In lots of cases, it's useful to define what's called a half life. It's just useful.
很多情况下有必要，定义一个称为半衰期的量，这个量很有用。
Unlike radioactive iodine, which has a short half life, cesium lingers in the environment.
碘驻留期短一半，而铯则悬浮在环境中。
Now, we also can usefully look at the half life, in this case, in the case of first order kinetics.
现在我们看看，这个一阶反应的半衰期。
Most people are not aware that caffeine has a half life of up to eight hours and can affect not only your ability to fall asleep, but also the quality of sleep you are getting.
大多数人都不知道，咖啡因有一个长达八小时的半衰期，不仅会影响你的入睡能力，而且还会影响你的睡眠质量。
Most famously, uranium-238 decays into lead-206 with a half life of 4.5 billion years, though radioactive rubidium and samarium are also useful for dating things billions of years old.
最为有名的就是铀- 238衰变为铅- 206的半衰期为45亿年，当然放射性铷和钐也同样对测算几十亿年前的物体的年龄很有用。
One of its main advantages is that you are at the centre of things, and that life doesn't come to an end at half-past nine at night.
它的一个主要优点是，你处于事物的中心，并且生活不会在晚上九点半结束。
One is not offered a beautiful princess and half a kingdom every day of one's life!
一位美丽的公主和半个王国，这真是千载难逢的机会！
For a brief moment during that stage of its life cycle, the tongue consists of two tiny half-tubes before merging into one.
在它生命周期的这一阶段，有短暂的一刻，其舌头由两个微小的半管组成，随后融合为一体。
There, every half hour, al-Jazari's most amazing invention comes to life once again.
每隔半小时，加扎利最令人惊叹的发明就会复活一次。
She was born without the lower half of her legs and has worn prosthetic ones all her life.
她生来就没有下半截腿，一辈子都戴着假肢。
The danger of nitrogen-16 is an issue only for plant workers and operators because its half-life is only seven seconds.
氮16的危险只针对于核电站工人和机器操作者而存在，因为它的半衰期只有七秒钟。
So in one universe, the atom decays within the first half-life, and you have an ex-cat. Or ex-qat.
在一个宇宙中，原子在第一个半衰期中衰变了，于是你有了一只前猫。
Radioactive iodine in food is of immediate concern, but it has a relatively short half-life and will naturally decay over a short time frame.
食品中的放射性碘直接引起人们的关注，但是它的半衰期相对较短并将在短时间内自然衰变。
As with radioactivity, stories have a half-life-in other words a period by which half of newly promoted stories are relegated to a nether page.
与放射性一样，故事有一个半衰期-换言之，就是新推荐的故事从首页到被下放的周期。
Iodine 131 has a half-life of eight days, meaning that every eight days it loses half its strength.
碘131有八天的半衰期，这意味着每八天其能量就下降一半。
The city's challenge, chiefly, is to dispose of cesium-137, a radioactive isotope with a half-life of 30 years.
这座城市面临的最大问题就是处理铯—137，这是一种半衰期为30年的放射性同位素。
However, iodine-131 has a short half-life of eight days, which means it will decay away completely in the environment in a matter of months.
但碘- 131则不同，它的半衰期是八天，意味着它需要数月时间才会完全消失。
Business opportunities have a half-life, just like uranium.
商业机会有半衰期，就像铀一样。
So, the half-life is just the time that it takes for half of the reactants to disappear.
半衰期实际上是,一半反应物消失的时间。
However, if the half-life is increased, the situation changes.
然而，如果半衰期增加，情况会改变。
Cesium-137, with a half-life of 30 years, is another dangerous substance emitted in a full-scale nuclear meltdown.
核反应堆完全熔解后，会释放出另一种危险物质铯- 137。铯- 137的半衰期为30年。
It accumulates in the cooling water of nuclear reactors and is often vented in small amounts to the environment. Its half-life is 12 years.
氚聚集在核反应堆的冷却水中，通常以微量排放到环境中，其半衰期为12年。
Radioactive iodine has a half-life of eight days and decays naturally within weeks.
放射性碘的半衰期为八天，几周内自然衰变。
Anyway, if you were to open this imaginary box after one half-life for the atom, you would have 1 a non-kitty or 2 a living-albeit-unreal cat.
反正，如果你在原子的一个半衰期后打开这只想象中的盒子，你可能会得到1一只“非猫”或者2一只活着且不存在的猫。
Now when you look at this you see these people handling the uranium pellets. Now uranium 235 in this form is very low in activity because uranium235 has a very long half-life.
现在，当你们观察这个，你们能看到这些人,铀正在处理铀芯块，现在,在这个形式里，是活跃度是很低的，因为铀5,的半衰期很长。
Nuclear plants use Plutonium-239, which has a chemical half-life of 24, 000 years, meaning anything leaked from Fukushima today will still affect the area for thousands of years to come.
核电站使用的钚239半衰期长达2万4千年，这也就意味着今天从福岛泄漏的物质将在今后几千年内对当地造成影响.
“The more we seek satisfactions in material goods, the less we find them there,” Ryan says. “The satisfaction has a short half-life -- it’s very fleeting.”
“越想在物质生活上寻找满足感，越难找到，”瑞安说：“这种满足感半衰期很短，很容易消失。”
“The more we seek satisfactions in material goods, the less we find them there,” Ryan says. “The satisfaction has a short half-life -- it’s very fleeting.”
“越想在物质生活上寻找满足感，越难找到，”瑞安说：“这种满足感半衰期很短，很容易消失。”
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