英語聽力文摘 宇宙輻射
Cosmic Radiation
上世紀(jì)早期，科學(xué)家發(fā)現(xiàn)一種神秘的輻射形式會破壞他們的實(shí)驗(yàn)。后來奧地利物理學(xué)家Victor Hess研究發(fā)現(xiàn)輻射可能來自天空。后來他多次坐熱氣球用各種儀器(包括測量放射電荷的驗(yàn)電器)收集資料。一次熱氣球旅行時，遇到日全食，他發(fā)現(xiàn)輻射的放射量維持不變，而推定輻射來自宇宙而非太陽。外太空的輻射蘊(yùn)含帶電的核分子，大多是質(zhì)子(帶正電)，可以穿透大氣層，引發(fā)基因突變和癌癥。
有資料表明每年有十萬多人死于來自太空輻射引發(fā)的癌癥。人們是怎么推斷出癌癥是因宇宙輻射產(chǎn)生?太陽輻射和宇宙輻射具體有什么區(qū)別?臭氧空洞和地球磁場減弱都讓人們遭受更多的輻射，那么是否有辦法能夠阻擋宇宙輻射的侵害?
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(帶電粒子)such as protons(質(zhì)子) and ions(離子).These particles drift to earth from space: The sun is a major source, especially during solar flares(太陽耀斑). 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 (遮擋)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.
注釋：
巡航高度(cruising altitude)：飛機(jī)完成起飛階段進(jìn)入預(yù)定航線后的飛行狀態(tài)稱為巡航。飛機(jī)發(fā)動機(jī)有著不同的工作狀態(tài)，當(dāng)發(fā)動機(jī)每公里消耗燃料最少情況下的飛行速度，稱為巡航速度。飛機(jī)以多大的速度飛行，要根據(jù)飛機(jī)飛行的距離、所需的時間、載荷要求、飛行的安全性、發(fā)動機(jī)的耐久性和經(jīng)濟(jì)性，以及氣候條件等情況確定的裝有不同發(fā)動機(jī)的飛機(jī)，其巡航速度、巡航高度和航程是不一樣的。
太陽耀斑(solar flares)：太陽耀斑是一種最劇烈的太陽活動。周期約為11年。一般認(rèn)為發(fā)生在色球?qū)又校砸步?ldquo;色球爆發(fā)”。其主要觀測特征是，日面上(常在黑子群上空)突然出現(xiàn)迅速發(fā)展的亮斑閃耀，其壽命僅在幾分鐘到幾十分鐘之間，亮度上升迅速，下降較慢。特別是在，耀斑出現(xiàn)頻繁且強(qiáng)度變強(qiáng)的時候。
