The Science Book

192 MARIE CURIE

L

ike many major scientific

discoveries, radiation was

found by accident. In 1896,

French physicist Henri Becquerel

was investigating phosphorescence,

which occurs when light falls on a

substance that then emits light of

a different color. Becquerel wanted

to know whether phosphorescent

minerals also emitted X-rays, which

had been discovered by Wilhelm

Röntgen a year earlier. To find out,

he placed one of these minerals on

top of a photographic plate that was

wrapped in thick black paper and

exposed both to the Sun. The

experiment worked—the plate

darkened; the mineral appeared

to have emitted X-rays. Becquerel

also showed that metals would

block the “rays” that caused the

plate to darken. The next day was

cloudy so he could not repeat the

experiment. He left the mineral on

a photographic plate in a drawer,

but the plate still darkened, even

without the sunshine. He realized

that the mineral must have an

internal source of energy, which

turned out to be the result of the

breakdown of atoms of uranium in

the mineral he was using. He had

detected radioactivity.

IN CONTEXT

BRANCH

Physics

BEFORE

1895 Wilhelm Röntgen

investigates the properties

of X-rays.

1896 Henri Becquerel

discovers that uranium salts

emit penetrating radiation.

1897 J. J. Thomson discovers

the electron while exploring the

properties of cathode rays.

AFTER

1904 Thomson proposes

the “plum pudding” model

of the atom.

1911 Ernest Rutherford

and Ernest Marsden

propose the “nuclear model”

of the atom.

1932 British physicist

James Chadwick discovers

the neutron.

It was necessary at this

point to find a new term

to define this new property

of matter manifested by the

elements of uranium and

thorium. I proposed the

word radioactivity.

Marie Curie

Rays produced by atoms

Following Becquerel’s discovery,

his Polish doctoral student, Marie

Curie, decided to investigate

these new “rays.” Using an

electrometer—a device for

measuring electrical currents—she

found that air around a sample of a

uranium-containing mineral was

conducting electricity. The level

of electrical activity depended

only on the amount of uranium

present, not on the total mass of the

mineral (which included elements

Marie Curie Maria Salomea Skłodowska was

born in Warsaw in 1867. At that

time Poland was under Russian

rule and women were not allowed

into higher education. She worked

to help finance her sister’s medical

studies in Paris, France, and in

1891 moved there herself to study

mathematics, physics, and

chemistry. There, she married her

colleague, Pierre Curie, in 1895.

When her daughter was born in

1897, she began teaching to help

support the family, but continued

to research with Pierre in a

converted shed. After Pierre’s

death, she accepted his chair at

the University of Paris, the first

woman to hold this position. She

was also the first woman to be

awarded a Nobel Prize, and the

first to be awarded a second

Nobel. During World War I, she

helped set up radiology centers.

She died in 1934 of anemia,

probably caused by her long

exposure to radiation.

Key works

1898 Emissions of Rays

by Uranium and

Thorium Compounds

1935 Radioactivity