Ionizing radiation 1 Flashcards
how much of ionizng radiation is natural ?
> 80% - of what we are exposed to daily
what are different sources of radiation exposure ?
radon cosmic rays terrestrial internal medical other
what is radon ?
causes most of the natural exposure
its a gas present in rocks, soil, water and air
how are we exposed to cosmic rays ?
produced in the galaxy and from the sun
when does your exposure to cosmic rays increase ?
at higher altitudes
- pilots are exposed to more of them
- pilots are thought to be exposed to about 20mSv per year
what is ionizing radiation ?
its a physical toxic agent
what is an example of a food containing lots of radioactive material ?
bananas because they contain lots of potassium
what does it mean by internal exposure to radiation ?
we are radioactive
- we contain carbon-14 and K-40
- sufficient amounts in the body to account for 10% of daily exposure
what is uranium-238 principally found in and what does it degrade into ?
principally in rock
converted to Ra-226 then to Ra-222 then to lead
when were x-rays discovered ?
1895 by roentgrn
what did becquerel observe ?
in 1896 he noticed that uranium salts emit radiation
- due to radioactive isotope
what did bergonie and tribondeau discover in 1906 ?
stem/immature cells are more sensitive than fully differentiated cells
younger tissues and organs are more radiosensitive than their adult equivalents
tissues and organs with the highest metabolic activity are the most radiosensitive
cells with the fastest rates of division are most sensitive- epithelial cells
what did workers with ionizing radiation discover ?
workers discovered that radioactive material could cause harm when handled
- they causes red sore skin and blisters and it also damaged their eyes
when are you most sensitive to ionizing radiation ?
most sensitive as a fetus, then your sensitivity decreases to adulthood and then sensitivity increases in the elderly
what did muller show ?
1927- showed that ionizing radiation is mutagenic in fruit flies
what was discovered in the 1940s?
discovery that ionizing radiation results in free radical generation via hydrolysis of water and that oxygen is a radiosensitizer
- proved the effects of ionizing radiation are caused indirectly
what happened in 1945?
atomic bombs - caused 100000 deaths
what happened in the 1950/60s?
atmosphere testing of nuclear weapons and windscale fire
- windscale fire was when the military reactor caught fire and released a lot of radiation
what happened in 1970/80s?
3 mile island and chernobyl
- chernobyl disaster was when the reactor exploded and release a lot of radiation, 50 people died
- russian authorities didnt provide antidote potassium iodide quickly enough
what can radium paint do ?
it glows in the dark so was used to paint the dials of watches
- used to produce luminous instruments in WW1
- it contains Ra-226 which gives off alpha particles which damage osteoblasts
- women using this paint in ww1 in the us used to use fine paint brushes which they licked to produce a fine tip and this caused them to suffer serious necrosis of jaw bone and many suffered cancer later in life
- radium concentrates in bone
what is 1 gray (Gy)?
1 joule of energy absorbed per kg of tissue
what varies with radiation type ?
biological effects
- same absorbed dose of x-rays and alpha particles produces different levels of damage
what tissue is more likely to absorb ionizing radiation ?
dense tissue such as bone
how much more damaging are alpha particles compared to x-rays ?
20x more damaging per unit of absorbed dose
what affects the biological damage ionizing particles can cause ?
size- the bigger it is the more likely it will interact with particles in cells
kinetics- slower it is the more likley it will interact with particles in cells
therefore alpha particles more readily interact with particles in cell - they are only dangerous to use internally because they cant penetrate the skin due to the dead cells (striatum corneum )
what does it mean by linear energy transfer?
probability that a collision will occur
what is 1 sievert (Sv)?
dose that produces the same biological effect as 1 Gy of x-rays
what distances do alpha particles travel before they cause damage ?
about 4 cm in the air before they collide with another particles and disperse energy
in the body it travels ony 40 micrometers before interactionn
what are the 2 components of ionizing radiation ?
electrical magnetic radiation-
what is 1 Sv equal to ?
1Gy * Wt
- x rays, gamma rays and beta particles have a Wt=1
- protons have a Wt=2
- neutrons have a variable Wt between 5-20 depending on kinetic energy
- alpha particles hvae a Wt=20
what does the radiolysis of water produce ?
produces hydroxyl radicals- small lipid solule highly diffusable
- they are very powerful oxidising agents
can produce hydrogen peroxide, superoxide anions and electrons are released
how are reactive oxygen species detoxified ?
- SUPEROXIDE DISMUTASE= copper-zincSOD and manganeseSOD present in mitochondria - this produces hydrogen peroxide from 2 oxygen molecules and 2 hydrogen molecules
- CATALASE= present in peroxisomes converts hydrogen perioxide into water and oxygen
- GLUTATHIONE peroxidases- present in most compartments of the cell - firstly reacts hydrogen peroxide with antioxidant GSH to produce water and GSSG- then GSSG reacts with NADPH and hydrogen ion to re-produced GSH
What do anti-oxidant scavengers do ?
present in the aqueous phase of the cell - GSH and ascorbic acid
- these react with free radicals to minimise free radical damage
in the lipid phase- vit E and carotenoids- present in cell membranes
what is the oxygen paradox ?
we need oxygen for life
oxygen is toxic to cells because mitochondria are a source of ROS
- the electron transport chain is not 100% efficient electrons leak producng superoxide anions which can then produce hydrogen peroxide in cells
what damage can free radical ROS do to DNA ?
it can cause single or double strand breaks- these are difficult to repair without altering fidelity of DNA
- this can lead to mutations that can lead to teratogenesis or cancer
- this can lead to cell death and then radiation syndrome
what are the 2 components of the effects of ionising radiation ?
DETERMINISTIC- threshold dose and severity increases with exposure
-severity and frequency increases with exposure up to a max effect
STOCHASTIC- have no threshold, probability of effect increases with dose but not with severity-effects increase in a linear manner with exposure, this implies no safe limit
what are the examples of deterministic and stochastic effects of ionising radiation ?
deterministic - radiation sickness, damage to skin and cataracts
stochastic- genetic damage and cancer and teratogenesis
