Alpha, Beta, Gamma Radiation Flashcards
Which ionizing radiation produces the greatest number of ion pairs per mm in air
alpha particles
What is the typical maximum range in air for alpha and beta particles in metres
alpha - 0.04m
beta - 0.4m
Gamma rays have a range of at least 1km in air.
However a gamma ray detector placed 0.5m from a gamma ray source detects a noticeably smaller counter-rate as it is moved a few centimeters further away from the source
Explain this observation
- Inverse square law of gamma radiation
Explain the most hazardous aspect of the presence of dust contaminated with an alpha emitter to an unprotected human entering the room
Dust may be ingested causing cells to be damaged
Give two sources of background radiation
Rocks
Cosmic rays
Nuclear waste
Describe how you would perform an experiment that demonstrates that gamma radiation obeys an inverse square law
GM tube + counter
Measurement of count rate at range of distances + ruler
Suitable range
Determine background radiation and subtract from reading
Safety precautions
Graph of corrected count rate against 1/d^2
Explain why gamma radiation obeys an inverse square law but alpha and beta radiation does not
Gamma not absorbed
Spreads uniformly from a point
Area over which it spreads is proportional to radius squared
Alpha and beta are absorbed in addition to spreading out
Type of decay Change in mass number
Change in proton number
Change in neutron number
Alpha: -2p-2n = -4
-2p -2n
Beta minus: +1p-1n = 0 n–>p = +1p
n–>p = -1n
Beta plus: -1p+1n=0
p–>n = -1p
p–>n = +1n
Gamma: No change No change
No change
Electron capture: -1p+1n = 0
p–>n = -1p
p–>n = +1n
A nuclide AXZ contains how many protons and neutrons, has what charge and has what mass
A-Z neutrons, Z protons
Charge = +Z*e where e is the charge of a proton
Mass = A*u where u is the atomic mass unit
Atomic number =
nucleon number = protons + neutrons
Radioactive/unstable atoms are trying to become more stable by trying to
obtain a lower energy level
What holds the protons and neutrons together in the nucleus
the SNF
Types of radiation and what they release (3)
1) Alpha - releases a helium nuclei
2) Beta - releases an electron
3) Gamma - releases a photon/gamma ray
Describe the composition and nature of alpha decay
+vely charged alpha particles composing of two protons, two neutrons and zero electrons meaning it is strongly ionising with other atoms making it dangerous as it can damage living cells.
High kinetic energy but slow moving
Alpha particle + 2 free electrons =
Helium nucleus (2p 2n) + 2 electrons = helium atom
Alpha decay equation
XAZ –> (X-4)B(Z-2) + 4a2
number of protons changes so new element
Alpha decay only happens in
very heavy atoms as their nuclei are too massive to be stable
Explain what happens to the distribution of kinetic energy in alpha decay
The nucleus recoils when the alpha particle is emitted so the kinetic energy is shared between the alpha particle and the nucleus in inverse proportion to their masses.
What happens to an alpha particle in a magnetic field
Slight deflection due to the positive charge caused by the two protons and zero electrons
Beta minus particle equation
n –> p + e + electron antineutrino
Beta plus particle equation
p –> n + e+ + ve
What is beta decay, when does it happen and what happens
beta decay occurs in a neutron-rich (no. neutrons > no. protons) isotope and occurs when a neutron changes to a proton and an electron antineutrino is emitted as the electron is ejected.
Beta minus decay equation
AXZ –> AY(Z+1) + 0B(-1) + electron antineutrino
A negative beta particle is represented as 0b(-1) because
it has a charge of -e
A beta emission makes the nucleus _____ neutron-rich causing it to
less
become more stable i.e. nearer the stability line
A positive beta particle is represented as 0b(+1) because
it has a charge of +e
Describe beta plus decay
a proton in a proton rich nucleus changes into a neutron and an electron neutrino is emitted as the positron is created.
Beta plus decay equation
AXZ –> AY(Z-1) + 0B(-1) + ve
Beta deflection in magnetic field
a lot of deflection (in the opposite direction to an alpha particle) as very fast moving
Positron naturalness
proton-rich nuclei are not naturally occurring radioactive substances and are created when high energy protons collide with nuclei and so positron decay is artificial
Why doesn’t positron decay occur after alpha decay
because it makes the nucleus more neutron rich therefore more unstable
How is (kinetic) energy distributed in beta decay
the nucleus, the beta particle and the antineutrino - the kinetic energy of the antineutrino is negligible when the electron has maximum kinetic energy This maximum kinetic energy is < than the energy released because the nucleus recoils in the opposite direction with kinetic energy.
How was the wavelength of the photons in gamma radiation discovered
Photons with wavelength < 0.1nm shown via diffraction of gamma radiation through crystals
Gamma photons are emitted from excited nuclei with energies of the order
1MeV
2 properties of gamma decay
- no change in nucleon/atomic number
- nucleons fall together (due to the SNF) making it more stable
- decrease in potential energy of the nucleus makes energy available to the surroundings so high energy photons/EM waves are emitted to conserve energy
Gamma ray deflection in magnetic field
no deflection as chargeless
One ways gamma rays are produced (not e capture)
After alpha or beta emission or electron capture, the daughter may be formed in an excited state leading to the emission of a gamma photon allowing the nucleus to lose energy. The excited state is usually short-lived and the nucleus moves to its lowest energy state, its ground state can be represented by an energy level diagram.
What is electron capture and how can it produce a gamma ray
Electron capture is where a proton-rich nucleus captures an inner shell electron that interacts with a proton forming a neutron making the nucleus unstable causing it to emit a neutrino which carries away the energy released in the decay. A gamma ray is then emitted when the inner-shell vacancy is filled upon de-excitation.
Electron capture particle equation
p + e –> n + ve + y
Electron capture decay equation
e + AXZ –> AY(Z-1) + ve
