Predict the diminishing radioactivity of a radioisotope

Description

HP-15C Owner's Handbook - Pages 093-094

A radiobiology lab wants to predict the diminishing radioactivity of a test amount of 131I, a radioisotope. The formula for Nt, the amount of radioisotope remaining after t days, is

Nt = N0(2-t/k),

where k = 8 days, the half-life of 131I, and N0 is the initial amount.
The program assumes t1 – the first day of measurement – is stored in R0, N0 – the initial amount of isotope – is stored in R1, and the limit value for radioactivity is stored in R2.

Note: For this program, the "Pause" value should be set to the default of 1000 ms to see the intermediate results.

Example:
2 STO 0
100 STO 1
50 STO 2
f A

Program Resources

Labels

Name Description
 A Loop over the days

Storage Registers

Name Description
 0 Day counter
 1 Initial amount of isotope
 2 Limit value for radioactivity

Program

Line Display Key Sequence
000
001 42,21,11 f LBL A
002 45 0 RCL 0
003 42 31 f PSE
004 8 8
005 10 ÷
006 16 CHS
007 2 2
008 34 x↔y
009 14 yˣ
010 45,20, 1 RCL × 1
011 42 31 f PSE
012 45 2 RCL 2
013 43,30, 9 g TEST x≥y
014 43 32 g RTN
015 3 3
016 44,40, 0 STO + 0
017 22 11 GTO A