# The half-life of lead is 22 years. How long will it take for a sample of this substance to decay to 80% of its original amount

66,229 results
1. ## math

An element has a half-life of 30 years. If 1.0 mg of this element decays over a period of 90 years, how many mg of this element would remain? Begin amount is 1.0 elapsed time is 90y half life 30 years n=9/30 n=3 90/2^2 90/8 = 11.25mg thinking it's wrong

2. ## Pre-Calc

Tritium, a radioactive isotope of hydrogen, has a half-life of 12.4 years. Of an initial sample of 69 grams, how much will remain after 75 years?

3. ## Chemistry(difficult)

A moon rock collected by a U.S. Apollo mission is estimated to be 3.70 billion years old by uranium/lead dating. Assuming that the rock did not contain any lead when it was formed, what is the current mass of 206Pb per 1.185 g of 238U in the rock? The

4. ## Calc

A sample of a radioactive substance decayed to 93.5% of its original amount after a year. a) What is the half-life of the substance? ? years (b) How long would it take the sample to decay to 10% of its original amount? ? years

5. ## Chemistry

Gallium65, a radioactive isotope of gallium, decays by first order-kinetics. The half-life of this isotope is 15.2 min. How long would it take for 7/8 of a sample of this isotope to decay? 15.2 min 30.4 min 45.6 min 48.0 min I'm not sure how to do this. I

6. ## Pre Calculus

Radium-221 has a half-life of 30 s. How long will it take for 95% of a sample to decay

7. ## Chemistry

the half-life of cobalt-60 is 5.20 years.. how many milligrams of a 2.000-mg sample remains after 6.55 years

8. ## maths

The half-life of lead is 22 years. How long will it take for a sample of this substance to decay to 80% of its original amount

9. ## Chemistry

A pure sample of tritium, 3H, was prepared and sealed in a container for a number of years. Tritium undergoes â decay with a half-life of 12.32 years. How long has the container been sealed if analysis of the contents shows there are 5.25 mol of 3H and

10. ## chemistry

a)indium-115 has a half life of 4.5 hours. if you start with a 12.0-mg sample of indium-115, how much will remain after 13.5 hours? b)how much of a 3.50-mg smaple of nickel-63 will remain after 368 years? the half-life of nickel-63 is 92 years?

11. ## Math - Exponential Decay

Radium decays exponentially. Its half-life is 1,690 years. How long will it take for a 50-gram sample of radium to be reduced to 5 grams? 1/2P = Pe^(-1690k) (ln1/2)/(-1690) = k 4 x 10^-4 = k 5 = 50e^-kt ln0.1 = -kt ln0.1/-k = t 5,630 years = t ...but

12. ## chemistry

A 1.00-g sample of carbon from a modern source gave 15.3 disintegrations per minute. A sample of carbon from an “old” source gave 920 disintegrations per hour. What is the age of the “old” sample of carbon? The half-life of carbon-14 is 5.73×103

13. ## Chemistry

Which radioactive sample would contain the greatest remaining mass of the radioactive isotope after 10 years? A. 2.0 grams of 198 Au B. 2.0 grams of 42 K C. 4.0 grams of 32 P D. 4.0 grams of 60 Co By the way the numbers next to the elements are their

14. ## science

The half-life of carbon 14 is 5730 years. if a 1 g sample of old carbon is 1/8 as radioactive as 1 g of a current sample, then the age of the old sample is about ___________years. 22,900 17,200 11,500 716

15. ## Pre-calculus

Trtitum, a radioactive isotope of hydrogen, has a half-life of 12.4 years. Of an into tail amount sample of 50 grams, how much will remain after 10 years?

16. ## College algerba

The​ half-life of a certain radioactive element is about 1500 years. After 2800 ​years, what percentage P of a sample of this element​ remains?

17. ## chemistry

How long will it take for 25% of the C-14 atoms in a sample of C-14 to decay? The half-life for the radioactive decay of C-14 is 5730 years. If a sample of C-14 initially contains 1.1 mmol of C-14 , how many millimoles will be left after 2275 years?

18. ## half-life

the half life of isotope X is 2.0 years how many years would it take for 4.0 mg sample of X to decay and have .50 mg of it remain?

19. ## chemistry

If there are 80 milligrams of a radioactive element decays to 10 milligrams in 30 minutes then what is the elements half life in minutes? Ok i narrowed it down to either 10 or 30...but im rly confused so if u could help it wuld be grea 80 40 1 min 20 2 min

20. ## calculus

The rate at which an amount of a radioactive substance decays is modeled by the differential equation dA/dt = kA, where A is the mass in grams, t is the time in years, and k is a constant. Answer the following. a) If a 100-gram sample of the radioactive

21. ## Chem 2

The half-life for the radioactive decay of U-238 is 4.5 billion years and is independent of initial concentration. a) How long will it take for 10% of the U-238 atoms in a sample of U- 238 to decay? b)If a sample of U-238 initially contained 1.9×1018

22. ## Math

An unknown radioactive substance has a half-life of 124 years. How long will it take a 67 grams sample to degrade to 18 grams?

23. ## Ap chemistry

if a 84g sample of thorium decays with a 10 minute half life, how much would the sample weight in a half hour?

24. ## chemistry

A moon rock collected by a U.S. Apollo mission is estimated to be 4.50 billion years old by uranium/lead dating. Assuming that the rock did not contain any lead when it was formed, what is the current mass of 206Pb per 1.150 g of 238U in the rock? The

25. ## science

the half life of tritium is 12.5 years. How much of a 1 g sample will remain after 25 years

26. ## Math

The half-life of strontium-90 is 28 years. How long will it take a 60 mg sample to decay to a mass of 15 mg?

27. ## word problem

The half life of cesium-137 is 30 years. Suppose we have a 10-g sample. a)Find a function that models the mass remaining after t years. b)How much of the sample will remain after 80 years? c)After how long will only 2 g of the sample remain? Thanks (a)

28. ## math

the half life of thorium -229 is 7340 years. how long will it take for sample of this substance to decay to 20% of its original amount

29. ## chemistry

Strontium-90 has half-life of 28 years. if a 1.00-mg sample was stored for 112 years. what mass of Sr-90 would remain?

30. ## science

Carbon-14 has a half-life of approximately 5,730 years. How many half-lives have occurred in a sample that contains 50 percent of the original amount of the parent isotope?

31. ## College algebra

The radioactive element has a half-life of about 28 years and sometimes contaminates the soil. After 47 years, what percentage of a sample of the elements remain?

32. ## Calculus

The half-life of Radium-226 is 1590 years. If a sample contains 100 mg, how many mg will remain after 4000 years?

33. ## physical science

cobalt-60 has a half-life of 5.26 years, how much of a 500 gram sample will be left after 21 years

34. ## Half-Life

Uranium-238 decays to Lead-206. The half life of Uranium-238 is 4.5 billion years. If you have a 100 g sample. How much sample will you have after 2 half lifes?

35. ## Physic

A sample of radium weighs 1000g.How long will it take to decay to 125g if its half-life is 1620 years?

36. ## Chemistry

carbon 14 has a half life of 5715 years. If you start with a 5 gram sample of 14C, what mass is left after 15,000 years?

37. ## Physics

The isotope carbon-14, 146C, is radioactive and has a half-life of 5730 years. If you start with a sample of 1000 carbon-14 nuclei, how many will still be around in 22920 years? I got 62.5 atoms, am I correct?? Thank you!!

38. ## chemistry

an original sample of K-40 has a mass of 25.00 grams. After 3.9x 10 to the ninth years, 3.125 grams of the original sample remains unchanged. What is the half-life ok K-40 in minutes? Is it 6.8328 x 10 to the 14th

39. ## chemistry

The isotype caesium -137, which has a half life of 30 years, is a product of nuclear power plants. How long will it take for the amount of this isotype in a sample of caesium to decay to one-sixteenth of its original amount? first half life 1/2 second 1/4

40. ## Chemistry (Dr.Bob222)

The half-life of P-32 is 14 days. How long after a sample is delivered can a laboratory wait to use a sample in an experiment if they need at least 10 percent of the original radioactivity? I need help on how to set up this problem. What is the general

41. ## chemistry

Strontium-90 decays through the emission of beta particles. It has a half-life of 29 years. How long does it take for 80% of a sample of strontium-90 to decay? Show process of how you got this

42. ## Chemistry *URGENT*

URGENT help! 3. A rock sample was dated using potassium-40, Neasyrenebt ubducated tgat 1/8 of the original parent isotope is left in the rock sample. How old is the rock? 5. When a sample of lava solidfied, it contained 28g of uranium-238. It that lava

43. ## Biology

The half-life of carbon-14 is 5,700 years. If a sample originally had 26 g of carbon-14, how much would it contain after 22,800 years?

44. ## Calculus

The half life of a certain radioactive substance is 10 years. How long will it take for 18 gms of the substance to decay to 6 gms? A. 6 ln 10 years B. 10 ln 6 years C. 10 (ln 3)/(ln 6) years D. 18 ln 10 years E. 10 (ln 3)/(ln 2) years

45. ## Math

Plutonium-239 has a half-life of 24 000 years. What percent of plutonium-239 remains after 10 000 years? (Answer=74.9%) AND After 30 hours, a sample of Plutonium 243 (PU^ 243) has decayed to 4 ^ -1/3 of its original mass. What is the half life of PU^ 243.

46. ## Science

An element has a half-life of 30 years. If 1.0 mg of this element decays over a period of 90 years, how many mg of this element would remain? Begin amount is 1.0 elapsed time is 90y half life 30 years n=9/30 n=3 90/2^2 90/8 = 11.25mg thinking it's wrong

47. ## chemistry

90Sr is one of the harmful radionuclides resulting from nuclear fission explosions. It decays by a first-order process with a half-life of 28 years. How many years would it take for 99.99% of a given sample released in the atmosphere to disintegrate?

48. ## Chem 3A

please help me with this chemistry problem. Half-Life A radium-226 sample initially contains 0.112 mol. How much radium-226 is left in the sample after 6400 years? The half-life of radium-226 is 1600 years.

49. ## Physics

Half life of radium is 44 years.The sample will reduce to 50% of its orignal value ater how many years?

50. ## Algebra

An isotope has a half-life of 97 years. how much of a 19-gram sample is left after 150 years?

51. ## matg

Cobalt-60 has a half-life of about 5 years. How many grams of a 300 g sample will remain after 20 years? (Points : 1)

52. ## SCIENCE

We did a radioactive decay and half life lab with m&ms and I do not understand these conclusion questions: 1. how many half lives would it take for 500 nuclei to decay to 6.25% of the original number of nuclei? My ans: 3125?- do not think that's right! 2.

53. ## chemistry

The half-life of stronitum-90 is 28 years. How many grams of this nuclide in a 4.00g sample will remain after 112 years?

54. ## Science

If a 20 gram sample of a radioactive substance has a half-life of 6000 years, how many grams would be present after 18000 years?

55. ## Science HELP 2nd question

A sample originally contained 2.5 g of rubidium 87 now contains 1.25 g. The half life of rubidium - 87 is 6 x 10 ( to the 10th) years. How old is the sample? Is this possible? why or why not?

56. ## Chemistry

Uranium-238 has half life of 4.51 * 10^9 years Uranium-234 has half life of 2.48 * 10^5 years Thorium-230 has half life of 8.0 * 10^4 years Radium-226 has half life of 1.62 * 10^3 years Lead-210 has half life of 20.4 years. The rate constant for the decay

57. ## Chemistry please help!

A Cesium 137 sample has a measured radioactivity of 50 microcuries.Cesium 137 has a half-life of 30 years. How long will it take this sample to be reduced to a residual radioactivity of 6.25 microcuries? Is there a formula to calculate half life?

58. ## Chemistry

The isotope caesium-137, which has a half life of 30 years, is a product of neuclear power plants. How long will it take for the amount of this isotope in a sample of caesium to decay to one sixteenth of its original amount. Explain answer 30 years 1/2 60

59. ## Chemistry

The half-life of C-14 is 5700 years. If it took seven half lives for a sample of C-14 to decay completely, how many years would have gone by?

60. ## chemistry

What percent of the original sample of strontium-90 (half-life = 28.9 years) will remain after the following time periods?after 18 years? after 47.5 years? after 1008 years?

61. ## Chemistry

If 25.0 g of a radioactive sample is left after 100.0 years and each half-life is 25 years, how much sample did you start with?

62. ## ChemB

The activity of carbon 14 in living tissue is 15.3 disintegrations per minute per gram of carbon. The limit for reliable determination of age is based on carbon 14 is .10 disintegration per min per gram of carbon. Calculate the max age of a sample that can

63. ## math

An unknown radioactive element decays into non-radioactive substances. In 100 days the radioactivity of a sample decreases by 64 percent. a)(a) What is the half-life of the element? half-life: b)How long will it take for a sample of 100 mg to decay to 51

64. ## chemistry

A 1.00-g sample of carbon from a modern source gave 15.3 disintegrations per minute. A sample of carbon from an “old” source gave 920 disintegrations per hour. What is the age of the “old” sample of carbon? The half-life of carbon-14 is 5.73×103

65. ## chemistry

Some radioactive nuclides have very short half-lives, for example, I-31 has a half-life of approximately 8 days. Pu-234, by comparison has a half-life of 24,000 years. Explain why both of these examples are dangerous, even though their half-lives are very

66. ## Engineering Math

An unknown radioactive element decays into non-radioactive substances. In 120 days the radioactivity of a sample decreases by 59 percent. What is the half life of the element? How long will it take for a sample of 100 mg to decay to 77 mg? The answer is

67. ## Physics

Half life of radium is 44 years.The sample will reduce to 50% of its orignal value after how many years?

68. ## geology

How old are the oldest meteorites yet studied and what is the minimum age of Earth since Earth is at least as old as the meteorites. We know the oldest meteorites contain equal amounts of uranium 238 and lead 206. Uranium 238 has a half life of 4.5 billion

69. ## science/math

write and solve an algebraic equation to find the original mass of the sample of the radioactive isotope uranium -235, which has a half-life of 704 million years your sample is about 700 million years old and weighs 120 grams

70. ## AP Calculus

An Initial amount of 100 grams of Thorium-234 decays according to the model: dP/dt=-0.02828P (where t is measured in years). a) Find the equation for the amount of Thorium left after t years. b) Determine the half-life of this radioactive isotope c) How

71. ## A.P. Chemistry

Thorium-232 undergoes alpha decay and has a half-life of 1.4 * 10^10 years. How long will it take for a 1.00mg sample of thorium-232 to be reduced to 0.5mg?

72. ## Calculus

The half-life of Kryponite-123 is 40 years. Suppose we have a 700-mg sample. Find the decay k, and the expected amount of Kryptonite left after 30 years. I need help setting this problem up.

73. ## science

Im having trouble understanding Half life and what not... 1.If each roll of the dice represents 10,000 years, what is the approximate half-life (in years) of the element Lokium? 2. If each roll of the dice is 10,000 years, what is the approximate half-life

74. ## math

one fifth of my life I wanted to become a teacher. 3/25 of my life I was a teenager. 9/25 of my life I was married to my husband. Three-fifth of my life my son was born. Fifteen years after that, my daughter was born. Seven years after that I got a divorce

75. ## science

Please help me with this question.... The isotope caesium-137, which has a half-life of 30 years, is a product of nuclear power plants. How long will it take for the amount of this isotope in a sample of caesium to decay to one-sixteenth of its original

76. ## physics

Radioactive nuclei are produced in an irradiated sample at the rate of 10 s-1. If the number in the sample builds up to a maximum of 1000, calculate the mean life and the half-life of the radioactive nuclei Using dN / dt = P - λ N dN / dt = 1000n /10/ 1 =

77. ## chemistry

The half life of gold-197 is 10.6. What fraction of a sample remains after 21.2 years?

78. ## science

Cobalt-60 has a 30 year half-life. How much of an 80 gram sample would remain after 60 years?

79. ## Chemistry

If the half life of Pu-239 is 2.4 x 10^4 years, how many years are required for a 20-gram sample of plutonium-239 to be reduced to a mass of 5 grams?

80. ## half life

tritium has a half life of 24.3 years .a sample of 0.1 is produced . will tthe mass of tritium change after 24.3 years

81. ## Science/Chemistry

22Na has a half-life of 951 days. How many grams of a 1.00 kg sample would be left after 4 years?

82. ## chem

Radioactive substances decay by first-order kinetics. How many years would be required for a sample containing strontium-90 to decrease to 58.32% of its initial activity? The half-life of strontium-90 is 2.88e1 years.

83. ## physics

The half-life of carbon-14 is 5730 years. How much of a 50 g sample of carbon-14 is present after 11,460 years?

84. ## College Algebra

The half-life of a radioactive material is about 34.6 years. How much of a 1-gram sample of the material is left after 30 years?

85. ## Calculus

Ba has a half-life of 283.2 hours. How long would it take for the 50 mg of Ba in a sample to decay to 1.0 mg?

86. ## chem

A typical dose of a radioactive sample is 27.0 mCi. How long does it take for the activity to reduce to 0.100 mCi? The half life of the sample is 211,000 y.

87. ## calculus

a radiotactive isotope lose 1/5 of its atoms in a sample decay after 14 years. find the half life.

88. ## physics

If the physical half-life of sulfur-35 is 87.1 days, and the biologic half-life in the testicle is 632 days, what is its effective half-life in this organ? I know i have to find the time and then the half-life. But im having trouble finding the time

89. ## math

The half life of iodine - 131 is 8 days. How long will it take for 7/8 of the sample to decay?

90. ## ryancon

The half-life of rubidium-87 (natural absorbance 27.83%) is 5.1x10^11 years. What mass of rubidium is present if an average sample decay rate of 35.0 disint./sec is detected? I've already converted years to seconds but not sure what to do after..

91. ## chemistry

A radium-226 sample initially contains 0.112mol. How much radium-226 is left in the sample after 6400 years. The half-life of radium-226 is 1600 years.

92. ## s103

the isotope caesium -137, which has a half life of 30 years, is a product of nuclear power plants. How long will it take for the amount of this isotope in a sample of caesium to decay to one sixteenth of its original amount? - explain answer 1/16 = 1/2^x

93. ## chemistry

With a half-life of 14.3 years, how long will it take for100 g of phosphorus32 to decay to 12.5 mg?

94. ## Physics HELP HELP

(for some reason I keep getting this wrong. I put 90 for c, 5.6 for h and 22 for M(x), Then I took the natural log of both sides, but I keep getting it wrong) The mass of a radioactive element at time x is given by the equation below, where c is the

95. ## math

You have just isolated a new radioactive element. If you can determine its half-life, you will win the Nobel Prize in physics. You purify a sample of 2 grams. One of your colleagues steals half of it, and eight days later you find that 0.1 gram of the

96. ## Science economic

Cesium 138 has a half life equal to 32.2 minutes. how long will it take for 2/4 of this sample to decay

97. ## Math

How long will it take for a 1 g sample of Polonium 210 to lose all but 1/28 of its radioactivity if the half-life is 140 d?

98. ## Math

How long will it take for a 1 g sample of Polonium 210 to lose all but 1/28 of its radioactivity if the half-life is 140 d?

99. ## Chemistry

After 1.78 years, 1.990 g of a radioisotope remains from a sample that had an original mass of 2.000 g. Calculate the half-life of the isotope.

100. ## calculus

Assume a substance has a half-life of 11 years and the initial amount is 144 grams. How much remains at the end of 5 years? How long will it be until only 30 % remains?