Quantum, Nuclear and X-rays CT

Question 1

Photoelectric effect

Answer 1

an interaction between a photon and an electron in a metal, in which the electron is removed from the surface of a metal

Question 2

Photons

Answer 2

a quantum of electromagnetic energy

Unit: electronvolt (eV)
Symbol: γ

Question 3

Planck constant

Answer 3

a fundamental constant that links the energy of a photon E and its frequency f,
E = hf

Unit: Js
Symbol: h

Question 4

electronvolt (eV)

Answer 4

the energy gained by an electron travelling through a potential difference of 1 volt

1 eV = 1.60 x 10⁻¹⁹ J

Question 5

Threshold voltage

Answer 5

the minimum forward bias voltage across a light-emitting diode (LED) when it starts to conduct and emit light

Question 6

Threshold frequency

Answer 6

the minimum frequency of the incident electromagnetic radiation that would eject electrons from the surface of a metal

Question 7

Threshold wavelength

Answer 7

the longest wavelength of the incident electromagnetic radiation that would eject electrons from the surface of a metal

Question 8

Work function of energy

Answer 8

the minimum energy needed by an electron to free itself from the surface of a metal. Work function (together with threshold frequency and threshold wavelength) is a property of the metal.

Question 9

Dispersion

Answer 9

the technical term for the splitting of light into its components

Question 10

Continuous spectrum

Answer 10

an emission spectrum that consists of a continuum of wavelengths

Question 11

Emission line spectrum

Answer 11

a spectrum with bright-coloured lines of unique wavelengths

Question 12

Absorption line spectrum

Answer 12

a spectrum with dark lines of unique wavelengths seen against the background of a continuous spectrum

Question 13

Energy levels/states

Answer 13

a quantised energy state of an electron in an atom

Question 14

Quantised

Answer 14

a quantity is said to be quantised when it has a definite minimum magnitude and always comes in multiples of the magnitude
restricting a variable, observable quantity to discrete values

Question 15

Transition

Answer 15

term used to describe a jump made by an electron between two energy levels

Question 16

Ground state

Answer 16

the lowest energy state that can be occupied by an electron in an atom

Question 17

de Broglie wavelength

Answer 17

the wavelength associated with a moving particle, given by the equation

λ = h/p or λ = h/mv

Question 18

Mass defect

Answer 18

the difference between the total mass of the individual separate nucleons and the mass of the nucleus

Question 19

Atomic mass unit

Answer 19

1/12 of the mass of a neutral atom of carbon-12

Symbol: u

Question 20

Binding energy

Answer 20

the minimum external energy required to completely separate all the neutrons and protons of a nucleus to infinity

Question 21

Fission

Answer 21

the process in which a massive nucleus splits into two smaller nuclei

Question 22

Fusion

Answer 22

the process in which two light nuclei join together to form a heavier nucleus

Question 23

Decay constant

Answer 23

the probability that an individual nucleus will decay per unit time

Unit: s⁻¹
Symbol: λ

Question 24

Activity

Answer 24

the rate of decay of a nuclei of a radioactive source

Unit: Bq (becquerel)
Symbol: A

Question 25

Count rate

Answer 25

the number of particles (beta or alpha) or gamma-ray photons detected per unit time by a Geiger–Müller tube

count rate is always a fraction of the activity of a sample

Question 26

Exponential decay

Answer 26

the decrease of a quantity where the rate of decrease is proportional to the value of the quantity

Question 27

Half life

Answer 27

the half life t₀.₅ of an isotope is the mean time taken for half of the active nuclei in a sample to decay

Question 28

Einstein relation (2)

Answer 28

E = hf and E = hc/λ

(E) energy of a photon [J]
(h) Planck’s constant [eV]
(f) frequency [Hz]
(c) wave speed [ms⁻¹]
(λ) wavelength [m]

Question 29

Speed of any type of charged particle

Answer 29

v = √2eV/m or v = √2Eᴋ/m

(v) electron speed [ms⁻¹]
(e) electron charge [C]
(V) voltage [V]
(m) mass of particle [kg]
(Eᴋ) kinetic energy [J]

Question 30

Einstein’s photoelectric equation

Answer 30

E = hc/λ = hf = Φ + 1/2mvₘₐₓ²

(E) energy of a photon [J]
(h) Planck’s constant [eV]
(f) frequency [Hz]
(c) wave speed [ms⁻¹]
(λ) wavelength [m]
(Φ) work function of the metal [J or eV]
(1/2mvₘₐₓ²) maximum kinetic energy of emitted photoelectron [J]

Question 31

Equations when incident radiation frequency equals threshold frequency (3)

Answer 31

hf₀ = Φ
∴
f₀ = Φ/h
∴
λ₀ = hc/Φ

(h) Planck’s constant [Js]
(f₀) threshold frequency [Hz]
(Φ) work function [J or eV]
(λ₀) threshold wavelength [m]
(c) wave speed [ms⁻¹]

Question 32

Momentum of a photon

Answer 32

p = E/c

(p) momentum [kgms⁻¹]
(E) energy of the photon [J]
(c) photon speed [ms⁻¹]

Question 33

The energy of a photon, absorbed or emitted, as a result of an electron making a transition between two energy levels E₁ and E₂

Answer 33

hf = E₁ - E₂
hc/λ = E₁ - E₂

(h) Planck’s constant [Js]
(f) frequency [Hz]
(c) wave speed [ms⁻¹]
(E) energy levels [J or eV]

Question 34

de Broglie wavelength equation

Answer 34

λ = h/p

(λ) wavelength [m]
(h) Planck’s constant [Js]
(p) momentum [kgms⁻¹]

Question 35

Finding wavelength using angle of separation

Answer 35

λ = 2d sinθ

(λ) wavelength [m]
(d) spacing of layers [m]
(θ) angle of diffraction [º]

Question 36

Einstein’s mass energy equation

Answer 36

E = mc²

(E) energy [J]
(m) mass [kg]
(c) speed of light [ms⁻¹]

Question 37

Activity (2)

Answer 37

A = (-)λN = ∆N/∆t

(A) activity [Bq]
(λ) decay constant [s⁻¹]
(N) number of undecayed nuclei
(t) time [s]

Question 38

Radioactive decay formula

Answer 38

A = A₀ e⁻*ᵗ

(A) activity [Bq]
(A₀) activity at time t = 0 [Bq]
(*) decay constant (λ) [s⁻¹]
(t) time [s]

Question 39

Half-life and decay constant relationship

Answer 39

λ = ln2/t₀.₅
= 0.693 / t₀.₅

(λ) decay constant [s⁻¹]
(t) time [s]

Question 40

Attenuation of x-rays as they pass through a uniform material

Answer 40

I = I₀ e⁻*ˣ

(I) transmitted intensity [Wm⁻²]
(I₀) initial intensity [Wm⁻²]
(*) attenuation coefficient (µ) [m⁻¹]
(x) thickness of the material [m]

Question 41

Electronvolt and Joules conversion

Answer 41

To convert from eV to J, multiply by 1.60 x 10⁻¹⁹

To convert from J to eV, divide by 1.60 x 10⁻¹⁹

Question 42

Observations of photoelectric effect

Answer 42

Textbook table 28.4

Question 43

Diagrams showing electron dropping to a lower energy level, emitted and absorbed

Answer 43

Textbook figure 28.18 a & b

(emission moving down, absorption moving up)

Question 44

Wave particle duality of light

Answer 44

Light interacts with matter (eg. electrons) as a particle - The evidence for this is provided by the photoelectric

Light propagates through space as a wave - The evidence for this comes from the diffraction and interference of lights using slits

Question 45

When electron receives energy of the same magnitude as its ground state value

Answer 45

Electron entirely removed from the nucleus

Question 46

Basic decays

Answer 46

When an unstable nucleus undergoes radioactive decay the nucleus before the decay is called the parent nucleus and after the decay is called the daughter nucleus

In α decay, the nucleon number decreases by 4 and the proton number decreases by 2

In β⁻ decay, the nucleon number is unchanged and the proton number increases by 1

In β⁺ decay, the nucleon number is unchanged and the proton number decreases by 1

In gamma decay, there is no change in nucleon or proton number

For the emission of an alpha particle use the notation He and for a beta particle use the notation e.

Question 47

Mass changes according to Einstein’s equation

Answer 47

The mass of a system increases when energy is added to it

The mass of a system decreases when energy is released from it

To calculate mass change add the mass of the decay particle to the daughter nucleus. Subtract the parent nucleus mass from this.

∆m = final mass - initial mass

Question 48

Stability comparison of different nuclides

Answer 48

In order to compare the stability of different nuclides, we need to consider the binding energy per nucleon.

Question 49

Determining binding energy per nucleon

Answer 49

Determine the mass defect for the nucleus

Use Einstein’s mass-energy equation to determine the binding energy of the nucleus by multiplying the mass defect by c²

Divide the binding energy of the nucleus by the number of nucleons

Question 50

Fusion and fission graph of binding energy per nucleon against nucleon number

Answer 50

Textbook figure 29.6

Question 51

Spontaneous decay

Answer 51

Radioactive decay is both spontaneous and random

Nuclear decay is spontaneous because:
1. the decay of a particular nucleus is not affected by the presence of other nuclei
2. the decay of nuclei cannot be affected by chemical reactions or external factors such as temperature and pressure

Nuclear decay is random because:
1. it is impossible to predict when a particular nucleus in a sample is going to decay
2. each nucleus in a sample has the same chance of decaying per unit time

Question 52

Aims of radiographers (2)

Answer 52

To reduce the patient’s exposure to harmful x-rays as much as possible

To improve the contrast of the image, so that the different tissues under investigation show up clearly in the image

Question 53

Types of x-rays used

Answer 53

Bone is a good absorber of radiation hence a hard X-ray is used

Muscle tissue is a poor absorber hence will require a longer exposure using much softer (long-wavelength, low-frequency) X-rays.

Question 54

X-ray tube diagram

Answer 54

Textbook figure 30.4