Herb Deruyter, Waterloo ON
Teach science as you do science, one variable at a time. Writing advice: One thought per sentence.
Simulating radioactive decay using pasta, reprinted from Chem 13 News, April 2007
High school science labs have access to radioactive sources
through science supply houses, but these isotopes are too longlived to illustrate the concept of half-life in a timely manner. A
simulation of radioactive decay using small dry pasta called
ditalini has given satisfactory results for senior biology,
chemistry and physics classes.
Ditalini are tiny tubes about 4 mm long and 3 mm in diameter. A
close-up of ditalini is shown in Figure 1. This pasta is
convenient to use in the simulation of radioactive decay because
it is economical, reusable and completely harmless.
Fig. 2 illustrates a plot of the number of pieces of ditalini pasta
against the number of the drop. Each successive drop
represents a unit of time. The half-life obtained for this particular
sample is about 4.5 time units. The half-life is the length of time
required for a sample to decline to half its size.
Number of
Ditalini
450
400
350
300
Parent Isotope
Daughter Isotope
250
200
150
100
50
0
0
2
4
6
8
10
Time
12
14
16
18
20
Fig. 2. A plot of student data
Fig. 1.
A Canadian penny is about 1.8 cm in diameter. Note that some
of the pieces of pasta lie on their sides while others stand on
Fig. 3 presents results from 7 replicate sets of student data. All
sets begin with 400 pieces of pasta. Though some variability is
evident the data reflect overall consistency in the rate of decay
and are suggestive of the reliability of the simulation.
end. Sixteen pieces are standing on end in this picture.
The property of the pasta particularly useful for the purposes of
this simulation is that a small fraction of these tubes will stand on
end. If each tube represents an atom of an imaginary radioactive
isotope then tubes that stand on end can represent those atoms
that have decayed into the daughter isotope. The simulation
begins with a count of the pasta in a shallow box. In this
example, students began with a count of 400 ditalini. The box is
swirled to mix the pasta and dropped from a small height of
about 5 to 10 cm. The standing pieces of pasta are counted and
removed, using tweezers, as the daughter isotope. The process
is repeated for 15 to 20 drops. Each drop of the box represents
a fixed unit of time. Table 1 presents a partial listing of data
collected by a pair of grade 12 biology students.
Table 1. Student data are plotted in Fig. 2
Number of
Drops
Number of
Number of
Total Number
Pasta
Pasta
of Pasta
Remaining
Removed
Removed
0
400
0
0
1
322
78
78
2
286
36
114
3
245
41
155
↯
↯
↯
↯
19
51
3
349
20
50
1
350
12 Chem 13 News/March 2009
Number of
Ditalini
450
400
350
300
250
200
150
100
50
0
0
2
4
6
8
10
12
14
16
18
20
Time
Fig. 3. The “decay” of seven replicate sets of ditalini
Data can either be tabulated and plotted manually or logged into
a spreadsheet such as MS Excel. The spreadsheet provides
the additional advantage of collecting student samples into a
larger class data set.
The material required for each pair of students consists of a
handful of pasta, a pair of tweezers and a small shallow
cardboard box. The lid or bottom from a box of greeting cards
works very well.
→
The merits of the simulation are its safety, consistency, low cost
and applicability to a number of science courses. Whether
examining exponential decay of radioisotopes in chemistry and
physics or studying radiometric dating in biology, the simulation
has proved a useful model in each context. ∎
Periodic Hidato winners
The winners for the December 2008 Periodic
Hidato prizes are Tyler Killam from Fiona
Clark’s class at Park View Education Centre in
Bridgewater NS and Brian Lawrence from Pat
Hallquist’s class at Lourdes High School in
Oshkosh WI.
Texting chemistry
Even though I am not from the texting generation, I have
become painfully aware that high school students love to text —
my teenage nieces are obsessed. They may in fact prefer it
over any other type of communication. So let’s bring chemistry
into the electronic age and the texting language.
For those like me, who have embarrassingly never sent a text,
the first few abbreviations are some well-accepted texts to get
you in the mood. Want more? There are 1,000 text message
abbreviations if you search “texting” on webopedia
www.webopedia.com/quick_ref/textmessageabbreviations.asp.
With all these abbreviations, none relate to chemistry. That is
our challenge. I have started you off with some chemistry texts
that I would like to see added to the language. Ask your
students to have some fun and create more chemistry texts and
send them to Jean Hein, [email protected] and TIA (Thanks
in advance).
They and their teachers win Fun Fly Sticks
donated from Educational Innovations. Go to
teachersource.com for more information about
this and other prizes.
Some common texts
Solution:
LOL – Lots of love or Laugh out loud
He
Li
Ti
V
Mn
H
Be
Al
Sc
Cr
N
Mg
B
Si
Ca
O
C
Na
P
K
F
Ne
S
Cl
Ar
PSOS – Parent standing over shoulder
MYOB – Mind your own business
BTW – By the way
CUL8R – See you later
FYI – For your information
Chemistry texts
CYPT – Check your Periodic Table
TSOL – Teacher standing over lab
MYOSF – Mind your own significant digits
UR -273K – You are the coolest (or you are an absolute zero)
BMEq – Balance my equation
LDD – Lewis Dot Diagrams
MOL – Mole obsessed lesson
CTM – Convert to moles
AIU – Always include units
LDT – Lab due tomorrow
RAO – Record all observations
PAIW – Pour acid into water
LEO GER – Lose electrons, oxidation; Gain electrons, reduction
BYOG – Bring your own goggles
WITWINC?– What in the world is not chemistry?
[JLH]
March 2009/Chem 13 News 13