Long or short half life? -sterilizing surgical instruments + treating cancer patients

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nettogrof
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Should a radioactive (gamma) source that is used to sterilize hospital equipment have a short or long half life?

Should a radioactive (gamma) source that is used to treat cancer patients, in radiotherapy, have a short or long half life?

I thought that both should have short half life's to reduce the time they are left in the patient's body and therefore reduce the harmful effects to cells? But my CPG workbook says that they should both have long half lifes to prolong the source since the machines will be used over a long period of time and it would be inconvenient to have to keep on replacing the source.

Please could someone tell me the correct answer and explain why?

By the way, the workbook agrees with my notes that a radioactive (gamma) isotope used as a medical tracer should have a short half life.

Thanks in advance!
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uberteknik
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(Original post by nettogrof)
Should a radioactive (gamma) source that is used to sterilize hospital equipment have a short or long half life?

Should a radioactive (gamma) source that is used to treat cancer patients, in radiotherapy, have a short or long half life?

I thought that both should have short half life's to reduce the time they are left in the patient's body and therefore reduce the harmful effects to cells? But my CPG workbook says that they should both have long half lifes to prolong the source since the machines will be used over a long period of time and it would be inconvenient to have to keep on replacing the source.

Please could someone tell me the correct answer and explain why?

By the way, the workbook agrees with my notes that a radioactive (gamma) isotope used as a medical tracer should have a short half life.

Thanks in advance!
The question as phrased is not ambiguous.

In the context of sterilisation equipment, the radio active source needs to have a long half life as it will be used over a number of years and the intensity of radiation must not drop off over that period or the efficacy of that sterilisation will also decline.

In the context of radiotherapy (again where radiation is directed at the cancer from a source external to the body), for the same reason as above, the radiation source needs a long half life.

In the context of medical tracers ingested and placed inside the body, the isotope needs to have a short half life to minimise any medium to long term unwanted damage to cells caused by the isotope remaining inside the body over a longer period.
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JohnnyDavidson
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The key is the difference between a radioactive source, and radiation. A radioactive spurce emits radiation.

For xrays and radiotherapy, the radioactive source is inside the machine, and only the radiaiton is exposed to the patient (exposure not contamination).
So the source requires a long half half, in order to have a near constant activity (emits the same rate of radiaton) for a long time.

For things like barium scans\radioactive tracers, the radioactive source is ingested by the patient, and then emits radiation while inside the patient (both contamination and exposure).
In this case, a short half life up to few days would be used, to prevent the patient being exposed to radiation for longer than necessary.
However if the half life was very short (such as seconds/minutes), a very large amount of radiation would be emitted onto a concentrated area in the body, in which case would be more harmful.
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