Tuesday

May 3, 2016
Number of results: 1,083

**chemistry**

I am having trouble understanding what the concept is for writing these out. Write a balanced nuclear equation for the alpha decay of each of the following radioactive isotopes: curium-243, 22589Ac
*December 5, 2013 by ellie*

**math**

if the rate for radioactive decay for a substance is r=-.0063 and time is being measured in days how do you find the half-life of the substance to the nearest hour?
*March 30, 2009 by mike*

**math**

Show that if a radioactive substance has a half life of T, then the corresponding constant k in the exponential decay function is given by k=-ln(2)/T I'm confused about how to show that that is true.
*September 4, 2014 by lucy*

**Chemistry**

The radioactive nuclide 18F decays by first order kinetics with a half life of 1.83 hr. How many hours will it take for 68.5% of a give quantity of 18F to decay?
*April 27, 2015 by Molly*

**Physics Help Please! Decay Questions**

archaeologist digging at the site of an ancient settlement discover the remains of a wooden structure. carbon 14 dating of the wood from the structure finds a decay rate of 180 decays/min. Knowing that the decay rate for living wood is 600 decays/min and the decay constant for...
*April 28, 2015 by Anonymous*

**Science**

What can scientists learn from the rate at which radioactive elements decay? A. a rock's absolute age* B. the relative age of rock layers C. where one soil horizon ends and the next begins D. the difference between molds and casts. After six half-lives, what percentage of a ...
*October 15, 2013 by Anonymous*

**Science**

What can scientists learn from the rate at which radioactive elements decay? A. a rock's absolute age* B. the relative age of rock layers C. where one soil horizon ends and the next begins D. the difference between molds and casts. After six half-lives, what percentage of a ...
*October 16, 2013 by Anonymous*

**Science**

What can scientists learn from the rate at which radioactive elements decay? A. a rock's absolute age* B. the relative age of rock layers C. where one soil horizon ends and the next begins D. the difference between molds and casts. After six half-lives, what percentage of a ...
*October 16, 2013 by Anonymous*

**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 substance decays to 95 ...
*March 19, 2012 by ronnieday*

**Physics**

Can someone give me an example of how to use this formula: 15.Obtain three half-life (T0.5) times from the graph. Average them.(T0.5)av. Or is there a web site i can go to that shows all steps to using pennies for radioactive decay experiment? .
*November 15, 2007 by Will*

**Algebra**

Determine if the equation y = 2^x represents exponential growth or decay I thought at first it was growth but now I think it might be decay because there is no "b" in a parentheses so do I assume b is less than 1 so it's decay? Please help
*November 22, 2010 by Jason*

**Science**

How much of a radioactive material with a half-life of 12,000 years is left after 36,000 years of decay?
*April 17, 2009 by Angie*

**precalculus**

Twenty percent of a radioactive substance decays in ten years. By what percent does the substance decay each year?
*March 3, 2011 by katrina*

**physics ASAP**

Can someone give me an example of how to use this formula: Obtain three half-life (T0.5) times from the graph. Average them.(T0.5)av. Or is there a web site i can go to that shows all steps to using pennies for radioactive decay experiment? .
*November 18, 2007 by Will*

**Science- Earth and its History**

What can scientists learn from the rate at which radioactive elements decay? A. a rock's absolute age* B. the relative age of rock layers C. where one soil horizon ends and the next begins D. the difference between molds and casts. After six half-lives, what percentage of a ...
*October 15, 2013 by Anonymous*

**Pre Calculus**

Exponential growth and decay find the half life of a radioactive substance if 220 grams of the substance decays to 200 grams in 4 years?
*October 25, 2011 by Josh*

**physic**

In a serious accident, a nuclear power plant's reactor vessel cracks, and all of the cooling water drains out. Although nuclear fission stops, radioactive decay continues to heat
*May 6, 2014 by joseph*

**geology / science**

the age of granite can be determind using radiometric dating, explain the basis for the determination of a 238 U- Pb radiometric date of 1120 Ma for a granite. I have as the answer 238 U decays to Pb with an experimental law, that is the amount of U and Pb in granite are ...
*April 18, 2007 by bex*

**ap calculus**

suppose that the amount in grams of a radioactive substance present at time t (in years) is given by A (t) = 160e-.70t. Find the rate of decay of the quantity present at the time when t = 4
*December 2, 2012 by steve b*

**pre calc**

A 50 gram sample of radioactive strontium will decay to 32 grams in 18 years. a. Find an equation that will model how much of our sample M will remain after t years.
*April 27, 2016 by andi*

**Chemistry**

Each of the following nuclides is known to undergo radioactive decay by production of a beta particle, ^0_-1e. Write a balanced nuclear equation for each process. (Use 'e' for an electron, 'p' for a positron, and 'n' for a neutron. Omit states-of-matter from your answer.) a...
*November 27, 2010 by Jane*

**Chemistry please check**

1. All of the naturally occurring radioactive decay series end when the radioactive elements have decayed to bismuth (Bi) hydrogen (H) lead (Pb) uranium (U) answer: Uranium (U) 2. This type of radiation can easily pass through a human. gamma ultra-violet beta alpha answer: ...
*February 15, 2008 by Mary*

**Chemistry**

The half-life for radioactive decay of 14C is 5730 years (it emits β-particles 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?
*April 8, 2010 by Zoa*

**12th grade**

The radioactive isotope of Carcon (^14C)has a half life of 5730. What is the decay constant of ^14C? If we start with a sample of 1000 carcon nuclei, how many will be left in 22920 years time?
*April 8, 2010 by Moe*

**Pre-Cal**

The radioactive isotope of Carcon (^14C)has a half life of 5730. What is the decay constant of ^14C? If we start with a sample of 1000 carcon nuclei, how many will be left in 22920 years time?
*April 8, 2010 by Moe*

**AP Environmental Science (URGENT)**

Strontium-90 is a radioactive waste product from nuclear reactors. It has a half-life of 29 years. How many years will it take for a quantity of strontium-90 to decay to 1/16 (one-sixteenth) of its original mass?
*January 11, 2012 by Heather*

**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.
*February 22, 2014 by sara*

**science**

radioactive decay occurs when atoms a) lose mass b) join with atoms of another element c) break down to form atoms of another element d) are exposes to chemical weather
*December 13, 2013 by victoria*

**chemistry**

Rates of chemical reactions usually depend on temperature and pressure. However, half-life of all radioactive elements is independent of both T and p. How can these decay rates be independent of T if we beleive in the Arrhenius equation?
*July 27, 2010 by Jin*

**college**

a certain radioactive isotope has a half life or 850 years.how many years would it take for a given amount of this isotope to decay to 70% of that amount?
*December 2, 2010 by Kiesha*

**calculus**

The rate of decay in the mass, M, of a radioactive substance is given by the differential equation dM dt equals negative 1 times k times M, where k is a positive constant. If the initial mass was 100g, then find the expression for the mass, M, at any time t.
*July 17, 2015 by Anonymous*

**chemistry**

The half-life for the radioactive decay of calcium-47 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?
*September 26, 2012 by Shay*

**physis**

Search: 2. Explain how radioactive decay has always warmed the Earth from the inside, and nuclear fusion has always warmed Earth from the outside.
*January 26, 2014 by barbara*

**Physic II**

The decay constant of a radioactive nuclide is 9.5x10^-3 s^-1 . At given instant, the activity of a specimen of the nuclide is 80 mCi. The time interval required for the activity to decline to 40 mCi is closest to: ?
*April 30, 2014 by huline3*

**Chemistry**

The half-life of phosphorus-32 is 14.26 days. The decay constant is k=4.86×10−2/days. If you accidentally spill phosphorus-32 onto your shoe, how long would it take before 99.9% of the radioactive material has decayed so that you can safely wear the shoes again?
*May 1, 2011 by Anonymous*

**chemistry**

Radioactive decay is a process that follows first-order kinetics. The half-life of 32P is 0.03920 years; how long (in minutes) would it take for the amount of 32P to decrease to 53.25% of its initial amount? I don't understand at all what to do here
*May 11, 2014 by sara*

**Physics Help Please**

archaeologist digging at the site of an ancient settlement discover the remains of a wooden structure. carbon 14 dating of the wood from the structure finds a decay rate of 180 decays/min. Knowing that the decay rate for living wood is 600 decays/min and the decay constant for...
*April 28, 2015 by Anonymous*

**Science**

Which of the following units are in order from smallest to largest? a) Epoch, period, era. b) Era, epoch, period. c) Period, era, epoch. d) Epoch, era, period. True or False? Folding, as well as motion along faults, can change the position of rock layers and how they line up ...
*September 23, 2014 by Sarah*

**Chemistry **

The age of wine can be determined by measuring the trace amount of radioactive tritium, 3H, present in a sample. Tritium is formed from hydrogen in water vapor in the upper atmosphere by cosmic bombardment, so all naturally ocurring water contains a small amount of this ...
*February 1, 2015 by Anonymous*

**Math+Growth/Decay**

3e^2x = G -3e^2x = G -3e^-2x = D 1/8e^2x = G -1/8e^-2x = D Would that be correct? I just made these examples up in my head. How can you tell if its growth or decay? I just look at the exponents. If is a negative then its decay? if its positive then its growth?
*March 11, 2009 by Chopsticks*

**Physics**

Is a small or large decay constant best for protection against gamma radiation? Hint: Calculate half thickness. Example: Decay constants for Pb, Al, water, and Fe are 0.77, 0.16, 107, and 0.44. Which is better for radiation shielding? The larger the decay constant, the fewer ...
*April 30, 2007 by Caleb*

**Physics**

A radioactive isotope of Bismuth undergoes Beta Decay with a half-life of 22 days. How long (in days) will it take the Activity (A) of the sample to decrease to one-ninth of its original value? Assume that the original activity is A0.
*November 30, 2015 by Ash*

**chemistry**

a radioactive material is undergoin nuclear decay. After 40 minutes, 25% of the sample remains. What is the half life of the sample? Pls say the formula how to calculate it a)10 mins b) 20 mins c) 40 mins d)80 mins e) 160 mins
*May 28, 2012 by star*

**Calculus-derivatives**

Verify if these are correct answers. 1. The derivative of f(x)=e^2x -e^-2x is f'(x)=2e^2x - 2e^-2x? 2.A certain radioactive substance is decaying so that at time t, measured in years, the amount of the substance, in grams, given by the function f(x)=3e^-3t. What is the rate of...
*March 6, 2012 by Matthew*

**Physics Help Please**

Scientists at Oak Ridge National Laboratory confirmed the existence of element 104 by creating 3000 atoms of it. If radioactive decay caused the number of atoms to drop by half within 4.0 s, how many atoms were left after 12 s? Show work please! Thank you!
*May 2, 2015 by Kim*

**Science**

Natural Uranium contains 15 percent Sm147. Sm147 is radioactive and decays by alpha decay. What will be the number of disintegrations per gram per second of the natural element? The half-life of Sm147 is 1.3x1010 years.
*September 30, 2012 by Nivia*

**chemistry**

Radioactive waste is difficult to dispose of due to the long time periods needed before the radiation effectively disappears. The US protocol is to store the waste for 10 half-lives of the material after which the waste is no longer considered radioactive. After this time, ...
*February 14, 2015 by danny*

**science**

Predicting Table of radioactive isotopes below Isotope type of decay Uranium-238 Alpha Nickel-63 Beta Iodine-131 Beta Radium-226 Alpha With the help of a periodic table, predict the element that forms in each case. Explain your reasoning.
*May 4, 2014 by Andrean*

**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 10 3min looks like ...
*March 4, 2007 by jojo*

**calculus**

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 half-life of the substance? (b) How long would it take the sample to decay to 65% of its original amount?
*November 9, 2012 by kela*

**chemistry**

the longest lived radioactive isotope yet discovered is the beta-emitter tellurium-130.it has been determinded that it would take 2.4 x 10^21 years for 99.9% of this isotope to decay. write the equation for this reaction, and identify the isotope into which tellurium-130 decays.
*July 12, 2010 by penelope*

**Pre Calc**

The half-Life of radioactive earthium is 2651 years. Find how many years it will take 100 grams of earthium to decay to 10 grams. I know the equation is A=Ae^(-rt) I tried working it out but I think I am doing it wrong. I did 10=100e^(-r*2651) Can anyone help? Thanks a lot
*January 13, 2011 by Alex*

**Science**

When Marie Curie Isolated uranium from pitchable, she realized that the [itchable was more radioactive than the uranium she had extracted. What did she conclude about her observations? pitchblende itself is a radioactive element the pitchblende sample contained an unknown ...
*January 7, 2015 by jeje*

**ChemB**

measurements of carbon 14 taken from linen wrappings of the book of isaiah from the dead sea scrolls indicate that the scrolls contain 79.5% of the carbon 14 expected in living tissue. how old are these scrolls if the half life of carbon 14 is 5730 years? All radioactive decay...
*January 22, 2012 by L.Bianchessi*

**Chemistry**

Write a nuclear equation for the following: Iodine 131 undergoes beta decay two times Plutonium 239 is an alpha emitter Th 234 undergoes beta decay once and then alpha decay How do I go about writing nuclear equations?
*December 6, 2010 by Jake*

**College Algebra**

This exercise uses the radioactive decay model. A wooden artifact from an ancient tomb contains 80% of the carbon-14 that is present in living trees. How long ago was the artifact made? (The half-life of carbon-14 is 5730 years. Round your answer to the nearest whole number...
*August 3, 2015 by Melany*

**Algebra**

Two different radioactive isotopes decay to 10% of their respective original amounts. Isotope A does this is 33 days, while isotope B does this in 43 days. What is the approximate difference in the half-lives of the isotopes? 3 days 10 days 13 days 33 days
*July 14, 2014 by Junior*

**Linear Algebra**

whats the exponential decay equation for 100 atoms that decay 1/20 per day
*January 12, 2012 by Anonymous*

**MATH help**

a certain radioactive isotope has a half life of approx 1,300 years . How many years to the nearest year would be required for a given amount of this isotope to decay to 55% of that amount. So I am not sure where to put the 1,300 1,300=2600*e^t or A=x*e^1300
*September 26, 2011 by HM*

**MATH help**

a certain radioactive isotope has a half life of approx 1,300 years . How many years to the nearest year would be required for a given amount of this isotope to decay to 55% of that amount. So I am not sure where to put the 1,300 1,300=2600*e^t or A=x*e^1300
*September 26, 2011 by HM*

**Math**

a certain radioactive isotope has a half life of approx 1,300 years . How many years to the nearest year would be required for a given amount of this isotope to decay to 55% of that amount. So I am not sure where to put the 1,300 1,300=2600*e^t or A=x*e^1300
*September 27, 2011 by HM*

**MATH help**

a certain radioactive isotope has a half life of approx 1,300 years . How many years to the nearest year would be required for a given amount of this isotope to decay to 55% of that amount. So I am not sure where to put the 1,300 1,300=2600*e^t or A=x*e^1300
*September 27, 2011 by HM*

**Science**

What can scientists learn from the rate at which radioactive elements decay? A. a rock's absolute age* B. the relative age of rock layers C. where one soil horizon ends and the next begins D. the difference between molds and casts. The relative age of a rock is A, its age ...
*December 15, 2015 by Brittany P.*

**chem**

Nuclide X has decay constant 1.08 h-1. It can decay in 2 branches, to nuclide Y or to nuclide Z: X --> Y, with decay constant 0.43 h-1, and X --> Z, with unknown decay constant. If there are 10 moles of nuclide X at time t = 0, how many moles of each daughter will there ...
*October 21, 2013 by Jane*

**Geology**

How do I do the foll9owing example? K-40 - A-40 (1.25 billion years) After careful analysis, a geochronologist determines that an unweathered, unmetamorphosed mineral sample contains 7 trillion atoms of the radioactive element K-40 and 105 trillion atoms of its decay product A...
*October 25, 2012 by Nicole*

**Calculus**

A fragment of bone is discovered to contain 20% of the usual carbon-14 concentration. Estimate the age of the bone to the nearest hundred years, given that Carbon-1 is radioactive with half-life of 5730 years and the rate of decay is given by the following differential ...
*May 21, 2014 by Kristin*

**Math with science**

Radioactive iodine treatment is so successful at treating hyperthyroidism that it has virtually replaced thyroid surgery. To the nearest full day, determine how long it will take for 400 millicuries of I-131, which has a half-life of 8 days, to decay to 3.125 millicuries. 56 ...
*July 27, 2008 by Liz*

**physics**

A building has become accidentally contaminated with radioactivity. THe longest lived material in the building is strontium-90 (atomic mass of 90 Sr 38 is 89.9077). If the building initially contained 5.0kg of this subtstance and the safe level is less than 10.0 counts/min, ...
*February 16, 2007 by soojung*

**Science**

If a radioactive isotope has half life of 5 days,how long will it take for its radioactive strength to be a maximum of one thousandth,(1/1000) of its original value?
*December 21, 2010 by Bree*

**chemistry**

If the radiicativr decay of nuclear explosion contains 90 Sr , with a half life of 28.1 years how long will it take for 99 of this radioaioot to decay
*December 5, 2011 by devin*

**College Physics II**

A typical gamma ray emitted from a nucleus during radioactive decay may have an energy of 736 keV. What is its wavelength? A microwave oven produces electromagnetic radiation at λ = 12.1 cm and produces a power of 778 W. Calculate the number of microwave photons produced ...
*November 25, 2010 by VJC*

**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
*November 8, 2009 by Lee*

**Algebra please check my answers**

1) The linear function f(x) contains the points (-10, -29) and (-2, 83). If g(x) = 25x - 50, which statement is true? A. The functions f(x) and g(x) both have positive slopes. <<< B. The functions f(x) and g(x) both have negative slopes. C. The function f(x) has a ...
*May 21, 2014 by David*

**Algebra 2 Decay **

You have 20 grams of phosphorus-32 that decays 5% per day. How long will it take for hlaf of the original amount to decay?
*February 17, 2012 by Peter*

**Biology**

Help please! Do organic fertilizer products (in bags or sacks) decay after some time? If yes, how long will it take to decay?
*March 8, 2012 by Namie*

**Science**

Which of the following characteristics x-ray photon emission? (a)electron capture (b)beta-decay (c)positron emmision (d)gamma-decay
*April 14, 2015 by Olushola*

**chemistry**

The question I am having trouble with is: Scientists originally were uncertain whether the oxygen gas produced during photosynthesis came from CO2, H2O, or from both. How could radioisotope tracers be used to settle that question? Chemistry - DrBob222 6CO2 + 6H2O ==> ...
*April 15, 2013 by Madison*

**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
*January 27, 2013 by Anonymous*

**PHYS**

Help! Initially there are 6x10^9 radioactive of element W (decay constant 0.173/day) in a sample. As a nucleus of W decays, it converts 2.67x10^-28 kg of its mass to energy and releases the energy. How much time (in days) is required for the sample to releae a total of 7.2x10...
*April 25, 2011 by Jenn*

**Science**

When Marie Curie isolated uranium from pitchblende, she realized that the pitchblende was more radioactive than the uranium she had extracted. What did she conclude about her observations? A. Pitchblende itself is a radioactive element. B. The pitchblende sample contained an ...
*March 5, 2015 by Anonymous*

**pre calculus **

The age of a document is in dispute, so archaeologists test for carbon-14. Due to radioactive decay, the amount A of carbon -14 present compared to the initial amount A0 after t years is given by the formula A(t) = A0e^-0.000124t . If 72% of the original amount of carbon- 14 ...
*February 8, 2014 by Raju*

**Science**

Under which of the following conditions would a fossil most likely form? a. a living thing dies and sediment is very slowly deposited on top of its body b. a living thing dies and sediment quickly covers its body* c. a living thing dies and its skeleton is left exposed to the ...
*October 30, 2013 by Anonymous*

**Calculus**

a certain radioactive substance is decaying so that at time t, measured in years, the amount of the substance, in grams, is given by the function f(t)=3e^-3t. What is the rate of decay of the substance after half a year: I first found the derivative of f(t)=3e^-3t which is f'(...
*February 14, 2015 by Sara*

**CHEMISTRY**

Suppose you had a detection device that could count every decay event from a radioactive sample of plutonium-239.052156 (t1/2 is 24,000 yr). How many counts per second would you obtain from a sample containing 0.126 g of plutonium-239? (The mass of Pu-239 is 239.052156 u. ...
*September 5, 2012 by Maryanne*

**Algebra I**

A sample of radioactive material weighing 45 grams has a decay rate of 4.25% each day. The equation y = 45(2.7)–0.0425t can be used to find the amount of material that still remains, where t is the number of days that have passed. Approximately what is the amount of material ...
*March 22, 2011 by Sarah*

**Chemistry**

The age of a rock can be estimated by measuring the amount of 40Ar trapped inside. The calculation is based on the fact that 40K decays to 40Ar by a first-order process. It also assumes that none of the 40Ar produced by the reaction has escaped from the rock since it was ...
*May 21, 2009 by Matt*

**science - biology**

A photosynthesis experiment uses Chlorella to track the route taken by 14C in photosynthesis. The 14C is provided from CO2 and no new sources of CO2 are available. After the experiment the scientist extracts all of the starch produced and analyses the Carbon present. She ...
*May 7, 2011 by jack*

**Science-3 questions.**

Which of the following best describes the climates of Europe and North America during the 1.8 million years of the Quaternary period? hot and dry cool and rainy periods followed by droughts warm and mild a series of ice ages followed by periods when the glaciers melted Which ...
*December 11, 2013 by Princess Anna*

**biology**

14 points Save A photosynthesis experiment uses Chlorella to track the route taken by 14C in photosynthesis. The 14C is provided from CO2 and no new sources of CO2 are available. After the experiment the scientist extracts all of the starch produced and analyses the Carbon ...
*May 7, 2011 by jack*

**Chemistry - radioactivity**

Hello Dr.Bob, could you please help me with this problem: Which of the following nuclides are most likely to decay via beta decay? a)200 78 Pt b)192 78 Pt c)188 78 Pt d)196 78 Pt
*November 17, 2015 by Laurus*

**Science**

Can anyone help me find the half-life of strontium-90? I also need an explanation on how to do it. Thanks!! Radioactive Decay of Strontium-90: At 0 years: 100% remaining At 28 years: 50% remaining At 56 years: 25% remaining At 84 years: 10% remaining At 112 years: 5% remaining.
*March 12, 2015 by Jane*

**chemistry**

if you start with 100mg of radioactive material that has a half life of one hour, how many mg's of radioactive material would you have in 10.2284952 hours?
*February 1, 2011 by carlos*

**Science**

If a radioactive isotope has half life of 5 days,how long will it take for its radioactive strength to be a maximum of one thousandth,(1/1000) of its original value? Can anyone give me a VERY SIMPLE explanation of this please? Thank you.
*January 29, 2011 by Korina*

**Chemistry**

If a 100.0 gram sample of a radioactive isotope goes through three half-lives, how much of the original radioactive isotope will remain?
*January 24, 2013 by OhSnap*

**Concentration and Reaction**

The rate of the following reaction: Radioactive decay of 90Sr, is characterized by the rate constant k = 0.024 year-1. What is the half-life (in years) for this reaction at the same conditions when the initial concentrations are 0.0356 M? (Round your answer to 3 significant ...
*November 20, 2010 by Confused*

**Chemistry**

It takes about 10^16 years for just half the samarium-149 in nature to decay by alpha-particle emission. Write the decay equation, and find the isotope that is produced by the reaction.
*July 14, 2010 by Phillip*

**Exponential Decay**

the half-life of carbon-11 is 20 minutes. How long will it btake for 600g of carbon-11 to decay to 30g?
*October 22, 2009 by Mark*

**physics**

Although most natural potassium nuclei are stable 39K (93.3%) or 41K (6.7%) nuclei, about 0.0117% are radioactive 40K nuclei, which have a half-life of 1.26 billion years. If you were worried about 40K radioactivity and wanted to wait for 97 % of the 40K in the environment to ...
*June 6, 2013 by Anonymous*

**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 growth is exponential...
*November 18, 2015 by Yasmine*

**chemistry**

can you tell me how the beta-plus decay process may be understood (i) at the level of individual nucleons and (ii) at the level of quarks, by writing a decay reaction in each case.
*May 2, 2009 by mathew -b*