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Nuclear Packet Radiation
last updated: 06/03/09
CHE 104 Packet 3 1
Concept Area I: Terminology
alpha, , particle band of stability beta, , particle binding energy carbon dating chain reaction electric force fission fusion gamma, , ray half-life mass defect nuclear reaction nuclear stability nucleon positron emission radiation radioactive decay series radioactivity radioisotope shielding strong nuclear force transmutation
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Concept Area II: Different Types of Radiation
a. You should be able to identify the three different main types of radioactivity: , , and . b. You should be able to identify the relative ease of penetration of the three main forms of radioactivity. c. You should be able to identify the danger to living tissue for the three main forms of radioactivity when outside or inside the tissue.
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First, Radiation is a Natural Phenomenon; however, humans can also create it.
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How much radiation are we exposed to on average?
Radiation exposure depends on where you live, what you do, and what medical procedures you have done. Let's look at two other books' tables on annual exposure...
Timberlake page 112
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Sources of radiation we're exposed to:
+ 292
+ 67
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Sources of radiation we're exposed to continued:
Risk of Radon Exposure
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So, what are the three main kinds of radiation?
alpha, :
beta, : gamma, :
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Alpha radiation is the _________, so it can be stopped by the __________ barrier. Beta radiation is the _______________ one. It can be stopped by a block of wood, thin sheets of metal. Gamma radiation is the __________. It's actually a form of ________. It needs several centimeters of lead to be stopped.
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Timberlake page 101
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(g/particle)
Actual Mass
2 4 0 1 0 +1
6.651024 9.111028 9.111028 0 1.671024 1.671024
Timberlake page 100
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Penetrating power of radioactive particles:
The penetrating power of radioactive particles can be measured in terms of what depth of water it takes to stop 50% of the radiation. Why water? Water is the main component of living tissue! Alpha radiation has the highest mass and charge and thus the lowest penetration about 0.03 mm. Beta radiation penetrates about 2 mm. Gamma rays have the lowest mass and thus the highest penetration at about 10 cm.
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So which form of radiation is the most dangerous...
outside the human body
What type of radiation is worst to sit beside? Why?
inside the human body
What type of radiation is worst to ingest? Why?
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Note about cancer radiation treatment: The radiation used in cancer treatment is given in units of mCi (millicuries) which are not easily converted to rems. However, thyroid cancer is given the highest dose amount - as high as 75 mCi if over 50 mCi are given the person must stay in the hospital to limit others exposure to radiation. Most other cancers seem to use less than 10 mCi per dose and usually there are few if no precautions for exposing others to the radiation used for treatment.
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So, how is radiation measured?
curies, Ci indicate that 3.71010 disintegrations per second have occurred becquerel, Bq indicate that one disintegration per second has occurred (SI unit) rad stands for radiation absorbed dose, and indicates how much radiation one gram of material has absorbed rem stands for radiation equivalent in humans, and shows the true amount of radiation absorbed since alpha, beta and gamma radiation are absorbed differently
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How do we detect radiation? Or, how a Geiger counter works:
The radiation ionizes the gas inside the detector. The electrons released from the ionization are detected by the voltmeter. We hear the detections as clicks. A Geiger counter only tells us radiation of some form is present. It can not differentiate between the different types of radiation.
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Concept Area III: Nuclear Reactions (Alchemy!)
a. b. c. d. e. f. You should understand what determines the stability of the nucleus, binding energy, mass defect, energy released in nuclear reactions. You should be able to explain what happens to the nucleus with the loss of subatomic particles. You should be able to complete nuclear reactions. You should be able to explain the difference between nuclear fission and fusion. You should be able to identify particles used in artificial transmutation and explain what each does. You should understand what a nuclear chain reaction is.
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Comparison of Chemical and Nuclear Reactions
Chemical Reactions One substance is converted into another, but atoms never change identity (transmutate). Only valence electrons are involved as bonds break and form. Reactions are accompanied by relatively small changes in energy and no measurable changes in mass. Reaction rates are influenced by temperature, concentration, catalysts, and the compound in which an element occurs. Nuclear Reactions Atoms of one element typically are transmutated into atoms of another element. Protons, neutrons, and other particles are involved; valence electrons rarely take part. Reactions are accompanied by relatively large changes in energy and measurable changes in mass. Reaction rates are affected by number of nuclei, but not by temperature, catalysts, or normally the compound in which an element occurs.
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Nuclear Decay Series
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Spontaneous Fission...
We know according to the Rutherford's nuclear atom view, all the protons and neutrons are at the center of the atom. We also know that like charges (like protons) repel each other.
So why do only some atoms (usually the big ones) spontaneous "fall apart" into other atoms? Why don't all atoms (like the small ones) fall apart too?
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Why does the nucleus of any atom stay together and not fly apart?
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Okay, so if nucleons like each other, why is atomic size limited?
The attractive strong nuclear force is only good for adjacent (touching) nucleons. The repulsive electrostatic force works over great distances!
So, the strong nuclear force can only compensate for (or overcome) the electric force for smaller atoms.
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Stability of Atomic Nuclei In this chart, each circle is a known isotope. The blue and green circles are stable or nonradioactive isotopes; the red circles are radioactive isotopes they spontaneous "fall apart". Notice very few of the known isotopes are stable!
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Nuclear Binding Energy
An atomic nucleus can contain as many as 83 protons and still be stable beyond 83, all atoms thus far discovered are unstable. For stability, the nuclear binding force must be greater than the electrostatic force. This can be determined by the nuclear binding b energy, E . The nuclear binding energy, is defined as the amount of energy needed to separate the nucleus of an atom into its protons and neutrons.
b
If E is positive, energy is needed to separate.
b
If E is negative, energy is released when separated thus spontaneous thus is happens readily, and we get radioactive atoms!
We also need to consider mass defect. The massCHE 104 Packet 3 26 of a nucleus is
Note that the nucleons for 56Fe have the least mass because 56Fe has the most binding energy keeping it together; thus it is the most stable atom. The more energy used to hold the nucleons together, the greater the mass defect in the nucleons. Since there are isotopes to either side of our most stable nucleus, this implies that there are two types of nuclear reactions: fusion and fission.
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This chart shows the binding energy versus atomic mass.
In fusion, nucleon is mass usually lost as isotopes "fuse" together because more energy is usually needed to keep the nucleons together in the larger isotopes.
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This chart shows the binding energy versus atomic mass as well a few isotopes are labeled.
Scientists predict that there will be islands of stability in the larger atomic numbers we just haven't found where these islands are yet. In fission, nucleon mass is changed as isotopes split apart. They gain mass if less binding energy is needed and lose mass if more binding energy is needed.
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Balancing Nuclear Reactions
In a balanced nuclear equation, the sum of the mass numbers of the reactant and the products are equal. sum of the atomic numbers of the reactant and the products are equal. and the atomic symbol must match the atomic number! For example:
251 98
Cf
247 96
Cm + He
4 2
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Types of Natural Nuclear Reactions
alpha emission or alpha decay
First recognized in 1903 by Rutherford and Soddy.
Note that mass number (A) goes down by 4 and atomic number (Z) goes down by 2. Nucleons are rearranged but conserved. Called alpha emission/decay because the atomic isotope transmutates to another atomic isotope by emitting an alpha particle.
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Alpha Decay
Timberlake page 103
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Complete the following alpha decay nuclear equations:
236 1. 92
U He + ____
4 2 4 2 214 82
1.
____ He+
Pb
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Types of Natural Nuclear Reactions
beta emission or beta decay
Note that mass number (A) is unchanged and atomic number (Z) goes up by 1. How does this happen?
Called beta decay because the atomic isotope transmutates to another atomic isotope by emitting an beta particle (an electron from the nucleus!).
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Beta Decay
Timberlake page 105
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Complete the following beta decay nuclear equations:
131 1. 53
I e + ____
0 -1
1.
____ e+ He
0 -1 3 2
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Other Types of Nuclear Reactions
Positron Emission: a positive electron
207
207
K-capture/e capture : the capture of an electron from the first shell of electrons (used to be called the K shell)
This occurs because an electron and proton combine to form a neutron. 0 e + 1 p 1 0n -1 1
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Other Types of Nuclear Reactions
Gamma emitter: only gamma radiation is emitted. Rare to occur without alpha or beta radiation emitted also.
99m 43
Tc Tc +
99 43
The "m" after the 99 in the reactants means that the Tc is in an excited metastable state.
Thyroid imaging using 99mTc
normal asymmetric scan indicates disease
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Summary of Nuclear Reactions:
Timberlake page 107
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Complete the following nuclear reactions:
1. 37
18
Ar + e ____
0 -1
1. 35
16
S Cl + ____
35 17
1.
____ + B
0 +1 11 5
1.
____ + Si
0 +1 30 14
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Artificial Nuclear Reactions
Rutherford identified the first artificial nuclear reaction with alpha particles (remember the gold foil?). In 1919, he noticed the following reaction: 4 He+14 N 17 O+1 H 2 7 8 1 Later Cockcroft and Walton used artificially accelerated protons to cause nuclear reactions: 7 Li+1 p 2 4 He 3 1 2
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In 1934, Fermi was able to use low energy neutrons to transmutate elements: 31 1 32 15 P + 0 n 15 O + Many of the elements greater than 92 began with the above reaction to form various isotopes that then naturally decayed to the new elements: 238 1 U + 0 n 239 U 92 92
239 92 239 93 0 U 239 Np + -1 e 93 0 Np 239 Pu + -1 e 94
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Nuclear Fission splitting nuclei
So far in our nuclear reactions, one element has transmutated into another element. However, sometimes we can split one atom into two new atoms nuclear fission! In samples of uranium that had been bombarded with neutrons, barium was found. At first they weren't sure why...
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Nuclear Fission!
bottom image similar to Timberlake page 121
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Nuclear fission chain reactions have three general steps:
Initiation: the reaction of a single atom is need to start the chain. Fission of 235U is initiated by the absorption of a neutron. Propagation: This part of the process repeats itself over and over, each step producing more product. The fission of 236U releases neutrons that initiate the fission of other uranium atoms. Termination: Eventually the chain will end. This could come about if the reactant is used up, or if the neutrons that continue the chain escape from the sample without being captured by 235U.
Timberlake page 121
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Nuclear Fusion fusing nuclei together
In fission we split nuclei into multiple atoms. In fusion we put together/fus...