c. My father was talking to his friend on mobile phone when I fell from the bicycle.
This sentence correctly uses the past continuous tense ("was talking") for the ongoing action and the simple past tense ("fell") for the completed action.
The sentence with the correct tense and sentence structure is: They were playing football when it started to rain.
This sentence correctly uses the past continuous tense ("were playing") to describe an ongoing action that was interrupted by another action ("started to rain").
Gamma-ray cameras can observe radiations from the radioisotopes that are concentrated in the organs.
In medical imaging, radioisotopes are often used in nuclear medicine to diagnose and treat various conditions.
These isotopes emit gamma rays as they decay, and the gamma-ray camera detects these rays to create images of the organs where the isotopes have accumulated.
The decay constant, λ "lambda", the reciprocal of the mean lifetime (in s−1), sometimes referred to as simply decay rate The mean lifetime, τ "tau", is the average lifetime (1/e life) of a radioactive particle before decay.
