Unit 08

Nuclear Structure

• Nuclear Structure

• Radiation

Unit 08 – Nuclear Structure – Slide 1

The Plan

Unit 08 – Nuclear Structure – Slide 2

Nuclear Structure

Nuclear Decays

Measuring Radiation

Nuclear Power Plants

Major Nuclear Power Accidents

New Possibilities for Nuclear Power

Definitions

Unit 08 – Nuclear Structure – Slide 3

~10-15m

Size of atom ~ 10-10m (100,000 times bigger)

Definitions

Unit 08 – Nuclear Structure – Slide 5

Element – determine by number of

protons (or electrons)

Every uranium atom as 92 protons

Atomic Number (Z) – number of

protons

Z = 92 for uranium

Nucleon – all the things inside a

nucleus, the protons and neutrons

Definitions

Unit 08 – Nuclear Structure – Slide 6

Mass Number (A) - number of protons

plus neutrons

Isotope – a sub-set of an element with a

specific number of neutrons

uranium 235

-143 neutrons and 92 protons

uranium 238

- 146 neutrons and 92 protons

U235

92

U238

92

Periodic Table

Unit 08 – Nuclear Structure – Slide 7

Oxygen

Unit 08 – Nuclear Structure – Slide 8

Like charges repel

Unit 08 – Nuclear Structure – Slide 9

p+p+

Need the strong force

Unit 08 – Nuclear Structure – Slide 10

p+p+

n

n

Add some neutral particles as “glue”

Like Goldilocks…..

Unit 08 – Nuclear Structure – Slide 11

• Too many protons? – too much repulsion

and it flies apart.

• Too many total nucleons? – too big for

strong binding to work

• Too many neutrons? – neutron turns into

a proton and it flies apart.

Make up of nucleus has to be “just right”….

Stable Nuclei

Ends here??

Unit 08 – Nuclear Structure – Slide 12

Binding Energy

Unit 08 – Nuclear Structure – Slide 13

The amount of

energy needed

to break into

pieces

Alpha Decay

Unit 08 – Nuclear Structure – Slide 14

Heavy nuclei can spit out an alpha

particle.

How do unstable nuclei change the

proton-neutron ratio?

Beta Decay

Unit 08 – Nuclear Structure – Slide 15

Lighter nuclei change a neutron into a proton

spitting out an electron (“beta particle”)

How do unstable nuclei change the

proton-neutron ratio?

Gamma Decay

Unit 08 – Nuclear Structure – Slide 16

The nuclei gets rid of the excess

energy by spiting out a high energy

electro-magneti can spit out an alpha

particle.

Some times the nucleus just has too

much energy.

How do you make radioactive material?

Unit 08 – Nuclear Structure – Slide 17

U235

92n

1

0

Sr94

38+ +Xe140

54U236 *

92

n1

0+ n

1

0+

Nuclear Decays

Unit 08 – Nuclear Structure – Slide 18

Nuclear Decays• One or more particles emitted from nucleus • May or may not turn into different element• e.g.

Th227

90 Ra223

88He

4

2

Different than fission!

Notice the numbers have to add up

Three Types (Different Effects!)

Unit 08 – Nuclear Structure – Slide 19

• Alpha – Helium nucleus emitted

• Why He emitted?

Th227

90Ra

223

88He

4

2+

Binding Energy

Decay Types – Beta

Unit 08 – Nuclear Structure – Slide 20

• Beta – electron or positron emitted

• Why neutrino?

C14

6N

14

7e

-

+ + n

Na22

11Ne

22

10e

+

+ + n

Energy of

emitted

positrons

Required for energy

conservation

Massless?

neutron turns into

proton

Decay Types – Gamma

Unit 08 – Nuclear Structure – Slide 21

• Gamma – photon emitted from the nucleus

• Gamma rays from nucleus • very short wavelength• 0.1 to 10MeV (as opposed to ~20eV from

atomic decay)

• No change in charge

Co60 *

27g+Co

60

27

Longer wavesHigher frequency

Enough

energy to

damage

cells

Gamma Rays

Unit 08 – Nuclear Structure – Slide 22

How does it decay?

Unit 08 – Nuclear Structure – Slide 23

Y94

39

140

55Cs

Sr94

38

Zr94

4018.8m1.2m

140

54Xe

1.3s

140

57La

1.0m

140

56Ba

12.7d

140

58Ce

1.6d

How does it decay?

Unit 08 – Nuclear Structure – Slide 24

Decay Chain

Unit 08 – Nuclear Structure – Slide 25

alpha

beta

Unstable thorium 232

Stable lead 208

Series of

decays,

not just one.

Summary

Unit 08 – Nuclear Structure – Slide 26

• Alpha (He nucleus) • Most deadly• Easiest to block

• Beta (electron or positron)

• Gamma (photon from nucleus • Least deadly • Toughest to block

Example 8.1: Decay products

Unit 08 – Nuclear Structure – Slide 27

27Si -> 27Al + ??

What type of decay is shown

below and what are the

unshown decay particles?

Example 8.1 (con’t)

Unit 08 – Nuclear Structure – Slide 28

Example 8.1: Decay products

Unit 08 – Nuclear Structure – Slide 29

27Si -> 27Al14 13

+ e+ + n

Question

Unit 08 – Nuclear Structure – Slide 30

What is the missing daughter particle in the alpha decay below?

Po210

84 He4

2+?

A)

B)

C)

Pb206

82

Pb210

82

Po206

84

Question

Unit 08 – Nuclear Structure – Slide 31

What is the missing daughter particle in the beta decay below?

In116

49e-+?

A)

B)

C)

Cd116

48

Cd115

48

Sn116

50

Question

Unit 08 – Nuclear Structure – Slide 32

In what type of radioactive decay are the mass numbers of the parent and daughter nuclei the same?

A. AlphaB. BetaC. GammaD. Both Alpha and BetaE. Both Beta and Gamma

Measuring Radioactivity

Unit 08 – Nuclear Structure – Slide 33

Different ways to measure radioactivity depending on need and/or available equipment.

Can be very confusing. In general:

1) Activity – Just count decay (Curie)

2) Energy deposited in some material (Rad)

3) Energy deposited in human body (REM)

Activity

Unit 08 – Nuclear Structure – Slide 34

• Just count number of decays per second.

•

• Simplest equipment (e.g. Geiger counter)

• Units • Becquerel (bq) 1 decay/sec• Curie (Cu) 3.7X1010 decay/sec (1g of Ra)

DN

DtR =

Example 11.1 Activity

Unit 08 – Nuclear Structure – Slide 35

A Geiger counter is held 6cm from a radioactive sample and gives a reading of 3200 counts of a period of 2 minutes. Assuming the Geiger counter covers 1/8 of the total area, what is the activity of the sample?

Measuring Radiation – Absorbed Dose

Unit 08 – Nuclear Structure – Slide 36

Rad (Radiation Absorbed Dose) – amount of radiation that deposits

100 erg/gram of materialor

0.01 J/kg of material

• Depends on the material absorbing radiation

• Internationally being replaced by Gray (Gy)

• 1Rad = 0.01Gy

Example 11.4 – Effect on Human

A beam of protons is directed at a 0.015kg cancer tumor. The particles have an energy of 5MeV each. If 1.6X1010 particles emitted every second, what is the absorbed dose delivered to the tumor in 25 seconds?

Unit 08 – Nuclear Structure – Slide 37

Absorbed Dose in Humans

Unit 08 – Nuclear Structure – Slide 38

Roentgen Equivalent Man (rem) – takes into account amount of harm done to human body

• More deadly radiation has higher “Relative Biological Effectiveness (RBE)” or “Q factor”

• International units are Siverts (Sv)

• 100 Rem = 1 Sv

Absorbed Dose in Humans

• X-rays have Q = 1 (by definition)

• medium energy neutrons Q=2.5 (1rad of neutrons 2.5 more harmful to humans than 1rad of x-rays.)

• Alpha particles Q=20!!! (very deadly but easy to stop)

Unit 08 – Nuclear Structure – Slide 39

Example 11.4 – Effect on Human

A beam of protons is directed at a 0.015kg cancer tumor. The particles have an energy of 5MeV and a relative biological equivalent of Q=4. If 1.6X1010 particles emitted every second, what is the biologically equivalent dose delivered to the tumor in 25 seconds?

Unit 08 – Nuclear Structure – Slide 40

Example 8.7 – Radiation Effects

A 0.5kg biological sample receives of dose of 456 rad from neutrons with an RBE of 6.2.

a) How much energy is absorbed by the sample?

b) What is the effective dosage in REM?

Unit 08 – Nuclear Structure – Slide 41

Effect on Human

Unit 08 – Nuclear Structure – Slide 42

There is 1.6 X 10-19 Joules (J) in one electron-volt (eV). How many Joules are in 5.6MeV?

A) 1.6 X 10-19JB) 1.6 X 10-13JC) 9X10-19JD) 9X10-13 JE) 18X 10-13J

Effect on Human

Unit 08 – Nuclear Structure – Slide 43

A beam of protons is directed at a 0.01kg cancer tumor. The particles have an energy of 9x10-13

Joules each. If 1.2X1010 particles emitted every second, what is the absorbed dose delivered to the tumor in 20 seconds?

A) 9X10-13 J/kg = 9X10-13GrayB) 8.2 GrayC) 12.4 GrayD) 21.6 GrayE) 80.2 Gray

Allowed Human Dose

• Average annual dose • 0.62rem (~50% natural, 50% medical)

• Nuclear Regulatory Commission (NRC) Limit for general public • 0.1rem/year (1mSv) above background

• Nuclear Regulatory Commission (NRC) Limit for rad workers• 5rem/year (50mSv) above background

• Any “external source” e.g. power plant• 0.02rem/year

Unit 08 – Nuclear Structure – Slide 44

Dose Effects on Humans

• Low does limits somewhat controversial

• Based on high dose cancer rates• 50rem – blood count change• 320rem – LD50/60 with no medical• 800rem - mortality

• Linear No Threshold Model (LNT)

• “2 bottles of aspirin will kill you, so 2 aspirin kills you a little” ??

Unit 08 – Nuclear Structure – Slide 45

Most conservative always best?

What is more harmful to the people 15 miles from the Fukushima power plant:

Having to evacuate their home orRadiation from plant? (~0.0001rem/hr)

Unit 08 – Nuclear Structure – Slide 46

Summary

Activity – Just counting • Curies • Becquales

Absorbed Dose - Energy Deposited • Roentgens• Rad• Gray

Biological Equivalent Dose – Damage to Humans • Sv• rem

Unit 08 – Nuclear Structure – Slide 47

Half Life

T1/2 – Average amount of time it

takes for half the sample to decay

Also average amount of time it

takes for the decay rate to drop to

half

Unit 08 – Nuclear Structure – Slide 48

Example 11.4

Unit 08 – Nuclear Structure – Slide 49

Barium-122 has a half-life of 2

minutes. A fresh sample weighing 80 g

was obtained. If it takes 10 minutes to

set up an experiment using barium-

122, how much barium-122 will be left

when the experiment begins?

Example 11.5

Unit 08 – Nuclear Structure – Slide 50

Carbon-14 has a half-life of 5730 years and is

used to date archaeological objects.

A fresh charcoal made from a tree contains

carbon-14 which will give a radioactive count of

13.60 disintegrations per minute per gram of

carbon. Prehistoric cave paintings were found in

Spain. A piece of charcoal found in the ancient

cave in Altamira, Spain gave 1.70 disintegrations

per minute per gram of carbon. From this

information, determine the age of the cave

paintings.

Question

Unit 08 – Nuclear Structure – Slide 51

Iodine-131 is used to destroy thyroid tissue in

the treatment of an overactive thyroid. The

half-life of iodine-131 is 8 days. If a hospital

receives a shipment of 200 g of iodine-131,

how much I-131 would remain after 32 days?

A. 100 g

B. 50 g

C. 25 g

D. 12.5 g

E. 6.2 g

Question

Unit 08 – Nuclear Structure – Slide 52

The half life of radon is 3.82

days. How long does it take for

60% of a 10kg sample of radon

222 to decay?

A.~1 day

B.~2.5 days

C.~5 days

D.~8 days

Question

You have 10 kg each of a radioactive

sample A with a half-life of 100 years, and

another sample B with a half-life of 1000

years. Which sample has the higher

activity?

A.sample A

B.sample B

C.both the same

D.impossible to tell

Unit 08 – Nuclear Structure – Slide 53