Interaction of Ionizing Radiation with Matter

Interaction of Ionizing Radiation with Matter Interaction of neutrons with matter Neutral particles, no repulsion with the positively charged nucleus: important projectile Origin of the neutrons: Nuclear reactor Neutron source Neutrons must be moderated Moderators: water, hydrogen, deuterium 9 Be + α 12 C+ n 9 Be + 241 Am 12 C+ n 1

Interaction of Ionizing Radiation with Matter Interaction of neutrons with matter Neutral particles, no repulsion with the positively charged nucleus: important projectile Slow (moderated) neutrons react with many nuclei: Neutron capturing (n,γ) reactions Radioactive isotopes of almost all elements can be produced this way 2

Interaction of Ionizing Radiation with Matter Interaction of neutrons with matter Cross-section / barn Neutron energy / ev Cross section is a measure for the probability of a nuclear reaction (barn = 10-23 m 2 ) 3

Interaction of Ionizing Radiation with Matter Neutron activation Non-destructive analytical method for trace analysis Suitable for qualitative & quantitative analyses (internal standard) λ N =Φ σ N T (1 e λt ) λ= decay constant of the daughter N = number of daughter atoms φ= fluence rate of neutrons σ= cross section N T = number of target atoms 4

Interaction of radiation with a biological system leads to an energy transfer The biological impact depends on: type of radiation type of irradiated biological material How to quantify the amount of transferred energy? How to quantify the biological impact? 5

Ion dose (exposure) I = produced charges mass of irradiated air I = Q m Radiation source SI Unit: I = C(As) kg = 6,25 10 18 Ion pairs kg air Ionization chamber Old unit: R (Roentgen) 4 2,58 10 C 1R = kg air C 1 kg air = 3,88 10 3 R Measurement of the ionization in an ionization chamber Gas filled container with a window of thin material Electric current is produced by ions which are produced by the influence of radiation 6

Energy dose absorbed radiation energy D = D = mass ΔW Δm the formation of 1 ion pair requires 34 ev SI unit: 1 Gy (Gray) 1 Gy = 1 J/kg Old unit: rd (rad) 1rd = 10-2 Gy Direct information about the transferred energy 7

Equivalent dose Damage of organic material (tissue) can only be expected if the energy is absorbed by the tissue (interactions radiation-matter) The bigger the absorption is, the bigger is the impact Highly ionizing radiation has a higher impact than weakly ionizing (α > n > β, γ, X) Energy dose exclusively reflects the pure energy value (not the impact) Equivalent dose H = D W W = weighting factor of the radiation SI Unit: 1 Sv (Sievert) 1 Sv = 1 J/kg old unit:1 rem 1 Sv = 100 rem (roentgen equivalent men) 8

Equivalent dose Representing the stochastic health effects of ionizing radiation on the human body. Equivalent Dose enables the comparison of different types of radiation. Equivalent dose H = D W W = weighting factor of the radiation normal cell damaged cell Radiation types X-rays, γ- and ß- radiation W Neutron radiation about 10 α - radiation 20 1 Biological sample after irradiation with β-particles Biological sample after irradiation with α-particles Dose rate: dh (Sv / h) dt relative destruction: 1 Energy dose: 2 Gy relative destruction: 1 Energy dose: 0.1 Gy 9

Dosimetry Ion dose measurable value Energy dose Information about the absorbed energy Equivalent dose Information about the biological impact Multiplication with the w factor of the particular material Multiplication with the weighting factor of the particular radiation 10

instantaneous physical process energy transfer Radiobiological functional chain minutes molecular & biochemical changes hours somatic cell cellular changes gamete cell days acute direct damage next generation weeks/ month neoplasms (cancer, leukemia) years non-malignant later damage deterministic stochastic genetic damage 11

Direct vs. Indirect Radiation Effect indirect direct 12

DNA damages Single-/ Double-strand breaks Chemical bond between Neighboring nucleotides Chemical modification of a nucleotide (mutation) / losing of one nucleobase Chemical linkage of two strands 13

DNA damages spontaneous radiation-induced Event per second per hour per year per mgy Single-strand break 1.4 ca. 5 x 10 3 ca. 4.4 x 10 7 1.0 Double-strand break 0.04 Depurination ca. 1.5 x 10 3 ca. 1.4 x 10 7 0.01 Base damage 0.8 ca. 1.25 x 10 3 ca. 1.1 x 10 7 0.95 Total 2.2 ca. 8 x 10 3 ca.7 x 10 7 ca. 2.0 14

Radiation damages 15

Stochastic vs. deterministic effects Bei den somatischen Strahlenwirkungen unterscheidet man zwischen stochastischen und deterministischen Strahlenwirkungen. http://www.kernfragen.de/kernfragen/lexikon/s/strahlenschaeden_beim_menschen.php 16

Deterministic radiation damages 17

Deterministic radiation damages Deterministic Radiation Damage 18

Deterministic radiation damages Strahlenverbrennung der Haut Strahlendermatitis und Epilation 19

Dose limits Equivalent Dose Limits StSG (28.12.2004) / StSV (01.01.2008) Equivalent Dose Limits (annual) Body Equivalent Dose Limits for tissues & organs (annual) Lens of eye Skin, hands, and feet 1 msv (public) 20 msv (people working with activity) max. 50 msv (exceptional with permission) 150 msv 500 msv 20

Shielding Lab coat: Shields already approx. 80% of soft β-radiation Neutrons: Moderation with materials that contain a lot of protons (e.g. water) Absorption with B, Gd or Cd (leads to secondary γ-radiation) 21

Square Root Law of Distance r1 H 2 = H 1 r 2 2 22

ALARA As Low As Reasonable Achievable Duration of stay (Aufenthaltszeit) Distance (Abstand) Shielding (Abschirmung) Activity Avoid contamination / incorporation 23

Dose estimation 24

Dose estimation Organ Dose Skin Dose Contamination H p 2 1m = A t h10 r HS = A t h 0.07 H A = t h F S c0.07 h 10 : Dose in msv per GBq and per hour in 1 m distance to the source h 0.07 : Dose in msv per GBq and per hour in 10 cm distance to the source Rule-of-thumb 1 GBq in 1 m distance during 1 h leads to a H p of 1/3 msv 25

Dose estimation 26

Dose estimation 27

Dose estimation A technician should work 3 h with 75 MBq I-125. The distance between the source and the body will be in average 0.5 m. What dose (Tiefenäquivalentdosis) will he accumulate? h 10 I-125 = 0.033(mSv/h)/GBq in 1 m distance A technician works 20 min without any shielding with 200 MBq of C-14. What skin dose did he accumulated? h 0.07 C-14 = 200 (msv/h)/gbq in 10 cm distance After 2h, a skin contamination of 10 cm 2 with 1000 Bq Cs-137 has been detected and cleaned. What skin dose has been accumulated? h c0.07 C-14 = 1.5 (msv/h)/(kbq/cm 2 ) 28