Nuclear Physics

Nuclear Symbols Mass number, A (p+ + no) Element symbol Atomic number, Z (number of p+)

Balancing Nuclear Equations Areactants = Aproducts 235 + 1 = 142 + 91 + 3(1) 92 + 0 = 56 + 36 + 3(0) Zreactants = Zproducts

Balancing Nuclear Equations #2 222 226 = 4 + ____ 222 Rn 86 88 = 2 + ___ 86 Atomic number 86 is radon, Rn

Balancing Nuclear Equations #3 95 235 + 1 = 139 + 2(1) + ____ 95 Y 39 39 92 + 0 = 53 + 2(0) + ____ Atomic number 39 is yttrium, Y

Alpha Decay Alpha production (a): an alpha particle is a helium nucleus Alpha decay is limited to heavy, radioactive nuclei

Alpha Radiation Limited to VERY large nucleii.

Beta Decay Beta production (b): A beta particle is an electron ejected from the nucleus Beta emission converts a neutron to a proton

Beta Radiation Converts a neutron into a proton.

Gamma Ray Production Gamma ray production (g): Gamma rays are high energy photons produced in association with other forms of decay. Gamma rays are massless and do not, by themselves, change the nucleus

Deflection of Decay Particles Opposite charges_________ each other. attract Like charges_________ each other. repel

Positron Production Positron emission: Positrons are the anti-particle of the electron Positron emission converts a proton to a neutron

Electron Capture Electron capture: (inner-orbital electron is captured by the nucleus) Electron capture converts a proton to a neutron

Types of Radiation

Nuclear Stability Decay will occur in such a way as to return a nucleus to the band (line) of stability. The most stable nuclide is Iron-56 If Z > 83, the nuclide is radioactive

A radioactive nucleus reaches a stable state by a series of steps A Decay Series

Half-life Concept

Sample Half-Lives

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NUCLEAR DECAY KINETICS

Decay Kinetics Decay occurs by first order kinetics (the rate of decay is proportional to the number of nuclides present) N0 = number of nuclides present initially N = number of nuclides remaining at time t k = rate constant t = elapsed time

Calculating Half-life t1/2 = Half-life (units dependent on rate constant, k)

Example Determine the amount of Rn-222 that remains after 5.0 days if the the half-life is 3.8 days and you started with 80,000 particles. No = 80,000 particles k = 0.182 day-1 N = ? First find decay constant. k = ln2 / t1/2

Example 2 Determine the activity of Rn-222 that remains after 7.0 days if the the half-life is 3.8 days and you started with 285 counts/min. Ao = 285 counts/min k = 0.182 day-1 N = ? First find decay constant. k = ln2 / t1/2

Example 3 Determine the percentage of Rn-222 that remains after 9.0 days if the the half-life is 3.8 days. No = ??? particles k = 0.182 day-1 N = ? First find decay constant. k = ln2 / t1/2

Nuclear Fission and Fusion Fusion: Combining two light nuclei to form a heavier, more stable nucleus. Fission: Splitting a heavy nucleus into two nuclei with smaller mass numbers.

Energy and Mass Nuclear changes occur with small but measurable losses of mass. The lost mass is called the mass defect, and is converted to energy according to Einstein’s equation: DE = Dmc2 Dm = mass defect DE = change in energy c = speed of light Because c2 is so large, even small amounts of mass are converted to enormous amount of energy.

Example Calculate the mass defect and energy released during this typical fission reaction.  + + 236.04556 g 87.91445 g 143.92284 g 4 x 1.00867 g 265.04556 g 235.87197 g DE = Dmc2 = .2917359 kg x 3.0 x 108 m/s DE = 8.752 x 107 J

Fission

Fission Processes A self-sustaining fission process is called a chain reaction.

A Fission Reactor

Fusion