Physics · nuclei · NEET
No. N is how many un-decayed nuclei are still present (a pure count, no unit). Activity R is how many of them decay each second (unit: per second). They are linked by R = lambda N, but they are different quantities. A sample can have a huge N yet a tiny activity if lambda is very small (long half-life).
No. lambda is a fixed property of the nuclide (probability that one nucleus decays per second) and never changes with time. Activity R depends on how many nuclei are left, so R keeps falling as the sample decays. In R = lambda N, lambda is constant but N and therefore R decrease with time.
lambda is the chance per second that any single nucleus decays. If you have N nuclei, the expected number decaying per second is lambda multiplied by N. So a larger lambda (unstable nuclide) or a larger N (bigger sample) both give a higher activity.
As nuclei decay, N keeps getting smaller. Since R = lambda N and lambda is fixed, a smaller N gives a smaller R. Activity follows the same exponential fall as N: R = R0 e^(-lambda t), and it halves every half-life just like N does.
Yes. If two samples have equal numbers of nuclei but are different nuclides, they have different lambda values. The one with the larger lambda (shorter half-life) has the higher activity, because R = lambda N.
The SI unit is the becquerel (Bq), where 1 Bq = 1 decay per second. A larger practical unit is the curie: 1 Ci = 3.7 x 10^10 Bq.
R = lambda N, where lambda is the decay constant (per second) and N is the number of un-decayed nuclei present. With time it also follows R = R0 e^(-lambda t).
Indirectly yes. More mass means more nuclei N, so a larger activity. But two samples of the same mass but different nuclides have different lambda and so different activity.
Activity halves after each half-life, exactly like N. After n half-lives the activity is R0 divided by 2 to the power n.
Activity is a scalar. It is just a count of decays per second and has no direction.
