Half life of substance

  • Thread starter somecelxis
  • Start date
  • #1
121
0

Homework Statement


a patient who is undergoing cancer theraphy is given 10 mins of irradiation from a radioactive source that has half life = 2 years. If the same source is to be used for same treatment 2 years later , how long should the patient should be irradiated?

the ans is 20 mins .. can someoene teach me how to do this?

Homework Equations




The Attempt at a Solution


i was told that:
at time = 0 (ie. Now) the patient undergoes 10 mins of irradiation. Lets say the amount of radioactivity of the source now is at 100%

We are told that it's half life is 2 years which means in 2 years the radioactivity of the source is at 50%.

So suppose it is 2 years later
if the patient's therapy lasts 10 min - he gets 50% dosage.
if the patients therapy goes another 10 min - he gets another 50% dosage
So a total of 20 min of therapy results in (50% + 50% = 100% same dosage as he received 2 years earlier)

but why if the patient's therapy lasts 10 min - he gets 50% dosage. ??[/B]
 

Answers and Replies

  • #2
BvU
Science Advisor
Homework Helper
2019 Award
13,599
3,286
You're doing the right thing. Dosage is proportional to the time and to the radioactivity of the source: dosage is something like the amount of radioactive decays, so activity (decays/time) times time.
 
  • #3
NascentOxygen
Staff Emeritus
Science Advisor
9,244
1,072
why if the patient's therapy lasts 10 min - he gets 50% dosage. ??
Instead of the patient, imagine there is a Geiger counter, and explain what it would record.
 

Related Threads on Half life of substance

  • Last Post
Replies
5
Views
1K
Replies
6
Views
19K
  • Last Post
Replies
10
Views
1K
  • Last Post
Replies
4
Views
1K
  • Last Post
Replies
1
Views
1K
  • Last Post
Replies
2
Views
2K
  • Last Post
Replies
7
Views
4K
  • Last Post
Replies
4
Views
2K
  • Last Post
Replies
7
Views
2K
  • Last Post
Replies
2
Views
8K
Top