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Radiation in the Environment radioactivity and radioactive decay biological impact and dose sources of radiation in the environment natural anthropogenic.

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Presentation on theme: "Radiation in the Environment radioactivity and radioactive decay biological impact and dose sources of radiation in the environment natural anthropogenic."— Presentation transcript:

1 Radiation in the Environment radioactivity and radioactive decay biological impact and dose sources of radiation in the environment natural anthropogenic case study (Chernobyl)

2 Po Pb Po Bi At Pb Po Tl Rn RaTh U Pa Th Bi Pb Tl U (stable) Uranium-238 natural decay series.

3 Radioactive Decay Laws: Activity (rate of decay) [Units: Becquerel (Bq) = 1 disintegration/s] N=N o e - t and t ½ = 0.693/ n p n = p n > p Nuclear Instability multiple isotopes Why are some nuclei unstable? e.g. 235 U and 238 U

4 Some Types of Radioactive Emissions Radiation Symbol Description Charge Mass No.(amu) alpha He nucleus +2 4 beta nuclear electron -1 0 gamma em radiation - - neutron nnuclear particle 0 1

5 Radiation and Living Organisms What does radiation do to the body? Ionising radiation ions and radicals abnormalities and cancers At high doses Radiation sickness (syndrome) Cell damage:Crypt cells white blood cells cells which produce red and white blood cells Symptoms: nausea, vomiting, diahorrea, fatigue

6 Radiological dose Absorbed dose: amount of energy absorbed by tissue Unit = Gray 1 Gy = transfer of 1J to 1 kg Dose equivalent:absorbed doses multiplied by a quality factor (QF) which reflects the damaging power of the radiation. D T (Sv) = D A (Gy) x QF QF for X-ray, and = 1 QF for = 20 Effective dosedose equivalent weighted to account for the different equivalent:susceptibilities of various tissue types to radiation damage H E = T D T W T W T weighting factor (International Commission on Radiological Protection (ICRP))

7 ICRP Weighting Factors (W T ) Tissue or organW T testes or ovaries0.25 breast0.15 red bone marrow0.12 lung0.12 thyroid0.03 bone surfaces0.03 remainder0.3 Whole body total1.00 Maximum Permissable Dose (Whole Body) H E (max) = 50(N-18) Damage to tissue depends on: dose received gender age

8 External vs Internal exposure Absorbed dose (distance) -1 (inverse square law) While for most of us, most radiation events may involve a small external dose, due to the distance between us and source, ingestion of radionuclides can provide us with a high dose from a dilute source at close range. Our physiological processes may also cause certain isotopes to concentrate in various body tissues: 90 Sr, 89 Sr, 32 P bones 131 Ithyroid In addition to a nuclides radiological half-life it is necessary to define an analogous biological half-life, t biol. This allows an effective half-life, t eff, to predict the impact of radioisotope ingestion. T eff = (t biol.t rad )/[(t biol +t rad )]


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