Alpha Particle

From decaying radon (氡) atoms can destroy the living cells they strike and increase the likelihood that those cells will later become cancerous. Researchers have now directly demonstrated that neighboring cells not suffering direct hits can be harmed, too. They"ve also taken a step toward showing how this type of radiation, called alpha particles, indirectly hurts those bystanders.
Radon derives from the decay of uranium (铀) and seeps naturally into the air from the ground. It"s the primary environmental source of alpha particles, which contribute to cancer risk by causing aberrations (失常) in DNA. Alpha particles from inhaled radon are second only to smoking as a cause of lung cancer.
Because a person"s exposure to alpha particles typically is low, researchers have had to estimate public health threats from radon by guess from the effects of higher doses of alpha radiation. Such data comes primarily from studies of survivors of the atomic bombs that destroyed Hiroshima and Nagasaki in Japan. The customary extrapolation (推测) assumes that cancer risk is proportional to the dose of radiation even at low doses.
Radiation"s effects in cell cultures don"t necessarily reflect what happens in "a whole organism, with its full range of defense repair mechanisms," says Duport. Processes such as DNA repair and cell death triggered by radiation damage could cancel the effect on, by stander cells observed in the lab, he suggests.
Furthermore, while a bystander effect can contribute to cancer, other cell-to-cell interactions in living tissue "may relieve increased risk." says Barry Michael, a radiation biophysicist at the Gray Cancer Institute in Northwood, England. One of these interactions halts cell division and hence cancer. "The jury is still out on whether cell-to-cell effects lead to a greater or lower risk," Michael says.

单选题 The passage"s main topic is ______.

【正确答案】 D

【答案解析】[解析] 文章第一段就告诉了读者本文的主题：科学研究证实，氡发出的辐射即α粒子不仅使受辐射的人体细胞癌变，而且使非直接辐射的附近的细胞也受到伤害。但是细胞与细胞之间的相互作用是会使癌细胞扩散还是降低细胞扩散，对此科学家们意见不一。

单选题 Alpha particles directly come from ______.

【正确答案】 B

【答案解析】[解析] 根据第一段最后一句“They"ve also taken a step toward showing how this type of radiation, called alpha particles, indirectly hurts those bystanders.”可知，研究者们也已经进一步证明这种叫作α粒子的辐射类型是如何间接地伤害那些局外人的。此处说的辐射类型指代来自腐蚀的氡原子的辐射，所以选B。

单选题 Which of the following is right for alpha particles?

单选题 How do the researchers conduct the study?
A. By studying the data got from the survivors who had experienced atomic radiation.
B. By carrying out the experiments in the lab.
C. By studying the features of radon and uranium.

【正确答案】 A

【答案解析】[解析] 根据第三段内容“researchers have had to estimate public health threats from radon by guess from the effects of higher doses of alpha radiation. Such data comes primarily from studies of survivors of the atomic bombs that destroyed Hiroshima and Nagasaki in Japan.”可知，研究者们不得不通过猜测a粒子的高剂量来估计氡对公众健康的威胁，这些数据主要来自对遭受伤害的日本广岛和长崎的原子弹的受害者的研究，所以选A。