Chapter 6 - Collision and Defects Flashcards

Question

Until when does the knockon atoms generation continues as a chain reaction

Answer 1

until the energy of the nth knockon atom is less than the displacement energy (25 eV)

Answer 2

When the energy transfered to the struck atom is higher than the energy of the projectile particle. This means no atomic displacements.

Answer 3

When the energy transfered to the struck atom is LESS than the energy of the projectile particle. Displacements happen producing vacancies and SIA (nculear stopping).

Answer 4

fission fragments

Answer 5

photons (damage by compton scattering

Answer 6

On the crystal structure of atoms in a solid and the PKA direction.

Answer 7

The average energy needed for displacements overa ll possible directions.

Answer 8

very large meaning that a neutron generates many tens and even hundreds of VI pairs

Answer 9

the nucleus and the electrons bound to the nucleus

Answer 10

with the atomic nuclei notthe electrons

Answer 11

Yes, pair production, compton scattering, and photo-electric effect

Answer 12

is the process that results in the conversion of a photon into an electron–positron pair. Since photon has no rest mass, we can say that this process converts energy into mass according to Einstein's mass energy relation E=mc2. gamma ray -> neutron -> electron and positron ejected

Answer 13

is the scattering of a photon by a charged particle, usually an electron. If it results in a decrease in energy (increase in wavelength) of the photon (which may be an X-ray or gamma ray photon), it is called the Compton effect. photon -> electron -> recoil electron and scattered photon (less energy)

Answer 14

phenomenon in which electrically charged particles are released from or within a material when it absorbs electromagnetic radiation (photon). The effect is often defined as the ejection of electrons from a metal plate when light falls on it

Answer 15

protons and electrons

Answer 16

fission fragments, accelerator produced heavy ions, recoil atoms from primary collisions.

Answer 17

interactions between charged particles and electrons

Answer 18

the energy loss per unit path length, is the retarding force acting on charged particles, typically alpha and beta particles, due to interaction with matter, resulting in loss of particle energy. Its application is important in areas such as radiation protection, ion implantation and nuclear medicine.

Answer 19

refers to the slowing down of a projectile ion due to the inelastic collisions between bound electrons in the medium and the ion moving through it.

Answer 20

The term inelastic is used to signify that energy is lost during the process (the collisions may result both in excitations of bound electrons of the medium, and in excitations of the electron cloud of the ion as well)

Answer 21

high energies

Answer 22

Yes, the electrons in themedium are excited (energized) and removed from the nucleus leading to ionization of the medium along ion-track

Answer 23

Most are thermalized and recaptured by nuclei. The energy is lost in the form of heat.

Answer 24

low energies

Answer 25

permanent atomic displacements which cause physicals and mechanical property changes (radiation damage and radiation effects).

Answer 26

The general creep mechanism are (i) dislocation slip; (ii) climb; (iii) grain-boundary sliding; and (iv) diffusion flow caused by vacancies.

Answer 27

The von Mises stress is used to predict yielding of materials under complex loading from the results of uniaxial tensile.

Answer 28

The temperature at which there is a pronounced decrease in a material’s ability to absorb force without fracturing. At this point, a material transitions from ductile to brittle. Also known as DBTT.

Answer 29

The ductile to brittle transition temperature is strongly dependant on the composition of the metal. Steel is the most commonly used metal that shows this behaviour. For some steels the transition temperature can be around 0°C, and in winter the temperature in some parts of the world can be below this. As a result, some steel structures are very likely to fail in winter.

Answer 30

is the number of times that an atom is displaced for a given fluence/flux. In other words it is the number of displacements in a given volume by a given flux.

Answer 31

Yes, as long as the avaliable energy is above the displacement threshold energy

Answer 32

Yes, as long as the avaliable energy is above the displacement threshold energy

Answer 33

R = atom_density * scattering cross section * flux

Answer 34

E = 1/2 * MV^2

Answer 35

T_max = [ (4*m*M)/(m+M)^2 ] * E

Answer 36

0.07 MeV, 0.035 MeV, 0.0175 MeV, 700 displacements

Answer 37

The energy needed to displace a lattice atom from its crystal site leaving behind a vacant lattice site.

Answer 38

It is half of the PKA energy since M=m (same atom collision).

Answer 39

one half of that of the previous generation until the recoil energy is less than the displacement energy threshold.

Answer 40

elastic collision

Answer 41

When the PKA's energy T is higher than Ec (the minimum ion energy for transferring enough energy to an electron to remove it from the atom)

Answer 42

the crystal structure of atoms in a solid, more specifically the direction (angle) at which the projectile strucks the stationary atom. (depends on the PKA direction)

Answer 43

The energy needed to produce a frenkel pair

Answer 44

25 to 50 eV

Answer 45

When the average knockon energy is 2Ed = T/2^{NF}

Answer 46

v = 2^{Nf} = T/2Ed

Answer 47

a head on collision of atom and electron must transfer a minimum energy equivalent to the binding energy of electrons in medium (I)

Answer 48

Ed < T < 2Ed because two times threshold energy means after creation it will still have the energy to displace one more PKA

Answer 49

minimum ion energy for transferring enough energy to an electron to remove it from the atom:

Answer 50

the number of displacements per unit volumen second DR = RR * v

Answer 51

A simple model for calculating the atomic displacements

Answer 52

1. cascade is created by a sequence of two body elastic collision between atoms 2. the energy Ed consumed in displacing an atom is neglected in the energy balance 3. energy loss by electronic stopping is treated by a cutoff energy 4. energy transfer cross section is given by a hard-sphere model 5. the arrengement of atoms in a solid is random and effects due to the crystal strucutre are neglected

Answer 53

the scattering (inelastic and elastic) cross section, the displacement energy threshold, the energy of the incoming neutron, the alpha factor.

Answer 54

1245 barns (fission)

Answer 55

dpa = flux * displacement cross section * time

Answer 56

because inelastic scattering begins and anisotropic scattering dominantes. Transmutations occur.

Answer 57

- small clusters making depleted zones in the form of stacking fault tetrahedra for fcc metals and cavities in bcc. - large clusters (voids or cavities)

Answer 58

dislocation loops

Answer 59

point defect clusters of vacancies and interstitials along with radiation induced/enhanced diffusion, precipitation and segregation

Answer 60

segregation is the enrichment of atoms, ions, or molecules at a microscopic region in a materials system

Answer 61

1. collapse of close frenkel pairs, recombination and uncorrelated recombination 2. interstitial cluster grow leading to identifiable small interstitial loops 3. vacancies migrate and adulate at interstitial clusters 4. the vacancy clusters sruviving stage 3 grow in size and the vacancy clusters dissociate thermally.

Answer 62

• Because the cross section for atomic collisions becomes large at the low energy end of the ion track, displacements are created in a compact region called a displacement spike

Answer 63

Because ions deal with an atomic cross section (10^-17 cm2) while neutrons is a nuclear cross section (10^-24)

Answer 64

For ions it varies with penetration depth while for neutrons it is uniform.

Answer 65

microscopic defects produced in materials due to irradiation

Answer 66

the changes in physical, mechanical, and chemical properties resulting from accumulated radiation damage

Answer 67

1. neutral elementary particles 2. charged elementary particles 3 high energy atoms or ions

Answer 68

interactions with electrons, and interactions with nuclei.

Answer 69

High energies

Answer 70

low energies

Answer 71

by the stopping power, or energy loss per unit path length of the radiation.

Answer 72

Most of the energetic electrons are thermalized and re-captured, which leads to the energy being dissipated as heat.

Answer 73

The displacement energy of lattice atoms in a given material is the binding energy that keeps the atom in its lattice site:

Answer 74

10 to 60 eVW

Answer 75

scattering events between them provide the atom with enough energy to get knocked out of its lattice site.

Answer 76

The atom that was knocked off of its lattice site

Answer 77

Tmax = [(4mM)/(m+M)^2] * E The average is just half of the maximum theoretical transfer

Answer 78

Yes, if it has enough energy.

Answer 79

Yes, it can create several more PKA since it has enough energy

Answer 80

Because at these energies the particle may interact with electrons first prior to displacing atoms. The electron ionization energy is in the order of KeV

Answer 81

A simplified model describing the interactions between a PKA and a material

Answer 82

That all energy loss by the particle is lost by ionization and no displacements are produced above Energy Ec. Similarly, below Ec all energy loss is by dipslacement collisions.

Answer 83

1. Cascade is created due to sequence of two-body elastic collisions which assume a hard sphwere model 2. no quantum effects therefore no displacements until T > Ed 3 No energy passsed to the lattice during collision phase 4. no atomic displacements above Ec and no ionization below Ed 5. effect of crystal structure is neglected and istherefore random 6. no annhihilation of defects assumed.

Answer 84

When an energetic particle displaces atoms from their lattice sites, the immediate result is vacant lattice sites which lead to zones devoid of atoms

Answer 85

From displacments forming a big enough depelted zone. The effect is swelling

Answer 86

If elements like B, Ni, and Fe are present, (n,alpha) reactions lead to the prdoction of Helium whih can stabilize the voids by forming gas filled caviites or bubbles.

Answer 87

Depends, if voids are from depelted zones yes but if stabilized by He bubbles, then no.

Answer 88

1. vacancies and SIA 2. iimpurity atoms produced by transmutaiton 3. thermal spikes due to impacted nuclei going into high energy states 4. displacement spikes (regions with high density of displacements, vacancies, SIA, produced by PKAs and secondary knock on atoms) 5. voids 6. bubbles/cavities (void stabilized by gases)

Answer 89

1% or less due to recombination of interstitials with adjacent vacancies.

Answer 90

Measurement of radiation damage can be tabulated in a non-material specific manner using the unit dpa = displacements per atom.

Answer 91

displacements per atom A dose of 5 dpa indicates that theoretically, every atom in the piece of material has been displaced 5 times.

Answer 92

Rd = N * xs_disp * flux

Answer 93

dpa = displacement damage rate * time / number density

Answer 94

xs_dpa = int( xs_n * v(t))dT elastic cross section sum of the number of atomic displacements (v(T)) produced by PKA with energies T from Ed to Tmax.

Answer 95

That even before reaching the cut off energy a major fraction of the energy will be lost into electronic excitation and ionization.

Answer 96

1. defect concertation increase with fluence 2. nuclear transmutation occurs 3. chemical reactivity changes 4. diffusion increases 5. new phases, 6. impurities are produced

Answer 97

Distortions on the lattice and aggregation due to the high binding energy

Answer 98

Because binding vacancies and impurity atoms results in alower overall free energy of the solid. The binding energy of a vacancy and a solute can be equal to that of the interstitials (0.2 to 1 eV)

Answer 99

Interstitial clusters are stable and posses higher mobility than vacancy clusters which are often unstable.

Answer 100

clusters form at the casade and the migrate away from the cascade region and can be absrobed at various sinks such as dislocations and grain boundaries.

Answer 101

are a form of extended defect which eventually results from clustering of both vacancies and interstitials. Dislocation loops resulting from vacancy and interstitial condensations are created from clusters of the respective defects, and either shrink or grow depending on the flux of defects reaching the embryo. Once they have reached a critical size, the loops become stable and grow until they unfaulty by interactions with other loops or with the network dislocations.

Answer 102

voids because the void is the stable form for small clusters of vacancies. However, as the number of vacancies in the cluster grows, the loop becomes the energetically favorable configuration.

Answer 103

the collapse of a void embryo into a vacancy loop is NOT favored by the presence of inert gas, such as He, in the void, and this is why voids can survive and grow.

Answer 104

dislocations preferentially absorb interstitials because they interact more strongly with interstitials than vacancies due to the larger lattice distortion caused by interstitials. This leaves the lattice depleted of interstitials and rich in vacancies. Therefore, voids swelling does occur.

Answer 105

1. intermediate temperatures (500C) 2. if less cold woring is present 3. in materials of larger grain size 4. in materials with fewer precipitates

Answer 106

because at low temperatures defects are not mobile enough and at too high of temperatures, the vacancy concentration reaches a value closer to the thermal equilibrium value, so there is no longer this driving force that would lead to void growth.

Answer 107

Cold working increases the dislocation density of a material, which restricts the nucleation and growth of voids.

Answer 108

Smaller grain size means more grain boundaries, which act as sinks for point defects, so they do not go on to form clusters and extended defects as readily

Answer 109

Precipitates act as recombination sites for vacancies and interstitials, thus reducing swelling.

Answer 110

Radiation harening is caused by increased number of defects: including point defects, impurity atoms, small defect clusters, dislocation loops, dislocation lines, cavities (voids/bubbles), and precipitates

Answer 111

Hardening starts to appear at 𝑇<0.4𝑇𝑚 (where in situ recovery effect is less), and at >0.1 dpa.

Answer 112

Elongation percentage is reduced (more brittle)

Answer 113

Helium gas is produced through transmutation of the component elements. The gas is insoluble in metals and thus tends to precipitate into bubbles. This can produce sever embrittlement and intergranular cracking

Answer 114

that helium embrittlement cannot be healed by annealing.

Answer 115

it decreases

Answer 116

Materials under stress can experience creep under irradiation from energetic particles at much lower temperatures than where thermal creep usually requires to kick in normally due to the generation of vacancies enhancing the thermal creep rate

Answer 117

1. radiation hardening 2. radiation embrittlement 3. Helium embrittlement 4. fracture toughness decreases 5. irradiation enhanced creep 6 low cycle fatigue life decrease and high cycle fatigue life increase

Answer 118

1. Density decreases (radiation swelling) 2. Electrical resistivity increases (conductivity decreases) 3. magnetic susceptibility decreases 4. thermal conductivity decreases due to the increase defect concentration.

Answer 119

1. Enhanced corrosion | 2. Irradiation assisted stress corrosion cracking

Answer 120

One reason is the radiolytic dissociation of environment including water. The presence of more radicals accelerates corrosion effects.

Answer 121

1. irradiation=induced depletion of chromium at grain boundaries 2. radiation hardening 3. localized deformation 4. selective internal oxidation 5. irradiation creep