A sample of a radioactive substance decayed to 94.5% of its original amount after a year. (Round your answers to two decimal places.)
(a) What is the halflife of the substance?
(b) How long would it take the sample to decay to 65% of its original amount?
 👍
 👎
 👁
 ℹ️
 🚩
2 answers

A certain radioactive isotope decays at a rate of 2% per 100 years. If t represents time in years and y
represents the amount of the isotope left then the equation for the situation is y= y0e0.0002t. In how many years will there be 93% of the isotope left? 👍
 👎
 ℹ️
 🚩
answered by Anonymous 
general equation
amount = starting (1/2)^(t/k) , where t is the time and k is the halflife period
a)
.945 = 1(.5)^1/k
ln .945 = (1/k)ln.5
1/k = ln.945/ln.5
k = ln.5/ln.945 = 12.25 years
b)
.65 = (.5)^t/12.25
t/12.25 = ln.65/ln.5 = .621488..
t = 7.61 years 👍
 👎
 ℹ️
 🚩
answered by Reiny
Answer this Question
Related Questions

maths
The halflife of lead is 22 years. How long will it take for a sample of this substance to decay to 80% of its original amount
 asked by Anonymous
 4,137 views

Science
Modeling Nuclear Processes Quick Check: Which phrase best describes nuclear fusion? (❌)a series of reactions in which particles from one reaction trigger the next reaction (❌)the spontaneous emission of radiation from an unstable nucleus (✔️)the
 asked by htsrhtdyjy
 17,111 views

chemistry
what is the density of an 84.7g sample of an unknown substance if the sample occupies 49.6cm3? what volume would be occupied by 7.75g of this same substance? PLEASE help need the answer tonight i have a test tomorrow i kind of not understand the second
 asked by heather
 6,021 views

Physics
Consider a radioactive sample with a halflife of one week. How much of the original sample will be left at the end of the second week? The third week? The fourth week?
 asked by Tracee
 5,341 views

algebra
Use the fact that after 5715 years a given amount of carbon 14 will have decayed to half the original amount to find the exponential decay model for carbon 14. In 1947, earthenware jars containing what was known as the Dead Sea scrolls were found by an
 asked by Kristina
 1,398 views

pre calculus
if 17 percent of a radioactive substance decays in 12 hours, what is the halflife of the substance? Round your answer to one decimal place.
 asked by joe bob
 1,006 views

Science
Ethan is observing chemical and physical properties of a substance. He heats a substance and observes that the substance turns from a brown solid to a black powder. He refers to several chemistry journals that claim this represents a chemical reaction.
 asked by SoAestheticallyPleasing
 2,678 views

Pre Calculus 1
thirty percent of a radioactive substance decays in four years. assuming the decay is exponential, find the half life of the substance. the beginning of 1975 the population of a country was 40 million and growing at a rate of 3% per year. Assume that the
 asked by Yasmine
 909 views

Chemistry
I did a lab the other day where we separated a mixture of NaCl, SiO2, and CaCO3. The Mixture was made by my professor and we did not know the original amounts of each compound. After recovering all of the compounds we found that there was.. 36.4% NaCl
 asked by Jessica
 4,864 views

Please help chemistry
Which statement best describes the effect of radioactive decay on a nucleus?(1 point) The resulting nucleus is more stable than the original nucleus. The nucleus can be of a different element than the original. ****The resulting nucleus is more stable than
 asked by heyo ❄
 411 views

math calculus
Find the halflife (in hours) of a radioactive substance that is reduced by 30 percent in 40 hours.
 asked by Urgent help
 11,021 views

Calculus
The radioactive element polonium decays according to the law given below where Q0 is the initial amount and the time t is measured in days. Q(t) = Q0 · 2(t/140) If the amount of polonium left after 700 days is 45 mg, what was the initial amount present?
 asked by Anonymous
 3,224 views

AP BIO
a student wished to test a sample of organic material to determine whether it was sugar, a dat, or starch. If she could perform only one of the following, which would be the most revealing? 1 test for the presence of carbon and hydrogen in the sample 2
 asked by bubba
 808 views

College Chemistry
Plaster of Paris is the compound calcium sulfate hemihydrate, CaSO4*1/2H2O What mass of water is liberated when a 2.763 gram sample is heated to constant mass? The sample is 2.763 grams How much of the 2.763 gram sample is water? I need an amount in grams.
 asked by Roy
 1,229 views

math with application
If 12 % of a radioactive substance decays in 7 hours, what is the halflife of the substance? Carry out all calculations exactly, then round the final answer to three decimal places. The half life is what hours?
 asked by liv
 1,056 views

stat.
A sample consists of the following n � 6 scores: 2, 7, 4, 6, 4, and 7. a. Compute the mean and standard deviation for the sample. b. Find the zscore for each score in the sample. c. Transform the original sample into a new sample with a mean of M � 50 and
 asked by Nickie
 1,403 views

chemistry
Suppose a substance has been prepared that is composed of carbon, hydrogen, and nitrogen. When 0.1156 gram of this compound is reacted with oxygen, 0.1638 gram of carbon dioxide (CO2) and 0.1676 gram of water (H2O) are collected. Assuming that all the
 asked by Chansa
 1,992 views

chemistry
The halflife for the radioactive decay of calcium47 is 4.5 days.If a sample has an activity of 4.00uCi after 13.5 days, what was the initial activity of the sample?
 asked by Shay
 2,571 views

Math
The halflife of a certain radioactive material is 38 days. An initial amount of the material has a mass of 497 kg. Write an exponential function that models the decay of this material. Find how much radioactive material remains after 4 days. Round your
 asked by Latanya
 3,281 views

math
An unknown radioactive element decays into nonradioactive substances. In 100 days the radioactivity of a sample decreases by 64 percent. a)(a) What is the halflife of the element? halflife: b)How long will it take for a sample of 100 mg to decay to 51
 asked by Rachel
 1,776 views
Still need help?
You can ask a new question or browse existing questions.