EXPLORING RADIOACTIVITY:
The energy stored in the nucleus of an atom was immediately apparent when atomic blasts brought an end to World War II. However, many of the long-term dangers were not known.
Today the use of nuclear reactions has a tremendous impact on your life.
For example, some power plants have nuclear reactions that are used in fission reactors that produce heat - which heats up water - creating steam thhat turns a turbine - which generates electricity. Also, hospitals and research laboratories routinely use radioactive materials to diagnose diseases, and treat some forms of cancer.
A few questions this section topic will be answering:
1. How does radiation exposure to these sources compare with exposure to other sources that occur naturally?
2. Some of these procedures generate hazardous radioactive waste - how can this hazardous material be stored safely?
3. How can you assess the risks of using nuclear reactions and weigh these risks against potential benefits?
THE NUCLEUS and RADIATION:
From previous knowledge, you know that chemical changes involve the ________________________ between different atoms in the reactant molecules and the formation of new bonds to form the product molecules.
In a nuclear reaction, changes occur within the ________________________ - involving the ________________________ and ________________________ within the nucleus of a single atom.
Recall that two ________________________ particles reside in the nucleus: the proton and neutron.
Also, recall that atoms of a given element have the ________________________ or protons; this number is known as the ________________________ number.
The atoms of a given element CAN have different numbers of ________________________ and therefore have different mass numbers (the mass number is the total number of protons and neutrons in the nucleus.)
Atoms with the same atomic number but different mass numbers are known as ________________________. The different isotopes of an element are distinguished by citing their ________________________.
For example, there are three naturally occurring isotopes of neon: neon-20, neon-21, and neon-22.
One reason that we must distinguish between different isotopes is that the ________________________ of an atom depend on the number of both protons and neutrons in its nucleus.
In contrast, we already know that an atom's chemical properties are ________________________ by the number of neutrons in the nucleus.
REACTIONS THAT THE NUCLEUS CAN UNDERGO:
A nucleus can undergo a reaction that changes its identity. Some nuclei are unstable and ________________________ emit particles and electromagnetic ________________________.
Such spontaneous emission from the nucleus of the atom is known as ________________________.
Those isotopes that are radioactive are known as ________________________.
An example is uranium-238, which spontaneously emits alpha rays. Recall, that these rays consist of streams of helium-4 nuclei known as alpha particles.
When a uranium-238 nucleus loses an alpha particle, the remaining fragment has an atomic number of 90 and a mass of 234. It is therefore a thorium-234 nucleus.
When a nucleus spontaneously decomposes in this way, it is said to have ________________________, or undergone radioactive decay.
Notice that the mass numbers is the same on both sides of the equation ( 238 = 234 + 4 ). Likewise, the sum of the atomic numbers on both sides is equal ( 92 = 90 + 2 ).
TRANSMUTATIONS:
Another way a nucleus can change identity is to be ________________________ by a neutron or by another nucleus.
Nuclear reactions that are induced in this way are known as nuclear transmutations.
For example, a chlorine-35 nucleus is struck
by a neutron ( 
); this collision
produces a sulfur-35 nucleus and a proton ( 
or 
).
Notice again that the sum of mass numbers and of atomic numbers is the same on both sides of the equation.
By bombarding nuclei with various particles, it is possible to prepare nuclides (an atom with a specific number of protons and neutrons) not found in nature.
PRACTICE PROBLEMS:
Indicate the number of protons and neutrons in each of the following nuclei:
I. chlorine-37
II. iridium-200
III. uranium-238
IV. Write a balanced nuclear equation for the nuclear transmutation in which a cobalt-60 nucleus is struck by a helium-4 nucleus (alpha particle), producing a copper-63 nucleus and a neutron.
V. Write a balanced nuclear equation for the nuclear transmutation in which an americium-245, Am, nucleus is struck by a proton, producing a plutonium-242 nucleus and a helium-4 nucleus (alpha particle).
HOMEWORK PROBLEMS:
Indicate the number of protons and neutrons in each of the following nuclei:
1a.) carbon-13
1b.) rubidium-85
1c.) 
1d.)
1e.) Write a balanced nuclear equation for the nuclear transmutation in which an aluminium-27 nucleus is struck by a helium-4 nucleus, producing a phosphorus-30 nucleus and a neutron.
1f.) Carbon-11, a radioactive nuclide used in medical imaging, is formed by reaction of a proton with nitrogen-14, yielding carbon-11 and helium-4. Write the nuclear reaction.
TYPES OF RADIOACTIVE DECAY:
Emission of radiation is one of the ways in which an ________________________ nucleus is transformed into a ________________________ one with less energy. The emitted radiation is the carrier of the excess energy.
Earlier this year we discussed the three most common types of radiation emitted by radioactive substances: ________________________ ( a ), ________________________ ( b ), and ________________________ ( g ) rays.
Alpha rays consist of streams of ________________________
nuclei known as alpha particles. The below equation show this
type of radioactive decay:
Beta rays consist of streams of ________________________.
Because the beta particles are electrons, they are represented
as 
. The superscript zero indicates
the exceedingly small mass of the electron in comparison to mass
of a proton or neutron. The subscript -1 represents the negative
charge of the particle, which is opposite of that of a ________________________.
Example: Iodine-131 is an example of an isotope that undergoes decay by beta emission:
Emission of a beta particle has the effect of converting a neutron within the nucleus into a proton, thereby increasing the atomic number of the nucleus by 1:
However, just because an electron is ejected from the nucleus, we need not think that the nucleus is composed of these particles, any more than we consider a match to be composed of sparks simply because it gives them off when struck.
The electron comes into being only when the ________________________ is disruptive.
Gamma rays consist of electromagnetic radiation
of ________________________ wavelength (very high energy
photons). Gamma rays are represented as 
. Such radiation neither changes the atomic number nor the mass
number of a nucleus.
Two other types of radioactive decay that occur
are positron emission and electron capture. A positron is a particle
that has the same mass as an electron but an opposite charge.
The positron is represented as 
.
Example: Carbon-11 is an example of an isotope that decays by positron emission:
The positron has a very short life because it is annihilated when it collides with an electron, producing gamma rays:
Emission of a positron can be thought of as converting a proton into a ________________________:
Electron capture is the capture by the nucleus of an inner-shell electron from the electron cloud surrounding the nucleus. Example: Rubidium-81 undergoes decay in this fashion:
Electron capture has the effect of converting a proton within the nucleus into a neutron:
Summary of the Particles Common to Radioactive Decay and Nuclear Transformers:
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PRACTICE PROBLEMS:
Write a balanced equation for each of the following reactions:
I. berkelium-250 undergoes alpha decay
II. einsteinium-255 undergoes alpha capture
III. californium-253 undergoes positron capture
Complete and balance the following nuclear equations by supplying the missing particle:
IV.
V. 
VI. 
VII. 
HOMEWORK PROBLEMS:
Write balanced equation for each of the following reactions:
2a.) thorium-230 undergoes alpha decay
2b.) thorium-231 undergoes decay to form protactinium-231.
2c.) Write a balanced nuclear equation for the reaction in which oxygen-15 undergoes positron emission.
Complete and balance the following nuclear equations by supplying the missing particle:
2d.) 
2e.) 
2f.) 
2g.) 
HALF-LIFE:
In a sample of radioactive nuclides, the decay of an individual nuclide is a ________________________. It is impossible to predict which nucleus will be the next to undergo a nuclear change.
How, then do you make sense out of things that cannot be predicted on an individual basis? One approach is to predict change for a given amount of a very large ________________________ of nuclei - for example, one half.
Scientists commonly discuss radioactive decay in terms of half-life.
The time it takes for one half of the ________________________ nuclides in a radioactive sample to decay is known as its half-life, or t 1/2.
Example: The half-life of fluorine-21 is approximately ________________________ seconds. If a sample of fluorine-21 contains one-million atoms, then 500,000 of the nuclei will decay within ________________________ seconds.
Within another ________________________ seconds, 250,000 atoms additional nuclei (one-half of those remaining) will decay, and so on.
Many radioactive nuclei have much longer half-lives. A sample of one million nuclei of strontium-90 will decay much more slowly because the half-life of strontium-90 is about ________________________.
Half-lives may be used to calculate the ________________________ of parent nuclides that remain after a certain amount of time.
PRACTICE PROBLEMS:
I. A certain nuclei has a half-life of approximately 30 seconds. What fraction of the original nuclei would remain after 5 minutes? If you began with 200 grams of this nuclei, how many grams would remain at the end of the five minutes?
II. A certain radioisotope started with a mass of 333 grams. Calculate the mass of this radioisotope after seven, (7) half-lives had elapsed.
III. Thorium-231 has a half-life period of 25.5 hours. You perform research at a chemical lab and need to order 100 grams of thorium-231 for an experiment. Determine the number of grams that you would need to order of the "parent" thorium-231 sample so that you receive the 100 grams of thorium-231 for the experiment you are about to perform for your research. You plan on performing the experiment at noon on Thursday. The chemical supply company can promise delivery of the material from Brazil (yes, the country) in EXACTLY 48.0 hours.
HOMEWORK PROBLEMS:
3a. Fluorine-21 has a half-life of approximately 5 seconds. What fraction (or percent) of the original nuclei would remain after 1 minute? If you started with 21 grams of the fluorine-21, how many grams of fluorine would remain after the one minute time period elapsed?
3b. Iodine-131 has a half-life of 8 days. What fraction (or percent) of the original sample would remain at the end of 32 days?
3c. The half-life of chromium-51 is 28 days. If a sample contained 510 grams, what mass (in grams) of chromium-51 would remain after 168 days? What mass of chromium-51 would remain after 1 year (365 days)?
NUCLEAR REACTIONS FOR ENERGY:
When you look at the stars - (And you SHOULD look at the stars because at one time you where star material! - the atoms that make you up) - you see reesults of some of the most ________________________ reactions in the universe.
Earlier you learned that chemical reactions absorb or release energy. Nuclear reactions give off ________________________ times more energy per gram of reactant than chemical reactions.
The light and heat that reach the Earth are the results of nuclear reactions within the sun.
SPLITTING NUCLEI - NUCLEAR FISSION:
Fission is a nuclear reaction in which a nucleus is broken into ________________________ nuclei, often by bombardment with ________________________ of relatively low energy.
Scientists first became aware of fission during their efforts to manufacture transuranium elements (synthesised element, that is one that does not exist in nature) in the 1930's. They discovered that uranium-235 nucleus breaks apart after absorbing a neutron.
The addition of a neutron makes the uranium nucleus unstable. The nucleus splits apart, forming two nuclei - usually with different atomic numbers - and emitting neutrons.
Because the mass of the products is ________________________ than the mass of the reactants, energy is ________________________. The neutrons emitted may be absorbed by other uranium-235 nuclei and cause them to undergo fission, which in turn releases more neutrons and more energy. This self-propagating reaction is called a chain reaction.
By noticing a reduction in mass, once the chain reaction occurred and energy was released - Einstein was able to develop his "famous" equation: E=mc2. The equation follows and obeys a law we learned very early in the year - The ________________________: Stating that matter is neither created nor destroyed (it just changes location and form - i.e. energy).
If the amount of uranium-235 is ________________________, many of the neutrons produced by the fission reaction pass through the material without being absorbed. Therefore, as the amount of uranium-235 is increased, the chance for a neutron's striking a nucleus and being absorbed is increased.
The ________________________ amount of material needed to sustain the chain reaction is called the critical mass. The critical mass depends on the number of neutrons produced by each fission and on the concentration and shape of the uranium material.
BIOLOGICAL EFFECTS OF RADIATION:
The increased pace of synthesis and use of radioisotopes has led to increased concern about the effects of radiation on matter, particularly in biological systems.
Alpha, beta, and gamma rays (as well as X-rays) possess energies far in excess of ordinary bond energies and ionization energies. Consequently, these forms of radiation are able to fragment and ionize molecules, generating unstable, highly reactive particles as they pass through matter.
The resultant radiation damage to living systems can be classified as either somatic or genetic.
Somatic damage affects the organism during its own lifetime.
Genetic damage, as the term applies has a genetic effect; it harms offspring through damage to genes and chromosomes, the body's reproductive material. Genetic effects are more difficult to study than somatic ones because they may not become apparent for several generations.
Somatic damage includes "burns," molecular disruptions similar to those produced by high temperatures. It also includes cancer.
CANCER is brought about by damage to the growth-regulation mechanism of cells, which causes them to reproduce in an uncontrolled manner.
In general, the tissues that show the greatest damage from radiation are those that reproduce at a Rapid Rate, such as bone marrow, blood-forming tissues, and the lymph nodes.
Leukaemia, which is characterised by excessive growth of white blood cells, is probably the major cause of cancer problems associated with radiation.
PRACTICE PROBLEMS: (E = mc2: Recall: c = 3.00 x 108 m / sec, and 1 Joule = 1 kg * m2 / sec2)
I. Calculate the amount of energy (in kJ) that is released in a nuclear reaction when the mass loss is 3.00 kilograms?
II. Calculate the mass (in grams) of a nuclei that was lost when 3.33 x 1015 kilojoules are released.
HOMEWORK PROBLEMS:
4a. Calculate the amount of energy (in kJ) is released in a nuclear reaction if the mass loss is 1.68 x 10-4 grams?
4b. One mole of radium-226 decays by alpha emission to yield 4.8 x 108 kJ of energy. Calculate the energy that is released when 1 gram of radium-226 decays? (The nuclear mass of radium-226 is 225.9771 grams / mole)
4c. When one mole of radon-222 decays by alpha emission, 5.4 x 108 kJ of energy are released. Calculate the mass that was converted into energy for this reaction?