4.4 unstable nuclei and radioactive decay radioactive decay in the late 1890s, scientists noticed...
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4.4 Unstable Nuclei 4.4 Unstable Nuclei and Radioactive and Radioactive DecayDecay
Radioactive decayRadioactive decay
• In the late 1890s, scientists noticed some substances spontaneously emitted radiation, a process they called radioactivity.
Radioactive DecayRadioactive Decay
• Nuclear reactions can change one element into another element.
Radioactive decayRadioactive decay
Radiation is rays and particles given off.
Reactions in a nucleus is nuclear reactions.
Unstable nucleiUnstable nuclei
• Elements that give off radiation are trying to make themselves more stable.
• They need a form where it does not take effort to exist
Nuclear Nuclear ChemistryChemistry
“Bravo” Test 1954 – 15,000 kilotonsVideo
Alpha ParticlesAlpha Particles
Alpha particles contain 2 p+ and 2 n.
Alpha radiation is alpha particles being given off.
Alpha radiationAlpha radiation
• The atomic number decreases by 2, and the mass number decreases by 4.
Alpha EquationAlpha Equation
Beta RadiationBeta Radiation
Each beta particle is an electron with a 1– charge.
Beta RadiationBeta Radiation
Beta emission converts Beta emission converts a neutron to a protona neutron to a proton
The mass number The mass number remains the same, but remains the same, but the atomic number the atomic number increases by one.increases by one.
Beta EquationBeta Equation
Electric Field Electric Field DeflectionDeflection
Gamma RaysGamma Rays
• Gamma rays are high-energy radiation with no mass and are neutral.
• Gamma rays account for most of the energy lost during radioactive decay.
Characteristics of Characteristics of RadiationRadiation
Unstable atomsUnstable atoms
• Atoms that contain too many or too few neutrons are unstable and lose energy through radioactive decay to form a stable nucleus.
• Few exist in nature—most have already decayed to stable forms.
242He
242 e01 01 00
Types of Radioactive DecayTypes of Radioactive Decay
alpha production (alpha production (He): He): helium nucleushelium nucleus
beta production (beta production (e):e):
gamma ray production (gamma ray production ():):
alpha production (alpha production (He): He): helium nucleushelium nucleus
beta production (beta production (e):e):
gamma ray production (gamma ray production ():):
ThHeU 23490
42
23892
234 234 090 91 1Th Pa e
0023490
42
23892 2 ThHeU
Specifying Specifying IsotopesIsotopes
19
XA
Z
X = the symbol of the element
A = mass number (protons + neutrons)
Z = the atomic number (number of protons)
Nuclear SymbolsNuclear Symbols
Element symbol
Mass number, A (p+ + no)
Atomic number, Z(number of p+)
U23592
Key to Balancing Key to Balancing Nuclear EquationsNuclear Equations
In nuclear reactions, both the atomic number Z and the mass number A must be conserved
Balancing Nuclear Balancing Nuclear EquationsEquations
226 488 2Ra
226 = 4 + ____222
222
88 = 2 + ___86
86
Atomic number 86 is radon, Rn
Rn
Alpha DecayAlpha Decay
Alpha production (Alpha production (): ):
an alpha particle is aan alpha particle is a
helium nucleushelium nucleus
Alpha decay is limited to heavy, radioactive
nuclei
238 4 23492 2 90U Th
4 2 4 22 2He or
Alpha (Alpha (αα) Decay) Decay
E1
P+N
P P-2 + He
4
2 E2
P+N -4
an alpha particle (helium nucleus) is an alpha particle (helium nucleus) is producedproduced
Alpha Alpha RadiationRadiation
Limited to VERY large nucleii.
Example of Alpha Example of Alpha DecayDecay
Ra222
88 86+ He
4
2 Rn
Radium 222 decays by α particle production to Radon 218
218
Beta DecayBeta DecayBeta production (Beta production ():):A beta particle is an A beta particle is an electron ejected from electron ejected from the nucleusthe nucleus
Beta emission converts a neutron to a proton
234 234 090 91 1Th Pa
0 01 1e or
Beta (Beta (ββ) Decay) Decay
Beta emission converts a neutron to a proton
E1
P+N
P P+1 + e0
-1 E2
P+N
Beta Beta RadiationRadiation
Converts a neutron into a proton.
Example of Beta Example of Beta DecayDecay
Notice the mass of the beta particle is zero; it is so small that is must be neglected.
C14
6 7 + e0
-1 N
14
Example of Beta Example of Beta DecayDecay
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
Gamma ray production (Gamma ray production ():):
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
0023490
42
23892 2 ThHeU
Gamma Ray ProductionGamma Ray Production
Gamma ray production (Gamma ray production ():):
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
0023490
42
23892 2 ThHeU