Interaction of Ionizing Radiation with Matter Interaction of

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: Neutron source Nuclear reactor Neutrons must be moderated Moderators: water, hydrogen, deuterium + 12 C+ n + 241 Am 12 C+ n 9 Be 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, ) reactions Radioactive isotopes of almost all elements can be produced this way 2

Interaction of Ionizing Radiation with Matter Cross-section / barn Interaction of neutrons with matter Neutron energy / e. V 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) l= decay constant of the daughter N = number of daughter atoms f= fluence rate of neutrons s= cross section NT = number of target atoms 4

Biological Action of Ionizing Radiation 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

Biological Action of Ionizing Radiation Ion dose (exposure) Radiation source Ionization chamber SI Unit: Old unit: R (Roentgen) 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

Biological Action of Ionizing Radiation Energy dose the formation of 1 ion pair requires 34 e. V SI unit: 1 Gy (Gray) 1 Gy = 1 J/kg Old unit: rd (rad) 1 rd = 10 -2 Gy Direct information about the transferred energy 7

Biological Action of Ionizing Radiation 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 ( > n > , , 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

Biological Action of Ionizing Radiation 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 normal cell damaged cell W = weighting factor of the radiation Dose rate: (Sv / h) Biological sample after irradiation with -particles relative destruction: 1 Energy dose: 2 Gy relative destruction: 1 Energy dose: 0. 1 Gy 9

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

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

Biological Action of Ionizing Radiation Direct vs. Indirect Radiation Effect indirect 12

Biological Action of Ionizing Radiation 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

Biological Action of Ionizing Radiation DNA damages spontaneous radiation-induced Event per second per hour per year per m. Gy Single-strand break 1. 4 ca. 5 x 103 ca. 4. 4 x 107 1. 0 Double-strand break 0. 04 Depurination ca. 1. 5 x 103 ca. 1. 4 x 107 0. 01 Base damage 0. 8 ca. 1. 25 x 103 ca. 1. 1 x 107 0. 95 Total 2. 2 ca. 8 x 103 ca. 7 x 107 ca. 2. 0 14

Biological Action of Ionizing Radiation damages 15

Biological Action of Ionizing Radiation 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

Biological Action of Ionizing Radiation Deterministic radiation damages 17

Biological Action of Ionizing Radiation Deterministic Radiation Damage Deterministic radiation damages 18

Biological Action of Ionizing Radiation Deterministic radiation damages Strahlenverbrennung der Haut Strahlendermatitis und Epilation 19

Biological Action of Ionizing Radiation Dose limits Equivalent Dose Limits St. SG (28. 12. 2004) / St. SV (01. 2008) Equivalent Dose Limits (annual) Body 1 m. Sv (public) 20 m. Sv (people working with activity) max. 50 m. Sv (exceptional with permission) Equivalent Dose Limits for tissues & organs (annual) Lens of eye 150 m. Sv Skin, hands, and feet 500 m. Sv 20

Biological Action of Ionizing Radiation 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 -radiation) 21

Biological Action of Ionizing Radiation Square Root Law of Distance 22

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

Biological Action of Ionizing Radiation Dose estimation 24

Biological Action of Ionizing Radiation Dose estimation Organ Dose Skin Dose h 10: Dose in m. Sv per GBq and per hour in 1 m distance to the source h 0. 07: Dose in m. Sv 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 Hp of 1/3 m. Sv Contamination 25

Biological Action of Ionizing Radiation Dose estimation 26

Biological Action of Ionizing Radiation Dose estimation 27

Biological Action of Ionizing Radiation 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(m. Sv/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 (m. Sv/h)/GBq in 10 cm distance After 2 h, a skin contamination of 10 cm 2 with 1000 Bq Cs-137 has been detected and cleaned. What skin dose has been accumulated? hc 0. 07 C-14 = 1. 5 (m. Sv/h)/(k. Bq/cm 2) 28