評論
打印
Science and technology
科學技術
Measurement
測量
Mass effect
質量效應
A better way to clean the world's one true kilogram
清潔世界上真正一千克的更好方法
IN SEVRES, on the outskirts of Paris, sealed beneath a triplet of bell jars in the laboratories of the Bureau International des Poids et Mesures, sits a small cylinder of platinum-iridium alloy.
在位于巴黎郊區(qū)的塞夫勒市，國際計量局實驗室里，一個三層的鐘形器皿里密封著一個鉑銥合金制成的小圓柱。
Put it on a scale, and it would weigh 1 kilogram—which is appropriate, since this lump of metal is not just a kilogram but The Kilogram, the ultimate reference standard for the way the Systeme internationale d'unites measures mass.
給這個小圓筒稱重，你會發(fā)現(xiàn)它重1千克，這個重量剛剛好，因為這個金屬塊不只代表1千克，而代表著千克單位，是國際單位體系中測重的最終參考標準。
Scientists like the metric system partly for its simplicity—everything is based on powers of ten, which makes calculation easy—and partly for the elegance of its foundations.
科學家親睞公制的部分原因在于其簡潔性，即任何物品以十為進制進行測量，方便運算；還有部分原因在于其成立基礎很好。
Of its seven fundamental units, six are defined with reference to unvarying constants of nature: the ampere, the candela, the second, the metre, the kelvin and the mole.
在那七個基礎單位中，有六個取決于自然界中的恒定物體：安培，坎德拉，秒，米，開氏度以及摩爾。
The kilogram is unique in that it is defined by reference to a lump of crude, man-made stuff.
唯獨只有千克單位取決于未加工的人造金屬塊。
Besides aesthetic niggles, that fact leads to an important practical problem.
除了一些美學上的吹毛求疵，這一事實還引出了一個重要的實際問題。
The international prototype kilogram, the technical name for the cylinder in Sevres, does not in fact keep a constant mass.
事實上，國際千克原器的重量并不是恒定的。
Over the years pollutants from the air settle on its surface, causing its mass to rise.
這些年來，空氣中的污染物落在這個金屬塊表面，增加了其重量。
Attempts to clean it then cause its mass to fall.
而試圖清潔其表面又會減少其重量。
As a result, what science understands by a kilogram has varied, but has done so in a way that is, by definition, unmeasurable.
結果導致千克單位的科學定義變了，根據(jù)這樣的定義，千克是無法測量出來的。
A clean sweep?
擦干凈了沒？
The cleaning that attempts to keep the kilogram constant is done by a member of staff at the bureau, using a combination of steam and a chamois-leather cloth soaked in ethanol and ether.
試圖保持金屬塊重量恒定的清潔任務由國際計量局員工來做，用蒸汽和浸泡過含乙醇溶液的油鞣革布來進行清潔。
But given the sensitivity of modern instruments, which can detect gains or losses of the order of billionths of a kilogram, it must be done properly.
但鑒于現(xiàn)代工具測量十分精細，物體重量增減十億分之一千克都可以測出來，這項清潔工作必須謹慎執(zhí)行。
Too gentle a rubdown leaves contaminants on the surface. Too vigorous a scrubbing erodes the metal itself.
擦拭太過溫柔，其表面會留有污染物；用力過猛，又會擦掉金屬本身的表面成分。
Worse, the IRK is not the only such cylinder in the world.
更糟的是，國際千克原器并不是這個世界上唯一的此類圓柱體。
Dozens of replicas exist in official laboratories in many countries.
還有幾十個類似的復制品存放在許多其他國家的官方實驗室里。
Each must be cleaned to the same exacting standards if it is to remain a true copy of the French original.
如果每個都要和法國原件那個如假包換的話，那么每個圓柱體都要被清潔得和現(xiàn)有法國標準一樣重。
In practice, that has often meant shipping the whole lot back to France so that the same person can scrub them all down.
那樣實際做起來就是要把別國圓柱體運到法國去，由同樣的人來做擦拭工作。
Now, though, Peter Cumpson and Naoko Sano, a pair of researchers at the University of Newcastle, in England, reckon they have come up with a better way.
然而現(xiàn)在，英國紐卡斯爾大學的皮特·坎普森和 佐野直之認為他們想出了更好的清潔方法。
In a paper just published in Metrologia, they describe the results of a method that combines traditional washing with a technique adapted from the chip-manufacturing business, which employs a combination of ultraviolet light and the ozone that such light synthesises from the air to strip pollutants away.
前不久他們在《計量學》上發(fā)表論文說，傳統(tǒng)清潔方法加上紫外線和臭氧這種合成光可以清潔掉金屬表面的污染物。
The idea of using ultraviolet light was first proposed back in the 1990s, says Dr Cumpson, but has yet to be adopted.
采用紫外線這個主意在上世紀九十年代就首次被提出來了，坎普森博士說，但是一直沒被采納。
This latest paper, which reports the results of using the method on strips of platinum-iridium alloy, shows that the method does a good job of removing the carbon-based gunk that settles onto the weights from the air.
根據(jù)這篇最新論文，在鉑銥合金條塊上進行的實驗顯示這種方法能夠很好地去除增加條塊重量的空氣碳黏質物。
Importantly, says Dr Cumpson, unlike a manual rubdown, his procedure can easily be standardised, and the kit necessary to perform it is cheap and widely available, allowing laboratories around the world to keep their own kilogram replicas clean.
重要的是，坎普森博士說，他們的清潔方法是可以標準化的，不像人工擦拭，而且這種方法所涉及的東西既便宜又唾手可得，可以清潔世界上所有實驗室的重量單位復制品。
It is not, however, perfect.
然而這種方法也算不上完美。
Besides atmospheric muck, researchers reckon that other things are altering the masses of the world's kilograms.
研究人員發(fā)現(xiàn)除了空氣中積攢下來的臟東西，其他東西也在影響著國際標準千克的重量。
One significant effect, says Dr Cumpson, is contamination with mercury.
坎普森博士說其中一個關鍵的影響因素就是水銀污染，
The likely source is not atmospheric pollutants, but lab accidents.
其污染源不是空氣污染物，而屬于實驗室偶然事件。
Say you drop a thermometer and it shatters, he says.
比如你把一個溫度計丟掉地面上，里面的水銀散開了，坎普森博士說，
A couple of blobs of mercury fall through the floorboards and evaporate slowly over the years. Some of that mercury is then deposited.
幾滴水銀落在地板上，隨著時間，慢慢蒸發(fā)在空氣中，其中一些會沉積。
Unlike the atmospheric junk, which simply encrusts the surface, mercury seeps into microscopic flaws in the cylinders' surfaces created by the polishing process.
和僅僅落在圓柱表面的空氣污染物不同，水銀會滲進圓柱體在擦磨過程中表面留下的微小缺陷里。
Once it gets in, it's in there for good. You can't remove it, says Dr Cumpson.
只要水銀滲進去了，它就會永遠留在圓柱體里了。你根本無法去除，坎普森博士說。
The missing Planck
被人遺忘的普朗克
It is problems like this—and the fact that the world's kilograms are changing in mass at different rates—that are behind a push to bring the kilogram into line with the rest of the SI, and to define it purely with reference to natural constants.
問題就在于此，再加上世界各國的千克標準重量正在以不同速率變化著，這些都敦促千克單位和SI體系下其他單位一樣恒定，要在純粹參考自然界恒量的基礎上定義千克。
Next year, the International Committee on Weights and Measures will discuss whether to tie it to something called Planck's constant, a number in quantum mechanics that relates the energy level of a photon to its wavelength.
明年，國際重量與測量委員會將會討論是否要將千克和普朗克恒量聯(lián)系起來，普朗克恒量是指量子力學中聯(lián)系光子能及其波長的數(shù)字。
A supersensitive electromechanical scale called a watt balance could then be used to define the kilo with reference to Planck's constant, finally liberating the SI from its reliance on fallible artefacts.
測量極其精準的機電天平—瓦特天平可以在參考普朗克恒量的基礎上定義千克重量，這就使得SI再不用依賴不精確的人工制品了。
That is the theory, at least.
以上至少在理論上是成立的。
But watt balances are fiendishly complicated bits of kit.
但是瓦特天平極其復雜。
There are only a handful in the world, a situation that is unlikely to change for the foreseeable future.
世界上瓦特天平也為數(shù)不多，在可預見的未來，其數(shù)量也不會有增減。
This means that, although the kilo will in theory be defined by an abstract constant, in practice so-called transfer standards will still be needed for the many countries without the nous or the cash to run a watt balance of their own.
這就意味著即使在理論上可以用抽象恒量來定義千克重量，許多國家在實際操作中還是要用到所謂的可變標準，因為他們本身即沒能力也無資金來動用一臺瓦特天平。
Translated into English, the upshot is that outside the most advanced countries, lumps of metal will continue to be used to define the kilo—although they will probably be made of gold, rather than platinum and iridium.
簡單講，就是發(fā)達國家以外的國家和地區(qū)會繼續(xù)用金屬塊來定義千克重量，盡管金屬塊可能用金制成，而非鉑銥合金。
These will be susceptible to exactly the same sorts of contamination that plague the current generations of kilogram.
但金屬塊重量仍會受到同樣的污染。
Luckily, Dr Cumpson's method ought to work on them, too.
所幸的是，坎普森博士的方法對它們也同樣奏效。
