How many half-lives have passed if a sample contains one-eighth of its original amount of radioactive material
455072
3 because:\n\n1 divided by 2= 1/2\n\n1/2 divided by 2=1/4\n\n1/4 divided bt 2=1/8
951626
It is very simple.  This method will help you when the fraction is not a nice one like 1/16.\n\n\nAt time zero you have, let's say N0 = 1600 atoms of protactinium-234.  After 26.76 hours, 1/16 remain:\n\nNt = 1600 / 16 = 100.\n\nNow in radioactive decay:\n\nNt = N0 * exp (-Lamda * t).\n\nYou have t, Nt, N0.  Calculate lambda\n\n100 = 1600 exp (-Lambda * 26.76)\n0.0625 = exp (-Lambda * 26.76)\nTaking Ln on both sides\nLn 0.0625 = - Lambda * 26.76\nLambda = - (Ln 0.0625) / 26.76 = 0.10361 h^(-1)\n\nHalf life = (Ln 2) / Lambda = 6.69 hours
830914
b) 16.5 hours\n\n66 hours/4 half lives = 16.5 hours\n\nYou start with 40 mg.  After 16.5 hours, you're left with 20 mg.  After another 16.5 hours, you have 10 mg.  After another 16.5 hours, you have 5 mg.  After yet another 16.5 hours, you have 2.5 mg.
985750
All elements with atomic number higher than 92 (Uranium) are artificially produced. To do so, they accelerate a neutron (which is hard since neutron has no charge) and then bombard a lighter nucleus with them. The nucleus absorbs a neutron, releases an electron (beta ray) and keeps a proton, so the atomic number will raise one number. (n -> e + p)\nThey do it again and again until they reach the element that they want. but the higher the atomic number, the lower the half life will be (they will last from few months to few micro seconds) when they say that an element is not yet produced but they put it in the periodic table, this means they have evidence that is should exist, but since the half life is short they are unable to detect it, so they have to wait for technology to advance so they can detect it.
414512
As soon as a living organism dies, it stops taking in new carbon. The ratio of carbon-12 to carbon-14 at the moment of death is the same as every other living thing, but the carbon-14 decays and is not replaced. The carbon-14 decays with its half-life of 5,700 years, while the amount of carbon-12 remains constant in the sample. By looking at the ratio of carbon-12 to carbon-14 in the sample and comparing it to the ratio in a living organism, it is possible to determine the age of a formerly living thing fairly precisely. \nA formula to calculate how old a sample is by carbon-14 dating is: \n\n\nt = [ ln (Nf/No) / (-0.693) ] x t1/2 \nwhere ln is the natural logarithm, Nf/No is the percent of carbon-14 in the sample compared to the amount in living tissue, and t1/2 is the half-life of carbon-14 (5,700 years). \n\nSo, if you had a fossil that had 10 percent carbon-14 compared to a living sample, then that fossil would be: \n\n\nt = [ ln (0.10) / (-0.693) ] x 5,700 years \nt = [ (-2.303) / (-0.693) ] x 5,700 years \n\nt = [ 3.323 ] x 5,700 years \n\nt = 18,940 years old \n\nBecause the half-life of carbon-14 is 5,700 years, it is only reliable for dating objects up to about 60,000 years old. However, the principle of carbon-14 dating applies to other isotopes as well. Potassium-40 is another radioactive element naturally found in your body and has a half-life of 1.3 billion years. Other useful radioisotopes for radioactive dating include Uranium -235 (half-life = 704 million years), Uranium -238 (half-life = 4.5 billion years), Thorium-232 (half-life = 14 billion years) and Rubidium-87 (half-life = 49 billion years).
941865
It is quite reliable when properly applied.  It can't be trusted when:\n\n(1) it is applied so far in the past that it is extreme extrapolation of limited data.\n\n(2) the sample and its food source were radiation-protected.\n\n(3) the sample came from a situation or time where the C14/C12 ratio was different from what it is today, or is unknown.\n\nFor all these reasons, the farther back in time you try to read, the less reliable the dating.
705042
No, radioactive decay is pseudo-random process. Even if you had two samples of the same material with the same mass, there is nothing to guarantee that the same number of particles would be ejected. If you decay time is small enough then statistically the two sample will yield similar results. \n\nIn your case if you assume the two samples are the same isotope, then you would expect the larger sample to emit twice as many particles as the smaller sample. The number of decays is proportional to the mass.
608949
cant answer secifically, but you should be able to back calculte taking elements present today and using the half lives as your main variable.
54817
Are you referring to radioactive decay rates of isotopes of the three elements (copper, aluminum and iron) that you listed? If so, the first answer gave you some info, but you should check it (e.g., because copper has more than one isotope and they all have different half-lives). One can't specify a half-life for stainless steel because it's a mixture of metal elements whose ratio isn't specified by the generic name.\nIf instead you're referring to some measure of chemical activity, such as corrosion life, you haven't given enough details. (Well actually you haven't given enough details either way.) You could google corrosion rate, reaction rate and similar terms if you want to go further with that.
163467
Probably most of it comes from radioactive decay.
815878
Radio-active decay is measured with half lives, that is a time when half the matter of a sample would have disintegrated.  That is a rate, which is not a speed, so the speed of light is totally unrelated.
860645
The its age is really close to 5730 years since almost 1/2 of the Carbon 14 remains.  The percentage left P = (1/2)^(T/H) where T is the time that has passed, and H is the half-life in years.  We know H is 5730 years, the current percentage left is 51% (0.51), and we want to find T.\n0.51 = 0.5^(T/5730)\nlogbase0.5 0.51 = T/5730\nT = 5730 logbase0.5(0.51)\nlog base 0.5 of 0.51 = ln(0.51) / ln(0.5) or 0.971431\nSo T = 0.971431 x 5730 or 5,566 years ago
164462
I'd estimate..... About 28 half-lives have passed, but don't trust me.
165489
The half-life of a radioactive element is the time it takes for half of its atoms to decay into something else. \n\nFor example, the half-life of I-125 is 60 days. Therefore, in 60days, one gram of I-125 will turn into half a gram of I-125  and half a gram of something else (the radioactive decay products of Iodin). After another 60 days have elapsed, only a quarter of a gram of the original I-125 will remain.\n\nThe radio active decay product of I-125 is tellurium-125 which is a stable. These elements decay by emitting radiations or capturing electron from near bys shells in order to become stable.
774612
The "half-life" of an element is important for determining the absolute age of a rock.\n\nThe answer is C.
470977
Certain radioactive isotopes have such short half-lives that they almost completely decay into daughter isotopes in less than 10 seconds or even less than 1 second. Look it up on Wikipedia.
715465
1) After k half-lives, the remaining amount of Barium-131 from the m miligrams to start with is: m / 2^k (mg)\n\nIn your case, m = 10 mg and k = 3.\n\n2) Time for m miligrams of any radioactive species to decay to n miligrams is t1.\n\nHalf-life t = t1 / log(2)(m/n)\n\nIn your case, t1 = 45minutes, m = 50mg and n = 6.25mg\n\n3) Density d = p(MW)/RT\n\np = 2\nMW = 14\nR = 0.0821\nT = 273 + 127 = 400