Energy Efficiency Tips for Homeowners

[tomcajot]

Homework Statement

Near the Fukushíma nuclear power plant, a fish was caught with a record amount of radioactive 137-Cs of 7.4 megabecquerels per kilogram. Calculate the number of active cesium nuclei in an 800 gram fish.

Relevant Equations

(Don't know how to add LaTeX, the relevant equations will be in the picture in the solution attempt)

 

[Steve4Physics]

Homework Statement:: Near the Fukushíma nuclear power plant, a fish was caught with a record amount of radioactive 137-Cs of 7.4 megabecquerels per kilogram. Calculate the number of active cesium nuclei in an 800 gram fish.
Relevant Equations:: (Don't know how to add LaTeX, the relevant equations will be in the picture in the solution attempt)

View attachment 293787

Hi @tomcajot and welcome to PF.

Here are some points to consider…

Your equation for A(t) is used to find the activity after a given time (t) has elapsed. This isn’t really appropriate in this question (Though the equation can be used if you realize what value to use for elapsed time.)

You have used ‘30’ as the half-life of Cs-137. This is the approximate half-life of Cs-137 in years, Your working implies that you have take t=1 year – i.e. you have assumed the sample has been decaying for 1 year. (The fish will have gone off by then.)

You have also used the half-life in years in an equation where the activity is in Bq (disintegrations per second). So you have a problem with mismatched units.