From: Hauser, Michael (MHauser@stlcc.edu)
Date: Thu Feb 13 2003 - 14:44:29 EST
I thought the M&M half-life lab was simple but effective. For an advanced,
kinetics based course, I would consider the following additions. Have the
students graph the natural log of the M&M counts versus time. Since this is
first-order data, the new graph should show y=mx + b behavior (a straight
line). The slope of this line (the "m"), is the rate constant, "k". If the
students use the relationship that half-life for a first-order relationship
is equal to 0.693/ k, they can calculate the "half-life" of the M&Ms. They
will have to assume an arbitrary unit of time like seconds, minutes, days,
years, etc, but the point will be made. Don't forget to mention that the
natural log of "one-half" IS 0.693, hence its appearance in the formula. If
they plot their Ln data, their slope should be very close to the 0.693
value!
Concerning the nuclear radiation lab, this is a neat way to alleviate a lot
of the fears held by the general population of citizens. How appropriate in
this day of "dirty bomb" terrorism threats and irradiated meat in grocery
stores that we explore this topic. I do have a device from Black Cat Systems
that hooks to a laptop and can measure radiation counts. My concerns: The
course literature mentions that only a licensed lab and lab supervisor
should have these materials. Is this true? Does it vary by state? Also, when
you purchase the radiation sources, how long do they last? Do you need to
constantly buy new sources?
Michael Hauser
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