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Structure of a Nucleus

• Up to element 20- equal protons to neutrons

• After 20- more neutrons are necessary to keep the nucleus together

• Above 83- added neutrons cannot make nucleus stable

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3

Nuclear ChemistryNuclear Chemistry

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RadioactivityRadioactivity

• One of the pieces of evidence for the One of the pieces of evidence for the fact that atoms are made of smaller fact that atoms are made of smaller particles came from the work ofparticles came from the work of

Marie CurieMarie Curie (1876-1934).(1876-1934).

• She discoveredShe discovered radioactivityradioactivity, , the spontaneous disintegration of the spontaneous disintegration of some elements into smaller pieces.some elements into smaller pieces.

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Marie Curie

• Discovered Polonium and Radium

• Developed mini portable x-ray machine for use during WWI

• Died of aplastic anemia due to prolonged exposure of radiation

• Won Nobel Prize in Physics – 1903

• Won Nobel Prize in Chemistry - 1911

6Nuclear Reactions vs. Nuclear Reactions vs. Normal Chemical Normal Chemical

ChangesChanges

• ““Normal” Chemical Reactions Normal” Chemical Reactions involve involve ELECTRONSELECTRONS, not protons and neutrons, not protons and neutrons

• Nuclear reactions Nuclear reactions involve the involve the NUCLEUSNUCLEUS

• The breaking apart of the nucleus The breaking apart of the nucleus releases a tremendous releases a tremendous amount of amount of energyenergy!!

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Nuclear Reactions

• A reaction that changes the nucleus of an atom

– Unstable nuclei

– Changes the number of protons and neutrons

– Gives off large amounts of energy

– Increases stability in the process

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Henri Becquerel - 1896• Realized that photographic plates were

being exposed to “rays” that were not caused by the sun since the plates were in a drawer.

• He had placed Uranium on a counter over the drawer!

• “Rays” were caused by radioactive decay

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Radioactive Decay

• The spontaneous disintegration of a nucleus into a lighter nucleus with the emission of particles or electromagnetic radiation (or both)

10Types of RadiationTypes of Radiation

e01

He42

• Alpha (Alpha (άά) – ) – a positively a positively charged helium isotopecharged helium isotope

•Beta (Beta (ββ) – ) – an electronan electron

•Gamma (Gamma (γγ) – pure energy; ) – pure energy; called called a ray rather than a a ray rather than a particleparticle

00

11

• NeutronNeutron

• Positron – Positron – a positive electrona positive electron

•Proton – Proton – usually referred to as hydrogen-1usually referred to as hydrogen-1

•Any other elemental isotope Any other elemental isotope

Other Nuclear ParticlesOther Nuclear Particles

e01

n10

H11

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Penetrating AbilityPenetrating Ability

Can also be blocked by clothing

Can also be blocked by foil and water

Can also be blocked by concrete

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Alpha Decay (Emission)

Loss of an -particle (a helium nucleus)

He42

U23892

Th23490 He4

2+

Types of Radioactive Types of Radioactive DecayDecay

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Alpha Alpha RadiationRadiation

Limited to Limited to VERY large VERY large atoms.atoms.

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Loss of a -particle (a high energy electron)*Neutron changes into a proton (which stays in nucleus) and a

beta particle is released (electron ejected from nucleus).

0−1 e0−1or

I13153 Xe131

54 + e0−1

Beta Decay (Emission)

Types of Radioactive Types of Radioactive DecayDecay

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Loss of a positron (a particle that has the same mass as but opposite charge than an electron)

C116 B115 + e0+1

Positron Emission

Types of Radioactive Types of Radioactive DecayDecay

Positron emission converts a proton to a neutronPositron emission converts a proton to a neutron

e0+1

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Gamma rays are high energy Gamma rays are high energy photonsphotons produced in association produced in association with other forms of decay.with other forms of decay.

Gamma rays are Gamma rays are massless massless and do not, by themselves, and do not, by themselves, change the nucleuschange the nucleus

00

23490

42

23892 ThHeU

Gamma Ray Production

Types of Radioactive Types of Radioactive DecayDecay

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Complete the Nuclear Reaction Wkst

as homework

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Stable Nuclei

• There are NO stable nuclei with an atomic number greater than 83.

• These nuclei tend to decay by alpha or beta emission.

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Radioactive Decay Series

An unstable radioactive nucleus reaches a stable state by a series of steps

Graphic – Wikimedia Commons User TosakaGraphic – Wikimedia Commons User Tosaka

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Radioactive Decay Series

• Large radioactive nuclei cannot stabilize by undergoing only one nuclear transformation.

• They undergo a series of decays until they form a stable nuclide (often a nuclide of lead).

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• Complete the Decay Series Activity

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Remember…

• Reactions can be– Chemical reactions where electrons interact– Nuclear reactions where nucleus breaks apart

AND NOW…We can force these reactions to occur!!!!!

25Artificial Nuclear Artificial Nuclear ReactionsReactions

New elements or new isotopes of known New elements or new isotopes of known elements are produced by artificially elements are produced by artificially bombarding (hitting) an atom with a bombarding (hitting) an atom with a subatomic particle such as a proton or subatomic particle such as a proton or neutron -- or even a much heavier particle neutron -- or even a much heavier particle such as such as 44He orHe or1111B.B.

26Artificial Nuclear Artificial Nuclear ReactionsReactions

Example of a Example of a reaction reaction is production is production

of radioactive of radioactive 3131P for use in studies of P for use in studies of

Phosphorous uptake in the body.Phosphorous uptake in the body.

31311515P + P + 11

00n n 32321515P + P +

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Aerial view of CERN and the surrounding region of Switzerland and France. Three rings are visible, the smaller shows the underground position of the Proton Synchrotron, the middle ring is the Super Proton Synchrotron (SPS) with a circumference of 7 km and the largest ring (27 km) is that of the former Large Electron and Positron collider (LEP) accelerator with part of Lake Geneva in the background.

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September 10, 2008The first beam in the Large Hadron Collider was successfully steered around the full 27 kilometres of the world's most powerful particle accelerator in Geneva, Switzerland.

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Learning Check

What radioactive isotope is produced in the following bombardment of boron?

10B + 4He ? + 1n 5 2 0