Half Lives and Radioactive Decay

In summary: There are 3.88914*10^25 molecules in a mole.In summary, there are about 93,000 molecules in the meteor.
  • #1
CharlieW95
3
0

Homework Statement



2. A meteor contains 6kg of molybdenum-93. Calculate:
a) The number of molybdenum molecules currently present in the meteor.
b) How long ago the meteor struck the Earth if the original amount contained 20kg of molybdenum.

Homework Equations


Answers:
2. a) 3.884x1022 molecules b) 6079.3 yrs

The Attempt at a Solution


Only topic i don't understand, exam tomorrow and i have no idea where else to go !

Any help is appreciated :)

(The answers were given, i need help working how to solve!)
 
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  • #2
Formulas:
N = No e-γt
where the decay constant, γ(gamma), and T1/2 are related by
γ[itex]\:[/itex]T1/2 = ln(2)
 
  • #3
Well...all you need to do is solve for t.
3.
Now N=0.1*No
0.1*No = No*e-γt
0.1=e-γt
ln 0.1=-yt
t=(ln 0.1)/-y=(ln 0.1)/-(ln2/T_1/2)=(ln 0.1)/-(ln2/3.76x10^5 a)=1249044.964 a≈1.25 million years
 
  • #4
Thank you both so much, understand 1 and 3 easily now. Question 2 is giving me grief!
 
  • #5
Are you sure about a? 4 thousand molecules sounds very low.
 
  • #6
sjb-2812 said:
Are you sure about a? 4 thousand molecules sounds very low.
I am sorry, I didn't quite catch that.
 
  • #7
CharlieW95 said:

Homework Statement


...Answers:
2. a) 3.884x1022 molecules

The answer to a) has been given as above, which is about 4000 molecules.
 
  • #8
sjb-2812 said:
The answer to a) has been given as above, which is about 4000 molecules.

copy pasting generally doesn't paste superscripts properly, so I would assume it's 1022
 
  • #9
sjb-2812 said:
The answer to a) has been given as above, which is about 4000 molecules.

lep11 said:
I am sorry, I didn't quite catch that.

SHISHKABOB said:
copy pasting generally doesn't paste superscripts properly, so I would assume it's 1022

Maybe, but even taking that into account, still seems low.
 
  • #10
3.884*1022 is low?
 
  • #11
Yes. How many molecules are there in a mole
 
  • #12
Not sure if this is correct, but I got N=n*N_A=(m/M)*N_A=(6.0*10^3g/92.90681261g/mol)*6.0221327*10^23 1/mol=3.88914...*10^25
,where N_A=Avogadro constant.
If you understood this, you can solve b easily, right?
 
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FAQ: Half Lives and Radioactive Decay

What is half-life?

Half-life is the amount of time it takes for half of a sample of radioactive material to undergo radioactive decay. This means that after one half-life, half of the original sample will remain, and after two half-lives, one quarter will remain, and so on.

How is half-life measured?

Half-life can be measured by observing the rate of decay of a sample of radioactive material. This is typically done by counting the number of decays per unit time and using that information to calculate the half-life.

What factors affect the half-life of a radioactive substance?

The half-life of a radioactive substance is determined by the type of radionuclide (radioactive element), the energy of the emitted radiation, and the chemical and physical properties of the substance. Temperature, pressure, and external radiation can also affect the half-life.

Can half-life be altered or changed?

No, half-life is a characteristic property of a radioactive substance and cannot be changed or altered. However, the rate of decay can be influenced by external factors such as temperature and pressure.

What is the significance of half-life in radioactive decay?

Knowing the half-life of a radioactive substance is important in a variety of fields, including medicine, energy production, and environmental protection. It allows scientists to accurately predict the rate of decay and the amount of radiation emitted, which is crucial for safety and regulatory purposes.

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