Math 131

sonrays06

sonrays06

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The half-life of cesium-137 is 30 years. Suppose that we start with 90 grams of cesium-137 in a storage pool.

How many half-lives will it take for there to be 10 grams of cesium-137 in the storage pool? (Round your answer to two decimal places.)
How many years is that? (Round your answer to one decimal place.)
 
sonrays06 said:
The half-life of cesium-137 is 30 years. Suppose that we start with 90 grams of cesium-137 in a storage pool.

How many half-lives will it take for there to be 10 grams of cesium-137 in the storage pool? (Round your answer to two decimal places.)
How many years is that? (Round your answer to one decimal place.)
Click to expand...

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sonrays06 said:
The half-life of cesium-137 is 30 years. Suppose that we start with 90 grams of cesium-137 in a storage pool.

How many years is that? (Round your answer to one decimal place.)
Click to expand...
Did you read what you were told to read?
 
sonrays06 said:
The half-life of cesium-137 is 30 years. Suppose that we start with 90 grams of cesium-137 in a storage pool.

How many half-lives will it take for there to be 10 grams of cesium-137 in the storage pool? (Round your answer to two decimal places.)
How many years is that? (Round your answer to one decimal place.)
Click to expand...
What is the definition of half-life?

Please show us what you have tried and exactly where you are stuck.

Please follow the rules of posting in this forum, as enunciated at:

READ BEFORE POSTING

Please share your work/thoughts about this problem.
 
Ok I’m just asking a question for help, just like everyone else is....
 
Does your disability prevent you from using a computer or from thinking?
 
So your disability might make it hard to type. (We cannot guess about such things unless you tell us.) If so, do you use voice recognition software? And obviously your disability does not prevent you from thinking or reading. So what is the answer to Subhotosh Khan’s question: what is the definition of “half-life”?
 
JeffM said:
So your disability might make it hard to type. (We cannot guess about such things unless you tell us.) If so, do you use voice recognition software? And obviously your disability does not prevent you from thinking or reading. So what is the answer to Subhotosh Khan’s question: what is the definition of “half-life”?
Click to expand...
Half-life, in radioactivity, the interval of time required for one-half of the atomic nuclei of a radioactive sample to decay
 
sonrays06 said:
Half-life, in radioactivity, the interval of time required for one-half of the atomic nuclei of a radioactive sample to decay
Click to expand...
Yes. Perfect.

Now we need an equation.

Let x be the amount of cesium-137 at the beginning of year ZERO. With me?

At the end of 30 years, how much is left in terms of x?

At the end of 60 years, how much is left in terms of x?

At the end of 90 years, how much is left in terms of x?

Can you form a general equation based on that information as to how much will be left after t years?
 
The first question from the first post is 9.46 half-lives.
Therefore, determining how many years is puzzling. is it dividing 30 by 9.46?
 
sonrays06 said:
The first question from the first post is 9.46 half-lives.
Therefore, determining how many years is puzzling. is it dividing 30 by 9.46?
Click to expand...
Where did you get 9.46 half-lives from? Let's think about it. After 30 years, the 90 grams will be reduced to 45 grams. After another 30 years, that will be reduced to 22.5 grams. After another 30 years, that will be reduced to 11.25 grams. And after another 30 years, that will be reduced to 5.625 grams. So the answer must be between 3 and 4 half years. Make sense? So that is somewhere between 90 and 120 years.

Would you please try to answer my questions from post # 14? They are meant to help you think through this type of problem.
 
JeffM said:
Where did you get 9.46 half-lives from? Let's think about it. After 30 years, the 90 grams will be reduced to 45 grams. After another 30 years, that will be reduced to 22.5 grams. After another 30 years, that will be reduced to 11.25 grams. And after another 30 years, that will be reduced to 5.625 grams. So the answer must be between 3 and 4 half years. Make sense? So that is somewhere between 90 and 120 years.

Would you please try to answer my questions from post # 14? They are meant to help you think through this type of problem.
Click to expand...
The half-life of cesium-137 is 30 years. Suppose that we start with 90 grams of cesium-137 in a storage pool.
How many half-lives will it take for there to be 10 grams of cesium-137 in the storage pool? <<< this was the first question and I got 9.46 right.

As far as how many years, 3? ?
 
sonrays06 said:
The half-life of cesium-137 is 30 years. Suppose that we start with 90 grams of cesium-137 in a storage pool.
How many half-lives will it take for there to be 10 grams of cesium-137 in the storage pool? <<< this was the first question and I got 9.46 right.

As far as how many years, 3? ?
Click to expand...
After 30 yrs (which is more than 9.46 or 3) the amount of cesium-137 is 45gms (90/2)
After another 30 yrs, a total of 60 yrs, the amount of cesium-137 is 22.5 gms (45/2)
After another 30 yrs, a total of 90 yrs, the amount of cesium-137 is 11.25 gms (22.5/2)
 
Jomo said:
Which is your answer; 9.46 or 3.

After 30 yrs (which is more than 9.46 or 3) the amount of cesium-137 is 45gms (90/2)
After another 30 yrs, a total of 60 yrs, the amount of cesium-137 is 22.5 gms (45/2)
After another 30 yrs, a total of 90 yrs, the amount of cesium-137 is 11.25 gms (22.5/2)
Click to expand...

The half-life of cesium-137 is 30 years. Suppose that we start with 90 grams of cesium-137 in a storage pool.

How many half-lives will it take for there to be 10 grams of cesium-137 in the storage pool? (Round your answer to two decimal places.)
9.46 half-lives << this answer is right

How many years is that? (Round your answer to one decimal place.)
? yr
 
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