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Physics notes chp9-10

Half life of a radioactive isotope: time taken for the mass of the isotope to decrease to half the initial
mass/ number.

Mass remaining: 0.5^n x mass

where n is the number of half lives.

Activity of radioactive isotope (Bq) : number of nuclei of the isotope…

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Carbon dating ­ in living things. Carbon ­ 14 ­ isotope.
C-14 formed in atmosphere by cosmic rays knocking out neutrons from nuclei.

Argon dating ­ rocks trap argon gas. Happens when nucleus captures inner shell electron.
by electron capture of beta minus decay.

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Radioactive tracers ­ tracers follows path of substance through a closed system.
Radioactive tracer in isotope:

Has half life stable enough for necessary measurements to be made and short enough to
decay after use.
Emits beta/gamma radiation so detected outside flow path

Choice of isotope for application determined by:


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Light isotopes ( Z: 0-20)- stable nuclei follow N=Z line

When Z>20, N:Z increases. Extra neutrons help bind nucleons together with electrostatic repulsive

Alpha emitters ( Z=60) ­ more neutrons than protons ­ unstable because of strong nuclear force
between nucleons can't overcome electrostatic forces between protons = alpha…

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Nuclear density

A is the mass number of the isotope/ atom.
u ( MeV) and r0 are constants that are given on the formula sheet.


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