P7 Flashcards
whats the radius of an atom?
1 x 10-10
most of an atom’s mass is where?
the nucleus
what’s the radius of the nucleus?
1/10000 the radius of the atom
atomic nuumber
smaller number, shows number of protons
mass number
larger number, shows total number of protons and neutrons
how can electrons move away from the nucleus
absorption of electromagnetic radiation
how can electrons move closer to the nucleus?
emission of electromagnetic radiation
isotopes
same number of protons and electrons, different number of neutrons
describe alpha
what it is: 2 protons, 2 neutrons (helium nucleus)
absorbed by: skin and paper
range in air: 5cm
ionising power: high
example decay:
219/86 Ra -> 215/84 Po + 4/2 He
causes mass of the nucleus to decrease
describe beta
what it is: high speed electron
absorbed by: thin aluminium
range in air: 1m
ionising power: medium
example decay:
14/6 C -> 14/7N + 0/-1 e
doesn’t change the mass of the nucleus, but charge increases
describe gamma
what it is: electromagnetic radiation
absorbed by: thick lead
range in air: infinite
ionising power: low
example decay: gamma ray emission does not change the mass or charge of the nucleus
describe JJ Thompson’s plum pudding model
- atom is a positive ball, with electrons embedded in it
what were the results of the alpha scattering experiment?
- most of the alpha particles passed straight through the foil
- a small number of alpha particles were deflected by large angles (> 4°) as they passed through the foil
- a very small number of alpha particles came straight back off the foil
this led to the discovery of the nucleus
what did the nuclear model show?
all the mass and positive charge is concentrated in the centre of the atom- the nucleus
What did Bohr do?
added electron orbits to the nuclear model
what did Chadwick do 20 years after the Nuclear model?
discovered neutrons
radioactive decay is…
random
what is half life?
the time it takes for the count rate, activity or number of radioactive nuclei of an isotope to fall to half its initial value
Alpha, Beta and Gamma are ___ which means they can remove electrons from atoms. In human cells, this increases risks of ____
ionizing, cancer
irradiation
the process of exposing an object to nuclear radiation
contamination
the unwanted presence of radioactive substances on other materials
where might background radiation come from?
naturally: rocks, cosmic rays
man made: nuclear weapon tests and accidents
what could level of background radiation be effected by?
job or location
short half-life
- high activity as more radiation is emitted per second
- more dangerous as they can provide a high dose
long half life
- emit less radiation per second but stay radioactive for a longer time
- some radioactive waste products need to be stored for hundreds of years before they’re safe
fission
the splitting of a large, unstable nucleus
spontaneous fission is ___ as usually the unstable nucleus must _____
rare
absorb a neutron
the nucleus undergoing fission splits into ____, roughly equal in size, and emits two or three ___ plus ____. ____ is released
two smaller nuclei, neutrons, gamma rays, energy
all the fission products have ___, so neutrons could go on to start a ____
kinetic energy, chain reaction
T/F the explosion of a nuclear weapon is an example of a controlled chain reaction
F- it’s uncontrolled. chain reactions in nuclear reactors are controlled to control energy release
fusion
the joining of two light nuclei to form a heavier one. in this process, some mass is converted into energy in the form of radiation
how is nuclear radiation used in exploration of internal organs, and state the benefits and risks
radioactive isotopes are taken into the body, and the radiation they emit can be detected outside the body
Benefits- doctors can investigate internal organs without surgery
Risks- increased danger of developing cancer
how is nuclear radiation used in control or destruction of unwanted tissiue, and state the benefits and risks
a beam of high energy radiation (usually gamma) is fired at a tumour
Benefits- cancerous tumours can be destroyed or diminished
risks- increased danger of developing new cancers
