NUCLEAR CHEMISTRYAn Energetic Concept

WHO DID WHAT

Wilhelm RoentgenLaboratory generated

phosphorescenceX-rays

WHO DID WHAT

Henri BecquerelInherited U salts (pitchblende)Natural phosphorescenceDiscovered spontaneous

phosphorescence

WHO DID WHAT

Marie & Pierre CurieStudied Becquerel

phosphorescence and named itDiscovered Po, Ra

ISOTOPE REVIEW

XA

Z

A—mass number

Z—atomic number

A – Z = number of neutrons

SO, WHAT IS RADIATION?

Instability due to n:p+

RadioisotopesGoal is stability

SO, WHAT IS RADIATION?

TYPES OF RADIATION

RutherfordElectric field effect on

radioactivityAlphaBetaGamma

TYPES OF RADIATION

TYPES OF RADIATION

Alpha ()Same as a He-4 nucleusA decreases by 4Z decreases by 2

TYPES OF RADIATION

AlphaNot very penetrating

Stopped by a sheet of paperVery ionizing

TYPES OF RADIATION

Beta ()Same as an electronA remains the sameZ increases by 1

e

TYPES OF RADIATION

BetaMore penetrating than

Stopped by a thin sheet of metal

Less ionizing than

TYPES OF RADIATION

Gamma ()Pure energyUsually accompanies and More penetrating than and

Somewhat blocked by several inches of Pb or several feet of concrete

Less ionizing than and

TYPES OF RADIATION

Positron (+)Same mass as Opposite charge of

F O + e18

9

18

8

0

+1

TYPES OF RADIATION

Electron captureThe opposite of emissionA remains the sameZ decreases by 1

DECAY SERIES

Continued radiation until stableFr-221 undergoes the following

decay series: ,,,,,

Fr At + He221 87

217 85

4 2

At Bi + He217 85

213 83

4 2

Bi Tl + He213 83

209 81

4 2

Tl Pb + e209 81

209 82

0 -1

Pb Bi + e209 82

209 83

0 -1

Bi Tl + He209 83

205 81

4 2

RATE OF RADIOACTIVE DECAY

Half-Lifet½ = 0.693/k

k = rate law constantFirst-order Kinetics

lnN = –kt + lnNo

N…amount after elapsed timet = elapsed timeNo = amount originally

UNITS OF RADIOACTIVE DECAY

curie (Ci)1 Ci = 3.7 x 1010 disintegrations per second

~activity of 1 g of Ra-226becquerel (Bq)

SI unit1 Bq = 1 dis/s…37 GBq = 1 Ci

UNITS OF RADIATION EXPOSURE

sievert (Sv)Dose absorbed by specific

tissueReplaced röntgen equivalent to

man (rem)1 Sv…nausea2-5 Sv…hair loss, hemorrhage3 Sv…death in 50% of people in

30 days>6 Sv…unlikely survivalTypical background exposure is

2.4 mSv/year

RATE OF RADIOACTIVE DECAY

The half-life of F-18 is 2 hours. If you receive a dose of 200 mCi at 8:00 AM, how long will it take for 10 mCi to remain in your body? At what time will you have 10 mCi in you?Solve for the value of kPlug into the linear equation

and solve for t

RATE OF RADIOACTIVE DECAY

2 h = 0.693/k…

k = 0.3465 h-1

ln(10 mCi) = –(0.3465 h-1)(t) + ln(200 mCi)

ln(10 mCi) – ln(200 mCi) = –(0.3465 h-1)(t)

– 2.996= –(0.3465 h-1)(t)

8.65 h = t

at 4:39 PM, you will have 10 mCi in you

RADIOACTIVE DATING

C-14 is a beta emitter with a half-life of 5730 years

Used to determine the age of carbon-based substances