I'm on a balcony where I see a European city ravaged by giant long-legged nightmares, while a wire-festooned tower climbs infinitely into the sky. I'm explaining this because you probably don't have a VR headset, and I want you to understand what I'm doing. I can wiggle my fingers and check my stats.

If there are 100 g of cobalt-60 in a sample, how much will be left after 15 years?ДЎ5 years is three half-lives so the fraction remaining will be (ВЅ) 3 = 1/8 = 12.5 g.My hands in Half-Life: Alyx can be seen floating in front of me. Suppose a sample has a count rate of 3,200 Becquerel (Bq) at the start, then its count rate after 8 days would be 1/16th of 3,200 Bq = 200 Bq. So if the half-life is two days, four half-lives is 8 days. This could then be incorporated into other data.

a decimal - 1/16 = 0.0625 of the original sample.

a fraction - a ВЅ of a ВЅ of a ВЅ of a ВЅ remains which is ВЅ x ВЅ x ВЅ x ВЅ = 1/16 of the original sample.

This could be stated as a fraction, decimal or ratio.ДЇor example the amount of a sample remaining after four half-lives could be expressed as: It should also be possible to state how much of a sample remains or what the activity or count should become after a given length of time. If a sample of a tree (for example) contains 64 grams (g) of radioactive carbon, after 5,730 years it will contain 32 g, after another 5,730 years that will have halved again to 16 g. The half-life of radioactive carbon-14 is 5,730 years. This process continues and although the activity might get very small, it does not drop to zero completely.

A third two-day period from four days to six days, sees the activity halving again from 20 Bq down to 10 Bq. Note that this second two days does not see the activity drop to zero, only that it halves again. It takes another two days for the activity to halve again, this time from 40 Bq to 20 Bq. The illustration below shows how a radioactive sample is decaying over time:ДЇrom the start of timing it takes two days for the activity to halve from 80 Bq down to 40 Bq. One Becquerel is equal to one nuclear decay per second. The activity of a radioactive substance is measured in Becquerel (Bq). These signals can be converted into clicking sounds, giving a count rate in clicks per second or per minute. It gives an electrical signal each time radiation is detected. The Geiger-Muller tube is a device that detects radiation. Half-life is the time it takes for half of the unstable nuclei in a sample to decay or for the activity of the sample to halve or for the count rate to halve.

Scientists cannot tell when a particular nucleus will decay but they can use statistical methods to tell when half the unstable nuclei in a sample will have decayed. It is not possible to say which particular nucleus will decay next but given that there are so many of them, it is possible to say that a certain number will decay in a certain time. A block of radioactive material will contain many trillions of nuclei and not all nuclei are likely to decay at the same time so it is impossible to tell when a particular nucleus will decay.

Half life in real life