Register to reply 
Calculating decay constants and halflife 
Share this thread: 
#1
Oct2608, 06:39 AM

P: 30

A scientist wishes to find the age of a sample of rock. Realising that it contains radioactive potassium, which decays to give a stable form of argon, the scientist started by making the following measurments:
decay rate of the potassium in the sample = 0.16Bq mass of potassium in the sample = 0.6x10^6g mass of argon in the sample = 4.2x10^6g The Molar mass of the potassium is 40g. show that the decay constant for potassium is 1.8x1017 and its halflife is 1.2x10^9years. 2. Relevant equations decay constant = a/N n=m/Mr 3. The attempt at a solution N=m/Mr N=0.6x10^6/40 N=1.5x10^8 N=1.5x10^8 x 6.02x10^8 N=9.03 x 10^16 decay constant = a/N decay constant = 0.16/9.03x10^16 I got this far then got stck as the answer was wrong, im not sure wher to go from here any help would be appreciated. 


#2
Oct2608, 07:02 AM

Emeritus
Sci Advisor
PF Gold
P: 9,781

You might want to check the value of Avogadro's Constant



#3
Oct2608, 08:18 AM

P: 30

oops that should have been 10^23 lol, thanks i'll try that
x 


#4
Oct2608, 08:29 AM

P: 30

Calculating decay constants and halflife
now i get 1.4448x10^15 which is still wrong, im so confused.
x 


#5
Oct2608, 08:37 AM

Emeritus
Sci Advisor
PF Gold
P: 9,781




#6
Oct2608, 08:39 AM

P: 30

9.03x10^15
x 


#8
Oct2608, 08:53 AM

P: 30

well i dont know what i did but i have just gotten the right answer thanks lol
xx 


#9
Oct2608, 08:54 AM

Emeritus
Sci Advisor
PF Gold
P: 9,781




#10
Oct2608, 08:56 AM

P: 30

thanks lol, i do that alot it seems, better brush up on those skills before the exam lol.



Register to reply 
Related Discussions  
Radioactive reactions halflife Decay ..physics 30  Introductory Physics Homework  3  
Decay equations: Given A0 &amp;amp; At, find halflife, lambda and N0  Introductory Physics Homework  14  
Radioactive decay and finding half life  Calculus & Beyond Homework  10  
Halflife and decay  Calculus & Beyond Homework  5  
Calc. the MM from decay and half life  Chemistry  4 