[nervouspupil123]

I don't understand it, there seems to be a real lack of consistency in the mark schemes! sometimes the source is chosen due to its short half life...and other times due to its long half life, can someone explain when to choose either one?

For example:"Sohanna is given a course of external radiation therapy using a radioactive isotope. This lasts a few minutes on each of 10 consecutive days. Select a suitable source and radiation type for Sohanna's treatment:"

I got the type of radiation right (gamma) but got the choice of the 2 gamma sources wrong. I chose the source with a 2.2 hour half life...when the answer was one with a 10.5 YEAR half life! surely this is not preferred due to the damage it would cause to healthy cells over time? if i'm wrong WHY is this the answer? WHY are long half lives useful? and WHEN are long half lives preferred over short, and vice versa. Truly confused :/

[nervouspupil123]

is it that palliative therapy uses a long half life? and therapy to cure does not?

[teachercol]

You want to be able to use the same source next week and not have to buy a new gamma machinefor the hospital.