Discussion question: If a nucleus undergoes radioactive decay it must be older than the other nuclei in the sample that haven’t decayed.
A. TrueB. False
Types of radioactive decay Gamma Beta (+,-, e.c.) Alpha
Neutron emission Fission Fusion
http://ie.lbl.gov/education/isotopes.htm
Beta Decay – electron and positron decay
Changes a proton to a neutron or a neutron to a proton
189F + e
β- 146C
e.c.
14162Smβ+
Why do some things decay, other don’t?
MagicNumbers
Image from http://pms.iitk.ernet.in/ICT/physics_courses/akj/AKJain_IITR_Ch_2.htm
Why do some things decay, other don’t?
MagicNumbers
Image from http://pms.iitk.ernet.in/ICT/physics_courses/akj/AKJain_IITR_Ch_2.htm
Radiometric Dating Carbon Dating
– Cosmic rays release neutrons– 14N + n → 14C + 1H
Half life of ~5760 years– Compare carbon-12 to carbon-14 ratio– Limitations
Must be organic Has the ratio of C-12 to C-14 always been
the same?– Calibration
50,000 years limit (not much C-14 left)
2 Nephi 2:26And the Messiah cometh in the fulness of time, that he may redeem the children of men from the fall. And because that they are redeemed from the fall they have become free forever, knowing good from evil; to act for themselves and not to be acted upon, save it be by the punishment of the law at the great and last day, according to the commandments which God hath given.
22688Ra eventually becomes 206
82Pb.
What is released in this process? A. only alphasB. only betasC. both but more alphas than betasD. both but the same number of alphas
and betasE. both but more betas than alphas
Penetration Depth Alpha– only a few cm through air Beta—only through air—blocked by
paper or sheet of metal Gamma rays—short wavelength light
—penetrate several cm lead or a meter of concrete. Easily penetrates the skin and interacts with human cells—these are the dangerous ones.
What has to be true for a particular type of nuclear
decay to happen? Conservation of . . .
– Energy, momentum, angular momentum Compare rest energy OK if we go down in energy – turn into
kinetic– Lepton number, Baryon number, …
Force to make it happen
For radioactive decay where No
is the number of nuclei you start with and N is the number of nuclei after a time t
toeNN
How do I solve for λ?
Discussion question: Over the course of 3 hours, 15% of a radioactive material decays. What is its half-life?
A. 4.1 hrsB. 12.8 hrsC. 24.0 hrsD. 68.6 hrsE. 84.2 hrs
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