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More Teaching Ideas for Kids (and Adult
Gene Carbaugh,
Re your concept, perhaps you would review a draft of a "decay scheme play"
(use a monospace font for the table).
> 1. Simulated Unstable Isotopes and Radioactive Decay
>
> I haven't used this yet but will throw it but will probably try it at
> the next suitable class opportunity.
>
> Create groups of 8-10 kids. Each group gets a sheet of newspaper on
> the floor. They then have to try to have everyone in the group
> standing on the sheet simultaneously. Let them try to figure out how
> to do it. They may try piggy-back, one-foot balancing, basket holds
> with arms, etc. Ideally, once they are in position time them for how
> long they can hold it. As kids lose their balance and fall off, note
> the time each one falls off. Note particularly the time to when there
> are only half of them left.
>
> You can go several directions with this. The kids on the newspaper
> represent an unstable atom. As each kid falls off, this can represent
> a radioactive decay to a more stable condition. When half of the kids
> have fallen off, you can say the half-life for that group was some
> time and compare it with another group. There will be two basic kinds
> of "decay particles" - boys and girls. This can lead to the
> discussion of different types of radiation.
>
> Gene Carbaugh
> Internal Dosimetry
> Pacific Northwest National Laboratory
> eh_carbaugh@pnl.gov
=================================================================
Jim Muckerheide Draft 2 August 24,
1995
Decay Chains: Demonstrating the U-238 decay series; and the primary source of
radium and radon
A "Play" with 20 students representing 40 U-238 atoms
(the 20 student "atoms" will decay in 1 half-life of U-238 -- 4.5 billion
years) [ include a U-238 decay scheme; also the thorium, etc decay schemes for
info ]
In 30 minutes, 20 students "decay" at, either: 1.5 min each, (or with advanced
students use the change in mean decay time (decay rate) due to the decay loss
of 1/2 the activity, the end rate is 1/2 the start rate, e.g., start at 1 min
after first decay, and end at 2 min between decays -- this is non linear which
may be plotted (a factor of 2 over 30 min on semi-log paper) to establish the
times.
[ a decay chart may be included ]
The students make up the cards as identified below, referring to the U-238
decay scheme.
The Play
1. Students assemble in one corner area of the room (representing the earth,
soil/rock, average about 2 ppm uranium).
2. Establish an order for decay, (or a method of random selection - teacher
directed, student tag, or other selection process) to identify the next atom
to decay.
3. At each 1.5 min, or by the decreasing decay rate, the student U-238 atom
DECAYS (releasing decay energy as an alpha or beta, plus many gammas) in each
decay, and becomes a new atom(s), (s/he changes the card).
4. Each group progressively "decays" following the table below, with reactive
and gaseous atoms "released" as noted.
[ While the total number of atoms is different, the "radioactivity" measured
in decays (or disintegrations) per second for each nuclide becomes the same as
the U-238 decay rate, since the same number of each nuclide are being
continuously created as are decaying. (But short-half-life atoms have many
fewer atoms for the same numbers of decays.) That's why the source of radium
(1600 year half-life) and radon, 3.8-day half-life, never decays away. They
are constantly released from the earth. This is "secular equilibrium". ]
Students make cards for each of the following decay steps/groups with the
following data:
[ Option: Add total gamma energy? And total decay energy? For each. ]
Under "No." is the number of student "atoms" that becomes the "steady state"
total based on the half-life of the atom/group of atoms.
Under "Change sequence" is the rate of "decay" based on the number in the
group at the time. The total number of atoms in a group "builds up" as some
decay until the rate of both increase and loss is the same ("secular
equilibrium").
Group Nuclide(s) Half-life Decay mode/energy* No. Change
sequence * does not include gammas
1. U-238 4.5 billion yr alpha / 4.2 MeV 0 1.5 min
(or)
2. The-234 24 days beta / .2 MeV and .1 MeV 1 1 + 15
sec Pa-234m 1.2 min beta / 2 MeV
Pa-234 6.7 hr beta / 0.2 MeV
3. U-234 245 thousand yr alpha / 4.7 MeV 5 2 + 45
sec 3 +
30 sec 4
+ 15 sec
5 + 10 sec
4. The-230 80 thousand yr alpha / 4.6 MeV 4 2 + 30
sec 3 +
15 sec 4
+ 10 sec
5. Ra-226 1600 years alpha / 4.8 MeV 3 2 + 20
sec 3 +
10 sec
"Atoms" decaying to radium, due to its greater chemical activity, may (not
necessarily) move with groundwater through the soil/rock, and may (not
necessarily) emerge with well water and surface water - [ the students move
along one side of the room ] The radium is available to be ingested with
drinking water and other pathways.
6. Rn-222 3.8 days alpha / 5.5 MeV 1 1 + 15
sec
"Atoms" decaying to radon, as a noble gas, lose chemical bonding in the
soil/rock/water, and may (not necessarily) move through the soil/rock/water
into the air [ students move away from the corner/wall into the room space,
"floating free" ] The radon is available to be inhaled (though usually exhaled
again except for the few that decay while in the lungs).
7. Po-218 3.1 min alpha / 6.0 MeV 1 1 + 5
sec Pb-214 27 min beta / 0.7 and 1.0 MeV
Bi-214 20 min beta / 1 to 3 MeV
Po-214 .00016 sec alpha / 7.7 MeV
"Atoms" decaying to the radon decay products (radon "daughters" or "progeny")
are no longer a noble gas, but they are "ionized" therefore have an electric
charge and "stick" to other materials, usually dust particles in the air
(where they are available to be inhaled), or to other surfaces, especially
electrically charged surfaces (like a TV screen). This is the primary source
of the radon "lung dose".
8. Pb-210 22 year beta / <0.1 MeV 2 1 + 30
sec 2 +
15 sec
9. Bi-210 5 days beta / 1.2 MeV 1 1 + 45
sec Po-210 138 days alpha / 5.3 MeV
10 Pb-210 stable