03/07/2015radiation safety - level 51 Radiation safety level 5 Frits Pleiter

03/07/2015radiation safety - level 52 Contents  atomic and nuclear physics(1)  interaction with matter(3) o sources and x-ray equipment (2) o shielding (3) o detection (4) o radiobiology (6) objective risk of radiation (6) subjective risk acceptation (6)  quantities and units(5)  regulations(7) o practical health physics (8 - 10) o waste (11)

03/07/2015radiation safety - level 53 Interaction with matter  -particles energy loss due to inelastic collisions with electrons straight track of excitations and ionisations typical energy5 MeV range in air30 mm range in tissue30  m 1,0 0,5 0,0 x N(x)/N(0) R

03/07/2015radiation safety - level 54 Interaction with matter electrons energy loss due to inelastic collisions with electrons scattering due to elastic collisions with electrons straggling of excitation and ionisation events "range" is not a meaningful concept: use "maximum range" relative energy loss due to bremsstrahlung  E brems / E = EZ / 800 typical energy1 MeV max. range in air5 m max. range in tissue5 mm 1,0 0,5 0,0 x N(x)/N(0) R gemiddeld R e,max

03/07/2015radiation safety - level 55 Interaction with matter  - -particles exponential attenuation of  -spectrum half-value layer d ½ reduces the intensity by a factor of two rule of thumbd ½  R ,max / 7 1,0 0,5 0,0 x N(x)/N(0) d½d½ R ,max

03/07/2015radiation safety - level 56 Interaction with matter  + -particles see interaction of  - -particles annihilation at the end of the range  + + e -  2  511 keV the two photons are emitted in opposite directions applied in PET-scan

03/07/2015radiation safety - level 57 Interaction with matter  - en x-ray photons foto-electric effect effect  Z 5 / E 3 only possible if E  > binding energy total energy transfer to (bound) electron atom is ionized  x-ray photon Auger electron nucleus  e-e-

03/07/2015radiation safety - level 58 Interaction with matter  - en x-ray photons Compton effect effect  Z partial energy transfer to (free) electron atom is ionized  x-ray photon Auger electron nucleus  e-e- '' 

03/07/2015radiation safety - level 59 Interaction with matter  - en x-ray photons pair formation effect  Z 2 only possible if E  > 2  511 = 1022 keV followed by annihilation e + + e -  2  511 keV nucleus e-e- e+e+

03/07/2015radiation safety - level 510 Interaction with matter  - en x-ray photons at low energy and large Z, photo-electric effect is dominant at high energy and large Z, pair formation is dominant in intermediate region, Compton effect is dominant photo-electric effect Compton effect pair formation

03/07/2015radiation safety - level 511 Shielding  -particles  -particle can not penetrate dead layer of skin no shielding of external radiation required high risk in case of internal contamination

03/07/2015radiation safety - level 512 Shielding  - -particles use low-Z material (lucite) to avoid bremsstrahlung wear safety glasses apply all-side shielding because of large range express range preferably in mass units: R   (in g/cm 2 ) because energy is transferred to electrons number of electrons per gram is a constant for most elements therefore, R   is (nearly) independent of material

03/07/2015radiation safety - level 513 Shielding  + -particles see shielding of  - -particles apply additional lead to shield annihilation radiation

03/07/2015radiation safety - level 514 Shielding  - and x-ray photons half-value layer d ½ reduces the intensity by a factor of two linear attenuation coefficient  = / d ½ exponential attenuation of photons T(d) = e -  d use preferably mass units d ½   (in g/cm 2 )  /  (in cm 2 /g)

03/07/2015radiation safety - level 515 Shielding mass units why mass units ?  -particles, electrons and photons transfer energy to electrons number of electrons per gram is a constant for most elements therefore, d ½   and  /  are (nearly) material independent (provided Compton effect is dominant)

03/07/2015radiation safety - level 516 Interaction with matter build-up factor small bundle geometry (left)T(d) = e -  d wide bundle geometry (right)T(d) = B  e -  d B = build-up factor due to scattering P collimator source absorber P source

03/07/2015radiation safety - level 517 Interaction with matter transmission of  -radiation

03/07/2015radiation safety - level 518 Interaction with matter choice of proper shielding material x-ray energies are usually small at low energy, photo-electric effect is dominant lead is an efficient shielding material the area on a laboratory table is limited lead has a very small volume to mass ratio lead is a convenient shielding material lead is expensive and can not be used for building constructions like a bunker around an accelerator or a  -irradiation facility concrete is the best shielding material

03/07/2015radiation safety - level 519 Interaction with matter choice of proper shielding material not the attenuation, but the required radiation level is crucial