# Radioactive decay characteristics as measured by a dosimeter

• B
If I put a dosimeter 1 meter away from a gamma sample that starts decaying at the moment I switch on the dosimeter then how would I measure the dose level received by the dosimeter, would it gradually decrease over the first half life or would it stay the same throughout the first half life until the end of the half life?

I ask this because I know isotopes have a exponential rate at which they decay , as in the majority of atoms can decay within the first part or the last part of the half life but how does that translate into actual levels seen by dosimeter?

If I put a dosimeter 1 meter away from a gamma sample that starts decaying at the moment I switch on the dosimeter then how would I measure the dose level received by the dosimeter, would it gradually decrease over the first half life or would it stay the same throughout the first half life until the end of the half life?

I ask this because I know isotopes have a exponential rate at which they decay

The decrease of dose level would be gradual and continuous.

jtbell
Mentor

It shows the amount remaining undecayed as time passes. The decay rate (number of decays per second) follows a similar curve because it's proportional to the remaining amount at every point in time.

Staff Emeritus
2021 Award
Let's be careful here. The dose is integrated so will always increase. The rate of dose will decrease exponentially.

PSRB191921
Well I was thinking in terms of real time radiation strength received by dosimeter rather than an accumulated dose of a person over a time interval.
I understand the dose decreases exponentially as it halves after each half life so 1/4 is left after the second half life but I was wondering how it decreases specifically within the margin of one half life, more linearly or also exponentially ?

jtbell the graph you referred to, does it mean that the first half lifes decay almost linearly within the margin of half life itself and the later ones decay more exponentially within the same margin of that half life?

mfb
Mentor
Don't call it dose if you mean the dose rate. That's like taking about the maximal distance of car if you mean the top speed.
more linearly or also exponentially ?
The dose rate decreases exponentially. That is a general statement that applies to all times. There is nothing special about the half-life time.