Supplemental shielding of BMIT SOE-1 at the Canadian Light Source

• Published in: Radiation physics and chemistry (Oxford, England : 1993) England : 1993), 2014-07, Vol.100, p.8-12
• Main Authors: Bassey, Bassey, Abueidda, Abdallah, Cubbon, Grant, Street, Darin, Sabbir Ahmed, Asm, Wysokinski, Tomasz W., Belev, George, Chapman, Dean
• Format: Article
• Language: English
• Subjects: Beams (radiation); Enclosure; Leakage; Light sources; Mathematical analysis; Monochromators; Particle physics; Secondary optical enclosure; Shielding; Single crystal monochromator
• ISSN: 0969-806X; 1879-0895
• DOI: 10.1016/j.radphyschem.2014.02.023

High field superconducting wiggler beamlines present shielding challenges due to the high critical energy of the synchrotron spectrum. An unexpected, but predictable, weakness in the secondary optical enclosure (SOE-1) was discovered on the BioMedical Imaging and Therapy (BMIT) insertion device (ID) beamline 05ID-2 at the Canadian Light Source (CLS). SOE-1 is a monochromatic beam hutch; the beam in it is supplied by three monochromators housed in an upstream primary optical enclosure (POE-3). The initial shielding of SOE-1 was based on a shielding calculation against target scattered and direct monochromatic (fundamental and harmonics) beams from the monochromators in POE-3. During a radiation survey of the hutch, radiation above the expected level was measured at the downstream end of SOE-1. This increment in radiation level is attributed to scattered white beam into SOE-1 by a K-Edge subtraction (KES) monochromator׳s crystal (a single crystal monochromator) in POE-3. Though this is peculiar to the BMIT beamline 05ID-2, it may not be uncommon for other beamlines that use single crystal monochromators. Calculations of the level of expected leakage radiation due to the scattered white beam arriving on the downstream wall of the SOE-1 are presented, as well as the supplemental shielding that will reduce the leakage to less than 1μSv/h as required at the CLS. Also presented are the installed supplemental shielding, and a comparison of the calculations and measurements of the dose rates on the back wall of SOE-1 End Wall, before and after installation of the supplemental shielding. •We discovered an unexpected weakness in the shielding of BMIT SOE-1 End Wall.•We predicted the source of the weakness-scattering of white beam into SOE-1.•White beam scattered into SOE-1 by the crystal of a single crystal monochromator.•We calculated and installed the required supplemental shielding.•With the installed supplemental shielding, we have fixed the weakness.