discovery of radiation roentgen (1895) discovered a mysterious form of radiation was given off even...
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Discovery of Radiation
Roentgen (1895)
•Discovered a mysterious form of radiation was given off even without electron beam. This radiation could pass through paper and other objects but not dense materials (lead, bone).
•Called them X-rays
•Studied fluorescent materials that glowed when hit with a beam of electrons.
Becquerel (1896)•Studied fluorescent minerals containing uranium.•Discovered radioactivity by accident on a cloudy day:•Thought that an external source was needed to produce the mysterious radiation.
•Found that uranium emits radiation without external source.
Thought radioactivity was a property of heavy elements.
Pierre and Marie Curie
During study, discovered new radioactive elements: Polonium and Radium.
Wondered how small mass can give off large amount of energy:
Explained by Einstein with E=mc2.
•Studied radioactivity and named types of nuclear radiation.
Rutherford
•Discovered that elements decay into other elements after emitting nuclear radiation. Called it Nuclear Decay.•Gold foil experiment revealed that the mass of an atom is concentrated in the nucleus (atom is mostly space)
Stable vs Unstable Stable vs Unstable IsotopesIsotopes
Atomic #s 1 − 19 Stable & unstable, naturally occurring isotopes
Atomic #s 20 − 82Mixture of stable and unstable isotopesNaturally occurring and man made
Atomic #s 83 and higherAll unstable
Unstable Unstable IsotopesIsotopes
•Unstable isotopes will automatically change into a more stable form
•Transmutation ═ the process of one element changing into another element
•Law of Conservation of Mass
•Net charge remains unchanged
Nuclear SymbolNuclear SymbolMass Number
XAtomic Number
whereMass Number = Protons + Neutrons
X = Symbol of Element
Atomic Number = # of Protons (Electrons)
**The atomic number tells the symbol to use
He42
Types of Radiation
• Alpha particle ()– helium nucleus
• Beta particle (-)– electron
e0-1
• Positron (+)– positron
e01
• Gamma ()– high-energy photon 00
Alpha Emission
He Th U 42
23490
23892
parentnuclide
daughternuclide
alphaparticle
Numbers must balance!!
occurs when the nucleus has too many protons which cause excessive repulsion.
Alpha Emission
U23592Pu239
94 He42
Ex. Plutonium-239 undergoes alpha decay
+
239
Atomic Mass: = 235
4+
94Atomic #: = 92 2+
Masses must be equal = Conservation of mass
XAZPo21084 He4
2
Ex. Polonium-210 undergoes alpha decay to produce this daughter nuclide. Solve for
+
Alpha Emission
Atomic Mass: 210
= A 4+
Atomic #: 84 = Z 2+
210
= A4- = 206
84 = Z2- = 82
XAZ = Pb20682
XAZ
Beta Emission
e Xe I 0-1
13154
13153
electron
occurs when the neutron to proton ratio is too great.
XAZPo21084
Ex. Polonium-210 undergoes beta decay to produce this daughter nuclide
+
Beta Emission
Atomic Mass: 210
= A 0+
Atomic #: 84 = Z -1+
210
= A0- = 210
84 = Z1+ = 85
XAZ = At21085
e01-
e Ar K 01
3818
3819
positron
Positron EmissionOccurs when the neutron to proton ratio is too small.
XAZPo21084
Ex. Polonium-210 undergoes positron emission to produce this daughter nuclide
+
Positron Emission
Atomic Mass: 210
= A 0+
Atomic #: 84 = Z +1+
210
= A0- = 210
84 = Z1- = 83
XAZ = Bi21083
e01
Gamma Emission
– Emission of high energy electromagnetic wave.
occurs when the nucleus is at too high an energy.
99 99 043 43 0Tc Tc
XAZPo21084
Ex. Polonium-210 undergoes gamma decay to produce this daughter nuclide
+
Gamma Emission
Atomic Mass: 210
= A 0+
Atomic #: 84 = Z 0+
A = 210
Z = 84
XAZ =
00
Po21084
Electron Capture
Pd e Ag 10646
0-1
10647
electron
occurs when the neutron to proton ratio in the nucleus is too small.
XAZPo21084
Ex. Polonium-210 captures an electron to produce this daughter nuclide
+
Electron Capture
Atomic Mass: 210
= A0+
Atomic #: 84 = Z-1+
A = 210
Z = 83
XAZ = Bi21083
e01-