Hulk it Flashcards
What is ionising radiation?
These are fast moving particles that collide with orbital electrons, ejecting them out of the orbital leaving behind a positively charged nucleus and negative electron, these are positive and negative ions.
What are the types of ionising radiation?
- Alpha particles are the nuclei of Helium atoms
- Beta particles have the mass of an electron where Beta plus (positron) is positively charged and Beta minus (electron) is negatively charged
- Gamma rays are photons with no mass or charge travelling at the speed of light
How is nuclear stability achieved?
Draw visual
Within the nucleus there are protons that repel each other, and tend to break up the nucleus, to overcome this, the nucleus contains neutrons that bind with each other and the protons.
Differences between smaller and larger nuclei in terms of nucleotides
Small Nuclei have equal numbers of protons and neutrons to maintain stability
Large Nuclei have more neutrons than protons to maintain stability, this is why larger nuclei tend to be more unstable
Draw a segre plot
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What are the different models of the atom?
- Thompson pudding
Rutherford Planetory
Bohr (Rutherford/bohr) - energy levels
Nuclear decay is..
random and spontaneous
Radioactive decay and its effect on mass
decay is not reducing mass but radioactive mass, the mass will not reduce eg. uranium becomes half lead
What is the attractive force (strong force) and is it present in the nucleus?
This is the force of attraction between the neutrons and protons, it acts over an extremely short range of 1 x 10^-15, this force is not present outisde the nucleus.
As distance increases, strong nuclear force decreases
What is the electromagnetic force, what is it inversely proportional to?
this is the repulsive force between protons and the attractive force between protons and electrons. It acts over a very large range and is inversely proportioal to distance squared. This electromagnetic force has a magnitude of 1/100 of the strong force
What is the weak nuclear force?
this is the force between the departing Beta particle and the daughter nucleus. It acts over a range of 1 x 10^-18m and has a strength of 1 x 10^-13
Why does alpha decay occur?
A nucleus with too many protons and neutrons breaks up emmitting alpha particles which are nuclei of helium atoms
Do alpha particles undergo many collisions, and why can they not penetrate deep into matter
Alpha particles are large and undergo many collisons as they pass through matter producing many ions. With each collision the alpha particle looses energy due to the large number of collisions it looses its energy quickly and comes to an abbrupt halt. Therefore, the alpha particle cannot penetrate deep into matter.
A thin sheet of paper or the top layer of human skin can absorb the alpha particles. Therefore, alpha particles are not a danger as an external source.
What occurs in beta plus decay?
Occurs in nuclei which contain too many protons or too many neutrons. A proton in the nucleus breaking up into a neutron and a beta plus particle - known as a position
What occurs in beta minus decay
This is the process of a neutron breaking up into a neutron and a beta minus particle
Why can beta particles penetrate further into matter?
Beta particles are much smaller than alpha particles, they undergo less collisons as they pass through matter and produce less ions. Therefore, they can penetrate further into matter, for example, a beta particle can penetrate 2m in air, 7cm in plastic and 1mm in lead
Momentum conservation during beta decay
During beta decay the parent nucleus is at rest with 0 momentum. After the decay, the daughter nucleus is at rest with 0 momentum, while the beta particle is in motion with some momentum. For momentum conservation to be valid, the total initial and total final momentum have to be 0, thus after the decay the momentum of the beta particle needs to be cancelled by the momentum of another particle, this particle is known as the neutrino, which has a near 0 mass and moves at a speed close to that of light, in an opposite direction to the beta particle.
where is the anti-neutreno found
beta minus decay
what happens when you rip a neutron out of a radioactive material?
a proton, electron and anti-neutrino come out
Draw beta plus and beta minus on a space time graph
diagram
Note- what happens in non-quantum measurements (beta decay)
- all these events occur simultaneously
- the ejected particles do not necessarily come from the same place
how does gamma radiation occur?
draw diagram
This is associated with alpha decay and gamma decay where the daughter nucleus is produced in an excited state.
When the daughter nucleus releases the excitation energy in the form of gamma radiation
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why is gamma radiation highly penetrating?
Gamma radiation consists of gamma photons that have negligable mass but move at the speed of light, carrying momentum and energy. Gamma radiation interacts very little with matter producing very few ions, therefore highly penetrating. Gamma radiation can penetrate 2m of lead.
1st law of radioactive decay:
Activity: this is the number of nuclei decaying per second
A proportional to N
A= wavelength (decay constant)N
units of A =Bq (Becquerat)
1Bq= 1dps (disintegrations per second)
Law 2 : Exponential decay law
N= No e ^-wavelength x t
or
A =Ao e ^-wavelength x t
- Half - ;life
Time taken for half the nuclei to decay.
T 1/2 = 0.693/ wavelength
Simplified decay law- how nuclei decay as a fraction of No
N=1/2^n x No
What does a gamma ray emit?
A photon - highly energised, very short wavelength, very high frequency
A gamma ray is a highly energetic, very short wavelength (energy)- smaller than an atom
All 3 forms of ionising radiation releases particles ie. evidence of decay is the ejected particles
Alpha/beta decay all release daughter nucleides - mass
but gamma releases a photon (energy with no mass)
Radiation capability
The ability to ionise/penetrate
Penetrating capability
Gamma- 2 protons, 2 neutrons
Beta- ejecting a positron/electron and neutrino and antineutrino
Alpha- whole proton, 2 x smaller than beta
draw magnetic field diagram
d
carbon 14 dating
love
What was einsteins problem
the mass of a proton +neutron is not the same as a neutron and proton parts
The parts of the nucleus weigh less than the parts
Mass defect formula
Mass defect- nucleus Change in E = mc^2 M proportional to E speed of light will not change if the mass disappeared there must be a relationship with energy
what did Einstein propose the mass defect was?
E proposed that this was not a defect, but the energy needed to bind a nucleus together
mass nucleus = mass of components + binding energy
Steps to find energy
- Find A and Z
- Find A-Z
- find the mass of all the separate parts
- Compare 3 with A
- this is the binding energy
Mass defect formula
Change in mass = Nmn +Zmp+ Zme - Matom
This difference in mass is stored as energy in the bonds that holds the nucleus together, this mass energy conversion is based on einsteins equation E=mc^2
BE is E in E=mc ^2
This is the energy equivalent of the mass defect that is sotred in the bonds between neutrons and neutrons and protons
How much is 1 amu
1u= 1/12 the mass of carbon
how many eV is 1 mega ev
1MeV = 10^6 eV
Variation of binding energy
The large atoms had a large amount of binding energy per nucleon while the small atoms had a low amount of binding energy per nucleon.
Therefore, the large atoms could be split up to release a large amount of energy which is known as fision while the small atoms can be made to combine to form a smaller atom and release the excess binding energy which is known as fusion.
Iron-56 has the highest amount of binding energy per nucleon indicating its strength
Nickel also sits next to iron - both are very hard
What is fision?
This is the process of releasing energy by splitting up a large nucleus by impacting it with a fast moving light particle, the light particle destabalizes the nucleus and breaks it up into smaller nuclei, in the process releases fast moving particles that carry away the fision energy.
