Radioactivity
posted by Sandhya .
1) An old wooden tool is found to contain only 11.9 percent of 14C that a sample of fresh wood would. How many years old is the tool?
2) A specimen taken from the wrappings of a mummy contains 7.02 g of carbon and has an activity of 1.34 Bq. How old is the mummy? Determine its age in years assuming that in living trees the ratio of 14C/12C atoms is 1.23E12.
Please check my answers
1)
For 14 C T 1/2 = 5570 years N/N0 = 11.9/100 = 0.119
N / N0 = e λ t 2.303 x In 0.119 = λt λ =0.6931 / 5570 =1.244 x 10 4
t = (2.303 x In0.119 x 5570) / 0.6931 = 17110 years
2)
R = 1.34 Bq = 1.34 decays / second
14 C atoms / 12 C atoms = 1.23 x 1012 = N0/N N/N0 = 10 12 /1.2
Number of atoms contained in 7.02 g of carbon
= (7.02 x 6.023 x 10 23) /14 = 3.02 x 10 23 N = 3.02 x 10 23
R = Nλ λ = 1.34 / 3.02 x 10 23 = 0.4437 x 10 23
2.303 x In (10 12 /1.23 ) = 0. 4437 x 10 23 x t
t = 61.82 x 10 23 seconds = 1.96 x 10 17 years

T 1/2 of C14=5730 yrs.
Here is the answer for the 1st one, hope it will be helpfull.
Lamda= ln2/(T1/2)
= 0.693/5730=1.209E4
N/N0= 11.9/100 = 0.119
N=N0 e^lamda*t
N/N0=e^lamda*t
ln(0.119)= 1.209E4t
t=ln(0.119)/(1.209E4)
t=17606.5 yrs. 
T 1/2 of C14=5730 yrs.
Here is the answer for the 1st one, hope it will be helpfull.
Lamda= ln2/(T1/2)
= 0.693/5730=1.209E4
N/N0= 11.9/100 = 0.119
N=N0 e^lamda*t
N/N0=e^lamda*t
ln(0.119)= 1.209E4t
t=ln(0.119)/(1.209E4)
t=17606.5 yrs.
(ps: this is also for my Montgomery College, Takoma Park college Dr. Shaleen Shukla PH 204 class)
Respond to this Question
Similar Questions

Nuclear physics
1) An old wooden tool is found to contain only 11.9 percent of 14C that a sample of fresh wood would. How many years old is the tool? 
Nuclear physics Repost
1) An old wooden tool is found to contain only 11.9 percent of 14C that a sample of fresh wood would. How many years old is the tool? 
physicsRadioactivity
A specimen taken from the wrappings of a mummy contains 7.02 g of carbon and has an activity of 1.34 Bq. How old is the mummy? 
chemistry/math
100g of bone contain ratio of 14C and 12C. 6.8% 14C is present in the living tissue, how old was the skeleton? 
Chemistry
A skull fragment found in 1936 at Baldwin Hills, California, was dated by 14C analysis. Approximately 100g of bone was cleaned and treated with 1 M HCl(aq) to destroy the mineral content of the bone. The bone protein was then collected, … 
Physics
An astronaut is taking a space walk near the shuttle when her safety tether breaks. What should the astronaut do to get back to the shuttle? 
Chemistry
The halflife for radioactive decay of 14C is 5730 years (it emits βparticles with energy of 0.16 MeV). An archaeological sample contained wood that had only 72% of the 14C found in living trees. What is its age? 
chemistry
Archeologists can determine the age of artifacts made of wood or bone by measuring the amount of the radioactive slope 14C present in the object. The amount of isolope decreases in a firstordrr process. If 12.8% of the original amount … 
URGENT! Due soon and I used 8 of 10 attempts
Archaeologists can determine the age of artifacts made of wood or bone by measuring the amount of the radioactive isotope 14C present in the object. The amount of isotope decreases in a firstorder process. If 14.5% of the original … 
science
Charcoal from an ancient campfire has a ratio of 14C to 12C that is one fourth that of new wood. About how old is the charcoal?