Topic 6 - Radioactivity Flashcards
What did Scientist JJ Thompson show through experiments?
Showed that atoms contain much smaller subatomic particles called electrons with a negative charge.
Supported this with a new model called the ‘Plum Pudding’ model.
That the pudding is made of positively charged material with the plums being the negatively charged electrons.
What did Ernest Rutherford (and friends) find out?
Carried out some experiments that involved studying what happened when positively charged subatomic particles, called alpha particles, pass through various substances. i.e. gold foil
He suggested that atoms were mostly empty space with most of their mass being the nucleus with a positive charge in the middle, with electrons circling around it.
How do electrons orbit?
Electrons can only exist in certain orbits,around the nucleus, called electron shells. > Electron configuration
What about electrons in a neon tube?
In a neon tube, the neon atoms absorb energy , transferred by the electricity because the electrons jump to higher shells.
When the electrons fall back again, they emit energy as electromagnetic radiation that we can see.
What did Niels Bohr amend?
He amended Rutherford’s model of the atom to explain observations like these by suggesting the electrons can only be in fixed orbits around the nucleus.
They cannot be part way between two orbits.
Explains lines in emission and absorption spectra.
What is ionisation?
Sometimes when an atom gains so much energy, that an electron can escape all together.
An atom that has lost or gained an electron is an ion.
Radiation that causes electrons to escape is called ionising radiation.
If an atom loses an electron, it has an overall positive charge making it a positive ion.
What is background radiation?
Being exposed to ionising radiation at a low level, from space and from naturally radioactive substances in the environment.
What is the main source of background radiation and where is it found?
Radon Gas
Produced by rocks that contain small amounts of uranium.
Radon diffuses into the air from rocks and soil and can build up in houses, especially with poor ventilation.
Amount of radon depends on type of rock and uranium content.
What else can contribute to background radiation?
Foods contain small amounts and hospital treatments like x-rays and gamma rays, also expose people to background radiation.
What are cosmic rays?
High-energy, charge particles stream out of the Sun and other stars.
How do you measure radioactivity?
Can be dedicated using photographic film, which becomes darker and darker as more radiation reaches it.
However, the film has to be developed in order to measure the amount of radiation.
What is a Geiger Müller tube? (GM tube)
Radiation passing through the tube ionises gas inside it and allows a short pulse of current to flow.
GM tubes can be connected to a counter, to count the pulses of current, or the GM tube may give a click each time radiation is detected.
The count rate is the number of clicks per second or minute
Need to take several readings and find the mean.
What does it mean when the nuclei of a radioactive substance is “unstable”?
Means it can easily change or decay.
You cannot predict when a nucleus will decay, it’s a random process.
What are Alpha Particles?
Contain 2 protons and 2 neutrons, just like a helium nucleus.
They have no electrons and a charge of +2
What are beta particles?
High energy, high-speed electrons.
A charge of -1
What are positrons?
High energy, high speed.
Same mass as electrons and charge of +1
What are gamma rays?
High-frequency electromagnetic waves.
No electric charge.
What can also be emitted from an unstable nucleus?
Neutrons = then theres a charge of +1
Describe some functions of each one.
Alpha Particles: -Will travel a few centimetres in air - Very ionising - Can be stopped by a sheet of paper Beta particles: - Will travel a few metres in air - Moderately ionising - Can be stopped by 3mm thick of aluminium Gamma rays: - Will travel a few kilometres in air - Weakly ionising - Need thick lead of several meters of concrete to stop
What happens during decay for particles?
Alpha Particles:
Mass number of nucleus goes down by 4 and atomic number goes down by 2
Beta - particles:
A neutron changes into a proton and an electron. The electron is ejected from atom.
Atomic number increases by 1 but no change to mass number.
Beta + particles:
A proton becomes a neutron and positron.
Atomic number goes down by 1 but mass stays same .
What happens if an neutron is ejected from atom?
.
The mass number goes down by 1 but atomic number doesn’t.
What happens when the nuclei loses energy in gamma radiation?
Lose energy when the subatomic particles in nucleus are rearranged. Helps to make more stable.
What is a nuclear equation?
Shows what happens during radioactive decay e.g.
- 225
RB ——> e + RB
- 225
- -1. 62
