Half-Life
Calculate radioactive decay and remaining quantity
How to use Half-Life
- 1Enter the initial amount and the substance half-life.
- 2Enter the amount of time that passes or the balance that you want to collect.
- 3View the remaining amount and the number of half-lives that have passed.
How half-life decay works
N(t) = N0 × (1/2)^(t / t_half)Half-life is the time it takes to halve a certain amount of decay; both radioactive and chemical decay follow this index pattern.
As a result of the index decline, the intra-temporal level of each is reduced by half and will never really be zero for a limited period of time.
The core formula for half-life is N(t) = N0 x (1/2)^ (t/t1⁄2), of which t1⁄2 is half-life. It describes index decline**, not linear decline — the most critical perception. Intuitively, many people think that "two half-lives are all gone" and that 25 per cent remains; after five half-lives, 3.125 per cent remain. It is usually assumed that after 10 half-lives the substance is basically "disappeared" (about one in 1,000).
The half-lives of common radioisotopes are extremely wide, ranging from hours to billions of years: about 5,530 years of carbon-14 (the base of an archaeological year, which exceeds the threshold of approximately 50,000 years), around 8 days of iodine-131 (for thyroid treatment, half-declining in more than one week), about 4.5 billion years of uranium-238 (equal to the Earth ' s age, for a year of geometrics), and about 6 hours of thium-99m (the medical profile, short half-life means that the patient is exposed to radiation for a short period). Half-lives are one of the core considerations in choosing which isotopes are tested or treated.
| After half-life | Residual | Remaining percentage | Declined |
|---|---|---|---|
| 0 | 1 | 100% | 0% |
| 1 | 1/2 | 50% | 50% |
| 2 | 1/4 | 25% | 75% |
| 3 | 1/8 | 12.5% | 87.5% |
| 4 | 1/16 | 6.25% | 93.75% |
| 5 | 1/32 | 3.125% | 96.875% |
| 10 | 1/1024 | About 0.098% | About 99.9 per cent |
The remaining proportion after different half-lives
Frequently asked questions
What's the half-life?
It takes half the time for material decay.
Will it be zero?
It's only coming close; one second of a half-life after n.
Half-life is only for radiation?
No, it also describes many level-I processes, such as drug removal and cooling.
Will half-life be affected by temperature, pressure?
The half-life of radioactive decay is almost unaffected by external conditions such as temperature, pressure, chemical state, which is the key characteristic of its difference from the rate of chemical reaction. Decreasing is a process within the atomic nuclear core, and external energy is far from sufficient to change the nuclear inner state. That is why carbon-14 is reliable for years - whether the samples are buried in the ground or stored in museums, with constant decay rates. Very few of the exceptions relate to electrocapture decay, and the external chemical environment may have minimal (usually less than 1 per cent) effects.
Is a drug half-life and a radioactive half-life one thing?
Mathematics are the same, but different mechanisms. The half-life of the drug refers to the time taken to halve the concentration of the drug in the blood, depending on metabolism and excretion, and is significantly affected by liver and kidney function, age, combined use, etc. The practical point is the interval between medications: drugs with short half-lives need to be taken more frequently, with long half-lives available once a day. It is generally assumed that after five half-lives, the drug is essentially removed from the body (about 3 per cent remaining), which is the basis for determining how long it can be replaced after the withdrawal.