1. Chapter 11
Radioactive Elements

2. Accidental Discovery of Nuclear Radiation
In 1896, French scientist Henri Becquerel accidentally left some uranium samples on a photographic plate & found outlines of the substance on the film
at first, he thought the uranium was giving off X-rays because the photographic paper had been exposed to sunlight
but when it worked without the sun, he hypothesized that the uranium had given off some invisible energy that had never been detected before, later called radiation

3. Background Info
it was known that certain substances glowed when exposed to sunlight (fluorescent)
but his experiment worked even when it wasn’t sunny
he determined that the element uranium was the source of nuclear radiation

4. Other Discoveries of Nuclear Radiation
Later, in 1898, Marie Curie & her husband, Pierre, discovered two other radioactive elements they named polonium & radium

6. An element that gives off nuclear radiation is said to be radioactive.
Properties include:
nuclear radiation from radioactive elements will alter photographic film
they produce fluorescence
electric charge can be found in the air surrounding radioactive elements
nuclear radiation damages cells in most organisms

7. Fluorescence

8. The Nucleus contains protons & neutrons held together by strong forces
strong forces are short-range forces that only work over a very short distance; therefore, the bigger the nucleus, the farther apart the protons & neutrons
as long as the protons & neutrons remain together due to the strong force, the nucleus remains stable
the bigger the nucleus, the more unstable it becomes

10. Radioactivity
when the strong force is not large enough to hold the nucleus together tightly, the nucleus can decay & give off matter & energy
this process where the nucleus breaks apart or decays is called radioactivity
all elements with 83 or more protons are radioactive

11. Binding Energy the energy required to break up the nucleus
if the binding energy within the nucleus is weak, the nucleus is unstable & will break apart or decay

12. Unstable
synthetic elements are unstable & decay quickly after being created in the laboratory
many isotopes of elements (no matter the nucleus size) are also radioactive
they are sometimes called radioisotopes

13. Isotopes
an atom of an element that has the same number of protons, but a different number of neutrons
many elements can have both radioactive & nonradioactive isotopes (see pg. 271 for examples)

15. 3 Types of Nuclear Radiation
alpha radiation (particles)
beta radiation (particles)
gamma radiation (waves of energy)

16. 3 Types of Radiation

17. Alpha Particles made of 2 protons + 2 neutrons
has an electric charge of +2
had an atomic mass of 4
more massive & most electric charge
lose energy more quickly when interacting with matter
least penetrating (cannot pass through a piece of paper)
very damaging to biological molecules within the body

19. Alpha Decay
when an atom loses an alpha particle, it is no longer the same element because the number of protons is different
the new element formed has an atomic number two less than the original radioactive element, and a mass number that is four less (it lost two neutrons too)

22. Transmutation
the process of changing one element to another through nuclear decay
the atomic mass at the beginning of the equation must equal the atomic mass at the end

23. How Smoke Detectors Work
when alpha radiation passes through matter, they exert an electrical force on the electrons
this force pulls the electrons away fro the atoms, giving the atom a positive charge (cation)

24. How Smoke Detectors Work
some smoke detectors will give off alpha particles to ionized the surrounding air
normally, an electrical current can pass through the ionized air to form a circuit
when smoke particles enter the ionized air, they absorbs the ions & electrons, thus breaking the circuit causing the alarm to go off

25. Beta Particles
move much faster than alpha particles & are more penetrating
these particles are stopped by Al foil
when a neutron in an unstable nucleus decays into a proton, it emits an electron called the beta particle
process is known as beta decay
caused by weak forces

27. Beta Decay/Transmutation
now that an extra proton was produced in the beta decay, the atom changes to another element
although the atom of this new element has a different atomic number, it still has the same atomic mass because the atom lost a neutron & gained a proton

28. Beta Decay

29. Gamma Rays most penetrating form of radiation
not made of protons, electrons, or neutrons
carry electromagnetic waves of energy
have no mass, no charge
move at the speed of light
stopped by thick, dense materials such as lead or concrete

31. Gamma Decay
alpha & beta decay are accompanied by gamma decay, the release of a gamma ray from the nucleus
since there is no mass or charge, the nucleus does not change into a different nucleus
since energy leaves, the nucleus moves to a lower energy state

35. Electromagnetic Spectrum

36. Decay Series
the series of steps by which a radioactive nucleus decays into a nonradioactive nucleus
spontaneous breakdown continues until a stable nucleus is formed

40. Artificial Transmutation
bombard atomic nuclei with neutrons, alpha particles, or other nuclear “bullets”
done in particle accelerators because of the need to hit the target nuclei with enough force with these high-energy particles

42. Particle Accelerator

43. Artificial Transmutation
first done by Ernest Rutherford who discovered the nucleus of the atom
Italian scientist Enrico Fermi was the first to use neutrons instead of charged particles
neutrons cause the nucleus to disintegrate, get trapped inside or pass right through
can be used to produce radioactive isotopes of natural elements (iodine)

46. Radioactive Half-Life
a measure of the time required by the nuclei of an isotope to decay
the half-life of a radioactive isotope is the amount of time it takes for half the nuclei in a sample of the isotope to decay
time varies from isotope to isotope
the nucleus left after the isotope decays is called the daughter nucleus

49. Radioactive Dating
the ages of materials such as rocks & fossils can be dated using radioactive isotopes & their half-lives
different isotopes are useful in dating different types of materials

51. Half-Life Decay of Uranium

52. Radioactive Dating
determine the amount of radioactive isotope & its daughter nucleus in a sample
calculate the number of half-lives that would have passed to create that amount of daughter nucleus compared to remaining isotope
that gives you the amount of time that has passes since the object formed