Nuclear Processes

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How can count rate against thickness be investigated?
Use Geiger tube, find background count rate. Add sealed source and vary thickness of absorber to measure count rates
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Outline alpha particles
Alpha - strongly ionising but not penetrating as each ionisation transfers lots of energy from the alpha particle so it loses energy. Soon becomes neutral when it gains two electrons. Stopped by few sheets of paper or foil
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Outline beta.
Beta - weakly ionising, electrons and positrons produce fewer ions per metre than alpha so travel further. Stopped by a few mm of aluminium.
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Outline gamma
Gamma - far less ionising, follows inverse square law. Not stopped by few mm of lead.
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Outline intensity-thickness graph and equations
Intensity varies exponentially with thickness. I=1o*e^-ux and x1/2=ln2/u where x is half thickness and u is absorption coefficient (m^-1)
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How does ionisation occur in body?
Ionising radiation removes electrons. In cells molecular bonds are broken. More energy=more damage, sex cells more at risk
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What happens in cloud chamber tracks?
In cloud chambers when a particle of radiation passes saturated vapour, it produces ions where vapour condenses to form a track. Tracks are straight for more ionisations. Alpha isn't defected in magnetic field but beta is.
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Whats aborbed dose?
Harm to cells is determined by energy and damage. Absorbed dose (Gy)= energy per kg = activity * energy per decay * time/mass
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How is treatment administered?
Treatment is targetted at small areas reducing threat of damage and damage relies on type of radiation and damage.
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What's effective dose? (Sv)
Effective dose = absorbed dose * quality factor (for alpha this is 20, but for beta and gamma it's 1)
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What's equation for risk?
Risk = effective dose* incidence per Sv
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What's formula for alpha decay?
Alpha decay -> Z/N -> Z-2/N-2 (Z = proton no, N=Neutron no)
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What's B+ decay?
B+ decay -> Z/N -> Z-1/N+1
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What's B- decay?
B- -> Z/N -> Z+1/N-1
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What's Pauli exclusion principle?
Pauli exclusion principle, particles which are in same position in space-time can't be in same state. Why nuclei need equal protons and neutrons. This applies for fermions, protons, electrons, neutrons. For bosons, photons, doesn't apply.
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What determines nuclei stability?
Nuclei are stable when protons and neutrons are equal. As neutrons increase beyond protons, nuclei become unstable. Strong nuclear force between protons and neutrons overcomes proton electrical repulsion.
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What's binding energy?
Binding energy = rest energy of nucleons+ electrons - rest energy of nucleus. Greater this is, the more stable the nucleus, more energy for protons and neutrons to separate.
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How is mass relevant for binding energy?
Rest energy used for binding energy and mass unit, u, where 1u=mass of one carbon-12 atom. Difference in mass is mass defect.
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What is A and how does it link to N and decay constant?
A=activity, no of nuclei which decay per second in Bq. A= N *λ (decay constant, s^-1 - probability of decay per s)
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What is half life and relationship between N and t?
T1/2 = half life = ln2/λ. Relationship between N and T is exponential.
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What is formula for rate of change of no of nuclei remaining?
dN/dt= -λN so N=Noe^-λt and same for activity, A.
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What is shown on the nuclear valley graph linking N, Z, and E?
In nuclear valley, there's a fusion hill where neutrons and protons rise in number causing binding energy to rise, at iron lake nuclei most stable, at coulomb slope there are more neutrons than protons and alpha decay may occur.
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Other cards in this set

Card 2

Front

Outline alpha particles

Back

Alpha - strongly ionising but not penetrating as each ionisation transfers lots of energy from the alpha particle so it loses energy. Soon becomes neutral when it gains two electrons. Stopped by few sheets of paper or foil

Card 3

Front

Outline beta.

Back

Preview of the front of card 3

Card 4

Front

Outline gamma

Back

Preview of the front of card 4

Card 5

Front

Outline intensity-thickness graph and equations

Back

Preview of the front of card 5
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