# If an x-ray source has an activity of 10^9 Becquerel then by the relation: Number of photons=Activity ∗ yield is the Number of photons equal to 10^9?

If an x-ray source has an activity of ${10}^{9}$ becquerel then by the relation:

is the Number of photons equal to ${10}^{9}$ ?
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ehedem26
A Becquerel is one radioactive decay per second. That is one nucleus decays per second, so ${10}^{9}$ Becquerels means ${10}^{9}$ nuclei decay each second.
But we don't necessarily get a photon from every decay. It's very common for nuclei to have different decay pathways available so some decays may generate photons and some may not. The fraction of decays that create a photon is called the yield (more precisely the photon yield).
Although it's probably a minor effect we should also bear in mind that not all the photons will escape to be detectable. For example some may Compton scatter off electrons in the bulk of your sample. This may reduce the yield further.
So in this case the number of photons detected per second is ${10}^{9}$ multiplied by the yield.