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

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 Typical figures for V = 50 KeV, I = 10 d = 1 m D - 1 Sv per d = 10 cm D Sv per minute

Radiation burns ( 3 Sv ) in a time 1m ~ 3 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 > 10 8

I = I o e - x =linear attenuation coefficient H 1/2 = 0.69/ X-RAY SHIELDING

For 50 keV X-rays H 1/ m in air H 1/2 - 3 cm in body tissue H 1/ mm in Pb For 50 keV X-ray energy I/I o = 1/10 for x = tenth value thickness = 0.23 mm For x = 2.3 mm therefore I/I o =

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

Perspex Shielded Enclosures Leaded Perspex outer shield

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 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

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

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