25.4 Radioactivity Flashcards
how are protons and neutrons held together?
strong nuclear force
what is stronger:
a) strong nuclear force
b) electrical force between charged particles?
a) strong nuclear force
=> has to overcome the electrical repulsion betw protons in the nucleus
what is the main condition for the strong nuclear force?
only works at very short distances (ie in a nucleus)
radioactive
atoms with unstable nuclei
how do nuclei become more stable? (2)
1) alter # or ratio of protons:neutrons
2) lower energy
radioactive decay
process through which atoms with unstable nuclei undergo to become more stable
types of radioactive decay
1) α
2) β
3) γ
parent
nucleus undergoing radioactive decay
daughter
resulting stable nucleus after a nucleus undergoes radioactive decay
α decay (cause, releases, change and what it’s stopped by)
cause: too many neutrons and protons
releases: 4 He / α
________2
change: Z - 2, AW -4
stopped by: human skin
β (-) decay
cause: too many neutrons
releases: 0 β (converts N-> P)
________ -1
change: Z + 1
stopped by: Al foil + plastic + glass
β (+) decay
cause: too many protons
releases: 0 β (converts P-> N)
+1
change: Z - 1
stopped by: Al foil + plastic + glass
electron capture
cause: too many protons
releases: 0 e (converts P-> N by capturing e)
-1
change: Z - 1
stopped by: Al foil + plastic + glass
γ decay
cause: too high energy
releases: 0 γ
________ 0
change: nothing
stopped by: lead + concrete
half-life
time it takes for a sample of radioactive substance to decay by (1/2)
how does radioactive decay change overtime?
radioactive decay decreases exponentially with time
k
decay constant: value that is inversely proportional to half-life (shorter half-life = larger k = faster decay)
Eb
nuclear binding energy: energy required to break up intact nucleus into individual nucleons
what is required for an atom to have an Eb?
1) protons
2) neutrons
what does a greater or lower Eb indicate?
greater Eb = more stable nucleus
lower Eb = less stable nucleus
Δm
mass defect: the change in mass as individual nucleons bind to form a nucleus
Δm equation
(total mass of separate nucleons) - (mass of nucleus)
what does a negative or positive Δm value indicate?
positive Δm = stable nucleus
negative Δm = unstable nucleus
=> want Δm to be more positive (indicates that the overall mass decreases when you bind the nucleons together -> better binding -> decrease mass)
Eb equation (2)
1) Eb = (Δm)(c^2)
2) Eb (in eV) = (Δm in amu) x 931.5 MeV
