So, I already asked a question on the topic, that helped me understand some more.
Now, here i find myself blocked again.
I don't know how to solve the following problem:

In a basement, you notice a radioactive Activity of $$A \; Bq\cdot m^{-3}$$ of 222Rn nuclids. $$A$$ is constant.
The question is the following: How many moles of Rn should be added at the end of each day, to keep $$A$$ constant, assuming no Rn is leaving the Room.

Now, to me it really doesn't make any sense. Since the decay is exponential. Any quantity i add would decay exponentially.

Now, It's clear to me that is i add a small enough quantity with the halflife value of Rn and that activity value, $$N(t)$$ the quantity of Rn nuclids decreases by such a small amount that i am tempted to just add the quantity that was lost in a day at the start of every new day. Basically saying that on this scale, we can say that $$A$$ is constant and by replenishing the lost Rn amount, we keep it in that "constant" zone. Is that correct ?
Because mathematically, it really can't be that an exponential process would be kept on a constant level, by adding a constant value at regular intervals.

• If you measure a constant rate of particle decays, it means that the lifetime of particle A is so large, more than a year ( see en.wikipedia.org/wiki/Island_of_stability ) , so for your basement experiment the rate is constant . . If you measure in day intervals 222Rn has a lifetime of 3.8 days, you should see the decay curve. – anna v Oct 15 at 9:54