7 Nuclear Physics Flashcards
when an electron moves from a higher energy state to a lower energy state…
photons are emitted
describe the emission spectra
an electron transfer to a lower energy level and emit photon
Isotopes tend to be more unstable because
they have an imbalance of protons and neutrons
state and define the two main characteristic of radioactive decay
- spontaneous: not influenced by external factors
- random: cannot predict the time of decay
Explain the relationship between penetrating power and ionizing ability.
Alpha = most ionising = lose energy quickly = least penetrating, can be stopped by paper/skin
explain this Z-N diagram
For Z<20, proton number = neutron number → stable
For Z>20, neutron-proton ratio increases because as proton number increases, the electrostatic repulsion becomes very strong and more neutron is required to ‘shield’ the protons from each other and bind the nucleons together → unstable
examples of radiation detectors
- Photographic film
- Geiger-Muller (GM) tubes
describe beta-minus decay
n → p + e-
describe beta-plus decay
p → n + e+
α particles are emitted by nuclei that
have too many nucleons
define half life
the time taken for the undecayed nuclei to halve
define mass defect (Δm)
the difference in mass between separated and combined nucleons
(mass ⇒ binding energy)
convert mass defect to binding energy
ΔE = Δm x 931.5 (MeV)
convert MeV to J
1 e = 1.6 x 10^-19 C
1 eV = 1.6 x 10^-19 J
1 MeV = 1.6 x 10^-13 J
define nuclear fission
an unstable atom absorbs neutrons and becomes unstable → the nucleus splits into two daughter nuclei; releases energy
What happens to the binding energy after fission/fusion
1) per nucleon
2) total
binding energy per nucleon increases as the nuclei becomes more stable.
→ total binding energy also increases
why do lighter nuclei undergo fusion while heavier nuclei undergo fission?
small mass → less protons → attractive nuclear forces between nucleons > repulsive electrostatic forces between protons → fuse
(vice-versa for large mass)
advantages of fusion
Reactants readily available in ocean; no harmful by-product
Moderator
slows down neutrons so they can be captured by a U-235 nucleus
Heat Exchanger
heat water to steam to be used to turn turbines and produce electricity
Chain reaction
A self-sustaining nuclear reaction where U-235 fission releases more neutrons and trigger more fissions… this is when the rate of neutron production ≥ the rate of neutron lost
what is quark?
fundamental particles that make up other subatomic particles such as protons and neutrons
define baryon
consists of 3 quarks;
baryon number = 1
what are the quark configurations of proton and neutron?
proton: uud
neutron: udd
why does proton have the longest half-life of all baryons?
lightest baryon → most stable
list the 4 fundamental interaction forces in order of strengths
strong > electromagnetic > weak > gravity
which interaction force is responsible for the radioactive decay of atoms?
weak
define exchange particles
virtual particles that mediate the a fundamental force between interacting particles
Explain how atomic spectra provide evidence for the quantisation of energy in atoms.
E=hf=h(c/λ), since atomic spectra consists of discrete wavelengths, atoms must contain discrete/quantised energy levels
describe the absorption spectra
- Electrons absorb photons and become ‘excited’
- Electrons de-excite and re-emit the photons but in all directions, so these wavelengths appear black in the direction of the observer.
define radioactive decay
an unstable atomic nucleus becomes more stable by emitting a particle (alpha, beta) or a wave (gamma)
state the nature of the 3 radiation
alpha = He nucleus (2p, 2n)
beta = high speed electron
gamma = EM radiation
what materials stop the 3 types of radiation
alpha = paper
beta = thin aluminum foil
gamma = thick lead
define background radiation
low level of radiation in our surroundings at all times
state the sources of background radiation
radon gas, rocks, food, cosmic rays
determine the background radiation
where the line plateaus
β- particles are emitted by nuclei that
have too many neutrons
β+ particles are emitted by nuclei that
have too many protons
γ particles are emitted by nuclei that
have too much energy
define the activity of a redioactive substance
number of decays per second
A = dN/dt = - λN
define binding energy (ΔE)
the energy to separate the nucleons in a nucleus
Calculate the binding energy per nucleon, in MeV, for K-40 (19 protons)
Nuclear mass = 39.953548 u
Mass of one neutron = 1.008665 u
Mass of one proton = 1.007276 u
- ∆m = nuclear - (p+n)
- convert u to kg!!
- ∆E = ∆mc²
- ∆E per nucleon (divide by 40)
- convert J to MeV!!
→ ∆E per nucleon = 8.594 MeV
Draw the graph of mass number against binding energy per nucleon, including the main features
mass
define nuclear fusion
two small nuclei join to produce a larger nucleus; release energy
In nuclear fission/fusion, how is the mass of the product compared to the mass of the reactant? Why?
mr > mp because part of the mass of the reactant is converted into energy.
In the graph of mass number (A) against B.E. per nucleon, what does the steeper graident for smaller A show?
fusion releases more energy (B.E.per nucleon increases more)
difficulty in making a fusion reactor
Very difficult to create heat and pressure that exists in the sun → need to input more energy than what comes out
Control Rod
absorbs neutrons to control the rate of reaction
Enrichment
increasing the % of U-235 ( more reactive/fissionable isotope) in a fuel used in a nuclear power station
Critical Mass
the minimum mass of nuclear fuel needed to sustain a chain reaction
why does nuclear fusion need high temperature?
need lots of energy to overcome the electrostatic repulsion between positively charged nuclei
define meson
a quark and an antiquark pair
what is lepton?
fundamental particles that cannot be broken down further (eg. electron)
how do you determine whether a particle interaction can occur?
check if QBLS are conserved
Q = charge
B = baryon number
L = lepton number
S = strangeness
The strong force applies only to particles made up of
quarks
The electromagnetic force only applies tp
particles with charge
The gravitational force only applies to
particles with mass
quark confinement states…
it is impossible to observe a free quark in isolation because more particles will be created when you try to separate a pair of quarks
draw the Feymann diagram for beta-plus decay
Mg-27 nuclei decay by β- to form Al-27. Explain why there’s a difference between the energy released in the decay and the total kinetic energy of beta particles and gamma rays.
another particle (anti-nutrino) is emitted
Fluorine (18,9) can be created when a proton traveling at high speed interacts with an oxygen nucleus (18,8). Explain why the proton must be traveling at high speed for this process to occur.
+ve nucleus repels proton;
proton must be close to nucleus for nuclear force to be effective (high electric potential energy);
so the proton needs high initial kinetic energy
range of wavelength for visible light
380 to 700 nm
