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WORKING WITH X-RAYS

KEELE UNIVERSITY. WORKING WITH X-RAYS. Dr D E Dugdale October 2012. ROTATING ANODE GENERATOR. X-RAY SPECTRUM. E max = eV. DOSE RATES Can be very high For anode of atomic number Z, operating voltage V, current I  Unfiltered dose rate = D  ZVI/d 2 at a distance d

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WORKING WITH X-RAYS

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  1. KEELE UNIVERSITY WORKING WITH X-RAYS Dr D E Dugdale October 2012

  2. ROTATING ANODE GENERATOR

  3. X-RAY SPECTRUM Emax = eV

  4. DOSE RATES • Can be very high • For anode of atomic number Z, operating voltage V, current I •  Unfiltered dose rate = D  ZVI/d2 • at a distance d • Typical figures for V = 50 KeV, I = 10 mA • @ d = 1 m D - 1 Sv per minute • @ d = 10 cm D - 100 Sv per minute

  5. Radiation burns ( 3 Sv ) in a time of • @ 1m ~ 3 mins. • @ 10 cm ~ 2 secs. • Using Ni filter or monochromator D  D/100 • To have radiation level below maximum allowed ( 7.5 micro Sv/hr ) requires shielding of > 108

  6. X-RAY SHIELDING I = Io e- x =linear attenuation coefficient H1/2 = 0.69/

  7.        For 50 keV X-rays H1/2 - 10 m in air H1/2 - 3 cm in body tissue H1/2 - 0.1 mm in Pb         For Pb @ 50 keV X-ray energy I/Io = 1/10 for x = tenth value thickness = 0.23 mm For x = 2.3 mm therefore I/Io = 10-10

  8. X-RAY LEAKAGE - Typical Arrangement Of X-ray Generator And Camera Leakage at joints must be less than 7.5 mSv/hr - but ALARA principle demands much less since extra shielding is reasonably achievable for X-rays

  9. Perspex Shielded Enclosures Leaded Perspex outer shield

  10. MINI MONITORS • Soft X-rays ( < 30 keV ) do not easily penetrate Geiger -Muller ( GM )tube walls. • Ideally tubes with Be end windows should be used - but even cheap general purpose GM tubes have some response down to 9 keV ( Cu K lines used in crystallography) • For GM tube MX-168 @ 10 keV • 1 c/s ~ 1 micro Sv/hr ( background ~ 0.5 c/s ) • 1 micro Sv/hr is only ~ 2 mSv/yr but nevertheless more shielding should be used • if any count rate above background can be detected

  11. PERSONAL MONITORS • Film badges and thermoluminesent detectors can detect doses > 0.05 mSv (~ 1/40 annual background) • Film badges are changed every month ( every 3 months for TLD’s) • Not likely to detect accidental exposure to collimated beams but should detect any diffuse scattered radiation • Wear at chest height with serial number facing outward

  12. WORKING PROCEDURES • Register each year as a radiation worker • (so that dose and training records can be kept ) • Follow the general rules of the University and the local rules of the Department for specific equipment and specific procedures • Local rules and local training are given by research supervisors and RPS • Never overide interlocks • Never operate if warning lights fail or if equipment is malfunctioning • Report all faults to the responsible technician immediately

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