Atomic, nuclear and particle physics Flashcards
What is discrete energy?
Atoms can only have discrete amounts of energy. The KE of the electrons and the potential energy of the electrons and nucleus can only take specific values.
Where does the emission spectrum come from?
When energy is supplied to an atom, electrons may move from the ground state (n=1) to an excited state (n=2,3,4) by absorbing exactly the right amount of energy to move to that level.
What is the emission spectrum?
- The set of possible wavelengths of light that can be emitted when electrons deexcite, as the result of discrete energy levels.
Can be used to identify different elements.
How do the energy levels in an atom work?
- They have negative values.
- The gaps between levels decrease as n increases
- Often measured in electron volts eV
How do electrons transition between energy levels?
How can you quantify the transition?
Electrons naturally transition towards the ground state. When transitioning to a lower energy state, electrons emit a photon. The photon energy is given by ΔE between energy levels, or
E = hf or E = hc/ λ
(J) (Planck’s constant) (Hz)
What is the absorption spectrum?
When white light is shone on a gas, electrons absorb photons with the right amount of energy for them to excite. Photons are emitted in all directions as the deexcite, resulting in very faint bars on the spectrum.
What is the notation for the proton, nucleon, and neutron numbers?
Z = the proton number
A = the atomic number
∴ N = A - Z
What is the notation for protons, neutrons, electrons, photons, and neutrinos?
Mass above charge: 1 1 p 1 0 n 0 -1 e 0 0 γ 0 0 v
What is an isotope?
It is an atom with the same proton number, but different neutron numbers and thus different mass and physical properties.
What is radioactive decay?
When an unstable nucleus randomly (unpredictable) and spontaneously (not affected by anything else) emits particles that carry energy away from the nucleus.
What is alpha decay? What is the notation?
It is a pair of neutrons and a pair of protons. It is heavy, positively charged, and has low penetrating power.
(Mass over charge:)
4 2 α
What is beta - decay? What does an equation look like?
A neutron in the nucleus turns into a proton and emits an electron and an electron anti neutrino.
(Mass over charge:)
(A Z)X => (A Z+1) Y + (0 -1) e + ̅νe
What is beta + decay? What does an equation look like?
A proton in the nucleus turns into a neutron and emits a positron and an electron neutrino.
(A Z)X => (A Z-1) Y + (0 +1) e + νe
What is Gamma decay, and how do you work out the wavelength of the gramma ray?
When the nucleus emits a photon with high frequency (gamma ray). It has no charge.
E = hc/ λ
How can you work out the rate of radioactive decay?
REDO check formula in two places
ΔN /Δt ∝ N
Rate ∝ number of nuclei that have not yet decayed.
What is a decay series?
A diagram showing the different decays that take place as a nucleus stabilises.
What is half life? What are the units for radioactivity
REDO
The time taken for the activity of a radioactivity of a sample (Bq - decays per second) to decrease by half.
What is the electromagnetic force?
A force that acts on any particle that has charge. It has infinite range, and
How can you work out the probability of radioactive decay?
Draw a tree diagram - the probability of a particular nucleus decaying within a half life is 0.5.
What are the four fundamental interactions, the particles they act on, and the range?
Electromagnetic/particles with charge/infinite range
Weak nuclear/protons, neutrons, electrons, neutrinos to create beta decay/short range (10⁻¹⁸ m)
Strong nuclear/protons and neutrons - holds together the nucleus/Short range (10⁻¹⁵m)
Gravitational/between all masses/infinite range
What is the atomic mass unit?
1/12 the mass of an atom of carbon 12
1u = 1.661 x 10⁻²⁷ kg
How is mass equated to energy?
E = mc²
What is the mass defect?
The mass of individual nucleons is larger than the mass of the nucleus. The difference is the mass defect.
δ = total mass of nucleons - mass of nucleus
δ = Zmp + (A-Z)mn - mnucleus
What is binding energy?
The work required to separate a nucleus into it’s constitute parts.
binding energy = δc²
What is the binding energy per nucleon?
The work required to remove one nucleon from the nucleus roughly = binding energy/nucleon number
The higher the binding energy/nucleon, the more stable the nucleus.
missing
electron volts measurement, conversion to mass
How can you easily convert energy to mass in atomic mass units?
Use u = 931.5 MeVc⁻² (=1.661 x 10⁻²⁷) data book
What is the binding energy curve?
What are the features?
It is a curve showing the binding energy per nucleon (y) against the nucleon number of different elements (x).
- The curve rises sharply for low nucleon no.
- The maximum point is the most stable position, at nucleon no. = 62 - nickel.
- There are some atoms that fall outside the curve.
- The curve drops away after nickel.
How can you work out if energy is released in a decay or other reaction?
Work out Δm = total mass of reactants - total mass of products.
If Δm > 0 energy is released, and decay occurs
If Δm < 0 energy must be supplied for the decay to occur.
What is the process of nuclear fission?
What is a chain reaction?
What does it look like on the binding energy curve?
- When a heavy nucleus splits into two lighter nuclei and releases some neutrons. Usually happens when the nucleus is hit by a neutron.
- If the neutrons released hit other nuclei to produce more fission it is called a chain reaction
- atoms move to the left
What is nuclear fission?
What does it look like on the binding energy curve?
- When two light nuclei join into a heavier one and energy is released.
- atoms move to the right
What happened yin the Rutherford experiment?
Alpha particles were directed at gold foil in a vacuum chamber.
The majority of α particles went straight through or had small deflections.
Very occasionally, α particles were reflected backwards.
What were the conclusions of the Rutherford experiment and why?
Check off notes
- In the Plum-pudding model of the atom, the positive charge could produce a force large enough to deflect α particles at small but not large angles.
- Rutherford concluded that the positive charge of the atom must be concentrated in the centre of the atom. IOW a nucleus.
A direct hit - large deflection
Close to nucleus - small deflection
What is an elementary particle?
A particle that is not made up of smaller component particles.
What are quarks?
There are six different flavours:
Up, down, top, bottom, strange, charm.
What are the names of the different combinations of quarks?
- Hadrons are particles made of quarks.
- Three quarks is a baryon.
Eg. proton (uud), neutron (udd) - A quark and an anti-quark is a meson
Eg. Pion
