Nuclear Physics Flashcards
(31 cards)
History of Atom?
In 5th century BC Democritius proposed all matter was made up of tiny identical lumps called atomos. 1804 Dalton put forward matter was made of tiny spheres called atoms which couldn’t be broken up. 100 years later Thompson discovered electrons could be removed from atoms and suggested atoms were spheres of positive charge will negative electrons stuck in and showed this in the plum pudding model. In 1909 Rutherfords scattering experiment was done by Geiger and Marsden where a stream of alpha particles were fired at a thin gold foil and when they struck a flourescent screen they flashed and it was circular so all angles could be detected. In 1919 proton was discovered by Rutherford by firing high energy particles at different gasses. In 1932 Chadwick provided evidence for the neutron
Conclusions from Rutherford Scattering Experiment?
Most atoms just passed straight through gold foil which shows most of atom is empty space. Some alpha particles were deflected by large angles which shows nucleus has a large positive charge. Nucleus must be small as very few deflected by more than 90 degrees. Most of the mass is in the nuclues since the alpha particles are deflected by the nucleus
Alpha Particle Structure?
2 Protons and 2 Neutrons and 0 Electrons
Working Out Nuclear Radius?
Closest Approach:
An alpha particle deflected at a nucleus at 180 degrees. Use the equation: Ek/Ep = Qnucleus x Qalpa / 4πε0 where Ep is the electric potential energy
Electron Diffraction:
Electron diffraction will electron beam at thin metal foil, use the equation: sinθ = 1.22λ / 2r where “r” is the radius of the nucleus the electrons have been scattered by
Intensity-Diffraction Graph?
It has symetrical peaks which are very high at small angles and then get much lower and close to zero from the second peak onwards
R0?
The value of R0 is 1.4x10^-15m
Radius of atom and Nucleus?
The radius of the nucleus is 0.05 nm. The radius of the nucleus is 1 fm.
Nuclear Radius against Nucleon Number Graph?
The graph between nuclear radius and nuceon number starts of at 0 with a steep postive gradient that gets progressively less steep. A graph of nuclear radius to nucleon number to the power of a 1/3 shows this as a straight line graph through the origin
Size of a molecule?
The size of a molecule is the number of atoms multiplied by the size of the atom
Nuclear Density Formula?
It is assumed in the formula R=R0A^1/3 that A∝V which means the volume each nucelon takes in the nucleus is the same. Since the mass of each nucleon is the same it means the density of nuclear matter is constant regardless how many nucleons make up the nucleus. All nucelons are assumed to be spherical.
Radioactive Decay?
An unstable nucleus releases energy and or particles until it reaches a stable form. An individual radioactive decay is random and cannot be predicted
Penetration of Nuclear Radiation?
Alpha is absorbed by paper or a few centimetres of air. Beta minus decay is absorbed by about 3 millimetres of aluminium. Ganna radiation is absorbed by a few centimetres of lead or several metres of concrete. Beta plus particles almost immediately annihilate with electrons so effectively have zero range
Alpha Smoke Detector Function?
Alpha particles go from the source to the detector. They ionise the air as they pass to the detector. The presence of smoke means more ionisation so less free charges. As less free charges are going to the detector it means there’s less current which means alarm goes off as it registers a drop in current
Alpha Particle Dangers?
Although alpha particles cannot penetrate the skin if ingested they can ionise the tissue which can cause serious damage
Beta Minus use?
A material is compressed and between it there is a beta detector and source. The thicker the material the more radiation it absorbs so if the amount is too high then it is made thinner so it absorbs less and is below the threshold
Gamma Radiation use?
Short half life radioactive tracers are used to reduce exposure and are injected or injested by the patient. A detector is used to detect the emitted gamma rays and the amount emitted give information on the condition. A rotating beam of gamma rays could be used to damage cancerous cells and cure the patients of cancer with this process
Sources of background radiation?
In the air from radioactive gases like radon released from rocks. Cosmic radiation from cosmic particles colliding. Living things as all plants and animals contain carbon 14. Man made radiation from industrial sources. The ground and buildings as nearly all rocks contain radioactive materials
Gamma Inverse Square Law?
A gamma source will emit gamma radiation in all directions. The intensity otherwise the radiation per unit area will decrease by the square of distance from a source
Isotope Decay?
Any sample of a particular isotope will have the same rate of decay and each unstable nucleus within the isotope will have constant decay probabilities
Activity?
The number of nuclei that decay each second
Half Life?
The average time it takes for the number of unstable nuclei to halve
Carbon Dating?
When living things die their carbon-14 level starts to fall. The amount of carbon 14 present can be used to identified the age by comparing the loss of carbon 14
Nuclear Stability?
Line of stability is found by plotting N against Z which is a curve with an increasing gradient. Below this line is beta plus decay as there are too many protons. Above the line is beta minus as there are too many neutrons. Near the top is alpha decay as these are nuclei with too many nucleons
Gamma radiation?
When the nucleus has excess energy and emits this energy as gamma ray without changing nuclear structure. Electron Capture where nucleus absorbs an electron and causes a proton to change into a neutron
