英语听力文摘 宇宙辐射

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Cosmic Radiation

上世纪早期，科学家发现一种神秘的辐射形式会破坏他们的实验。后来奥地利物理学家Victor Hess研究发现辐射可能来自天空。后来他多次坐热气球用各种仪器(包括测量放射电荷的验电器)收集资料。一次热气球旅行时，遇到日全食，他发现辐射的放射量维持不变，而推定辐射来自宇宙而非太阳。外太空的辐射蕴含带电的核分子，大多是质子(带正电)，可以穿透大气层，引发基因突变和癌症。

有资料表明每年有十万多人死于来自太空辐射引发的癌症。人们是怎么推断出癌症是因宇宙辐射产生?太阳辐射和宇宙辐射具体有什么区别?臭氧空洞和地球磁场减弱都让人们遭受更多的辐射，那么是否有办法能够阻挡宇宙辐射的侵害?

Did you know that cosmic radiation is up to one-hundred times greater at cruising altitude than on the ground? Learn more on this Moment of Science.

Did you know that cosmic radiation is up to one-hundred times greater at cruising altitude(巡航高度) than on the ground? If you need another reason to dislike flying, this Moment of Science is for you.

Like all radiation, cosmic radiation is made of electrically charged particles(带电粒子)such as protons(质子) and ions(离子).These particles drift to earth from space: The sun is a major source, especially during solar flares(太阳耀斑). Just like more familiar forms of radiation, for example Radon and X-rays, high dose cosmic radiation may be associated with health problems such as cancer.

Luckily, most cosmic radiation is screened out (遮挡)by our atmosphere before it ever reaches the ground. At sea level, the atmosphere is thick and screens out a lot, but at high altitudes, such as the cruising altitudes of many commercial airplanes, we are less protected.

Is this a reason to avoid flying? Well, not really. While radiation levels are greater in aircraft than on the ground, your overall dose is still quite small. You would need to spend thousands of hours in the air to suffer even a slight increase in your risk of health problems. But, cosmic radiation might be a concern for flight crews, who fly day after day over many years. For most of us, when it comes to cosmic radiation we are on pretty safe ground.

注释：

巡航高度(cruising altitude)：飞机完成起飞阶段进入预定航线后的飞行状态称为巡航。飞机发动机有着不同的工作状态，当发动机每公里消耗燃料最少情况下的飞行速度，称为巡航速度。飞机以多大的速度飞行，要根据飞机飞行的距离、所需的时间、载荷要求、飞行的安全性、发动机的耐久性和经济性，以及气候条件等情况确定的装有不同发动机的飞机，其巡航速度、巡航高度和航程是不一样的。

太阳耀斑(solar flares)：太阳耀斑是一种最剧烈的太阳活动。周期约为11年。一般认为发生在色球层中，所以也叫“色球爆发”。其主要观测特征是，日面上(常在黑子群上空)突然出现迅速发展的亮斑闪耀，其寿命仅在几分钟到几十分钟之间，亮度上升迅速，下降较慢。特别是在，耀斑出现频繁且强度变强的时候。