Tile Calorimeter Phase I

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Radiation Testing of ATLAS TileCal Electronics

Overview

ATLAS is a large high energy physics experiment being prepared for the CERN LHC facility. It requires electronics that can be operated with good reliability in a radiation field for a period of 10 years. After reviewing the literature on radiation tolerant electronics it has been concluded that even with prudent design and making full use of existing information the final systems must be radiation tested before being qualified for mass production. ATLAS contains a number of different systems with varying requirements. This proposal is for the Tile Calorimeter system.

Requirements

Based on the calculated radiation field, the Tile Calorimeter electronics will receive a dose from ionizing radiation of ~ 2 Gy/year (0.2 Krad/year) corresponding to a total lifetime dose of 20 Gy [1]. It is also exposed to a neutron fluence of 10¹¹ 1-MeV-equivalent neutrons/cm²/year [1]. The relevant neutron energy spectrum ranges from ~100 Kev to ~2 MeV. A safety factor of 5 must be applied for uncertainties in the flux. In addition, because the actual exposure is at a much lower dose rate than the test exposure, an additional factor of 1.5 must be applied to the neutron exposure and a factor of 5 to the ionizing particle exposure for the bipolar components[2]. Thus the planned exposures are 500 Gy (50 Krad) for ionizing radiation and 7.5 x 10¹² 1-MeV-equivalent neutrons/cm².

It is proposed to expose sequentially 5 identical printed circuit boards to these levels. The electronics will be powered and executing test operations during the exposure. This will allow a determination of the dose at failure and the nature of any change in the properties with dose. The electronics under test would be connected to a nearby computer by a light cable assembly. The board to be tested this fall measures 3"x2"x0.5". At a later date we plan to test two boards measuring 4"x27"x0.5".

It is proposed that the test dose be delivered over a period of 3 hours. Thus the proposed rates would be 7 x 10⁸ 1-MeV-equivalent neutrons/cm²/sec and 170 Gy/hr (17 Krad/hr). The total duration of the test would be ~15 hours plus the time required to exchange test boards. If there were no access restrictions this could be done in 5 minutes.

References

1. Technical Design Proposal for the ATLAS Tile Calorimeter, Dec. 1996, p 14.
2. ATLAS Policy on Radiation Tolerant Electronics, http://www.cern.ch/Atlas/GROUPS/FRONTEND/WWW/radtol2.ps.