Nuclear Decay

The Atom- Review The atom consists of two parts: 1. The nucleus which contains: protons neutrons 2. Orbiting electrons. Atom of different elements contain different numbers of protons. The mass of an atom is due to the number of protons and neutrons.

X A Z Isotope Symbol Review A = number of protons + number of neutrons Mass number = number of protons + number of neutrons X A Element symbol Z Atomic number = number of protons A = number of protons + number of neutrons Z = number of protons A – Z = number of neutrons **Number of neutrons = Mass Number – Atomic Number**

Fill in the chart for each isotope U 235 92 U 238 92 A Z Number of protons Number of neutrons 235 A Z Number of protons Number of neutrons 238 92 92 92 92 143 146 Isotopes of any particular element contain the same number of protons, but different numbers of neutrons.

Most of the isotopes which occur naturally are stable. A few naturally occurring isotopes and all of the man-made isotopes are unstable. Unstable isotopes can become stable by releasing different types of particles. This process is called radioactive decay and the elements which undergo this process are called radioisotopes. The products of this decay are called daughter isotopes

Radioactive Decay Radioactive decay results in the emission of either: an alpha particle (a), a negative beta particle (electron) (b-), a positive beta particle (positron) (b+), or a gamma ray (g). In a nuclear reaction the MASS and ATOMIC NUMBER must be the SAME on both sides of the equations

X Y + He Alpha Decay A Z A - 4 Z - 2 4 2 An alpha particle is identical to that of a helium nucleus. It contains two protons and two neutrons. X A Z Y A - 4 Z - 2 + He 4 2 unstable atom alpha particle more stable atom

Ra Rn He Alpha Decay + Loss of 2 protons & 2 neutrons: 226 88 Rn 222 86 He 4 2 + Loss of 2 protons & 2 neutrons: Atomic # decreases by 2 Mass # decreases by 4

X Y + He Rn + Y He Rn He + Po Write your own Alpha Decay What is Y? A Z Y A - 4 Z - 2 + He 4 2 What is Y? Rn 222 86 + Y A Z He 4 2 Rn 222 86 He 4 2 + Po 218 84

U + He U + Th Write the equation for the alpha decay of Uranium-234 92 + Th 230 90

X + Pb He He + Pb Po Find the missing starting material A Z 214 82 4 2 218 84

X Y + e Beta Emission A Z Z + 1 -1 beta particle (electron) A beta particle is a fast moving electron which is emitted from the nucleus of an atom undergoing radioactive decay. Beta emission occurs when a neutron changes into a proton and an electron. X A Z Y Z + 1 + e -1 beta particle (electron) proton stays in nucleus

Beta Emission Po 218 84 At 218 85 e -1 + Neutron splits emitting negative particle leaving a proton. Atomic # increases by 1 Mass # stays the same (electrons have no mass)

X Y + e Th Y + e Th Pa + e Write your own Beta Emission What is Y? A Z -1 What is Y? Th 234 90 Y A Z + e -1 Th 234 90 Pa 91 + e -1

C + C N + e Write the equation for the beta emission of carbon-14 14 7 + e -1

X Bi + e Pb Bi + e Find the missing starting material A Z 214 83 -1 -1 Pb 214 82 Bi 83 + e -1

X e + Y Electron Capture A Z -1 Z-1 Electron Capture is the opposite of Beta Emission The capture of the electron allows a proton to turn into a neutron X A Z e -1 + Y Z-1

At e Po Electron Capture 218 85 e -1 Po 218 84 + Capture negative particle, forming a neutron from a proton Atomic # decreases by 1 Mass # stays the same (electrons have no mass)

X e + Y Ar e + Y Ar e + Cl Write your own Electron Capture What is Y? Z e -1 + Y Z-1 What is Y? Ar 37 18 e -1 + Y A Z-1 Ar 37 18 e -1 + Cl 17

Ni + Ni e + Co Write the equation for electron capture of nickel-59 59 28 e -1 + Co 27

X e + C N e + C Find the missing starting material A Z -1 14 6 14 7 -1 -1 + C 14 6 N 14 7 e -1 + C 6

X Y + e Positron Emission A Z Z - 1 +1 positron mass stays in nucleus A positron is like an electron but it has a positive charge. During positron emission a proton changes into a neutron and the excess positive charge is emitted. X A Z Y Z - 1 + e +1 positron mass stays in nucleus

At Po e Positron Emission 218 85 Po 218 84 e +1 + Proton splits emitting positive particle leaving a neutron. Atomic # decreases by 1 Mass # stays the same (positrons, like electrons, have no mass)

X Y + e B Y + e B Be + e Write your own Positron Emission What is Y? A Z Y Z - 1 + e +1 What is Y? B 8 5 Y A Z + e +1 B 8 5 Be 4 + e +1

O + O N + e Write the equation for the positron emission of oxygen-16 7 + e +1

X Cu + e Zn Cu + e Find the missing starting material A Z 66 29 +1 66 +1 Zn 66 30 Cu 29 + e +1

Gamma Decay When atoms decay by emitting a or b particles to form a new atom, the nuclei of the new atom formed may still have too much energy to be completely stable. These atoms will emit gamma rays to release that energy. Gamma rays are high energy radiation Gamma rays are not charged particles like a and b particles. There is no change in mass or atomic number X A Z + g

Summary Reaction What happens? Mass # Atomic # -4 -2 No change +1 -1 Alpha Decay a Lose Helium Nucleus -4 -2 Beta Decay b- Lose electron from nucleus (neutron turns into proton) No change +1 Electron Capture Gain electron in nucleus (proton turns into neutron) -1 Positron Emission b+ Lose positron (proton turns into neutron) Gammy Decay g Emit high energy gamma ray

Nuclear Stability Not all isotopes are radioactive The strong nuclear force holds all nuclei together Otherwise protons would repel each other Neutrons space out protons and make nucleus stable Not all isotopes are radioactive Only unstable nuclei decay In smaller atoms stable isotopes have equal numbers of protons and neutrons In larger atoms stable isotopes will have more neutrons than protons Too many or too few neutrons makes the nucleus unstable

Nuclear Stability Graph Dark band = stable nucleus Areas off line = radioactive

Fission Fission is when a nucleus splits This is what happens in nuclear power plants Neutrons emitted during fission reactions can cause other fission reactions This is a chain reaction In a nuclear reactor the chain reaction is controlled with control rods

Chain Reaction Each reaction allows multiple other reactions to occur Controlled vs Uncontrolled

Fusion When two or more elements fuse (combine) to form one new heavier element The energy released by the sun and all stars is due to fusion reactions in the core This process releases more energy than fission Fusion reactions are hard to contain because the reactants are a plasma and at very high temperatures, no solid material can contain a plasma

Fission Fusion Nucleus splits Nuclei combine Energy is released End product is lighter than reactants End product is heavier than reactants Nuclear Change Can’t contain reaction Reaction can be harnessed LOTS of energy released