Physics - 11 - Atomic Physics...IB PHYSICS | UNIT 11 | ATOMIC PHYSICS Radiation IB PHYSICS | UNIT 11 | ATOMIC PHYSICS 11.1 Standard Notation 27Al 13 What do you notice about the notation

ATOMIC PHYSICSIB PHYSICS | UNIT 11 | ATOMIC PHYSICS

RadiationIB PHYSICS | UNIT 11 | ATOMIC PHYSICS

11.1

Standard Notation

Al2713

What do you notice about the notation written below? Can you determine what each color represents?

XAZ

Mass Number

Atomic Number

Try This

Na2311

Mass Number 23

Atomic Number 11

# of Protons 11

# of Neutrons 12

MgMass Number 25

Atomic Number 12

# of Protons 12

# of Neutrons 13

2512

Sample IB Question

A nucleus of Californium (Cf) contains 98 protons and 154 neutrons. Which of the following correctly identifies this nucleus of Californium?

25498Cf

98154Cf

98252Cf

154350Cf

Isotopes vs Nuclides

C126 C14

6

Isotopes

of Carbon

Same # of protons

Same # of neutrons

NuclideSingle atom

configuration

Fundamental Forces

B115

Remember Coulomb’s Law?

𝐹 = 𝑘𝑞1𝑞2𝑟2

Opposite charges attract

Like charges repel

Fundamental Forces

Strong Nuclear Force

Electromagnetic Force

Gravitational Force

Weak Nuclear Force

• Very short range

• Very strong

Like Velcro

Unstable Nuclei

Line of Stability

More neutrons than protons

Neutrons serve as a buffer between repelling protons

Radioactivity

Radioactivity is a process where unstable elements decay into new elements and

release energy as particles and/or waves

Alpha Decay

An unstable nucleus sheds alpha particle (helium nucleus) made from 2 protons and 2 neutrons

ZAX → 𝑍−2

A−4X + 24He

ParentNuclide

DaughterNuclide

AlphaParticle

Complete the missing notation:

92238U → Th + 2

4He90234

Alpha Decay - Predict

88222Ra → 86

218Rn + ______

84208Ra → Pb + 2

4α82204

24He

Beta-Negative Decay

In an unstable nucleus, sometimes a neutral neutron is converted into a positive proton and negative electron. When this happens, another particle called an antineutrino ( ҧ𝑣𝑒) is also formed

01n → 1

1p + −10e + ҧ𝑣𝑒

ҧ𝑣𝑒𝑛

𝑝

𝑒−

anti- Charge

= 0

Beta-Negative Decay

Beta-Negative Decay

**The proton stays and the electron and antineutrino flies away as “radiation”

ZAX → 𝑍+1

AX + −10e + ҧ𝑣𝑒

ParentNuclide

DaughterNuclide

Electron Antineutrino

Beta-Positive Decay

In an opposite process, a positive proton can be converted into a neutral neutron and positively charged electron (known as a positron). When this happens, another particle called an neutrino (𝑣𝑒) is also formed

11p → 0

1n + +10e + 𝑣𝑒

𝑣𝑒𝑝

𝑛

𝑒+

Beta-Positive Decay

ZAX → 𝑍−1

AX + +10e + 𝑣𝑒

ParentNuclide

DaughterNuclide

Positron Neutrino

614C → ___N + −1

0e + ҧ𝑣𝑒

1223Mg → ___Na + +1

0e + 𝑣𝑒

Beta Decay - Predict

90234Th → 91

234Pa + −10e + ҧ𝑣𝑒

53131I → 54

131Xe + _____ + ҧ𝑣𝑒−10e

714

1123

Gamma Decay

90234Th∗ → 90

234Th + 00γ

After an unstable nucleus has emitted an alpha or beta particle, it can contain excess energy that is released as gamma radiation

Particle Review

Particle Name

11p Proton

01n Neutron

−10e Electron

+10e Positron

ҧ𝑣𝑒 Antineutrino

𝑣𝑒 Neutrino

24He Alpha Particle

Ionizing Radiation

𝛽

𝛾

𝛼

More mass allows particles to more efficiently transfer energy and ionize an atom

Most mass

Most ionizing

Radiation Penetration

𝛽

𝛾

𝛼5 cm of air

30 cm of air

Highly Penetrating

Radiation Deflection

𝛽𝛾

𝛼

magnetic field out of screen

-10

+2

Radiation Deflection

+

–

𝛽𝛾

𝛼

-10

+2

Summary of α, β, and γ

Property Alpha (α) Beta (β+ or β-) Gamma (γ)

Relative Charge +2 +1 or -1 0

Relative Mass 4 0.0005 0

Typical Penetration 5 cm of air 30 cm of air Highly penetrating

Nature Helium nucleus Positron or Electron Electromagnetic wave

Typical Speed 107 m s-1 2.5 × 108 m s-1 3.00 × 108 m s-1

Notation 24He or 2

4α −10e or−1

0β γ or00𝛾

Ionizing Effect Strong Weak Very Weak

Abosorbed by Paper or skin 3 mm of AluminumIntensity halved by 2

cm of Lead

The Math Always Adds Up

90234Th → 91

234Pa + −10e + ҧ𝑣𝑒

1223Mg → 11

23Na + +10e + 𝑣𝑒

92238U → 90

234Th + 24He

90234Th∗ → 90

234Th + 00γ

Remembering Alpha and Beta

ZN

Z-2N-2

Proton Number, Z

Neu

tro

n N

um

ber

, N

ZN

Z+1N-1

Proton Number, Z

Neu

tro

n N

um

ber

, Nα Decay β- Decay

Mass # Mass #

92238U → 90

234Th + 24He 90

234Th → 91234Pa + −1

0e + ҧ𝑣𝑒

-4 same

Mass #

Same

Alpha Decay

82

PbLead

83

BiBismuth

84

PoPolonium

85

AtAstatine

86

RnRadon

87

FrFrancium

88

RaRadium

89

AcActinium

90

ThThorium

91

PaProtactinium

92

UUranium

93

NpNeptunium

94

PuPlutonium

95

AmAmericium

96

CmCurium

97

BkBerkelium

98

CfCalifornium

ZN

Z-2N-2

Proton Number, Z

Neu

tro

n N

um

ber

, N

ZN

Z+1N-1

Proton Number, Z

Neu

tro

n N

um

ber

, N

88226Ra → 86

222Ra + 24He

α Decay β- Decay

Mass #

- 4

α Decay of Radium-226

Beta Decay

82

PbLead

83

BiBismuth

84

PoPolonium

85

AtAstatine

86

RnRadon

87

FrFrancium

88

RaRadium

89

AcActinium

90

ThThorium

91

PaProtactinium

92

UUranium

93

NpNeptunium

94

PuPlutonium

95

AmAmericium

96

CmCurium

97

BkBerkelium

98

CfCalifornium

ZN

Z-2N-2

Proton Number, Z

Neu

tro

n N

um

ber

, N

ZN

Z+1N-1

Proton Number, Z

Neu

tro

n N

um

ber

, N

91234Pa → 92

234Ra + −10e + ҧ𝑣𝑒

α Decay β- Decay

β- Decay of Protactinium-234

Mass #

SameMass #

- 4

Keeps right on going…92

238U

90234Th

91234Pa

92234U

90230Th

82

PbLead

83

BiBismuth

84

PoPolonium

85

AtAstatine

86

RnRadon

87

FrFrancium

88

RaRadium

89

AcActinium

90

ThThorium

91

PaProtactinium

92

UUranium

88226Ra

86222Rn

84218Po

82214Pb

83214Bi

84214Po

83210Bi

81210Ti

82210Pb

81206Ti

82206Pb

Valley of Stability

Sample IB Question

Half-LifeIB PHYSICS | UNIT 11 | ATOMIC PHYSICS

11.2

Where does Radiation Come From?

Background Radiation

Radon Gas Maps

A person would receive a dose equivalent of 1 mrem from any of the following activities:• 3 days of living in Atlanta• 2 days of living in Denver• 1 year of watching television (on average)• 1 year of wearing a watch with a luminous dial• 1 coast-to-coast airline flight• 1 year living next door to a normally operating

nuclear power plant

Is Radiation Dangerous?

Radiation Sickness – 100 rem or more

Symptoms: Nausea and vomiting

Other Radiation Effects

*Values taken from the book Energy for Future Presidents →

Likelihood of cancer increases by 1%* for every radiation dose of 25 rem

*Note: This percent likelihood is added to the 20% chance from natural causes

Radioactive Decay92

238U

90234Th

91234Pa

92234U

90230Th

82

PbLead

83

BiBismuth

84

PoPolonium

85

AtAstatine

86

RnRadon

87

FrFrancium

88

RaRadium

89

AcActinium

90

ThThorium

91

PaProtactinium

92

UUranium

88226Ra

86222Rn

84218Po

82214Pb

83214Bi

84214Po

83210Bi

81210Ti

82210Pb

81206Ti

82206Pb

Half-Life

The amount of time it takes for one half of the original sample to decay

Radioactive Nuclide Half-life

Uranium-238 4.5 × 109 years

Radium-226 1,600 years

Radon-222 3.8 days

Francium-221 4.8 minutes

Astatine-217 0.03 seconds

This can be in the scale of seconds, minutes, days or even years!

Half-Life of Dice # of Rolls # of Dice

0 120

1

2

3

4

5

6

7

8

9

10

The RulesAny dice that are rolled a

6 have decayed into a

new isotope and are

removed from the sample

Half-Life =

Half-Life Example

How many half-lives does it take for there to only be __% of the original sample remaining?

100% / 2 = 50% remains after 1 half-life

50% /2 = 25% remains after 2 half-lives

25% /2 = 12.5% remains after 3 half-lives

12.5% /2 = 6.25% remains after 4 half-lives

6.25% /2 = 3.125% remains after 5 half-lives

Half Life Problem:

How many half-lives does it take for 100 g of a radioactive sample to decay to 12.5 g?

If the half-life of the sample is 7 years, how long will this take?

The half-life of radium-226 is 1601 years. What percentage remains undecayed after 4804 years?

100 g → 50 g → 25 g → 12.5 g 3 Half-Lives1 2 3

(3 half-lives) × (7 years) = 21 years

(4804 years) × (1201 years) = 4 Half-Lives

100% → 50% → 25% → 12.5% → 6.25%1 2 3 4

Radiocarbon Dating

How old is a sample of rock that has 6.25% of its original C-14. The half-life of C-14 is 5,730 years.

100% → 50% → 25% → 12.5% → 6.25%1 2 3 4

(3 half-lives) × (5730 years) =

22,920 years

Half-Life Examples

Energy and Mass DefectsIB PHYSICS | UNIT 11 | ATOMIC PHYSICS

11.3

Unified Atomic Mass Unit

When measuring and reporting the mass of individual atoms and subatomic particles, kilograms are inconveniently large…

The unified atomic mass unit is defined as one-twelfth of the mass of an isolated carbon-12 atom

1 u = 1.661 × 10-27 kg

1 mole of Carbon Atoms = 0.012 kg

0.012 kg

6.02 × 1023= 1.99 × 10−26 kg

1.99 × 10−26 kg

12=

Unified Atomic Mass Unit

Electron (me) 9.110 × 10-31 kg 0.000549 u

Proton (mp) 1.673 × 10-27 kg 1.007276 u

Neutron (mn) 1.675 × 10-27 kg 1.008665 u

Unified atomic mass unit 1.661 × 10-27 kg

This is the only time that we will ever use 7 sig figs. In this case, rounding to 1.01 u just wouldn’t cut it…

𝑝 𝑛𝑒−

IB Physics Data Booklet

Einstein’s Famous Equation

According to Albert Einstein, “mass and energy are

different manifestations of the same things”

Einstein’s Famous Equation

E = mc2

What is the energy equivalence of 1 g of matter?

Energy

[J]

Mass

[kg]Speed of Light3.00 × 108 m s-1

E = (0.001 kg)(3.00 × 108 m s-1)2 = 9 × 1013 J

IB Physics Data Booklet

E = mc2

New Unit for Energy!

What is the energy equivalence of 1 proton (1.673 × 10-27 kg)?

Electron-Volt eV𝐸𝑛𝑒𝑟𝑔𝑦 𝑖𝑛 𝑒𝑉 =

𝐸𝑛𝑒𝑟𝑔𝑦 𝑖𝑛 𝐽

1.60 × 10−191 MeV = 106 eV

𝐸 = 1.673 × 10−27 3 × 108 2 = 1.5057 × 10−10 J

1.5057 × 10−10 J

1.60 × 10−19= 941,062,500 𝑒𝑉 ≈ 𝟗𝟒𝟏𝑴𝒆𝑽

New Unit for Mass

𝐸 = 𝑚𝑐2

𝑚 =𝐸

𝑐2=𝑀𝑒𝑉

𝑐2= 𝑴𝒆𝑽 𝒄−𝟐

Unified Atomic Mass Unit

Electron rest mass (me) 9.110 × 10-31 kg 0.000549 u 0.511 MeV c-2

Proton rest mass (mp) 1.673 × 10-27 kg 1.007276 u 938 MeV c-2

Neutron rest mass (mn) 1.675 × 10-27 kg 1.008665 u 940 MeV c-2

Unified atomic mass unit 1.661 × 10-27 kg 1.000000 u 931.5 MeV c-2

1 + 1 > 2

Electron rest mass (me) 0.000549 u

Proton rest mass (mp) 1.007276 u

Neutron rest mass (mn) 1.008665 u

Unified atomic mass unit 1.000000 u

A neutral Carbon-12 atom contains:

6 protons6 neutrons6 electrons

What is the total mass in terms of u?

6 × 1.007276 u

6 × 1.008665 u

6 × 0.000549 u12.09894 u

Mass Defect

Mass sum of the Carbon-12 subatomic particles:

6 × 1.007276u + 6 × 1.008665u + 6 × 0.000549u = 12.09894u

Mass of Carbon-12 atom: 12.00000u

Mass Defect 12.09894u − 12.00000u = 𝟎. 𝟎𝟗𝟖𝟗𝟒𝐮

Where did the mass go?

Energy

Binding Energy

Binding Energy is the energy required to separate all of the nucleons

…or the energy released when a nucleus is formed from its nucleons

Mass Defect → Binding Energy

𝟎. 𝟎𝟗𝟖𝟗𝟒𝐮 = 0.09894 × 931.5 𝑀𝑒𝑉 𝑐−2 =

Unified atomic mass unit 1.661 × 10-27 kg 1.000000 u 931.5 MeV c-2

E = mc2

92.1626 𝑀𝑒𝑉 𝑐−2

= (92.1626 𝑀𝑒𝑉 𝑐−2)(𝑐2)

= 𝟗𝟐. 𝟐 𝑴𝒆𝑽

Binding Energy per Nucleon

Binding Energy for Carbon-12 = 92.2 MeV

Number of Nucleons for Carbon-12 = 12

6 protons6 neutrons6 electrons

Binding Energy per Nucleon = 92.2 𝑀𝑒𝑉

12=

7.7 𝑀𝑒𝑉 𝑝𝑒𝑟 𝑁𝑢𝑐𝑙𝑒𝑜𝑛

Mass Defect → Binding Energy

Highlight the peaks

These high points represent the most

stable nuclei

Most Stable:

Iron-56

Calculate the Binding Energy

Nuclide # of p # of n # of e Atomic Mass

Helium-4 2 2 2 4.002603u

me 0.000549u

mp 1.007276u

mn 1.008665u

1u 931.5 MeV c-2

2 × 1.007276 u

2 × 1.008665 u

2 × 0.000549 u

Mass Defect

0.030377 𝑢 ×931.5 𝑀𝑒𝑉 𝑐−2

1 𝑢= 28. 296 𝑀𝑒𝑉 𝑐−2

4.032980 𝑢 – 4.002603 𝑢 = 0.030377 𝑢

𝐸 = 𝑚𝑐2 = 28. 296 𝑀𝑒𝑉 𝑐−2 𝑐2 = 𝟐𝟖. 𝟐𝟗𝟔𝑴𝒆𝑽

Convert mass

to MeV c-2

Calculate the Binding Energy

Nuclide # of p # of n # of e Atomic Mass

Fluorine-19 9 10 9 18.998403u

me 0.000549u

mp 1.007276u

mn 1.008665u

1u 931.5 MeV c-2

9 × 1.007276 u

10 × 1.008665 u

9 × 0.000549 u

Mass Defect

0.158672 𝑢 ×931.5 𝑀𝑒𝑉 𝑐−2

1 𝑢= 147.8 𝑀𝑒𝑉 𝑐−2

19.157075 𝑢 – 18.998403 𝑢 = 0.158672 𝑢

𝐸 = 𝑚𝑐2 = 147.8 𝑀𝑒𝑉 𝑐−2 𝑐2 = 𝟏𝟒𝟕. 𝟖 𝑴𝒆𝑽

Convert mass

to MeV c-2

Calculate the Binding Energy

Nuclide # of p # of n # of e Atomic Mass

Iron-56 26 30 26 55.934936u

me 0.000549u

mp 1.007276u

mn 1.008665u

1u 931.5 MeV c-2

26 × 1.007276 u

30 × 1.008665 u

26 × 0.000549 u

Mass Defect

0.528464 𝑢 ×931.5 𝑀𝑒𝑉 𝑐−2

1 𝑢= 492.26 𝑀𝑒𝑉 𝑐−2

56.463400 𝑢 – 55.934936 𝑢 = 0.528464 𝑢

𝐸 = 𝑚𝑐2 = 492.26𝑀𝑒𝑉 𝑐−2 𝑐2 = 𝟒𝟗𝟐. 𝟐𝟔𝑴𝒆𝑽

Convert mass

to MeV c-2

Fission and FusionIB PHYSICS | UNIT 11 | ATOMIC PHYSICS

11.4

IB Physics Data Booklet

Sample IB Questions

13H3 Nucleons (3 MeV per Nucleon) × (3 Nucleons)

= 9 MeV

0.1 𝑢 ×931.5 𝑀𝑒𝑉 𝑐−2

1 𝑢= 93.15 𝑀𝑒𝑉 𝑐−2

𝐸 = 𝑚𝑐2 = 93.15 𝑀𝑒𝑉 𝑐−2 𝑐2 =

𝟗𝟑. 𝟏𝟓𝑴𝒆𝑽

Mass Defect

Intro to Fusion and Fission

Calculating the Binding Energy

Nuclide # of p # of n # of e Atomic Mass

Iron-56 26 30 26 55.934936u

me 0.000549u

mp 1.007276u

mn 1.008665u

1u 931.5 MeV c-2

26 × 1.007276 u30 × 1.008665 u26 × 0.000549 u

56.463400 u – 55.934936 u = 0.528454 uMass Defect

0.528454 u ×931.5 MeV c−2

1 u= 492.26 MeV c−2

𝐸 = 𝑚𝑐2 = 492.26 MeV c−2 c2 = 𝟒𝟗𝟐. 𝟐𝟔 𝐌𝐞𝐕 Binding Energy

Calculating the Binding Energy

26 × 1.007276 u + 30 × 1.008665 u + 26 × 0.000549 u→ 55.934936 u

56.463400 u – 55.934936 u

Mass Defect

0.528454 u ×931.5 MeV c−2

1 u= 492.26 MeV c−2

𝐸 = 𝑚𝑐2 = 492.26 MeV c−2 c2 = 𝟒𝟗𝟐. 𝟐𝟔 𝐌𝐞𝐕 Binding Energy

2611p + 300

1n + 26−10e → 26

56Fe

56.463400 u→ 55.934936 u

0.528454 u

Energy Released in Decay

88226Ra → Rn +

Complete the Alpha Decay reaction for Radium-226 and calculate the energy released

Radium-226 226.0254 u

Radon-222 222.0176 u

α-particle 4.0026 uBinding Energy 4.84 MeV

Mass Defect 0.0052 u

1 u 931.5 MeV c-2

86222

24He

226.0254 u→ 222.0176 u + 4.0026 u

226.0254 u→ 226.0202 u

Mass Defect = 226.0254 u - 226.0202 u = 0.0052 u

Binding Energy = 0.0052 u × 931.5 = 4.84 MeV

Fission

Chain Reaction

Fission

01n + 92

235U → 3793Rb + 55

141Cs + 201n + 0

0γ1.675 390.173 154.248 233.927 2 × 1.675

391.848 × 10-27 kg

× 10-27 kg × 10-27 kg× 10-27 kg × 10-27 kg × 10-27 kg

391.525 × 10-27 kg>

Binding Energy 181.14 MeVMass Defect 0.19446 u

391.848 × 10-27 kg - 391.525 × 10-27 kg = 0.323 × 10-27 kg

0.323 × 10−27 𝑘𝑔 ×1 𝑢

1.661 × 10−27 𝑘𝑔= 𝟎. 𝟏𝟗𝟒𝟒𝟔 𝒖

0.19446 𝑢 × 931.5 = 𝟏𝟖𝟏. 𝟏𝟒 𝑴𝒆𝑽

Fusion

Fusion

12H + 1

2H → 23He + 0

1n

Hydrogen-2 2.0141 u

Helium-3 3.0161 u

Neutron 1.0087 u

Binding Energy 3.1671 MeVMass Defect 0.0034 u

(2.0141 u + 2.0141 u) – (3.0161 u + 1.0087 u) = 0.0034 u

0.0034 u × 931.5 = 3.1671 MeV

4.0282 u 4.0248 u

Conditions for Fusion

It’s significantly more difficult to create fusion reactions here on earth

+

+

• High Pressure

• High Temperature

Fusion as a Power Source

Fusion reactions have been successfully controlled using strong magnetic fields but the energy used to run the magnets exceeds the energy released in the reaction…

Fusion vs. Fission

Fission

Fu

sio

n

The Particle AdventureIB PHYSICS | UNIT 11 | ATOMIC PHYSICS

Adapted from www.partic leadventure.org

Lawrence Berkeley National Laboratory

11.5

The Search for the Fundamental

People have long asked:"What is the world made of?" and "What holds it together?"

Why do so many things in this world share the same characteristics?People have come to realize that the matter of the world is made from a few fundamental building blocks of nature.

The word "fundamental" is key here. By fundamental building blocks we mean objects that are simple and structureless -- not made of anything smaller.

Even in ancient times, people sought to organize the world around them into fundamental elements, such as earth, air, fire, and water.

Is the Atom Fundamental?

People soon realized that they could categorize atoms into groups that shared similar chemical properties (as in the Periodic Table of the Elements). This indicated that atoms were made up of simpler building blocks, and that it was these simpler building blocks in different combinations that determined which atoms had which chemical properties.

Moreover, experiments which "looked" into an atom using particle probes indicated that atoms had structure and were not just squishy balls. These experiments helped scientists determine that atoms have a tiny but dense, positive nucleus and a cloud of negative electrons (e-).

Is the Nucleus Fundamental?

Because it appeared small, solid, and dense, scientists originally thought that the nucleus was fundamental. Later, they discovered that it was made of protons (p+), which are positively charged, and neutrons (n), which have no charge.

Are Protons/Neutrons Fundamental?

Physicists have discovered that protons and neutrons are composed of even smaller particles called quarks.

As far as we know, quarks are like points in geometry. They're not made up of anything else.

After extensively testing this theory, scientists now suspect that quarks and the electron (and a few other things we'll see in a minute) are fundamental.

Scale of the Atom

While an atom is tiny, the nucleus is ten thousand times smaller than the atom and the quarks and electrons are at least ten thousand times smaller than that. We don't know exactly how small quarks and electrons are; they are definitely smaller than 10-18 meters, and they might literally be points, but we do not know.

It is also possible that quarks and electrons are not fundamental after all, and will turn out to be made up of other, more fundamental particles. (Oh, will this madness ever end?)

What are we looking for?

Physicists constantly look for new particles. When they find them, they categorize them and try to find patterns that tell us about how the fundamental building blocks of the universe interact.

We have now discovered about two hundred particles (most of which aren't fundamental). To keep track of all of these particles, they are named with letters from the Greek and Roman alphabets.

Of course, the names of particles are but a small part of any physical theory. You should not be discouraged if you have trouble remembering them.

Take heart: even the great Enrico Fermi once said to his student (and future Nobel Laureate) Leon Lederman, "Young man, if I could remember the names of these particles, I would have been a botanist!"

The Standard Model

Physicists have developed a theory called The Standard Model that explains what the world is and what holds it together. It is a simple and comprehensive theory that explains all the hundreds of particles and complex interactions with only:• 6 quarks.• 6 leptons. The best-known lepton is the electron. We will talk about leptons later• Force carrier particles, like the photon. We will talk about these particles later.

All the known matter particles are composites of quarks and leptons, and they interact by exchanging force carrier particles.

The Standard Model

The Standard Model is a good theory. Experiments have verified its predictions to incredible precision, and all the particles predicted by this theory have been found. But it does not explain everything. For example, gravity is not included in the Standard Model.

These slides will explore the Standard Model in greater detail and will describe the experimental techniques that gave us the data to support this theory. We will also explore the intriguing questions that lie outside our current understanding of how the universe works.

Matter and Antimatter

For every type of matter particle we've found, there also exists a corresponding antimatterparticle, or antiparticle.

Antiparticles look and behave just like their corresponding matter particles, except they have opposite charges. For instance, a proton is electrically positive whereas an antiproton is electrically negative. Gravity affects matter and antimatter the same way because gravity is not a charged property and a matter particle has the same mass as its antiparticle.When a matter particle and antimatter particle meet, they annihilate into pure energy!

What is Antimatter?

Slow down! "Antimatter?" "Pure energy?" What is this, Star Trek?The idea of antimatter is strange, made all the stranger because the universe appears to be composed entirely of matter. Antimatter seems to go against everything you know about the universe.

But you can see evidence for antimatter in this early bubble chamber photo. The magnetic field in this chamber makes negative particles curl left and positive particles curl right. Many electron-positron pairs appear as if from nowhere, but are in fact from photons, which don't leave a trail. Positrons (anti-electrons) behave just like the electrons but curl in the opposite way because they have the opposite charge. (One such electron-positron pair is highlighted.)If antimatter and matter are exactly equal but opposite, then why is there so much more matter in the universe than antimatter?

Well... we don't know. It is a question that keeps physicists up at night.(The usual symbol for an antiparticle is a bar over the corresponding particle symbol. For example, the "up quark" u has an "up antiquark" designated by , pronounced u-bar. The antiparticle of a quark is an antiquark, the antiparticle of a proton is an antiproton, and so on. The antielectron is called a positron and is designated e+.)

QuarksQuarks are one type of matter particle. Most of the matter we see around us is made from protons and neutrons, which are composed of quarks.

There are six quarks, but physicists usually talk about them in terms of three pairs: up/down, charm/strange, and top/bottom. (Also, for each of these quarks, there is a corresponding antiquark.) Be glad that quarks have such silly names -- it makes them easier to remember!

Quarks

Quarks have the unusual characteristic of having a fractional electric charge, unlike the proton and electron, which have integer charges of +1 and -1 respectively. Quarks also carry another type of charge called color charge, which we will discuss later.The most elusive quark, the top quark, was discovered in 1995 after its existence had been theorized for 20 years.

The Naming of Quarks

The naming of quarks began when, in 1964, Murray Gell-Mann and George Zweig suggested that hundreds of the particles known at the time could be explained as combinations of just three fundamental particles. Gell-Mann chose the name "quarks," pronounced "kworks," for these three particles, a nonsense word used by James Joyce in the novel Finnegan's Wake:"Three quarks for Muster Mark!“

In order to make their calculations work, the quarks had to be assigned fractional electrical charges of 2/3 and -1/3. Such charges had never been observed before. Quarks are never observed by themselves, and so initially these quarks were regarded as mathematical fiction. Experiments have since convinced physicists that not only do quarks exist, but there are six of them, not three.

How did quarks get their silly names?

There are six flavors of quarks. "Flavors" just means different kinds. The two lightest are called up and down.

The third quark is called strange. It was named after the "strangely" long lifetime of the K particle, the first composite particle found to contain this quark.

The fourth quark type, the charm quark, was named on a whim. It was discovered in 1974 almost simultaneously at both the Stanford Linear Accelerator Center (SLAC) and at Brookhaven National Laboratory.

The fifth and sixth quarks were sometimes called truth and beauty in the past, but even physicists thought that was too cute.

The bottom quark was first discovered at Fermi National Lab (Fermilab) in 1977, in a composite particle called Upsilon ().

The top quark was discovered last, also at Fermilab, in 1995. It is the most massive quark. It had been predicted for a long time but had never been observed successfully until then.

Leptons

The other type of matter particles are the leptons.

There are six leptons, three of which have electrical charge and three of which do not. They appear to be point-like particles without internal structure. The best known lepton is the electron (e). The other two charged leptons are the muon(μ) and the tau(τ), which are charged like electrons but have a lot more mass. The other leptons are the three types of neutrinos (v).They have no electrical charge, very little mass, and they are very hard to find.Quarks are sociable and only exist in composite particles with other quarks, whereas leptons are solitary particles. Think of the charged leptons as independent cats with associated neutrino fleas, which are very hard to see.

For each lepton there is a corresponding antimatter antilepton. Note that the anti-electron has a special name, the "positron."

Lepton Decays

The heavier leptons, the muon and the tau, are not found in ordinary matter at all. This is because when they are produced they very quickly decay, or transform, into lighter leptons. Sometimes the tau lepton will decay into a quark, an antiquark, and a tau neutrino. Electrons and the three kinds of neutrinos are stable and thus the types we commonly see around us.

When a heavy lepton decays, one of the particles it decays into is always its corresponding neutrino. The other particles could be a quark and its antiquark, or another lepton and its antineutrino.

Physicists have observed that some types of lepton decays are possible and some are not. In order to explain this, they divided the leptons into three lepton families: the electron and its neutrino, the muon and its neutrino, and the tau and its neutrino. The number of members in each family must remain constant in a decay. (A particle and an antiparticle in the same family "cancel out" to make the total of them equal zero.)

Although leptons are solitary, they are always loyal to their families!

Neutrinos

Neutrinos are, as we've said, a type of lepton. Since they have no electrical or strong charge they almost never interact with any other particles. Most neutrinos pass right through the earth without ever interacting with a single atom of it.

Neutrinos are produced in a variety of interactions, especially in particle decays. In fact, it was through a careful study of radioactive decays that physicists hypothesized the neutrino's existence.

For example: (1) In a radioactive nucleus, a neutron at rest (zero momentum) decays, releasing a proton and an electron. (2) Because of the law of conservation of momentum, the resulting products of the decay must have a total momentum

of zero, which the observed proton and electron clearly do not. (Furthermore, if there are only two decay products, they must come out back-to-back.)

(3) Therefore, we need to infer the presence of another particle with appropriate momentum to balance the event. (4) We hypothesize that an antineutrino was released; experiments have confirmed that this is indeed what happens.

Because neutrinos were produced in great abundance in the early universe and rarely interact with matter, there are a lot of them in the Universe. Their tiny mass but huge numbers may contribute to total mass of the universe and affect its expansion.

Fundamental Particles

Charge QuarksBaryon Number

23 u c t 1

3

−13 d s b 1

3

All quarks have a strangeness number of 0 except the strange quark that has a strangeness number of –1

Charge Leptons

−1 e μ τ

0 𝑣𝑒 𝑣μ 𝑣τ

All leptons have a lepton number of 1 and antileptons have a lepton number of –1

Symbol Name

u Up

d Down

c Charm

s Strange

t Top

b Bottom

Symbol Name

e Electron

μ Muon

τ Tau

𝑣𝑒 Electron Neutrino

𝑣μ Muon Neutrino

𝑣τ Tau Neutrino

Antiparticles have the opposite charge as their corresponding particle and have a bar over their symbol

Symbol Name Charge

s Strange −13

ҧ𝑠 Antistrange +13

Build your own models

(Name)Charge = #Baryon # = Lepton # =

Charge Color

23 Green

−23 Blue

13 Purple

−13 Pink

1 Yellow

−1 Gold

0 White

Create a colored circle for each of the fundamental particle and antiparticles. There should be 24 circles in total when you are done.

For each circle, choose the color based on the charge in the chart to the right and include all of the information listed on the example below

(Symbol)

Front Back

Hadrons, Baryons, Mesons, & the Standard ModelIB PHYSICS | UNIT 11 | ATOMIC PHYSICS

11.6

Fundamental Particles

Charge QuarksBaryon Number

23 u c t 1

3

−13 d s b 1

3

All quarks have a strangeness number of 0 except the strange quark that has a strangeness number of –1

Charge Leptons

−1 e μ τ

0 𝑣𝑒 𝑣μ 𝑣τ

All leptons have a lepton number of 1 and antileptons have a lepton number of –1

Symbol Name

u Up

d Down

c Charm

s Strange

t Top

b Bottom

Symbol Name

e Electron

μ Muon

τ Tau

𝑣𝑒 Electron Neutrino

𝑣μ Muon Neutrino

𝑣τ Tau Neutrino

Antiparticles have the opposite charge as their corresponding particle and have a bar over their symbol

Symbol Name Charge

s Strange −13

ҧ𝑠 Antistrange +13

IB Physics Data Booklet

Classifying Particles

Leptons Hadrons

Electrons

Muons

Tau

Neutrinos

Pion (π)

Kaon (Κ)

Others

Proton

Neutron

Others

Mesons Baryons

Fundamental ParticlesSymbol Name Charge Baryon #

u Up +23

13

d Down −13

13

c Charm +23

13

s Strange −13

13

t Top +23

13

b Bottom −13

13

Symbol Name Charge Baryon #

തu Antiup −23 −1

3

തd Antidown +13 −1

3

തc Anticharm −23 −1

3

ҧs Antistrange +13 −1

3

ҧt Antitop −23 −1

3

തb Antibottom +13

−13

Symbol Name Charge Lepton #

e Electron −1 1

μ Muon −1 1

τ Tau −1 1

𝑣𝑒 Electron Neutrino 0 1

𝑣μ Muon Neutrino 0 1

𝑣τ Tau Neutrino 0 1

Symbol Name Charge Lepton #

തe Antielectron (positron) +1 −1

തμ Antimuon +1 −1

തτ Antitau +1 −1

ҧ𝑣𝑒 Electron Antineutrino 0 −1

ҧ𝑣μ Muon Antineutrino 0 −1

ҧ𝑣τ Tau Antineutrino 0 −1

Baryons

All Baryons are formed from a combination of 3 quarks or antiquarks

Rule: Charge must be an integer value (-1, 0, or +1)

u

d

Up Quark

Charge =

Down Quark

Charge =

Proton

Neutron

u u

u

d

d d

2/3

-1/3

(uud)

(udd)

+1

0

Mesons

All Mesons are formed from a combination of a quark and antiquark

Rule: Charge must be an integer value (-1, 0, or +1)

Kaon

D-Meson

dҧs

dതu

+1

3

−1

3

−2

3

−1

3

0

-1

Quark Confinement

Quarks have never been observed on their own

dҧs

The amount of energy required to overcome the strong nuclear force holding the quarks together gets converted into mass and forms a new quark pair

d

ҧs

ҧs

d

Conservation

For an interaction to be possible, the following must stay conserved:

Baryon # Lepton # Charge Strangeness

𝑛 → 𝑝 + 𝑒− + ҧ𝑣𝑒Baryon # 1

Lepton # 0

Charge 0

1 0 0

0 1 -1

1 -1 0

This interaction is valid because all properties are conserved

Conservation

𝑛 + 𝑝 → 𝑒+ + ҧ𝑣𝑒

𝑝 + 𝑒− → 𝑛 + 𝑣𝑒1 0

0 1

+1 -1

1 0

0 1

0 0

Baryon #

Lepton #

Charge

YesValid

1 1

0 0

0 +1

0 0

-1 -1

+1 0

Baryon #

Lepton #

Charge

NoInvalid

Exchange Particles

At the fundamental level of particle physics, forces are explained in terms of the transfer of exchange particles (gauge bosons) between

the two particles experiencing the force

These interactions are not observable so we call them virtual particles

Types of Forces

Weakest Strongest

photon

Sample IB Question

The Standard Model

Sample IB Question

The Standard ModelMost

Common

Currently

Undiscovered

Feynman Diagrams &the Higgs BosonIB PHYSICS | UNIT 11 | ATOMIC PHYSICS

11.7

IB Physics Data Booklet

The Standard Model

The Large Hadron Collider

The Large Hadron Collider

5.4 miles

The Higgs Boson

Higgs Boson

Feynman Diagrams

Useful to represent, analyze, and predict particle interactions

Feynman Diagrams | The Rules

1. You can only draw two kinds of lines

Matter Particle Force (exchange)

Particle

Feynman Diagrams | The Rules

2. You can only connect these lines if you have two lines with arrows (one pointing in, one pointing out) meeting a single wiggly line

Interaction

Feynman Diagrams | What’s Wrong?

What’s wrong with these vertices?

No straight

lines

Both arrows

point intovertex

2 squiggles

at vertex

Arrow Direction

Left-pointing

means

antiparticle

Right-pointing

means

particle

Representing Time

The x-axis on a Feynman Diagram represents time and is read from left to right. Everything left of the vertex is the “before” condition.

e+

e-

ɣ

before after

Match these!

a photon spontaneously

“pair produces” an electron and

positron

a positron absorbs a photon and keeps going

an electron emits a photon and keeps

going

an electron and positron annihilate

into a photon

Beta-Negative Decay

𝑛 → 𝑝 + 𝑒− + ҧ𝑣𝑒

Beta-Positive Decay

𝑝 → 𝑛 + 𝑒+ + 𝑣𝑒

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