P4 Flashcards
What did john dalton do?
Thought that everything was made off tiny spheres called atoms
What did JJ Thomson do?
Discovered electrons that could be removed from atoms. Thomson made the plum pudding model
What did the plum pudding model suggest?
Atoms were spheres of positive charge with tiny negative electrons stuck on them
What did Rutherford discover?
1909 he fired a beam of alpha particles at thin gold foil(alpha scattering experiment) he discovered the nucleus
What happened in Rutherford’s scattering experiment?
Fired a beam of alpha particle at thin gold foil. If the atom was a plum pudding it would be expected for the particles to pass through but a lot of them deflected off and some even deflected back from where they were fired
Why Rutherford scattering experiment was important?
Because alpha particles were deflected back , scientists realised that most of the mass must be concentrated at the centre in a tiny nucleus. It must have a positive charge as it repelled positive alpha particles. They also realised most of the alpha particles went straight through because the majority of the atom is empty space. This was the first nuclear model for the atom
What did Niels Bohr discover?
Said electrons orbiting the nucleus do so at a certain distance called energy levels. He was right
What was Rutherford’s nuclear model?
Positively charged nucleus surrounded by a cloud of negative electrons
How did the nuclear model change?
Evidence suggested nucleus was made off a group of particles called protons(positive charge)
What did James Chadwick do?
Proved the existence of neutrons which explained the imbalance between atomic and mass numbers.
What is the atoms radius?
1 x 10^-10
What is the basic structure of an atom?
Positively charged nucleus containing both protons and neutrons , surrounded by shells containing negatively charged electrons
What is the radius of the nucleus?
Less than 1/10000 of the radius of the atom
Where is most of the mass concentrated in an atom?
The centre
What charge do atoms have?
0
protons =electrons so they cancel each other out
How might electromagnetic radiation change the arrangement of electrons?
If they absorb EM radiation they move to a higher energy level , further from the nucleus. If they release EM radiation they move to a lower energy level that is closer to the nucleus
What is an ion ?
A charged atom
What is the atomic number?
Number of protons in an atom. Also electrons
What is the mass number of an atom?
Number of protons and neutrons in its nucleus
What is an isotope?
Atoms with the same number of protons but a different number of neutrons , it has a different mass number
How stable are isotopes?
Usually an element has one or two stable isotopes. Others are unstable
What happens to unstable isotopes?
Tend to decay into other element and give out radiation as they try to become more stable. Go through process of radioactive decay.
What is the process of radioactive decay?
try to balance the number of protons and neutrons in their nucleus or get rid of any excess energy
What do radioactive substances do?
Spit out one or more types or ionising radiation from their nucleus. Also release neutrons when they decay to rebalance the number of protons and neutrons.
What are the particles of ionising radiation spit out by radioactive substances?
Alpa
Beta
Gamma
What is ionising radiation?
Radiation that knocks electrons off atoms, creating positive ions. The ionising power of a radiation source is how easily it can do this
What is alpha radiation?
When an alpha particle is emitted from the nucleus . An alpha particle is two neutrons and two protons (like a helium nucleus)
What is alpha radiation used for?
Smoke detectors , it ionises air particles causing a current to flow. If there is smoke in the air , it binds to the ions- menaing the current stops and the alarm sounds
What is radiation?
Some atomic nuclei are unstable . So radiation is given out to change the atom to become more stable
Features of alpha particles?
- Dont penetrate very far into materials and are stopped quickly . They can only travel a few cm in the air and are absorbed by a sheet of paper
- because of size , they are strongly ionised
What is beta radiation?
A Beta particle is simply a fast moving electrons released by the nucleus. Beta particles have virtually no mass and a charge of -1
Features of beta radiation?
- moderate ionising. They penetrate moderately far into materials before colliding and have a range in air of a few metres. They are absorbed by a sheet of aluminum
- every beta particles emitted, a neutron in the nucleus has turned into a proton
What is Gamma radiation?
Waves of electromagnetic radiation released by the nucleus
Features of Gamma radiation?
- Penetrate far into a material without being stopped and will travel a long distance through air
- weakly ionising as they tend to pass through rather than collide with atoms. Eventually they hit something an do damage
- they can be absorbed by thick sheets of lead or metres of concrete.
What is the activity?
Rate at which a source of unstable nuclei decays
How is activity measured?
In becquerel (Bq)
What is the count rate?
Number of decays recored each second by a detector
What is an alpha particle?
Consists of two neutrons snd protons , same as the helium nucleus
What is a beta particle?
A high speed electron ejected from the nucleus as the neutron turns into a proton
What is gamma ray?
Electromagnetic radiation
What do nuclear equations do?
Represent radioactive decay by using element symbols
How is alpha particles represented in an equation?
4
He
2
How is a beta particle represented in an equation?
0
e
-1
What form are nuclear equations written in?
Atom before decay —> atom after decay +radiation emitted
What is the rule for nuclear equations?
Total mass and atomic numbers must be equal on both sides
What happens when an atom emits an alpha particle ?
Atomic number reduces by 2 and mass number reduces by 4
What happens to the charge of the nucleus when alpha particles are emitted?
The charge of the nucleus decreases. As the proton is positively charged and neutron is neutral
What happens when beta decay occurs?
A neutron in the nucleus turns into a proton and releases a fast moving electron
What happens to the nucleus during beta decay?
Number of protons in the nucleus increases by 1. This increases the positive charge of the nucleus (atomic number). Because the nucleus has lot a neutrons and gained a proton during beta decay , the mass of the nucleus does not change
What will happen in both alpha and beta radiation?
A new element will be formed , as the number of protons changes
What are gamma rays a way off?
Getting rid of excess energy from a nucleus. So there is no change to the atomic mass or atomic number of the atom
Word to describe radioactive decay?
Random
How to measure radiation?
Geiger muller tube and counter , which records the count rate-the number of radiation counts reaching it per second.
What is the half life?
The time it takes for the number of nuclei of the isotope in a sample to halve , or the time it takes for the count rate from the sample containing the isotope to fall to half the intial level
What happens over time to a radioactive substance?
It decreases over time as each time a radioactive nucleus decays to become a stable nucleus the activity will decrease
What are the risks of ionising radiation ?
Can enter living cells and ionise atoms within them. This can damage the cells (which can cause things like cancer) or kill them off completely. Thats why its important tou know the precautions to take when working with any sources of radiation
What is radioactive contamination?
Unwanted presence of materials containing radioactive atoms on other materials. The hazard from contamination is due to decay of the contaminating atoms , the type of radiation emitted effects the level of hazard.
What is irridation?
The process of exposing an object to nuclear radiation . The irradiated object does not become radioactive.
What does the seriousness of irradiation or contamination depend on?
The sourcd
Most dangerous radiation sources outside the body?
Gamma and beta
Why beta and gamma are so dangerous outside the body?
They can penetrate the body get to the delicate organs
Why alpha is less dangerous outside the body?
It cant penetrate the skin and is easily blocked by a small air gap
What sources are worst when irridate ?
All high levels or irridation are dangerous but especially beta and gamma
What source most dangerous inside the body?
Alpha because all their damage is very localised . So contamination rather than irradiation , it the major concern.
Why beta and gamma aren’t as dangerous inside the body?
Radiation is absorbed over a wide area and some passes put of the body altogether. Gamma sources are the least dangerous inside the body , as they mostly pass straight out , they have the lowest ionising power.
Why knowing how radiation effects our bodies can help us?
The more we understand the better we can protect ourselves. Important that research is published.
