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Nuclear Chemistry. “Bravo” Test 1954 – 15,000 kilotons. Chapter 19: Radioactivity and Nuclear Energy. Objective 12: To learn the types of radioactive decay (Section 19.1) Objective 13: To learn to write nuclear equations that describes radioactive decay (Section 19.1) - PowerPoint PPT Presentation
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Nuclear Chemistry
“Bravo” Test 1954 – 15,000 kilotons
Chapter 19: Radioactivity and Nuclear EnergyObjective 12: To learn the types of radioactive decay (Section 19.1) Objective 13: To learn to write nuclear equations that describes radioactive decay (Section 19.1) Objective 14: To learn how one element may be changed into another by particle bombardment (Section 19.2)
What makes an atom radioactive?
Radioactivity: the spontaneous decomposition of a nucleus to form another nucleus and produce one or more particles. -the heavier the atom, the more likely it is to be radioactive-if the number of protons in the nucleus exceeds 83, then the nuclide is radioactive-all of the positive charge is concentrated in one area; therefore the nucleus is unstable
Types of Radioactive Decay
alpha production (a, He): helium nucleus
beta production (b, e):
gamma ray production (g):
ThHeU 23490
42
23892
234 234 090 91 1Th Pa e
g0023490
42
23892 2 ThHeU
Specifying Isotopes
5
XA
Z X = the symbol of the element
A = mass number (protons + neutrons)
Z = the atomic number (number of protons)
Nuclear Symbols
Element symbolMass number, A (p+ + no)
Atomic number, Z(number of p+)
U23592
Key to Balancing Nuclear Equations
In nuclear reactions, both the atomic number Z and the mass number A must be conserved
Balancing Nuclear Equations
226 488 2Ra a
226 = 4 + ____222
222
88 = 2 + ___86
86
Atomic number 86 is radon, Rn
Rn
Alpha DecayAlpha production
(a): an alpha particle is
ahelium nucleus238 4 234
92 2 90U He Th
Alpha decay is limited to heavy, radioactive
nuclei
238 4 23492 2 90U Tha
4 2 4 22 2He or a
Alpha (α) Decay
E1
P+N
P P-2 + He4
2 E2
P+N -4
an alpha particle (helium nucleus) is produced
Alpha Radiation
Limited to VERY large nucleii.
Example of Alpha Decay
Ra222
88 86 + He4
2 RnRadium 222 decays by α particle production to Radon
218
218
Beta DecayBeta production (b):A beta particle is an electron ejected from the nucleus
234 234 090 91 1Th Pa e
Beta emission converts a neutron to a proton
234 234 090 91 1Th Pa b
0 01 1e or b
Beta (β) Decay
Beta emission converts a neutron to a proton
E1
P+N
P P+1 + e0-1 E2
P+N
Beta Radiatio
nConverts a neutron into a proton.
Example of Beta DecayNotice the mass of the beta particle is zero; it is so small that is must be neglected.
C14
6 7 + e0-1 N14
Example of Beta Decay
Th234
90 91 + e0-1 Pa
234
Thorium 234 decays by β particle production to Protactinium 234
(notice: no change in mass number A, and an increase of 1 in atomic number Z)
Gamma Ray ProductionGamma 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
g0023490
42
23892 2 ThHeU
Gamma Ray ProductionGamma 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
g0023490
42
23892 2 ThHeU
Positron ProductionPositron emission:Positrons are the anti-particle of the electron
Positron emission converts a proton to a neutron
NeeNa 2210
01
2211
e01
Positron Production
E1
P+N
P P-1 + e01 E2
P+N
Positron emission converts a proton to a neutron
Electron CaptureElectron capture: (inner-orbital electron is captured by the nucleus)
Electron capture converts a proton to a neutron
g0020179
01
20180 AueHg
Alpha Particle Emission
Beta Particle Emission
Gamma Ray Emission
Symbol or or
Mass Heavy Light No Mass
How it changes the
nucleus
Decreases the mass number by 4
Decreases the atomic number by 2
Converts a neutron into a proton
Increases atomic number by 1
No change to the nucleus
Penetration Low Medium High
Protection provided by…
Skin Paper, clothing Lead
Danger Low Medium High
242He
242a e01 b01 g00
Types of Radiation
NuclearStability
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 Decay Series
A radioactive nucleus reaches a stable state by a series of steps
Graphic – Wikimedia Commons User Tosaka
Alpha Particle Emission
Beta Particle Emission
Gamma Ray Emission
Symbol or or
Mass Heavy Light No Mass
How it changes the
nucleus
Decreases the mass number by 4
Decreases the atomic number by 2
Converts a neutron into a proton
Increases atomic number by 1
No change to the nucleus
Penetration Low Medium High
Protection provided by…
Skin Paper, clothing Lead
Danger Low Medium High
242He
242a e01 b01 g00
A Decay SeriesA radioactive nucleus reaches a stable state by a series of steps
Graphic – Wikimedia Commons User Tosaka
Particle BombardmentNuclear transformation involves changing one element into another by bombarding it with small nuclei, protons, or neutrons in a particle accelerator