Discovery of Radioactivity

at the end of the 1800at the end of the 1800’’s …s …

RoentgenRoentgen BecquerelBecquerel CurieCurie

X-raysX-rays Uranium emitsUranium emitssomething!something!

RadioactivityRadioactivity

Roentgen discovered X-rays: Roentgen discovered X-rays: 18951895

Roentgen Roentgen discovered that discovered that cathode ray tubes cathode ray tubes emit x-raysemit x-rays

Roentgen quickly Roentgen quickly discovered uses for discovered uses for X-raysX-rays

Natural Radioactivity - 1896Natural Radioactivity - 1896

1896 Becquerel 1896 Becquerel discovered that discovered that uranium uranium substancessubstances emit emit radiationradiation

Marie CurieMarie Curie found emission of rays by uranium found emission of rays by uranium

compounds compounds atomic property of element uranium atomic property of element uranium

(U) (U)

1898 discovered thorium (Th) also gave 1898 discovered thorium (Th) also gave off radiationoff radiation

1898: Curies reported 2 new elements:1898: Curies reported 2 new elements: polonium (Po) & radium (Ra)polonium (Po) & radium (Ra)

also radioactivealso radioactive

RadioactivityRadioactivity nucleusnucleus of element of element emits subatomic emits subatomic

particles & electromagnetic wavesparticles & electromagnetic waves

nucleus changesnucleus changes in intoto different element different element process: nuclear process: nuclear ““decaydecay”” or or ““transmutationtransmutation””

original nucleus is original nucleus is ““unstableunstable””

Natural RadioactivityNatural Radioactivity

Becquerel & Curie believed Becquerel & Curie believed more than 1 more than 1 kind of radiationkind of radiation was emitted by was emitted by substances:substances:

1899 discovered 1899 discovered alpha raysalpha rays (() ) & & beta rays beta rays (())

1900 discovered 1900 discovered gamma rays (gamma rays ())

Radioactivity – Rutherford Radioactivity – Rutherford again!again!

RadioactivityRadioactivity•3 radiation types behave differently3 radiation types behave differently in in magnetic & electric fieldsmagnetic & electric fields

•3 radiation types: different penetration power3 radiation types: different penetration power

(alpha rays): (alpha rays): stopped by paperstopped by paper

(beta rays): (beta rays): stopped by thin metal stopped by thin metal foilfoil

(gamma rays): (gamma rays): only partially blocked only partially blocked by by lead and concretelead and concrete

000000gamma gamma (())

-1-1

1/18361/1836

(0.0005)(0.0005)or or 00

eebeta (beta ())

+2+2444 4 He or He or 44alpha (alpha ())

ChargeChargeMassMass(amu)(amu)

Isotope Isotope NotationNotation

Type of Type of RadiationRadiation (symbol)(symbol)

22

-1-1

00

22

TABLE O

-1-1

beta particle beta particle (negative (negative electron):electron):

11 00 n n 11 11 p + p + 00 -1 -1 ee

positronpositron (positive beta particle) (positive beta particle)

11 11 p p 00 +1+1 e e + + 11 0 0 nn