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. Uranium-238 natural decay series.Po Pb Bi At Tl Rn Ra Th U Pa
206
210
214
218
222
226
230
234
238 81 84 83 82 85 86 88 90 92 91
(stable)
Uranium-238 natural decay series.  

3. Radioactive Decay Laws:
Why are some nuclei unstable?
Activity (rate of decay) n p
n = p
n > p
[Units: Becquerel (Bq) = 1 disintegration/s]
N=Noe-t and t½ = 0.693/
Nuclear Instability
multiple isotopes
e.g. 235U and 238U

4. Some Types of Radioactive Emissions
Radiation Symbol Description Charge Mass No.(amu)
alpha  He nucleus
beta  nuclear electron
gamma  em radiation
neutron n nuclear particle

5. Radiation and Living Organisms
What does radiation do to the body?
Ionising radiation ions and radicals
abnormalities and cancers
Cell damage:
Crypt cells
white blood cells
cells which produce red and white blood cells
At high doses Radiation sickness (syndrome)
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.
DT (Sv) = DA (Gy) x QF
QF for X-ray,  and  = 1
QF for  = 20
Effective dose dose equivalent weighted to account for the different
equivalent: susceptibilities of various tissue types to radiation
damage
HE = TDTWT
WT weighting factor (International Commission on
Radiological Protection (ICRP))

7. ICRP Weighting Factors (WT)
Tissue or organ WT
testes or ovaries 0.25
breast
red bone marrow 0.12
lung
thyroid
bone surfaces 0.03
remainder 0.3
Whole body total 1.00
Maximum Permissable Dose (Whole Body)
Damage to tissue depends on: dose received
gender
age
HE (max) = 50(N-18)

8. External vs Internal exposure
Absorbed dose  (distance) (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:
90Sr, 89Sr, 32P bones
131I thyroid
In addition to a nuclides radiological half-life it is necessary to define an
analogous biological half-life, tbiol. This allows an effective half-life, teff, to
predict the impact of radioisotope ingestion.
Teff = (tbiol.trad)/[(tbiol+trad)]