Section 8: Program Branching and Controls 93
Examples
Example: Branching and Looping
A radiobiology lab wants to predict the
diminishing radioactivity of a test amount
of
131
I, a radioisotope. Write a program to
figure the radioactivity at 3-day intervals
until a given limit is reached. The formula
for N
t
, the amount of radioisotope
remaining after t days, is
N
t
= N
o
(2
−t /k
),
where k = 8 days, the half-life of
131
I, and N
0
is the initial amount.
The following program uses a loop to calculate the number of millicuries
(mCi) of isotope theoretically remaining at 3-day intervals of decay.
Included is a conditional test to check the result and end the program
when radioactivity has fallen to a given value (a limit).
The program assumes t
1
—the first day of measurement—is stored in R
0
,
N
0
—the initial amount of isotope—is stored in R
1,
and the limit value for
radioactivity is stored in R
2
.
| ¥
000-
Program mode.
´ CLEAR M
000-
(Optional.)
´ b A
001-42,21,11
Each loop returns to this
line.
l 0
002- 45 0
Recalls current t which
changes with each loop.
´ ©
003- 42 31
Pauses to display t.
8
004- 8
k.
÷
005- 10
”
006- 16
−t/k.
2
007- 2
®
008- 34
y
009- 14
2
−t / k
.
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