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Radiation Flashcards

1
Q

How is radiation classed?

A

Ionizing - forms ions by knocking electrons out

Non-ionizing

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2
Q

What are the different types of radiation?

A

High energy photons (X-rays, gamma rays), electrons (beta), alpha (He nucleus), heavy ions (fissile and PKAs), neutrons, protons, mesons, positrons

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3
Q

What are the effects of neutron radiation?

A

Interact with materials by scattering (elastic, inelastic) or absorption (radiative capture)

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4
Q

What are the effects of alpha radiation?

A

Charged and ionising - pass materials and strip off electrons causing the formation of electron-hole pairs

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5
Q

What are the effects of beta radiation?

A

Ionising but with high atomic mass materials for shielding causes Bremsstrahlung radiation

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6
Q

What is B- decay?

A

atom -> atom+1 + B- (electron) + anti-neutrino

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7
Q

What is B+ decay?

A

atom -> atom-1 + B+(positron) + neutrino

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8
Q

What is the nature of the atoms in beta decay?

A

The three atoms are of definite momentum and so the spectrum is continuous.

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9
Q

What is the nature of the atoms in alpha decay?

A

The two particles have defined energy levels leading to a spectrum with discrete energy lines

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10
Q

How does the kinetic energy of beta decay vary with intensity?

A

Because beta particle is so light the nuclear recoil energy is practically zero, the decay energy is shared between the beta particle and the anti neutrino, hence the energy ranges from 0 to almost the total decay energy

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11
Q

What is the half life?

A

The time for the number of radio nuclides to drop too half the initial number

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12
Q

What is the dose and its units?

A

The energy deposited by radiation in a material, Gray (Gy) or J/kg

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13
Q

What is the unit of equivalent dose?

A

Sievert (Sv)

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14
Q

What are the different types of isotopes?

A

Long-lived - eg Biological

Short-lived - decay as excite

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15
Q

What is the half value layer?

A

The thickness of material required to reduce the intensity of radiation by 50%

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16
Q

What is the attenuation length?

A

the reciprocal of the linear attenuation coefficient or mean free path

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17
Q

What are the different stages of gamma radiation?

A

Prompt gamma - fission in reactor core
Decay gamma - decay of fission product
Activation gamma - capture of neutron

18
Q

What are the main ways gamma radiation ionises?

A

Photoelectric effect, Compton scattering, pair production

19
Q

What is the photoelectric effect?

A

Gamma photon interacts with and transfers its energy to an atom ejecting electrons

20
Q

What is Compton scattering?

A

Incoherent scattering - incident photon loses enough energy to eject electron, remaining photon energy scattered, probability decreases with increasing photon energy

21
Q

What is pair production?

A

interaction via coulomb force, energy of photon is converted into electron-positron pair, positron has very short range and recombines with a free electron and is converted into two gamma photons

22
Q

What is the stopping power of a material?

A

The average energy loss of the particle per unit path length MeV/cm

23
Q

What is electronic stopping?

A

The slowing down of the radiation due to inelastic collisions between bound electrons in the medium and the ions moving through it

24
Q

What is nuclear stopping?

A

The slowing down of the radiation due to elastic collisions (ballistic) between the radiation particles and atom in the medium.

25
What is the bragg curve?
energy loss per unit length, density of ionisation increases until peak (bragg peak) then drops to 0
26
What is the range and what does it depend on?
The penetration depth, density, range and effective atomic mass
27
What is LET?
Linear energy transfer - the amount of energy an ionising particle transfers to the medium
28
What is radiation damage?
The disruption of the initial structure by high energy radiation
29
What are effects of radiation damage?
dimensional changes, phase changes, amorphization, optical embrittlement, hardening, creep phase separation, resolution, corrosion
30
What are some effects on reactor environments?
Possible dissociation and/or activation of coolant Thermal - softening, creep of fuel cladding Embrittlement of structural components e.g. RPV welds Enhanced corrosion of cladding and RPV Fuel/clad interaction Fission gas release => increase rod internal pressure Segregation of elements
31
What are the main steps of radiation damage?
Transfer of energy from the energetic incident radiation particle to a lattice atom to create primary knock on atom (PKA) moment of PKA away from its lattice site through the lattice creating more PKA Evolution of a displacement cascade: single vacancies and interstitials but also clusters of defects. The cascade reaches a maximum in damage during the ballistic phase after which there is usually some degree of recovery.
32
What are the different types of structure defects?
Point defects: include missing atoms (i.e. vacancies), incorrectly positioned atoms (e.g. interstitials) and chemically inappropriate atoms (dopants). Point defects may exist as single species or as ‘small’ clusters, bubbles or voids containing multiple species. Line defects or dislocations extend through the crystal in a line or chain. The dislocation, line has a central core of atoms that are located well away from usual crystallographic sites (in ceramics this extends, in cylindrical terms a nanometre or so). Planar defects extend in two dimensions. Many different types exist the most common of which is the grain boundary. Other common types include stacking faults, inversion domains and twins. Precipitates are larger clusters and so extend too far to be point defects
33
What are the universal damage concepts?
Displacive radiation damage is initiated upon formation of Frenkel pair defects in the lattice The concentration of Frenkel pair defects in an irradiated material far exceeds the equilibrium thermodynamic concentration of Frenkel defect pairs. The radiation damage response of a material is determined by the fate of these excess Frenkel pairs in the lattice.
34
What is the criteria for radiation resistant materials?
Resistance to void swelling, amorphisation
35
What is fluence?
Total number of ions or neutrons incident on the surface
36
What is flux?
Rate at which ions or neutrons are incident on the surface
37
What is dose?
Total number of events per unit volume | Deposited energy is dose multiplied by energy per particle
38
What is the most radiation resistant material?
Er2Zr2O7
39
What are the critical amorphisation conditions?
The temperature or dose at which a material amorphises
40
What is chemical rate theory?
fate of irradiation-induced point defects Harmless - defect annihilation Medium - depends on compound Harmful - defect aggregation
41
What is the Kinchin-Pease model?
estimation of the number of displaced atoms per PKA

Nuclear (8 decks)

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