Download Review and Radioactivity

Review and
Radioactivity
Put together by THE Coach Hyde
Radioactivity
 Nucleus contains almost all the mass of an atom (p/n have
all mass)…electrons are negligible (little mass)
 EX. Marble sitting in middle of football field
 When a nucleus decays (loses particles) matter and energy
is given off (lots of energy)
 This happens spontaneously (naturally)
 Occurs mostly in large elements because attraction forces
aren’t as strong to hold particles within nucleus
 Large nuclei are unstable and decay more than small nuclei
Nuclear Decay
 When unstable nuclei decay…particles and energy
(called nuclear radiation) are emitted (given off)
 3 types of nuclear radiation
 A. Alpha-particles
 B. beta-particles
 C. gamma-electromagnetic wave
Alpha
 Very massive particle (made of p/n)
 Most electric charge
 Lose energy quickly
 Least penetrating power-stopped by paper
 Charge =+2…….mass + 4
 Transmutation occurs=changing one element to
another through nuclear decay
symbol
Alpha Particle in Depth
1) The nucleus of an atom splits into two parts.
2) One of these parts (the alpha particle) goes zooming
off into space.
3) The nucleus left behind has its atomic number
reduced by 2 and its mass number reduced by 4 (that
is, by 2 protons and 2 neutrons).
OK, write the alpha decay equations for these
five nuclides. The answers are on the next slide
Beta particle
 An electron is emitted (given off) from nucleus decay
 Much faster and penetrate more than alpha
 Go thru paper….stopped by foil
 Undergoes transmutation like alpha
 Charge is -1………mass .0005 (small)
131
131
I
53
+
e-
Xe
=
54
Beta Decay
Beta decay is somewhat more complex than alpha decay is. These points present a simplified view of what beta decay
actually is:
1) A neutron inside the nucleus of an atom breaks down, changing into a
proton.
2) It emits an electron and an anti-neutrino (the anti-particle of a neutron)
3) The atomic number goes UP by one and mass number remains unchanged.
Here is an example of a beta decay equation:
Beta Decay Continued
The nuclide that decays is the one on the left-hand side of the
equation.
2) The order of the nuclides on the right-hand side can be in
any order.
3) The way it is written below is the usual way.
4) The mass number and atomic number of the antineutrino
are zero and the bar above the symbol indicates it is an antiparticle.
5) The neutrino symbol is the Greek letter "nu.“
6) Notice that all the atomic numbers on both sides ADD UP
TO THE SAME VALUE and the same for the mass numbers.
Here's your first set of exercises. Write out the full beta decay
equation. Then click the link to see the answer
Gamma Rays
 Most powerful and penetrating of all
 No mass and no charge
 Given off by nucleus during alpha/beta decay
 Lead and concrete can only stop gamma rays
Gamma-rays
A nucleus which is in an excited state may emit one or more
photons (packets of electromagnetic radiation) of discrete
energies. The emission of gamma rays does not alter the number
of protons or neutrons in the nucleus but instead has the effect of
moving the nucleus from a higher to a lower energy state
(unstable to stable). Gamma ray emission frequently follows beta
decay, alpha decay, and other nuclear decay processes.
Half-life
 The amount of time a radioactive isotope takes for
half the nuclei of a sample to decay
 Very hard stuff so pay attention
 Used in science to date rocks, fossils, bones..etc
Half Life Table
Problems examples
 The half life of calcium is 10 days. How much of a
100 g sample will remain after
 A. 20 days
 B. 30 days
 C. 40 Days
 D. 50 days
Another look
 A sample of Phosphorous-18 originally has 30g.
Phosphorous-18 has a half life of 2,000 years. In
_______________ years, how many grams would
remain undecayed?
 A. 2,000 yrs
 B. 4,000 yrs
 C. 8,000 yrs
Another look
 At the end of 45 days, 100 g of Carbon-14 has
decayed to 12.5 g. What is the ½ life of Carbon 14?
The Geiger–Müller counter, also called a Geiger counter, is an
instrument used for measuring ionizing radiation used widely in
such applications as radiation dosimetry, radiological protection,
experimental physics and the nuclear industry