P1- Atomic structure Flashcards
Radius of an atom
1 x 10^-10
Definition of isotopes
Atoms with the same number of protons but a different number of neutrons
Democritus’ Atomic theory (500BC)
Small spheres that make up everything
John Dalton’s ‘solid spheres’ (1800s)
Different solid spheres that are unique to each element
JJ Thompson’s Plum Pudding model (1897)
A ball of positive charge with negative electrons embedded within. An even distribution of charge and mass
Ernst Rutherford’s Nuclear model (1909)
Tried the Gold foil alpha scattering experiment. Found that most of the mass of the atom must be concentrated at the centre in a tiny positively charged nucleas. Most of the atom is empty space.
Niels Bohr’s Planetary model (1913)
Discovered electron shells/energy levels which were fixed distances away from the nucleus
Ernst Rutherford discovery (1913)
Discovered protons which made up a nucleus. All proton particles had the same positive charge adding to the overall charge of the nucleus
James Chadwick discovery (1932)
Proved the existence of the neutron, which explained the imbalance between the atomic and mass number
Where can electrons move in the atom
Within the energy levels
What happens if an atom gains energy by absorbing EM radiation
Move to a higher energy level (further away from nucleus)
What happens if an atom loses energy by releasing EM radiation
Move to a lower energy level (closer to the nucleus)
What is radioactive decay
Unstable isotopes tend to decay into other elements and give out radiation as they try to become more stable
What types of ionising radiation do radioactive substances spit out
Alpha, beta and gamma radiation (or sometimes neutrons)
What is ionising radiation
Radiation that knocks electrons off atoms, creating positive ions
Radiation emission is…
Completely random
What does radiation emission being completely random mean
You can never predict when a sample will decay and give off radiation
How can you approximately predict how many decays emitted from a source over an extended period of time
Calculating its half life
What does ionising mean
How dangerous radiation is
What is an alpha particle
Two protons and two neutrons (like a helium nucleus)
The range in air for an alpha particle
A few centimetres
The penetrating power for an alpha particle
Low
What is an alpha particle stopped/absorbed by
A sheet of paper, Skin
The ionising power for an alpha particle
Srongly ionising
What is a beta particle
High speed electrons released by the nucleus. They have virtually no mass.
The range in air for a beta particle
A few metres
The penetrating power of a beta particle
Moderate
What is a beta particle stopped/ absorbed by
Around 5mm of aluminium
The ionising power of a beta particle
Moderately ionising
What is a gamma particle
Waves of high frequency Electromagnetic radiation released by the nucleus
The range in air for a gamma particle
Infinite (can travel through space)
The penetrating power of a gamma particle
High
What are gamma particles stopped/ absorbed by
Thick sheets of lead or multiple metres of concrete
The ionising power of gamma particles
Weakly ionsing
What are nuclear equations
Ways of showing radioactive decay by using element symbols and alpha/beta/gamma particles
Mass number of alpha particle
4
Atomic number of alpha particle
2
Mass number of beta particle
0
Atomic number of beta particle
-1
Mass number of gamma particle
0
Atomic number of gamma particle
0
What are gamma rays a way of getting rid of
Excess energy from the nucleus
What can radiation be measured with
A Geiger-Muller tube and counter which records count rate (number of radiation counts reaching it per second)
Definition of Half-Life
The time it takes for a number of radioactive nuclei or the count rate in a sample to decrease by half/ 50%
What happens when a radioactive nucleus decays to become a stable nucleus
The activity as a whole decreases
Why are sources with a short half life dangerous at the start
Because of the high amount of radiation they emit at the start, but then they quickly become safe
What is Background radiation
The low-level radiation that’s around us all the time
3 places background radiation comes from
1) Radioactivity of naturally occurring unstable isotopes which are all around us (in air, food, building materials and rocks)
2) Radiation from space known as cosmic rays which mostly come from the sun. The Earth’s atmosphere protects us from much of this
3) Radiation due to human activity like the fallout from nuclear explosions or nuclear waste (this only represents a tiny proportion)
What does the radiation dose tell you?
The risk of harm to body tissues due to exposure to radiation
What is radiation dose measured in?
Sieverts (Sv)
2 things that can affect your radiation dose
-Where you live
-Whether your job involves radiation
What is Irradiation?
Exposure to radiation
Does irradiating something make it radioactive?
No
3 ways to reduce the effects of irradiation
-Keeping sources in lead lined boxes
-Standing behind barriers
-Using remote controlled arms
What is contamination?
Radioactive particles getting onto or into objects, e.g touching a radioactive source without gloves on
What might contaminating atoms do?
Decay and release radiation which causes harm to a person
Why is contamination dangerous?
Radioactive particles could get inside the body
3 ways to prevent contamination
-Wear gloves
-Use tongs
-Wear protective suits
What are the 2 most dangerous radioactive sources outside the body?
Beta
Gamma
Why are beta and gamma the most dangerous radioactive sources outside the body?
Beta and gamma can penetrate the body/skin and get to the organ whereas alpha can’t penetrate the skin
What is the most dangerous radioactive substance inside the body?
Alpha
Why is alpha the most dangerous radioactive substance inside the body?
They do all their damage in a very localised area, so contamination (rather than irradiation) is the major concern with alpha particles in the body
3 risks of using radiation
1) It can enter living cells and ionise atoms within them leading to tissue damage
2) Lower doses cause minor damage without killing cells, increasing risk of cancer
3) Higher doses kill cells completely causing radiation sickness (vomiting, tiredness)
What is radiotherapy?
Treating cancer with radiation
How does radiotherapy work?
Gamma rays are directed carefully with the right dosage to kill cancer cells without damaging too many cells
What is the use of tracers?
Can be used to diagnose life threatening conditions and the risk of one is very small
2 types of nuclear reaction
-Nuclear Fission
-Nuclear Fusion
What is Nuclear Fission?
Splitting a large, unstable nucleus
What 3 things form when the atom in nuclear fission splits?
-2 new lighter elements (roughly the same size)
-2 or 3 neutrons
-Gamma rays
What do all nuclear fission products have?
Kinetic energy
Why is spontaneous fission rare?
Because the nucleus has to absorb a neutron before it splits
What is a chain reaction (as a result of nuclear fission)?
If any of the neutrons formed from nuclear fission are moving slow enough ti be absorbed by another nucleus, more fission occurs
How do nuclear weapons work?
When uncontrolled chain reactions quickly lead to lots of energy being released as an explosion
What is Nuclear Fusion
The joining of two light nuclei to form a heavier nucleus
What happens to the mass of the nuclei in this reaction?
-The heavier nucleus doesn’t have as much mass as the two separate, light nuclei did
-Some of the mass of the light nuclei is converted to energy
Which nuclear reaction releases more energy?
Nuclear Fusion
