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Radioactive Decay Laura, Tanisha and Katie
Radioactivity? What’s that? •Radioactivity is the result of disintegration or decay of an unstable nucleus that requires no external force. •Energy and matter is released from the nucleus.
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Artificial Radioactivity •There are many unstable isotopes found throughout nature, but others can be produced in a laboratory by nuclear reactions. •Unstable isotopes that are produced in domains are known as ARTIFICIAL RADIOACTIVITY
Stable and Unstable Nuclei •Stable Nuclei: Stable nuclei tend to have the same number of neutrons and protons up to a mass number A of 30 or 40. •Unstable Nuclei: as the nucleus gets bigger, more and more protons repel each other so more neutrons are needed to hold the nucleus together. If the atomic number is too large, this becomes impossible. As a result there aren’t any completely stable nuclides above Z=83
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3 types of radiation Alpha… Beta… Gamma…
Alpha Radiation and Decay Alpha particles are nuclei of helium atoms. They are very tightly bound and not very energetic (they're so weak, they can barely get through paper)
Alpha decay happens because a strong nuclear force can’t hold large nuclei together.
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This is an example of an equation representing what alpha decay would look like.
Take a minute to look at it. What observation can you make?
Transmutation In this example we consider 222/88 Ra the parent nucleus, while 218/86 Rn is the daughter nucleus. See how the mass number (top number) decreases by 4 and the atomic number (bottom number) decreases by 2. That happens in every alpha decay. Once you subtract 2 from atomic number, you take the new atomic number and find it on the periodic table, this is your new element (daughter nucleus) in the in the final equation. The parent nucleus has a greater mass than the daughter nucleus. When the numbers decrease it takes away energy to create new numbers, this is called extra energy. The alpha particle takes this extra energy away as kinetic energy. Transmutation is what is happening to the elements above, it is the process of one element changing into another element.
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The standard equation for Alpha Decay is...
Where… X= Parent nucleus Y= daughter nucleus Z= Atomic Number A= Atomic Mass
Beta Radiation and decay There are two types of beta decay, beta plus decay and beta minus decay.
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This is an example of a Beta
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Gamma Decay When a nucleus decays by alpha or beta emission, the daughter is often left in an excited state. The nucleus then emits a gamma ray to drop down to its ground state. When it drops down to its ground state it emits a photon, however, a gamma ray photon often has much more energy than a photon emitted by an atom.
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In radioactive samples, not all of the nuclei decay at the same time. Instead, they decay one at a time over a period of time. This is a random process, and we use the term half-life to describe it.
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The half-life is the time it takes for the parent nucleus to decay into the daughter nucleus. These times all vary by the isotope and can range from fractions of a second to thousands of years.
The quantity of a sample remaining is one half-life to the exponent time interval divided by the half-life all times the quantity of the original sample. If we were to put all that information into an equation, it would look like this...
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Where… N = quantity of sample remaining (kg, Moles, Bq) No = quantity in original sample (kg, Moles, Bq) ∆t = elapsed time (seconds,minutes,years) T1/2 = half life (seconds,minutes, years)
In case you didn't understand the first explanation of half life, here is Bill Nye explaining it once again… Bill Nye Explains Half Life - YouTube
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Logarithms… Exponent Form y = b^x
Logarithmic Form logby = x where x = log(y)/log(b)
A 15 kg sample of Lithium has a half-life of 30 minutes. How long will it take to decay to 3 kg?
Step 1: Step 2: Step 3: Step 4: Step 5:
N=No(½)t/(t 1/2) 3=15(½)t/30 15 (0.2=(½)t/30) log log(0.2)=log(½)t/30 log(½) ( 2.32= t/30 ) x 30 t= 69.6 min
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The End
Bibliography -
radioactive decay." World Encyclopedia. 2005. Encyclopedia.com. 31 May. 2015 . McGraw-Hill Ryerson. Physics. N.p.: n.p., 2003. Print.
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