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# Why is specific nuclear activity (Bq/kg) not considering the surface area (cm^2)?

2018-06-05 08:20:31

I have some basic questions regarding nuclear radiation:

How come the specific activity (Bq/kg) only depends on the mass number and halftime of the emitter?

Therefore, the emitted ions (let's say by an alpha source) are a function of the mass number, halftime and the specific energy of the emitter, right?

Why the surface area is not part of the equation? How do the alpha particles penetrate from the the "inside" of the emitting material to the surface?

Thanks a lot,

Daniel

The specific activity is the number of decays per second, not the amount of radiation emitted from some object. Therefore the absorption of emitted radiation within the object is not relevant - the same number of nuclei decay per second regardless of whether the decay products escape the sample or not.

The specific (meaning per unit mass) activity relates to the number of decays per unit time (number of alpha particles emitted per unit time) and it depends on the number of unstable nuc

• The specific activity is the number of decays per second, not the amount of radiation emitted from some object. Therefore the absorption of emitted radiation within the object is not relevant - the same number of nuclei decay per second regardless of whether the decay products escape the sample or not.

2018-06-05 09:05:22
• The specific (meaning per unit mass) activity relates to the number of decays per unit time (number of alpha particles emitted per unit time) and it depends on the number of unstable nuclei in the sample and the half life.

It is highly likely that given the short range of alpha particle the number of alpha particles emitted from a source is less than that number.

To measure the specific activity is therefore likely to be difficult for alpha emitters.

One way is to try and use a very thin sample so that absorption of the alpha particle is minimised.

2018-06-05 09:51:04