The key difference between specific activity and total activity is that the specific activity can be taken by dividing the total activity by the total isotope amount, whereas the total activity is the total isotopic activity in the volume of the fraction that is used in the measurement, multiplied by the total volume of the sample.
In brief, specific activity can be described as the activity per quantity of a radionuclide, while total activity can be described as the sum of all activity of all the isotopes that are present in a given sample
CONTENTS
1. Overview and Key Difference
2. What is Specific Activity
3. What is Total Activity
4. Specific Activity vs Total Activity in Tabular Form
5. Summary – Specific Activity vs Total Activity
What is Specific Activity?
Specific activity can be described as the activity per quantity of a radionuclide. It is a physical property of radionuclides. Moreover, activity is a quantity that is related to radioactivity. The SI unit for activity is becquerel, Bq. The unit Bq refers to the number of radioactive transformations per second that exists in a particular radionuclide. However, the older unit of measurement that was used for this was Curie (Ci).
Typically, the probability of radioactive decay for a given radionuclide is a fixed physical quantity; we can say that the number of decays that exists per given time for a specific number of atoms (atoms belonging to the radionuclide) is a fixed physical quantity. Therefore, the specific activity can be described as the activity per quantity of atoms belonging to a particular radionuclide. In common, the specific activity is given by Bq/kg. However, we should not be confused with the amount of specific activity and the level of exposure to ionizing radiation. Therefore, the exposure or absorbed dose should also not be confused with these terms.
What is Total Activity?
The total activity can be described as the sum of all activity of all the isotopes that are present in a given sample. According to thermodynamics, it refers to the measure of the effective concentration of a species (in this context, isotopes) in a mixture. Moreover, the chemical potency of the chemical species depends on the activity of a real solution in a similar way to that of the concentration of an ideal solution.
What is the Difference Between Specific Activity and Total Activity?
The terms specific activity and total activity are used to describe the activity of radioisotopes. In fact, the key difference between specific activity and total activity is that specific activity can be taken by dividing the total activity by the total isotope amount, whereas total activity is the total isotopic activity in the volume of the fraction that is used in the measurement, multiplied by the total volume of the sample.
Below is a summary of the difference between specific activity and total activity in tabular form for side by side comparison.
Summary – Specific Activity vs Total Activity
Specific activity can be described as the activity per quantity of a radionuclide. Meanwhile, total activity can be described as the sum of all activity of all the isotopes that are present in a given sample. Therefore, the key difference between specific activity and total activity is that specific activity can be taken by dividing the total activity by the total isotope amount, whereas total activity is the total isotopic activity in the volume of the fraction that is used in the measurement, multiplied by the total volume of the sample.
Reference:
1. “Activity – Specific Activity.” Nuclear Power.
2. “Activities and their Effects on Equilibria.” Chemistry Libretexts
Image Courtesy:
1. “Preparing medical radioisotope targets” By Brookhaven National Labor (CC BY-NC-ND 2.0) via Flickr