P7 Flashcards
Where in the atom does nuclear radiation come from
The nucleus
What is ionising radiation
Radiation that changes an atom into an ion
What can ionising radiation cause
Cancer- mutates dna and kills cells
What is radiation
The particles or waves being emmited by radioactive substances
In a radioactive atom, why are particles or waves emmited
The nucleus is unstable and so it emits particles or waves to form a more stable atom. This process is called radioactivity or radioactive decay
What is nuclear fission
Big nuclei being split into 2 or more daughter nuclei
What is nuclear fusion
2 smaller atoms joining together - making a bigger atom / nucleus
When was daltons’s model of the atom
1808
What did dalton come up with
All matter is made up of tiny spherical atoms, atoms can’t be broken into smaller parts, atoms of particular elements are identical and differ from those of other elements
When was JJ thompsons plum pudding model discovered
1904
What did jj thompson come up with
He knew there were electrons, he knew there was no electric charge so he came up with a sphere of positive charge with electrons evenly distributed
When was rutherfords nuclear model of the atom discivered
1911
3 of rutherfords observations
- Most alpha particles went straight through meaning most of the atom is empty space
- some particles are deflected meaning the nucleus is very small and in the centre
- very few particles are repelled back meaning the nucleus is positively charged
What does an alpha particle contain
2 protons and 2 neutrons
When was bohr’s plantenary model of the atom discovered
1914
What did bohr discover
The electrons are aranged in shells which orbit the nucleus. They can move between shells by emitting or absorbing electromagnetic radiation
3 reasons as to why some atoms are radioactive
- nucleus is unstable
- the nucleus has too many neutrons or not enough
- nucleus is too big and wants to break up
What is a radioisotope
The nucleus of isotope is unsavke
What is activity?
The number of unstable nuclei that decay every second
What is Count-rate?
The number of decays recorded each second by a detector
What is half-life?
The time that it takes half the atom in a sample to decay
What process is radioactive decay?
Spontaneous (can’t be controlled and not affected by temperature)
How is alpha radiation stopped?
By paper
How is beta radiation stopped?
A sheet of aluminium a few metres thick
How are gamma rays stopped?
Thick walls of concrete or lead
Why was rutherfords model accepted?
-agreed exactly with the measurements geiger and marsden made in their experiements
-explained radioactivity in terms of changes that happen to an unstable nuclei when emmiting radiation
-predicited existence of neutrons
Problems with the plum pudding model:
Could not explain why some alpha particles were scattered through large angles
Radioactive decay
An unstable nucleus becoming more stable by emitting alpha or beta particles
Why are most nuclei stable?
Because the protons and neutrons inside a nucleus are held together by a string nuclear force
Irridated
When an object is exposed to ionising radiation, but does not hecome radioactive
Radioactive contamination
Unwanted presence of materials containing radioactive atoms on other materials
What may cause ionisation?
X-rays, fast moving protons and neutrons
How do workers who use ionising radiation reduce their exposure?
-keep as far away as possible from the source
-spending little time in at-risk areas
-sheilding themselves by staying behind thick concrete barriers
Example of radiation in use:
Smoke alarms (contain the radioactive isotope that sends out alpha particles in a circuit)
Current model of the atom:
-radius of atom is 1x10^-10
-electrons in energy levels move within the atom
-if they gain energy by absorbing EM radiation, they move to a higher energy level
What do unstable isotopes do to other elements?
They tend to decay into other elements and give out radiation as they try to become more stable (radioactive decay)
What does ionising radiation do to electrons?
It knocks them off atoms, creating positive ions. The ionising power of a radiation source is how easily it can do this
Nuclear equations:
Atom before decay ➡️ atom after decay + radiation emitted
Risks of ionising radiation:
It can enter living cells, damage them or kill them
Irradiation
Exposure to radiation
How to control irriadation:
-The source may be in a different room and remote control arms are used to handle it
-keeping sources in lead-lined boxes
–standing behind barriers
How is something contaminated?
If unwanted radioactive atoms get onto, or into an object
Example of contamination:
If you touch a radioactive source without wearing gloves
How can you reduce contamination?
-Wear gloves and use tongs
-wear protective suits
Why are alpha particles less dangerous?
It can’t penetrate skin
How are alpha particles dangerous in the body?
-They damage very localised areas so contaminate them
How are beta particles less damaging in the body?
Radiation is absorbed over a wider area and some passes out the body altogether
How are gamma sources not dangerous in the body?
-they mostly pass straight out and have the lowest ionising power
