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People Behind the Science

Marie Curie (1867–1934)

arie Curie was a Polish-born French medical applications of radium, and she was
Mscientist who, with her husband, awarded the 1911 Nobel Prize for Chemis-
Pierre Curie (1859–1906), was an early try in recognition of her work in isolating
investigator of radioactivity. From 1896, the pure metal.
the Curies worked together, building on the At the outbreak of World War I in
results of Henri Becquerel, who had dis- 1914, Marie Curie helped to equip ambu-
covered radioactivity from uranium salts. lances with X-ray equipment and drove the
Marie Curie discovered that thorium also ambulances to the front lines. The Inter-
emits radiation and found that the mineral national Red Cross made her head of its
pitchblende was even more radioactive than Radiological Service. She taught medical
could be accounted for by any uranium and orderlies and doctors how to use the new
thorium content. The Curies then carried technique. By the late 1920s, her health
out an exhaustive search and in July 1898 began to deteriorate: continued exposure
announced the discovery of polonium, to high-energy radiation had given her leu-
followed in December of that year with kemia. She entered a sanatorium and died
the discovery of radium. They shared the on July 4, 1934.
1903 Nobel Prize for Physics with Henri Throughout much of her life, Marie the Nobel Prize money and other financial
Becquerel for the discovery of radioactivity. Curie was poor, and the painstaking rewards to finance further research. One of
The Curies did not participate in Becquer- radium extractions were carried out in the outstanding applications of their work
el’s discovery but investigated radioactivity primitive conditions. The Curies refused has been the use of radiation to treat can-
and gave the phenomenon its name. Marie to patent any of their discoveries, wanting cer, one form of which cost Marie Curie
Curie went on to study the chemistry and them to benefit everyone freely. They used her life.

Source: Modified from the Hutchinson Dictionary of Scientific Biography. © Research Machines plc 2003. All Rights Reserved. Helicon Publishing is a division of Research Machines.

as heavier and heavier nuclei were formed. Eventually, the star were born from an exploding supernova, then spread into
materials were fused into nuclei around iron, the element with space as dust. In a process to be discussed in chapter 15, this
the lowest amount of energy per nucleon, and the star used up dust became the materials of which planets were made, includ-
its energy source. Larger, more massive dying stars explode ing Earth. The point for the present discussion, however, is
into supernovas (discussed in chapter 14). Such an explosion that the energy of naturally radioactive elements, and the
releases a flood of neutrons, which bombard medium-weight energy released during fission, can be traced back to the force
nuclei and build them up to more massive nuclei, all the way of gravitational attraction, which provided the initial energy
from iron up to uranium. Thus, the more massive elements for the whole process.

SUMMARY
Radioactivity is the spontaneous emission of particles or energy from neutron-to-proton ratio that is too large become more stable by beta
an unstable atomic nucleus. The modern atomic theory pictures the emission. Gamma ray emission occurs from a nucleus that was left in a
nucleus as protons and neutrons held together by a short-range nuclear high- energy state by the emission of an alpha or beta particle.
force that has moving nucleons (protons and neutrons) in energy shells Each radioactive isotope has its own specific rate of nuclear dis-
analogous to the shell structure of electrons. A graph of the number of integration. The rate is usually described in terms of half-life, the time
neutrons to the number of protons in a nucleus reveals that stable nuclei required for one-half the unstable nuclei to decay.
have a certain neutron-to-proton ratio in a band of stability. Nuclei that Radiation is measured by (1) its effects on photographic film,
are above or below the band of stability, and nuclei that are beyond (2) the number of ions it produces, or (3) the flashes of light produced
atomic number 83, are radioactive and undergo radioactive decay. on a phosphor. It is measured at a source in units of a curie, defined as
10
Three common examples of radioactive decay involve the emis- 3.70 × 10 nuclear disintegrations per second. It is measured where
sion of an alpha particle, a beta particle, and a gamma ray. An alpha received in units of a rad. A rem is a measure of radiation that takes
particle is a helium nucleus, consisting of two protons and two neu- into account the biological effectiveness of different types of radiation
trons. A beta particle is a high-speed electron that is ejected from the damage. In general, the natural environment exposes everyone to 100
nucleus. A gamma ray is a short-wavelength electromagnetic radiation to 500 millirems per year, an exposure called background radiation.
from an excited nucleus. In general, nuclei with an atomic number Lifestyle and location influence the background radiation received, but
of 83 or larger become more stable by alpha emission. Nuclei with a the average is 130 millirems per year.

346 CHAPTER 13 Nuclear Reactions 13-24