Nuclear Decay

Graphic: www.lab-initio.com

Nuclear Symbols

Element symbolMass number, A (p+ + no)

Atomic number, Z(number of p+)

U23592

Balancing Nuclear Equations

235 1 142 91 192 0 56 36 03U n Ba Kr n

Areactants = Aproducts

Zreactants = Zproducts

235 + 1 = 142 + 91 + 3(1)

92 + 0 = 56 + 36 + 3(0)

Balancing Nuclear Equations #2

226 488 2Ra

226 = 4 + ____222

222

88 = 2 + ___86

86

Atomic number 86 is radon, Rn

Rn

Balancing Nuclear Equations #3

235 1 139 192 0 53 02U n I n

235 + 1 = 139 + 2(1) + ____95

3992 + 0 = 53 + 2(0) + ____

3995

Atomic number 39 is yttrium, Y

Y

Alpha DecayAlpha production

(): 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 Th

4 2 4 22 2He or

Alpha Radiation

Limited to VERY large nucleii.

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 Radiatio

nConverts a neutron into a proton.

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

Electron CaptureElectron capture: (inner-orbital electron is captured by the nucleus)

Electron capture converts a proton to a neutron

g0020179

01

20180 AueHg

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

Graphic – Wikimedia user : Napy1kenobi

A Decay Series

A radioactive nucleus reaches a stable state by a series of steps

Graphic – Wikimedia Commons User Tosaka

Half-life

Graphic - http://cafreetextbooks.ck12.org/science/CK12_Earth_Science_rev.pdf

Decay KineticsDecay occurs by first order kinetics (the rate of decay is proportional to the number of nuclides present)

0

ln N ktN

N = number of nuclides remaining at time t

N0 = number of nuclides present initially

k = rate constant

t = elapsed time

Calculating Half-life

1/ 2ln(2) 0.693tk k

t1/2 = Half-life (units dependent on rate constant, k)

Sample Half-Lives