NUCLEAR CHEMISTRY An Energetic Concept

WHO DID WHAT Wilhelm Roentgen Laboratory generated phosphorescence X-rays

WHO DID WHAT Henri Becquerel Inherited U salts (pitchblende) Natural phosphorescence Discovered spontaneous phosphorescence

WHO DID WHAT Marie & Pierre Curie Studied Becquerel phosphorescence and named it Discovered Po, Ra

ISOTOPE REVIEW X A Z A—mass number Z—atomic number A – Z = number of neutrons

SO, WHAT IS RADIATION? Instability due to n:p + Radioisotopes Goal is stability

SO, WHAT IS RADIATION?

TYPES OF RADIATION Rutherford Electric field effect on radioactivity Alpha Beta Gamma

TYPES OF RADIATION

Alpha (  ) Same as a He-4 nucleus A decreases by 4 Z decreases by 2

TYPES OF RADIATION Alpha Not very penetrating Stopped by a sheet of paper Very ionizing

TYPES OF RADIATION Beta (  ) Same as an electron A remains the same Z increases by 1 e

TYPES OF RADIATION Beta More penetrating than  Stopped by a thin sheet of metal Less ionizing than 

TYPES OF RADIATION Gamma (  ) Pure energy Usually 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 + e

TYPES OF RADIATION Electron capture The opposite of  emission A remains the same Z decreases by 1 K + e  Ar

DECAY SERIES Continued radiation until stable Fr-221 undergoes the following decay series: , , , , ,  Fr  At + He At  Bi + He Bi  Tl + He Tl  Pb + e Pb  Bi + e Bi  Tl + He

RATE OF RADIOACTIVE DECAY Half-Life t ½ = 0.693/k k = rate law constant First-order Kinetics lnN = –kt + lnN o N…amount after elapsed time t = elapsed time N o = amount originally

UNITS OF RADIOACTIVE DECAY curie (Ci) 1 Ci = 3.7 x disintegrations per second ~activity of 1 g of Ra-226 becquerel (Bq) SI unit 1 Bq = 1 dis/s…37 GBq = 1 Ci

UNITS OF RADIATION EXPOSURE sievert (Sv) Dose absorbed by specific tissue Replaced röntgen equivalent to man (rem) 1 Sv…nausea 2-5 Sv…hair loss, hemorrhage 3 Sv…death in 50% of people in 30 days >6 Sv…unlikely survival Typical 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 k Plug into the linear equation and solve for t

RATE OF RADIOACTIVE DECAY 2 h = 0.693/k… k = h -1 ln(10 mCi) = –( h -1 )(t) + ln(200 mCi) ln(10 mCi) – ln(200 mCi) = –( h -1 )(t) – 2.996= –( 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