Nuclear Flashcards
Binding energy
The amount of energy required to split a nucleus into all its separate constituent nucleons. It is equivalent to the mass defect.
(Or the energy required to bind together the nucleons, where nuclei with higher binding energy per nucleon are more stable as more energy needed for separation)
Closest approach
A method of estimating a nuclear radius by firing an alpha particle at it. It involves calculating the distance at which all the alpha particle’s kinetic energy is converted to electric potential energy.
Contamination
The introduction of radioactive material to another object. The object is consequently radioactive.
Control rods
Rods found in nuclear reactors to absorb neutrons and control the rate of reaction. They can be raised or lowered depending on the rate required.
Critical mass
The smallest mass of fissile material required in a fission reactor for a chain reaction to be sustained.
Electron capture
A process that occurs in proton-heavy nuclei, in which an electron is drawn into the nucleus, causing a proton to transition into a neutron. An electron neutrino is also produced.
Z= 82. Z= 81
²⁰⁵Pb + e– → ²⁰⁵Tl + v(e)
Irridation
The exposure of an object to radiation. The exposed object does not become radioactive
Mass defect
The difference in mass between a nucleus and the sum of the masses of its constituent nucleons
Decay constant
The probability that a particular nucleus will decay per time (s^-1)
The fraction of the total number of nuclei that decay per second.
Rutherford conclusions
1) most alpha particles passed through undeflected → most atoms must be empty space.
2) many were deflected → must be part of an atom that’s positively charged.
3) very few were deflected backwards → the charged nucleus must be very small compared to the size of the atom.
Electron diffraction
• High speed electrons are fired at a thin sheet of material
• as they pass through the atoms they diffract, concentric circles is formed on a screen behind the material.
(More accurate)
Sintheta = (1.22lambda)/2R
1Bq
1 decay per second
Intensity unit
Wm^-2
Radioactive decay equations
N = Noe^-(lambda)t
Nuclei number
Activity
Mass
Count rate
Nuclear waste treatment
1) should be cooled in cooling ponds to reduce temps to safe levels
2) stored in thick (several metres) concrete containers deep underground for hundreds of years/vitrified
3) all handling should be done remotely
95% spent fuel rods (3% vol)
4% sludges and resins (7% vol)
1% clothes worn etc (90% vol)
Below iron
Above iron
Fusion
Fission
Why does fusion release more energy
Due to the larger nucleus having a larger binding energy per nucleon.
Density of a nucleus
P =m/v
m = 3Au (mass number x atomic unit)
V=4/3πr
R=RoA^⅓
Therefore density = 3Au/4π(RoA^⅓)³
=3u/4πRo³
Therefore density is independent of radius and a constant. As Ro = 1.05x10^-15. should always be x10^17 magnitude.
Why is inverse square law not always accurate
1) dead time
2) may not be pure gamma, could have beta in it
Explain why there is an imbalance in the number of neutrons and protons in a larger nucleus
More neutrons are needed to hold the nucleus together to add to binding force, to reduce repulsion between protons and therefore reduce instability
Why are gamma rays useful for medical diagnosis
Low half life therefore doesn’t remain in body too long after medical diagnosis
High penetration therefore can leave body
Weakly ionising therefore less damage to body
What provides evidence for the existence of:
Electrons
Energy levels in nuclei
1) existence of X-ray line spectra
2) existence of gamma radiation
How to use R = RoA⅓
Ro is a constant and therefore can be worked out.
Or proportionality (R1/A⅓) = (R2/A⅓)
Therefore R1 = (A1/A2)⅓ x R2
Benefits of nuclear power?
1) less pollution
2) little Co2 produced (not pollution)
3) high energy density
Purpose of a moderator
To slow down fast neutrons produced during nuclear reactions. By slowing down these neutrons, the probability of their interaction with fissile material (like uranium-235 or plutonium-239) increases. This enhanced interaction improves the efficiency of the nuclear reaction, allowing sustained and controlled energy production. .
Why does the number of collisions needed depend on the nucleon number of the moderator atoms?
Collisions are elastic
More nucleons = larger mass
Therefore less KE transferred to nucleus therefore more collisions are needed
