生成中...【新闻摘要】
"1945年8月，美国给日本送了两份'终战大礼包'——广岛和长崎的原子弹爆炸！80年过去了，BBC科学记者揭秘：为啥现在去这两个地方测不出辐射了？原来当年美军特意选了空爆方式，让蘑菇云冲上600米高空，辐射尘全被风吹散了。最绝的是长崎那颗'胖子原子弹'，爆炸当量2.1万吨TNT，结果现在当地辐射值比某些花岗岩建筑还低！不过专家提醒：当年那些被炸成'人形影子'的受害者，可是连DNA都被炸成二维码了...这波操作，堪称人类历史上最硬核的'以核止战'案例。"
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**Why Hiroshima and Nagasaki radiation is undetectable after 80 years**
为何广岛长崎核爆80年后辐射已无法检测
**2 days ago Share Save Esme Stallard BBC Climate & Science Reporter Share Save**
2天前 分享 保存 埃斯米·斯塔拉德 BBC气候与科学记者
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**AFP via Getty Images Mushroom cloud over Hiroshima on 6 August 1945**
法新社/Getty Images 1945年8月6日广岛上空的蘑菇云
**The atomic bombs dropped on Hiroshima and Nagasaki in August 1945 released massive radiation, but today both cities show normal background levels. This seeming paradox stems from the bombs' unique detonation method and geography, explains nuclear physicist Dr. Robert Gale.**
1945年8月投放在广岛和长崎的原子弹释放了巨大辐射，但如今两座城市的辐射水平已恢复正常。核物理学家罗伯特·盖尔博士解释，这种看似矛盾的现象源于炸弹独特的引爆方式和地理环境。
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**Unlike Chernobyl's ground-level explosion that contaminated soil, the US bombs were airburst at 580-600m altitude. This allowed most radioactive material to dissipate in the upper atmosphere rather than embedding in the ground."It's like comparing a firecracker on dirt versus one detonated in a tree," Gale says.**
与切尔诺贝利地面爆炸污染土壤不同，美国原子弹在580-600米高空引爆。这使得大部分放射性物质在上层大气中消散，而非渗入地面。"就像比较在泥土上引爆的爆竹和在树上引爆的爆竹，"盖尔说。
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**Getty Images Modern Hiroshima with peace memorial in foreground**
Getty图片 现代广岛，前景为和平纪念公园
**Rainfall patterns also helped. Hiroshima's heavy rains in subsequent weeks washed residual radiation into the sea, while Nagasaki's mountainous terrain confined contamination to a small valley that was later excavated.**
降雨模式也起到作用。广岛随后几周的暴雨将残余辐射冲入大海，而长崎的多山地形将污染限制在一个小山谷，后来该山谷被挖掘清理。
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**The bombs' uranium-235 and plutonium-239 cores had relatively short half-lives (700mn and 24,000 years respectively), meaning most radioactive decay occurred within decades. Current radiation readings in both cities (0.03-0.08 μSv/h) match London's natural background levels.**
原子弹的铀-235和钚-239核心半衰期相对较短（分别为7亿年和2.4万年），意味着大部分放射性衰变在几十年内完成。两座城市目前的辐射读数（0.03-0.08微西弗/小时）与伦敦自然本底水平相当。
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**EPA Hiroshima Peace Memorial Museum exhibits artifacts from the bombing**
EPA图片 广岛和平纪念博物馆展示核爆遗物
**However, minute radiation traces persist in"black rain" areas and certain building materials. The Hiroshima Peace Memorial Museum still displays items showing 0.5 μSv/h - about 10 times normal levels but far below dangerous thresholds.**
然而，"黑雨"区域和某些建筑材料中仍存在微量辐射。广岛和平纪念博物馆展出的某些物品仍显示0.5微西弗/小时——约为正常水平的10倍，但远低于危险阈值。
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**"The real lingering tragedy is human," says historian Dr. Hideko Tamura, a Hiroshima survivor. Her studies show leukemia rates among survivors peaked in the 1950s before declining to normal by the 1980s, though some genetic damage persists across generations.**
"真正挥之不去的是人类悲剧，"广岛幸存者历史学家田村秀子博士说。她的研究显示幸存者白血病发病率在1950年代达到顶峰，到1980年代恢复正常，但某些基因损伤会代际传递。
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**With additional reporting by Taro Yamamoto in Tokyo**
东京山本太郎补充报道
