Answer:
C. Barium-137
Explanation:
We have barium-137
- Required to identify the radioisotope that undergoes gamma decay to produce Ba-137.
We need to know that when a radioisotope undergoes gamma decay its mass number and the atomic number remains unchanged.
- The atomic number of Ba-137 is 56 while the mass number is 137.
- We need to identify the choice whose atomic number is 56 and mass number is 137.
In this case,
- Cesium-137 has a mass number 137 and atomic number 55
- Cesium-138 has a mass number 138 and atomic number 55
- Barium-137, has a mass number, 137 and atomic number 56.
- Barium-138 has a mass number 138 and atomic number 56
Therefore the correct choice is C. Barium-137
