radiation Flashcards
what makes atoms unstable
unstable nucleus
- it’s an isotope (radioisotope)
- same no. protons diff no. neutrons
how do atoms get stable
give out NUCLEAR radiation at random (decay)
give out ALPHA, BETA, GAMMA
alpha
He⁴ ₂
2 protons + 2 neutrons
+2 charge
mass 4
alpha absorbed by
paper/air
alpha ionising power
STRONG
big mass knocks atoms off easily
attracts electrons off
looses KE quickly
beta
e ⁰-₁
high speed electron
-1 charge
1/1800 mass
beta absorbed by
aluminium
beta ionising power
WEAK repels electrons off
smaller mass
loses KE less quicklt
gamma
high frequency emag. wave
fastest - speed of light
0 charge
0 mass
gamma absorbed by
thick lead or conceete
gamma ionising
VERY WEAK
- has to hit directly
- no mass
- loses KE slowly
magnetic field affect on radiation
DEFLECTS alpha / beta in opposite direction (oppositely charged)
no affect on gamma (no charge)
background radiation
exists all around from natural sources (ground rocks space)
subtract from radioactive source
ionise
knock electrons off other atoms
as soon as radiation ionises it loses KE
increase likelihood of ionising = smaller penetrating distance
detect radiation
GM tube and counter
photographic film (clear>dark)
why do unstable atoms decay
to become stable
alpha decay
proton no. down 2
mass no. down 4
new element
beta decay
proton no. up 1
mass no. SAME (neutron become proton and electron)
new element
gamma decay
gives of gamma radiation (had too much energy)
no change to numbers
same element
neutron radiation/ decay
eject a neutron
proton no. has no change
mass no. down 1
same element
how to measure activity
gm tube and counter or rate meter
becquerels
how many nuclei are decaying per second
1Bq = 1 decay per second
half life
how long (average) it takes for the activity to go down by HALF - this is constant
or how long it takes for the number of unstable nuclei to go down by half
longer time irons out fluctuations due to random decay
what fraction of the orrigional substamce is still unstable
1/2^no. half lives
uses of radiation (medical)
destroying/ shrinking tumors - gamma (penetrates into body) - long 1/2 life dont replace regularly
radioactive tracer for imaging - gamma (penetrates out body) - short wont cause damage to healthy cells
sterilisation of surgical tools - gamma (penetrates through packaging) - long dont replace regularly
uses of radiation (industrial)
smoke alarms - alpha (smoke can block particles) - long 1/2 life dont replace regularly
thickness control - beta (paper) gamma(steel) can pass through - long dont replace regularly
radioactive tracker for locating leaks - gamma (can penetrate out) - medium (long enough to measure short enought to not contaminate)
carbon dating - beta - 5700 years (C-14)
radioactive dating of rocks - fraction of unstable:stable isotopes - long
dangers of radiation
irradiation
contamination
irradiation
- alpha/beta/gamma hits object
- object doesnt becoe radioactive
- can be vlocked with shielding
- stops when source is removed
contamination
- occurs if radioactive source is on or in the object
- contaminated object will be radioactive as long as source is in/on it
- once object is contaminated radiation cant be blocked from it
- it can be very difficult to remove contamination
+/- of contamination
+ isotopes can be ued as tracers
+ uses of short half life means exposure is limited
+ imaging can replace invasive surgery
- isotopes may not go where wanted
- can be difficult to remove
- exposure can damage healthy cells
radioactive waste
- daughter nuclei have a long 1/2 life + are very hot
- difficult to dispose of so are placed in COOLING PONDS to absorb the heat and radiation
- need to be safely stored for a long time till activity drops
precautions to dispose radioactive waste
- strong/thick containers
- not rust (dont leak)
- stored securely - so terrorists cant steal
- stored deep in water
- not near water table (cant contaminate drinking water)
fusion
2 light nuclei COMBINE to form large nucleus
mass is lost - changes to energy - E = mc^2
- to overcome electrostatic repulsion between protons they move fast + close to fuse (increase temp + pressure)
- this fuels stars
fission
large nucleus SPLIT into 2 smaller nuclei (+2/3 neutrons)
- slow moving neutron collides w nucleus
- SPLINTS into 2 daughter nuclei (+2/3 neutrons)
- energy released as KE of products
- neutrons from one fission cause fission of another (chain reaction)
nuclear reactor
- fuel rods, moderator, control rods, water, steam, electrical output
nuclear(fuel) -> thermal(water) -(boils)-> KE(steam) -> KE(turbine) -> electrical
fuel rods
contain U-235 nuclei
- slow moving neutron collides w nucleus + splits it
moderator
- neutrons release in fission are travelling too fast to cause split
- slowed down by moderator
GRAPHITE/WATER
control rods
- if every neutron caused fission reactions would go out of control + cause explosion
- control rods ABSORB NEUTRONS to slow reaction rate
- lowered/raised to absorb more / less
BORON
