Useful Things to Memorize (Midterm)

Question 1

What is the mass of a proton, relative to an electron?

Answer 1

1836x

Question 2

What’s the maximum angle of scattering for a large projectile relative to small target?

Answer 2

0.03 degrees

Question 3

Maximum angle of scattering for two equal masses?

Answer 3

90 degrees

Question 4

Maximum angle of scattering for a projectile much smaller than target.

Answer 4

180 degrees

Question 5

What is the maximum energy lost to an electron by a proton

Answer 5

0.22% (4/1836)

Question 6

Is the energy deposit of an electron with a large target big or small?

Answer 6

Very small

Question 7

What make up the vast majority of interactions? Hard or Soft?

Answer 7

Soft

Question 8

Angle between scatterings of two equal masses?

Answer 8

90 degrees

Question 9

When is the only time that a charged particle has a magnetic field strength comparable to its electric field strength?

Answer 9

At relativistic speeds

Question 10

Maximum kinetic energy of a photoelectron

Answer 10

hf - W

Question 11

Total energy of a particle in special relativity

Answer 11

(gamma)mc^2 E = T + RestEnergy

Question 12

Approximate rest energy of an Electron, Proton and Neutron

Answer 12

Electron - 0.511 MeV Proton - 938.3 MeV (say 1000) Neutron - 939.6 MeV (say 1000)

Question 13

What is binding energy proportional to

Answer 13

Proportional to Z^2 Inversely proportional to n^2

Question 14

How does an Auger electron form

Answer 14

A vacancy exists in a low shell An electron from an upper shell drops down to fill vacancy This releases energy, which excites an upper shell electron and ejects it

Question 15

Low Z atoms fill K-shell vacancies primarily by ________ High Z atoms fill K-shell vacancies primarily by ___________

Answer 15

Auger Electron Emission Characteristic Radiation

Question 16

What is the fluorescent yield for vacacnies higher than the L-Shell

Answer 16

Practically zero

Question 17

Relation between hard angle of a sphere to area

Answer 17

= dA/r^2

Question 18

For a flat faced detector, the hard angle is equal to what?

Answer 18

Area of detector/r^2

Question 19

Equation for beam fluence of parallel beam

Answer 19

N/A where N is average number of particles

Question 20

Fluence relation by the inverse square law

Answer 20

F1/F2 = r2^2/r1^2

Question 21

What is the interaction cross section of the coulomb force

Answer 21

Infinite

Question 22

What does the Probability of an interaction depend on?

Answer 22

number of tar/cc Interaction cross section dx or, (cross section)(N)/dA or Nint/N

Question 23

What does the number of interactions rely on?

Answer 23

(n_targets/cc)(cross section)(Fluence)(dA)(dx)

Question 24

What are the 3 types of interactions of a charged particle with an atomic electron?

Answer 24

Inelastic Scattering Inelastic Radiative scattering Electron capture

Question 25

What is the approximate radius of an atom?

Answer 25

Bohr radius, 0.53 \* 10^-8 cm

Question 26

What is the differential cross section proportional to?

Answer 26

Z1^2 and Z2^2

Question 27

What is the approximate total cross section for elastic p-p scattering

Answer 27

10^-19 cm^2

Question 28

What is the approximate magnitude of the proton scattering by a heavy nucleus?

Answer 28

10^-19 cm^2

Question 29

What is the primary mechanism by which projectile charged particles lose radiative energy?

Answer 29

Brensstrahlung Radiation

Question 30

What approximation is made when a fast moving charged particle interacts with a charged target

Answer 30

Straight trajectory approximation

Question 31

What is the classical interaction cross section with an electron proportional to?

Answer 31

Proportional to Z1^2 Inversley proportional to (beta)^2

Question 32

At relativistic speeds, what is the approximate cross section of interactions with an electron? What about at non relativistic speeds?

Answer 32

10^-19 cm^2/e for relativistic 10^-16 cm^2/e for non relativistic

Question 33

Why are small energy losses much more dominant?

Answer 33

Because they occur for large impact parameters. Large impact parameters have correspondingly large cross sections.

Question 34

About how much smaller is collision stopping power with a nucleus relative than with an electron?

Answer 34

About 1000x smaller. So normally it is negligible, especially for heavy projectiles

Question 35

True or false. For all charged particles, nuclei collision stopping power should be taken into account.

Answer 35

False. It's negligible for all charged particles. Of course for a more accurate result, use it anyway if u have a table. But otherwise don't bother.

Question 36

What are the impact parameters for Hard and Soft collisions.

Answer 36

Hard - small parameters Soft - larger parameters (This is why the VAST majority of interactions are soft)

Question 37

True or false. A proton will lose a substantial amount of its energy to an electron in a hard collision.

Answer 37

False. At most, it's still only 0.22%. That FAR exceeds the BE of the electron usually, but its still nothing substantial to the proton.

Question 38

True or false. In a soft collision, energy transferring to electron is so small that BE and Excitations can't be ignored.

Answer 38

True

Question 39

True or false. Atomic electrons can still be considered free is a soft collision.

Answer 39

False. These interactions are inelastic

Question 40

What is collision stopping power proportional to?

Answer 40

Proportional to Z1^2 Inversely proportional to (beta)^2

Question 41

Remember these graphs

Answer 41

Question 42

Why do projectiles usually not experience full interactions with the nucleus?

Answer 42

Due to shielding around the nucleus. You need to approach a distance between nucleus and K-shall orbital to not experience shielding.

Question 43

What is radiation yield defined as

Answer 43

(average energy lost to radiation)/(total beginning energy) ONLY when projectile is brought to rest

Question 44

What is the general rule of thumb for electrons in water.

Answer 44

Above 0.5 MeV, you can approximate that electrons lose about 2 MeV/cm in water

Question 45

Remember this image of stopping powers for electrons in Water

Answer 45

Question 46

True or false. Heavy particles have much less range straggling than electrons because they deviate from a straight line significantly less.

Answer 46

True

Question 47

Just remember: Energy is lost ONLY to electrons. These interactions determine the path length Energy is NOT lost to the nucleus, BUT interactions with nucleus change directions, and therefore the range

Question 48

Difference between R_csda and R_max

Answer 48

R_csda = Path length = range assuming NO nuclear scattering R_max = range with FEWEST nuclear scattering

Question 49

Ratio between R_max/R_csda for high Z atoms

Answer 49

0.5

Question 50

Units of dose

Answer 50

Gray = J/kg

Question 51

If the medium is thin, how much energy on average is lost to electrons?

Answer 51

S_c^eP = S_c^et

Question 52

What method must be used to calculate energy lost in a thick medium

Answer 52

Residual Range Method

Question 53

Difference between slow and fast primary/secondary electrons

Answer 53

Slow - set in motion from soft collisions. Have almost no range. Get absorbef on site locally Fast - Delta-rays. Energetic enough to leave interaction site. May possibly escape medium

Question 54

True or False, Brems radiation is absorbed in mass.

Answer 54

FALSE! It escapes. When calculating E_abs for dose, you do NOT include radiation energy

Question 55

What types of energy contribute to dose in dm

Answer 55

ONLY COLLISION ENERGY! Nothing else!

Question 56

At what depth that CPE-delta begin at for heavy particle beams?

Answer 56

At a depth greater than R_csda for the most energetic possible secondary electrons For electron beams, it's impossible to predict.

Question 57

Dose of a beam to a material

Answer 57

D = (S_c^edxN_particles)/(mass traversed through)

Question 58

T_Emax = Delta = energy of electrons that have an R_csda less than the thickness of a material. Those will NOT leave

Answer 58

Then use that number and restrictive stopping power into dose equation

Question 59

Dose around some point for a thin medium

Answer 59

(fluence)(S_c^e/rho)

Question 60

Dose at any point

Answer 60

(fluence)(S_c^e/rho)for T at x (this only applies for heavy particles due to very small straggling)

Question 61

Roughly where does the bragg peak occur

Answer 61

At a depth = R_csda

Question 62

Roughly how much larger is dose at bragg peak than at surface?

Answer 62

5-10x larger

Question 63

Why is fluence of a heavy beam even for the most part then drop very heavily at the end?

Answer 63

Due to electron capture

Question 64

What is the naming convention for primary and secondary electrons

Answer 64

Primary electron is ALWAYS the higher of the two energies. By this sense T_{lost mas} = T/2

Question 65

Remember these diagrams of electron beams

Answer 65

Question 66

Dose at any point x can be calculated by using \_\_\_\_\_\_\_\_\_\_\_. This is ALWAYS valid

Answer 66

(fluence)(restrictive stopping power)

Question 67

In general, σ_{cp int} ____ σ_{photon int}

Answer 67

\>\>

Question 68

Compton found that a scattered wave generally has ______ wavelength

Answer 68

longer

Question 69

Classical wave theory says that scattered waves are formed from

Answer 69

Charged particles oscillating due to Electric field from incoming EMR. The scattered wave has f = original wave

Question 70

For compton scattering Low hf lose _____ % of their E High hf lose ______ % of their E

Answer 70

small CAN LOSE large

Question 71

When can electrons be considered free?

Answer 71

When E_tr \>\> BE

Question 72

For a low hf, electron can't be considered free. Instead we get two other interactions which are,

Answer 72

Rayleigh Scattering PE effect

Question 73

Rayleigh scattering mechanism

Answer 73

Atomic electrons vibrate with same frequency as incoming wave They radiate a scattered wave with that energy Then they relax There's no excitation or ionization T_tr^R = 0

Question 74

Mechanism of PE Effect

Answer 74

Absorption interaction Atom absorbs photon, photoelectron is ejected Vacancy exists in atom and needs to be filled (nucleus also recoils, but very slightly, energy is negligible) Vacancy is filled either through Auger electrons or characteristic x-rays

Question 75

Energy of a photo electron

Answer 75

T_pe = hf - BE

Question 76

Energy transferred to atom in PE Effect

Answer 76

T_tr = T_pe + T_{Auger e}

Question 77

Approximately how many electrons/g are there for Hydrogen 2 \<= Z \<= 20 Z \> 20

Answer 77

N_A N_A/2 \<= N_A/2

Question 78

Approximately what percent of e-e interactions have very small energy loss?

Answer 78

90%

Question 79

How come S_C/rho for high Z is \< low Z

Answer 79

Because as Z increases, I also increases and so does the delta correction factor. In addition, n_e/g decreases

Question 80

Why do heavy charged particles lose essentially no energy to Bremmstrahlung radiation? (and thus S_R = 0) for heavy charged particles.

Answer 80

Because the energy loss depends 1/m² This is why electrons lose energy, but not charged particles.

Question 81

What is radiative stopping power proportional to?

Answer 81

Z_tar² and E_prof

Question 82

What is orbital velocity dependent on?

Answer 82

Z_eff/n

Question 83

What is orbital radius dependent on?

Answer 83

a₀n²/Z_eff

Question 84

Radius of an approximated nucleus sphere

Answer 84

(1.2E-13)A^1/3

Question 85

Quick approach to find mean free path length?

Answer 85

Recall: MFPL is the dx at which P_int = 1. Solve from there.

Question 86

Hard angle of a sphere

Answer 86

4π

Question 87

Regardless of photon energy, a photon scattered in a compton scatter has energy of approximately ____ for 90 degree scatters, and ____ for back scatters.

Answer 87

0. 5 MeV 0. 25 MeV