Daniel B. answered • 05/11/21
A retired computer professional to teach math, physics
The rate k being negative means that the quantity is DECAYING.
A positive rate would mean that the quantity is INCREASING.
There are a couple ways to interpret the rate k.
1) Instead of talking about half life as measure of decay,
you could measure it by the percentage that decays per day;
that would be ek.
2) Exponential functions are sometimes visualized using a log-plot:
the scale of the vertical axis is logarithmic.
In such a plot an exponential appears as a straight line and k is
the slope of the line.
By the way, were you actually told to express the constant k as a percentage?
I also find that confusing, because 100% does not represent anything meaningful.
Sometimes decay rate is measured as a percentage using the formula
A(t) = (1-r)^t
In that case r = 0% means no decay, and r = 100% (= 1) means instantaneous decay.
Seta C.
Thank you so much. No, we weren't asked to express it as a percentage or even show the decay rate. But I am doing a report on the use of iodine-131 in medicine for the treatment of thyroid cancer, and one of my paragraphs is on the radioisotope itself. I thought it might be useful to also show the decay rate if someone, like a caregiver, was to be exposed to iodine-13. Do you think it's necessary in this case?05/11/21