有一个科学术语叫做半衰期（half life）。例如，铀238的半衰期约为45亿年，意思就是，每过45亿年，一个U-238原子核会有一半的概率衰变。有一个著名的射击游戏叫做《半条命》，其实这个游戏的英文名是half life，本意就是“半衰期”，所谓“半条命”实际上是望文生义的误译。

《Half -Life》

为了帮助大家理解这个概念，美国韦尔斯利学院（Wellesley College）的化学教授Mala Radhakrishnan博士写了一首诗《我们半衰期的日子》（Days of Our Half Lives）。

Mala Radhakrishnan

这首诗形式上是一个幽默的感情故事，实际讲的是U-238衰变成一系列核素的过程。我的朋友、科普作家徐泓把这首诗翻译成了中文，下面请大家欣赏。

Days of our half lives

My dearest love, I'm writing you to tell you all that I've been through.

我的至爱，我写信告诉你我所经历的一切。

I've changed my whole identity,

我的身份已经改变彻底，

But loved, I cannot pretend to be.

但曾经爱过，不能掩饰。

When I was uranium 238,

当我还是铀-238时，

You were on my case to start losing weight.

你对我的体重一直挑剔。【注释：on sb's case : 不停地指责】

For five billion years I hoped and I prayed,

我期待和祈祷了五十亿年，

And finally I had an alpha decay.

终于进行了一次α衰变。

Two protons, two neutrons went right out the door,

两个质子、两个中子离开了我的身体，

And now I was thorium 234.

我变成了钍-234。

But my nucleus was still unfit for your eyes,

我的原子核仍入不了你的眼，

Not positive enough for its large size.

尺寸很大却没有足够的正电。

But this time my half-life was really not very long,

但这次我的半衰期并不是很长，

Because my will to change was quite strong.

因为我改变自己的意愿非常强。

It took just a month, not even a millennium,

只用了一个月，不需要千年，

To beta decay into protactinium.

我变成镤，因为一次β衰变。

But you still rejected me right off the bat,

但你马上拒绝了我：【注释：right off the bat : （美国俚语）立刻，马上】

Protactinium—who's heard of that?

镤——有谁听说过？

So, beta decay, I did much more to become uranium 234.

于是又一次β衰变，我重新变回自己，

Myself again, but a new isotope,

以一种新的同位素，铀-234。

You still weren't satisfied, but I still had hope.

你仍然不满，但我心存希望。

Three alpha decays, it was hard, but I stayed on

我又经历了三次α衰变，尽管艰辛，却有始有终，

Through thorium, through radium, and then radon.

成为钍，成为镭，然后成为氡。

I thought I would finally please you,

我想我终于能够让你欢愉，

My mass was a healthy 222.

以我健康的222的质量数。

But you said, although I like your mass,

然而你说，虽然你喜欢这个数字，

I do not want to be with a noble gas.

但是不想跟一个惰性气体在一起。

You had a point, I wasn't reactive,

你说得有道理，我不具备活泼性，

So in order to please you, I stayed proactive.

所以为了取悦你，我保持积极性。

A few days later I found you and said,

几天后我找到你，告诉你我是铅，

Two more alpha decays and now I am lead.

为此我又进行了两次α衰变。

You shook your head,

你摇了摇头表示，

You were not too keen on my mass number of 214.

你不太喜欢我的质量数214。

I had a bad experience with that mass before,

确实有糟糕的体验伴随着这个数字，

An unstable astatine walked right out the door.

曾经溜出门外有个不稳定的砹原子。

So in order to change, I went away,

我离开你为了继续改变，

But all I could do was just beta decay.

可是我只能进行β衰变。

My hopes and my dreams started to go under,

我的希望和梦想开始辜负，

Because beta decay doesn't change a mass number.

因为β衰变不改变质量数。

To bismuth, then polonium, I hoped and I beckoned,

变成铋，再变成钋，

我期待着，召唤着，

My half-life was 164 microseconds.

以164微秒的半衰期，

And then finally I alpha decayed,

终于α衰变为铅-210，

And then I was lead with the prize worthy mass of 210.

一个值得称赞的数字。

I've got to admit I was getting quite tired,

我不得不承认我已十分厌倦，

My patience with you had nearly expired.

我对你的耐心几乎到了极限。

You were more demanding than any I dated,

你比我约会过的任何人都难满足，

And much of my energy had already been liberated.

而我的大部分能量都已经释放出。

But you still weren't happy, but you had a fix,

你仍然不高兴，提出了方案以求满意：

I really like the number of 206.

“其实我喜欢206这个数字”。

So I waited for years until the day,

于是我等待多年，直到这天，

Which began with another beta decay.

我开始再一次β衰变。

And then one more, and finally in the end

接着又一次，终究

I alpha-ed to lead 206, my friend.

我α衰变成了铅-206。

To change any further I wouldn't be able,

至此，我无力进行任何改变，

No longer active, but happily stable.

不再活跃，变得稳定，我很情愿。

It took me billions of years to do,

这花费了我亿万年时间，

And look how I changed and all just for you.

看我完全为你如何改变。

And wait, what did you say?

——等一下，你说什么呢？

“You've gotten so old,

“你已经这么老了，

that I'd rather be with a young lass of gold”

而我更愿意和年轻的金姑娘在一起。”

Well, I gave up.

好吧，我放弃。

We're through, my pumpkin.

我们结束了，亲爱的。【注释：pumpkin : （口语）亲爱的】

Shouldn't all my effort be counting for something?

难道我所做的努力什么都不值？

Well, you won't be able to rule me anymore,

不，以后你再也不能对我控制，

Because I'm leaving you, not for one atom, but four.

因为我要离开你，不是为了一个，而是四个原子。

That's right. When you were away defusing,

没错，正当你在外面无所事事，

I met some chlorines that I found quite amusing.

我遇到了一些很有趣的氯原子。

So we're going to form PbCl4,

我们将要结合成四氯化铅，

And you won't be hearing from me anymore.

我的情况你再也不会了然。

See, over the years I've grown quite wise,

经年的我已经豁然开朗，

I've learned that love is about compromise.

我明白了爱意味着互让。

You still have half of your half-lives to live,

你的生命还有半个半衰期，

So now you go out there, it's your turn to give.

现在轮到你去给予和努力。