NE 301 - Introduction to Nuclear ScienceSpring 2012

Classroom Session 2:

•Natural Radioactivity•Chart of the Nuclides•Nuclear Stability (Binding Energy, BE)•Radioactive Decay Types•Radioactive Decay and Growth•Isotopes and Decay Diagrams•Nuclear Reactions

• Energy of nuclear reactions• Neutron Cross Sections• Activation Calculations

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Prelude…Please bring clickers to class.

Please bring calculators.

Get in pairs/groups, feel free to talk across tables.

Time on task please. I want everybody working to get answers.

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Radioactivity in Nature

Discovered in 1896 by Henri Becquerel Using photographic plates Notice: no natural sensors for radiationMarie Curie: differences between radioactivity of Uranium and Uranium minerals Discovered Polonium then Radium (both

1898) Main radioactive minerals are:

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Main Radioactive Minerals

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Main Naturally Occurring Isotopes:

Trivia:14C production:

~22,000 at/s/m2 of earth surface

3H production:~2,500 at/s/m2

Global Planetary Equilibrium Inventory of:

63 tons of 14C3.5 kg of 3H

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A Bit of History… Filling the Periodic Table

The Periodic Table of the Elements 1869 by Dmitri Mendeleev

a) Elements Known: 1 – H to 83 – Bi. Plus U and Th. Some stable elements later (Hf -1922, Re-

1925)b) Natural Unstable Elements:

Po, Rn, Fr, Ra, Ac, and Pa (mainly by Curies)

c) Artificial Elements 43-Tc , 61-Pm , 85-At, and Transuranics (Np,

Pu, Am, etc)

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Isotopes…40 kinds of atoms with different half-lives were foundProblem: Only 13 spots available in the Periodic TableFrederick Soddy in 1913: Isotopes = “In the Same Place” Nobel Prize 1921 It was later discovered that stable atoms also can have isotopes (e.g.

Sn has 10 stable and 18 unstable ones).

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Atomic and Nuclear Nomenclature

X element symbol (H, He, Na, Xe, U, etc.) represents the number of charges in the nucleus (thus electrons, thus chemical behavior).

A = Mass number = protons + neutrons = Nucleons.

Z = atomic number = protons. X and Z are redundant and normally we only

write AX.e.g. 235U, 16O, 3H, 14C

ZAX

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NuclidesAtoms differing by atomic number of mass number

Radionuclide: Unstable

nuclide

Table of nuclidesProvide accurate mass of each nuclide

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Chart of the Nuclides

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Chart of the Nuclides

Z

N

IsobarsIsotopes

Isotones

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Trivia:Nuclides

known:

Found in Nature:

Main Nat. Radioactive:

Produced by cosmic rays:

~2800

258 Stable25 with Z<80 reported radioactive (7 not confirmed)

235U, 238U, 232Th and decay families.

14C, 10Be, 7Be, 3H

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Nuclear IsomersCertain Nuclides with different physical properties Half-lives Modes of decayMetastable states of the same nuclide Either decay by -emission Transmute to other nuclides (,

decay, etc)Suffix “m” next to A. (i.e. 60mCo, 99mTc)

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DownloadRadDecay, by Charles Hacker

Play with it:

1. How to find nuclides2. Half-life3. Understand Decay products

) ’s) ’sc) ’sd) X-Rayse) electrons

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Nuclear Stability

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Stability of Nuclei – General Observations

In general, nuclei with an even number of protons or neutrons are more stableAs the protons increase electromagnetic forces increase and more neutrons are needed to provide attractive nuclear force to keep the nucleus togetherCertain Z or N numbers are particular stable (Higher BE) 2, 8, 20, 28, 50, 82, 126

Magic Numbers

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Stability with Even or Odd Z

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Stability with Even or Odd N

Even Z, Even N = 159

Even Z, Odd N = 53Odd Z, Even N = 50Odd Z, Odd N = 4

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Let’s do some accounting…For example: Mass of Oxygen Atom:

Mp=1.007276 amuMn=1.008665 amuMe=5.48e-4 amu

168

16.131912 amu

8 1.007276 amu

( ) 8 1.008665 amu 15.994915 amu8 5.48 4 amu

p

n O

e

Zm

A Z m MZm e

Mass Defect = Binding

Energy (BE)

1 amu = 931.49 MeV

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Nuclear Stability and Binding Energy (BE)

Higher BE = Higher Stability

Compare BE of 12C and 14C:

To understand stability and radioactive decay, please calculate BE for the following ISOBARS (A=73):

73Zn, 73Ga, 73Ge, 73As, 73Se, 73Br, 73KrEverybody!

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Isobars = A

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Notice radioactive decay stabilizes atoms:

Question:

Do fission products normally have - or + decay?

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Chart of the Nuclides

Z

N

Z=N

i.e. Fission products are neutron rich

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Another

Example:Notice several stable possibilities

If we graph naturally occurring atoms…

Fission

Fusion

Reaction EnergeticsReaction reactants and products

If E is positive: reaction exothermic

releases energyIf E is negative, reaction endothermic

requires energyEndoergic and exoergic is sometimes used

A + B C + D + E

Please remember…

BALANCE!

Before starting to work

Balancing Reactions

nucleons 1 +16 = 16+1Charges

01n 8

16O 716N1

1p

1 16 16 0 10 8 7 1 1

1 16 16 10 8 7 1

n O N e p or

n O N H

(+) 0 + 8 = 7 + 1(-) -0 -8 = -7 -0 e- missing

0 1So in reality the reaction is:

Calculating Q…

Q-value for the reaction is:

Using atomic mass tables:

1 16 16 10 8 7 1n O N H

( )1.008665 15.994915 16.006101 1.007825 0.010346 amu

931.494 MeV 0.010346 amu 9.637 MeV1 amu

A B C DM M M M MM

Endothermic reaction. Only a few fission neutrons can do it