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

Isotopes Atomic MassAtomic NumberNeutronsProtonsElectrons Carbon Carbon Carbon = - = -=

The extra neutron causes 235 U to produce the unstable 236 U. Thus causing a chain reaction that eventually leads to a big BOOM!!!

The splitting of a nucleus accompanied by the release of neutrons and a large amount of energy

The process of combining nuclei to produce a nucleus of greater mass

Approx. 200,000 Japanese deaths (mostly Civilians) Only 2 nuclear weapons have ever been used in war.

n Nuclear Reaction any change that involves nucleus

Radioactivity n Antoine Henri Becquerel accidently discovered uranium ores emit invisible rays.

n his 2 students, Marie Curie and Pierre Curie, isolated several radioactive elements. n 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 together As 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 4 2 Hedecreases 4 decreases by 2 beta decay 0 -1 βno changeincreases by 1 positron emission 01β01βno changedecreases by 1 electron capture x-ray photon no changedecreases by 1 gamma emission 00γ00γno change

Radioactive Decay Nucleus unstable when too many Protons & undergoes Radioactive decay

Band of Stability n 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 n Radium decays into radon and alpha particles. 88 Ra > 86 Rn  4 2  4 = 2  e 4 n 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 38 Sr 90 --> 39 Y    -    = -1 e 0 Beta particles - high speed e-

Electron Capture nucleus catches one close electron which combines with a proton to form a neutron.

Beta Radiation 38 Sr 90 --> 39 Y    n High speed e - from nucleus? How is mass the same for Y 90 but the charge is greater!

Beta Radiation 38 Sr 90 --> 39 Y    n Consider neutron decay... 0 n 1 --> ? + -    0 n 1 --> 1 p   

* Isotopes chemically alike as protons & electrons determine chemical properties

Gamma Radiation n Iron - 60 decays to Co-60 & gamma particles. 26 Fe 60 --> 27 Co 60 +    +    0   = electromagnetic rad. n high energy photons.

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

How they discovered Isotopes:

Hydrogen –Hydrogen has 3 isotopes Hydrogen-1 = “Protium” 1 1 H Hydrogen-2 = “Deuterium” 2 1 H Hydrogen-3 = “Tritium” 3 1 H

Nuclear Fusion Nuclear fusion - 2 small nuclei COMBINE  larger element. Fusion releases more energy than fission because very high temp 40,000,000 o C fusion of hydrogen into helium keeps the sun burning.

Fusion n Fusion is how the sun continually produces energy H β  4 2 He + a lot of energy

Fusion Fusion – the combining of atomic nuclei

Fission Fission – the splitting of a large nucleus

Fission (cont.) n Fission is what nuclear power plants use for energy. n U – a neutron = a chain reaction of neutrons and energy

The Thorium Decay Series 90 Th > 2  Ra Ra > -    + 89 Ac Ac > -    + 90 Th Th > 2  Ra Ra > 2  Rn Rn > 2  Po 216 Pg 97 & 97 b

The Thorium Decay Series 86 Rn > 2  Po Po > 2  Pb Pb > -    + 83 Bi 212  or  83 Bi > 2  Tl Tl > -    + 82 Pb 208 n 82 Pb 208 is stable

n Chernobyl n Hurt

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  1 st ½ life 25 g  2 nd ½ life 12.5 g  3rd 4 th ½ life life 6.25 g  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?

Transmutation conversion 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 n Example nuclides with magic numbers of nucleons includes: These proton and neutron numbers are called “Magic Numbers.” Magic numbers are:

Half-life n time needed for 1/2 of the particles to decay.

1. 86 Rn 217  He + ____ U  He + Y + ____ Ba-140beta 56 Ba- 140  57 La b o gamma

Radiation Practice 1) *U – → U – 235 2) Ag – → 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 Th  Mo n +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 n There are two processes that make use of the enormous amount of energy in a nucleus: Fusion and Fission

Ionizing Radiation nInIonizing radiation = radiation with enough energy to knock an electron off an atom and create an ion. nXnX-rays and gamma rays will ionize almost any molecule or atom nRnRadiation is harmful, but when used carefully it can be used in medical and scientific procedures. - --

X-Rays in Medicine

n Transuranium Elements - are all elements with an atomic number of 93 or greater –all radioactive –all man-made (SYNTHETIC)

LeptonsUp quarks Charm quarks e+νee+νe 1udud 3|V ud | 2 cdcd 3|V cd | 2 μ+νμμ+νμ 1usus 3|V us | 2 cscs 3|V cs | 2 τ+νττ+ντ 1ubub 3|V ub | 2 cbcb 3|V cb | 2

58 Nuclear Stability and Binding Energy n Example 26-1: Calculate the mass deficiency for 39 K. The actual mass of 39 K is amu per atom.

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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