Stability of Nuclides

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This presentation discusses three ways to assess the stability of nuclides.

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What determines the stability of a nucleus?:

What determines the stability of a nucleus? Stable nuclei do not spontaneously decay Unstable nuclei undergo a spontaneous change, such as: Emitting a quantum of gamma energy Emitting a particle Capture of an inner electron (K-capture) 3 rules help to estimate stability

Rule 1: The greater the binding energy per nucleon, the more stable the nucleus:

Rule 1 : The greater the binding energy per nucleon, the more stable the nucleus Binding energy – energy needed to separate nucleus into protons & neutrons Mass Defect – difference between the calculated mass of an atom and its actual mass Use E=mc 2 to convert mass defect to energy Calculate 

Rule 2: Nuclei of low atomic numbers with a 1:1 neutron-proton ratio are very stable:

Rule 2: Nuclei of low atomic numbers with a 1:1 neutron-proton ratio are very stable Low atomic number elements – neutron:proton ratio is close to 1 As Atomic # ↑, neutron:proton ratio ↑ Plotting the stable nuclei produces a “band of stability” (see Fig. 28.9) Image from http://algebralab.com/practice/practice.aspx?file=Reading_TheBandOfStability.xml

Rule 3: The most stable nuclei tend to contain an even number of both protons and neutrons:

Rule 3: The most stable nuclei tend to contain an even number of both protons and neutrons

Predicting Decay Type based on the Band of Stability:

Predicting Decay Type based on the Band of Stability A – Have excess neutrons; Beta decay B – Have excess protons; Positron emission or K-capture C – Too large for stability; Alpha decay Image from http://algebralab.com/practice/practice.aspx?file=Reading_TheBandOfStability.xml

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