Radioactivity

What you don’t see ...... can hurt you!.

IsotopesAtomic Mass

Atomic Number

Neutrons

Protons Electrons

Carbon-

12 12

6

6

6

6

Carbon-

13 13

6

7

6

6

Carbon-

14 14

6

8

6

6

- =

- =

- =

The extra neutron causes The extra neutron causes 235235UU to produce the to produce the unstable unstable 236236U.U. Thus causing a chain reaction that Thus causing a chain reaction that eventually leads to a big eventually leads to a big BOOM!!!BOOM!!!

The The splittingsplitting of a nucleus of a nucleus

accompanied by the release accompanied by the release

of of neutrons neutrons and a large and a large

amount of amount of energy energy

The process of The process of combiningcombining nucleinuclei

to produce a nucleus of to produce a nucleus of greater massgreater mass

Approx. Approx. 200,000200,000 Japanese Japanese deaths (mostly Civilians)deaths (mostly Civilians)

Only Only 22 nuclear weapons have nuclear weapons have ever been used in war.ever been used in war.

Nuclear Reaction any change that involves nucleus

Radioactivity 1896 - Antoine Henri Becquerel

accidently discovered uranium ores emit invisible rays.

his 2 students, Marie Curie and Pierre Curie, isolated several radioactive elements.

Marie Curie named the process by which uranium gives off rays of radioactivity – radioactive decay

The Atomic Nucleus

Made of nucleons..+ proton & neutral - neutron.

held by“strong nuclear force.”

STRONG NUCLEAR FORCE = force

that holds the nucleus togetherAs size of nucleus increases, a stronger

force needed to hold nucleus

Radioisotope – unstable isotope which undergoes radioactive decay

Type of Decay

Particle emitted

Change in mass #

Change in atomic #

alpha decay

42He decreases

4decreases

by 2

beta decay 0-1β no change increases

by 1

positron emission

01β no change decreases

by 1

electron capture

x-ray photon

no change decreases by 1

gamma emission

00γ no change no change

Radioactive Decay

Nucleus unstable when too many

Protons & undergoes Radioactive decay

Band of Stability As long as the ratio of neutrons to

protons is between 1.0 and 1.5, the atom will be stable.

How can these radiation be stopped?

Alpha Radiation Radium - 226 decays into radon -222

and alpha particles.

88Ra226 --> 86Rn222 + 24

24 = 2e4

Alpha particles - helium nuclei

Use “Radioisotope, Radio Activity &Radioactive

Decay” to describe the above Nuclear Reaction The Radioisotope, Radium 226, undergoes

radioactive decay to form Radon. The type of radioactivity emitted is Alpha radiation

Beta Radiation

38Sr90 --> 39Y90 + -

- = -1e0

Beta particles - high speed e-

Electron Capture nucleus catches one close electron which

combines with a proton to form a neutron.

Beta Radiation

38Sr90 --> 39Y90 + -

High speed e- from nucleus?

How is mass the same for Y90 but the charge is greater!

Beta Radiation

38Sr90 --> 39Y90 + -

Consider neutron decay...

0n1 --> ? + -

0n1 --> 1p1 + -

* Isotopes chemically alike as protons & electrons determine chemical properties

Gamma Radiation

Iron - 60 decays to Co-60 & gamma particles.

26Fe60 --> 27Co60 + +

0 = electromagnetic rad.

high energy photons.

Where is Radiation in our Life Carbon – 14 dating Nuclear Waste X-rays Radiation therapy for cancer

How they discovered Isotopes:

Hydrogen

–Hydrogen has 3 isotopes • Hydrogen-1 = “Protium” 1

1H

• Hydrogen-2 = “Deuterium” 21H

• Hydrogen-3 = “Tritium” 31H

Nuclear Fusion

Nuclear fusion - 2 small nuclei COMBINE

larger element.Fusion releases more energy than fission because only @ very high temp 40,000,000oC

fusion of hydrogen into helium

keeps the sun burning.

Fusion Fusion is how the sun continually

produces energy.

4 11H + 2 0

-1β 42He + a lot of energy

Fusion

Fusion – the combining of atomic nuclei

Fission

Fission – the splitting of a large nucleus

Fission (cont.)

Fission is what nuclear power plants use for energy.

U – 235 + a neutron =

a chain reaction of

neutrons and energy

The Thorium Decay Series

90Th232 --> 24 + 88Ra228

88Ra228 --> -+ 89Ac228

89Ac228 --> - + 90Th228

90Th228 --> 24 + 88Ra224

88Ra224 --> 24 + 86Rn220

86Rn220 --> 24+ 84Po216

Pg 97& 97 b

The Thorium Decay Series

86Rn220 --> 24 + 84Po216

84Po216 --> 24 + 82Pb212

82Pb212 --> -+ 83Bi212 or

83Bi212 --> 24 + 81Tl208

81Tl208 --> -+ 82Pb208

82Pb208 is stable

ChernobylHurt

Half-life Pg 96& 97a

If you have 100 g of Uranium,

How many half lives are

needed to reach ~ 3% of the original radioactivity.

100 g 50 g 1st ½ life

25 g 2nd ½ life

12.5 g 3rd 4th ½ life life

6.25 g

3.125 g 5th ½ life

Half – Life Problems:

1) If I have 50g of Pb-208 and it has decayed during 2 half-lives, how much is remaining?

2) If I have 25g of U-235 and it has a half-life of one day, how much will be left after a week?

Critical Mass & The Enola Gay

Nuclear Activities

Directions: Each student will hold 3, 6 or 9 ping pong balls. Divide the room into two sections. Throw one ping pong ball. The rule is that when a student is hit by one ping pong ball, three must be released randomly.

1. What happened? Why?

Directions: Now put the entire class within a 3 meter radius and try again.

2. What happened? Why?

Transmutationconversion of an atom of one

element to another

can induce by striking nuclei with high velocity charged particles

44

Neutron-Proton Ratio and Nuclear Stability

Example nuclides with magic numbers of nucleons includes:

nucleus magicdoubly a Pb

nucleus magicsingly a Sn

nucleus magicdoubly a Ca

nucleus magicdoubly a Ca

nucleus magicdoubly a O

nucleus magicdoubly a He

12620882

70120

50

284820

204020

816

8

242

These proton and neutron numbers are called “Magic Numbers.”Magic numbers are:

2 8 20 28 50 82 126

Half-life

time needed for 1/2 of the particles to decay.

1. 86Rn217 He + ____

3. 234 U He + Y + ____

Ba-140 beta

56Ba-140 57La140 -1 b o +

2134

2 84

gamma

Radiation Practice

1) *U – 235 + → U – 235

2) Ag – 107 + → In – 111

3) N – 12 + → O -12

4) Fe – 57 + → Ni - 61

7. Show the equation for the fission of Th-232 with one fission product being Mo-96 plus the release of 2 neutrons

23290 Th Mo +

96 10

10 n + n

Pg 108

If I had 20g of U-235 & it decayed over 3 half-lives, how much would I have left?

1) If I have 10g of U-235 and it has decayed over 7 half-lives, how much U-235 will I have remaining?

2) If I have 40g of Pb-208 and it has a half life of 15 seconds, how much will remain after 1 minute?

3) If I have 20g of Pt- 144 remaining after it decayed for a week. Given that it has a half-life of a day, how much did I have originally?

Fusion vs. Fission

There are two processes that make use of the enormous amount of energy in a nucleus:

Fusion

and

Fission

Ionizing Radiation

Ionizing radiation = radiation with enough energy to knock an electron off an atom and create an ion.

X-rays and gamma rays will ionize almost any molecule or atom

Radiation is harmful, but when used carefully it can be used in medical and scientific procedures.

-

--

X-Rays in Medicine

Transuranium Elements - are all elements with an atomic number of 93 or greater–all radioactive

–all man-made (SYNTHETIC)

Leptons Up quarks

Charm quarks

e+νe 1 ud

3|Vud|2

cd

3|Vcd|2

μ+νμ 1 us

3|Vus|2

cs

3|Vcs|2

τ+ντ 1 ub

3|Vub|2

cb

3|Vcb|2

58

Nuclear Stability and Binding Energy

Example 26-1: Calculate the mass deficiency for 39K. The actual mass of 39K is 39.32197 amu per atom.

amu 32307.39

amu 0104.0 amu 1740.20 amu 1387.19

amu 0.000545819 amu 1.008720 amu 1.0073 19

electrons and neutrons, protons, of masses of sum

Fission & Fusion Demos

Directions: Blow up a balloon. Pinch and twist in the center. Nuclear Fission!

Directions: Put 2 drops of water on the overhead projector. Nuclear Fusion!

Questions:1. Why do Doctors use radioactive isotopes which have

short half lives?

2. What happens to the nucleus during Nuclear Fission?

3. How many half-lives does Radon need to live out to get rid of about 87.5% of the radioactivity?

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