By Lucy Martin and Alex Mogul
Henri was born on December 15, 1852 in
He became Professor of Applied Physics
in the Department of Natural History in
Besides working with natural radioactivity
he studied the plane polarization of light,
the absorption of light by crystals, and
In 1903 he was awarded half of the Nobel
Prize while Pierre and Marie Curie were
awarded the other half for their
continuation of Becquerel’s study.
Becquerel published is finding in 2 main
books: the Annales de Physique et de
Chimie and the Compte Rendus de
l’Academie des Sciences.
Henri married Mlle. Janin and had a son,
Jean, who also became a physicist.
He died on August 25, 1908 at Le Croisic.
Henri’s Great Discovery
Henri Becquerel began to study the
effect of uranium salts on
He meant to test their ability to fog
the film when exposed to light
Becquerel found that when exposed to
light, the uranium salts would fog the
However, bad weather one day
interfered with the sunlight needed to
continue the experiment
Although no sunlight was exposed to
the salts, the uranium still fogged the
Even when Becquerel wrapped the
film in opaque paper so no sunlight
could enter, the uranium salts
continued to fog the film
Henri’s Discovery (cont’d)
Henri experimented with diverse
compounds of uranium and found that
all uranium compounds produced the
He concluded that the uranium atom
was, therefore, responsible for the
Marie and Pierre Curie continued this
discovery, to show that the fogging
was due to rays and particles given
off by the uranium
These rays and particles are called
radiation, and the process by which
materials, like uranium, give off these
rays is called radioactivity
For these valuable discoveries,
Becquerel and the Curies together
won the Nobel Prize in physics in
Disproving Dalton’s Theory
Disproved John Dalton’s theory that all
elements are composed of tiny
indivisible atoms, showing that atoms
Becquerel’s discovery of radioactivity
led to further discoveries to refute
The nuclei of radioactive atoms
(radioisotopes) are unstable due to too
many or too few neutrons and/or
These unstable nuclei go through
radioactive decay during which they
spontaneously cast off radiation
The particles emitted from the atom
cause the nucleus to stabilize itself again
and form a non-radioactive isotope
This new isotope is of a different
identity than the radioactive atom and
belongs to another element
1. What was so amazing about Henri Becquerel’s experiment?
2. What makes an atom radioactive, and, once you know this, how do you
know that uranium is radioactive? What can you tell about uranium’s
3. After a radioactive atom has stabilized itself and formed a non-
radioactive isotope is it a new element? Why?
4. What theory did Henri’s experiment disprove?
5. How would our lives be different if radiation was not discovered?
1. Even though the uranium salts had not been exposed to lights, the photographic paper still
2. An atom is radioactive when the nucleus is unstable, having has too many or too few
neutrons and/or protons, and it releases this unstable energy through radiation. The rays on the
photographic film in Becquerel’s experiment appeared even when the uranium was not
exposed to sunlight, so these rays must have been radiation. Therefore, uranium’s nucleus was
unstable, and in order to stabilize, it needed to let go of the extra energy until it reached an
ideal neutron to proton ratio. Click here and go to question #5.
3. It is a different element. When an element gives off radiation, protons are emitted from the
atom, therefore, the atomic number has changed.
4. He disproved John Dalton’s theory that all elements are composed of tiny indivisible
atoms, showing that atoms can divide.
5. We would not have x-rays and we would lose a valuable cancer treatment.
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