# Finding the quantity of a radioactive substance and standard units

When finding the quantity of a radioactive substance remaining after a half life of time t, using the formula, T1/2=.693/lambda. do u have to convert the time to standard units, the second, if it is in mins, or yrs or days or months watever?

## Answers and Replies

EIRE2003 said:
When finding the quantity of a radioactive substance remaining after a half life of time t, using the formula, T1/2=.693/lambda. do u have to convert the time to standard units, the second, if it is in mins, or yrs or days or months watever?

No, but t and T1/2 has to be in same units.

OlderDan
Science Advisor
Homework Helper
EIRE2003 said:
When finding the quantity of a radioactive substance remaining after a half life of time t, using the formula, T1/2=.693/lambda. do u have to convert the time to standard units, the second, if it is in mins, or yrs or days or months watever?

Lambda will have the appropriate units of reciprocal time included. If you know the half life and solve for lambda, the answer will have the correct units for lambda. If you are given lambda and calculate T1/2, it will have the correct units. If you are given lambda without units, you don't have enough information to find T1/2.