mm thick MS plates up to 600 mm, two layers each of MS plates and lead brick stacks between 600 to 1700 mm and 2x 40mm thick MS plates between 1700 and 2000 mm of elevation from the floor.  Lead brick stacks are held in place using MS cover plates on both sides. Lead bricks (Interlocking type, 40 mm thick) were cast from billets (with 4% antimony).  Dimensional check, density check, visual inspection and finally radiometry test were carried out to ensure quality of the final product. The shielding structure installed across the beam-lines is in two halves with a hole for beam line pipe (fig 1). The other type of hybrid shielding structure is without hole & installed in the vicinity of the beam lines.  Four fastened brackets with a provision to adjust their location to accommodate near by beam-line components support each structure. Adequate care has been taken during machining and assembly of hybrid structure so that C.G. remains close to its centre plane.

Figure 1: Beam line Hybrid Shielding structure


Figure 2: Indus-1 layout with modified shielding arrangement

A maze entry layout was designed such that there is no direct streaming of the radiation. Multiple access through maze was proposed for an easy and quick approach to various storage ring components for   maintenance, measurements, etc. 3.0 Shielding Optimisation:

There was a need of dividing the Indus-1 hall into three partitions for the machine operation requirements (fig.2). Necessary changes in the layout were done by providing two additional concrete labyrinths with interlocking sliding glass doors. Presently machine is under operation with the above scheme.

Present height of concrete maze is 3000mm with two layers of interlocking modular concrete blocks. In order to optimize the height of concrete mazes, a calibration set-up has been designed and fabricated which collect survey data result at various height & location inside the Indus-1 hall. There is a proposal to change dipole chambers to increase beam ports and beam-lines. The Present flexible design of the shield shall be able to take care of this major modification in future.

4.0 Results & Conclusions: