Ch. 18 - Nuclear Chemistry

_z^AX

X: letter symbol

Z: atomic # (proton #)

A: mass #

Isotope

atoms w/ same # of protons (same Z) but different # of neutrons

Radioactive Decay Format

_Z^AX = _U^BS + _V^CT

A = B + C

Z = U + V

α particle

₂⁴He

β particle

_-1⁰e

γ particle

₀⁰r

positron particle

₊₁⁰e

neutron particle

₀¹n

Stability

• Atoms w/ even # of proton and neutron MORE STABLE

• magic proton # : 2, 8, 28, 82, 20, 50, 126 SUPER STABLE

• |mass # - atomic mass| > 2 or Z > 83 NOT STABLE

Type of decay will be determined by the _____

N / Z ratio

(neutron # / proton #)

neutron #

(mass # - atomic #)

1-20 protons (Z)

Threshold: 1

• N/Z > th, β decay —→ _-1⁰e (product side)

• N/Z < th, positron emission —→ ₁⁰e (product side)

• N/Z < th, e- capture —→ _-1⁰e (reactant side)

20-40 protons (Z)

Threshold: 1.25

• N/Z > th, β decay —→ _-1⁰e (product side)

• N/Z < th, positron emission —→ ₁⁰e (product side)

• N/Z < th, e- capture —→ _-1⁰e (reactant side)

40-83 protons (Z)

Threshold: 1.5

• N/Z > th, β decay —→ _-1⁰e (product side)

• N/Z < th, positron emission —→ ₁⁰e (product side)

• N/Z < th, e- capture —→ _-1⁰e (reactant side)

>83 protons (Z)

Threshold: 1.6

• N/Z > th, β decay —→ _-1⁰e (product side)

• N/Z < th, α decay —→ ₂⁴He (product side)

Decay Kinetics Equations

ln(A_t / A_o) = -kt

k * t_1/2 = 0.693

A_t / A_o = A / A+B

rock contains A and B. B is the decay product of A

• A is the # OF ATOMS, NOT MASS OF ATOMS

mass defect (thermodynamic stability)

difference in mass between actual and hypothetical formation of a nucleus

ΔE

ΔE=Δmc²

ΔE=(hypothetical mass - actual mass)*c²

1 amu = 1.66×10^-27 kg = 931.5 MeV/c²

hypothetical mass

(proton # * mass_proton) + (neutron # * mass_neutron)

actual mass

given

nucleon

neutron

MeV/atom —→ MeV/nucelon

÷ mass #

MeV/atom —→ MeV/mole

× 6.022×10²³

Particle accelerator

uses an electric field to accelerate charged particle (typically ₂⁴He) to bombard the atom

_Z^AX (₂⁴He, ₀¹n) means (X + ₂⁴He —→ Y + ₀¹n)

fission

splits a larger atom into smaller ones (most electric power is generated through fission)

Breeder reactors (fission)

convert the non-fissionable nuclide, ²³⁸U, to a fissionable product

²³⁸U + ₀¹n —→ ²³⁹Pu + ₀¹n

fusion

fuse two or more lighter atoms into a larger one

control rods

control rods in the nuclear fission reactors are composed of a substance that absorbs neutrons

• Ag, In, Cd