射线为什么能损伤细胞？为什么医生要控制X光剂量？
How does radiation damage cells, and why do doctors limit X-ray doses?
α、β、γ等电离辐射有足够能量从原子中撞出电子，产生的离子和自由基能直接打断DNA链或诱发错误修复。细胞可能死亡，也可能带着突变存活下来，突变长期累积就可能致癌。所以医生在拍X光、CT时尽量压低剂量，用铅衣保护敏感器官，力求辐射获益大于风险。
Ionizing radiation (alpha, beta, gamma) carries enough energy to knock electrons out of atoms; the ions and free radicals produced can break DNA strands or corrupt repairs. Cells may die or survive with mutations that accumulate into cancer over time. That is why X-ray and CT doses are kept as low as possible and lead aprons protect sensitive organs — the goal is benefit far outweighing risk.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#电离辐射 #DNA #剂量
为什么铁是“最稳定”的元素？
Why is iron the most stable element?
每个核子的平均结合能（比结合能）在中铁附近达到峰值。轻核聚变更放能、重核裂变更放能，都趋向铁；所以铁处在能量谷底，最不易再变。
The average binding energy per nucleon peaks near iron. Light nuclei release energy by fusing, heavy ones by fission, both trending toward iron; it sits at the energy minimum and is least eager to change.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#结合能 #铁峰 #核稳定
为什么地球上造出可控核聚变这么难？
Why is practical controlled fusion on Earth so hard?
要让轻核克服排斥并聚合，需上亿度高温与足够密度、足够约束时间，三者乘积需超过劳森判据。磁约束或惯性约束都要同时搞定这三件事，工程极难。
To fuse light nuclei past their repulsion needs temperatures of hundreds of millions of degrees, plus enough density and confinement time—their product must beat the Lawson criterion. Magnetic or inertial confinement must nail all three at once, which is brutally hard.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#核聚变 #劳森判据 #等离子体
什么是核聚变？
What is nuclear fusion?
核聚变是轻核（如氢的同位素）在极高温度和压力下结合成较重核并释放能量的过程。太阳的能量就来自核聚变，人类正努力在地球上实现可控聚变发电。
Nuclear fusion is light nuclei such as hydrogen isotopes combining into heavier ones under extreme temperature and pressure, releasing energy. The Sun is powered by fusion, and humans are working toward controlled fusion power.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#核聚变 #氢 #太阳
核电站与原子弹都靠裂变，原理有什么不同？
Nuclear power plants and atomic bombs both use fission — how do they differ?
中子轰击铀-235等重核使其分裂，放出能量和更多中子，中子再去轰击其他核，形成链式反应。反应堆用控制棒吸收中子，把链式反应维持在中子产额恰好平衡的稳定速率，还要靠慢化剂调节中子速度；原子弹则把裂变材料瞬间压缩到超临界，让链式反应在极短时间内失控增殖、释放全部能量。原理相同，差别在控制。
A neutron strikes a heavy nucleus such as uranium-235, splitting it and releasing energy plus more neutrons, which split further nuclei in a chain reaction. A reactor uses control rods to absorb neutrons and a moderator to tune neutron speeds, holding the chain at a steady rate; a bomb compresses fissile material to supercriticality so the chain multiplies explosively in microseconds. Same physics, opposite goal.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#核裂变 #链式反应 #控制棒
为什么说放射性物质的“半衰期”是固定不变的？
Why is a radioactive material's half-life said to be fixed?
半衰期是半数原子核衰变所需的平均时间，只由核本身决定，不受温度、压强或化学状态影响。所以它像原子的“内部时钟”，可用来定年。
The half-life is the average time for half the nuclei to decay; it depends only on the nucleus, not on temperature, pressure, or chemistry. Like an internal clock, it is used for dating.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#半衰期 #放射性 #衰变
原子核由什么组成？
What is the atomic nucleus made of?
原子核由带正电的质子和不带电的中子组成，二者统称核子。质子数决定元素种类，中子数则决定同位素。
The nucleus is made of positively charged protons and neutral neutrons, together called nucleons. The proton count defines the element, and the neutron count defines the isotope.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#原子核 #质子 #中子
α、β、γ 三种射线有什么不同？
How do alpha, beta, and gamma rays differ?
α 是氦核、最重最易被挡；β 是电子或正电子流；γ 是高能光子、穿透最强。三者电离能力和穿透力正好相反排列，防护方式也不同。
Alpha is a helium nucleus, heaviest and easiest to stop; beta is a stream of electrons or positrons; gamma is a high-energy photon, most penetrating. Their ionizing power and penetrability rank in opposite order, so shielding differs.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#α射线 #β射线 #γ射线
核辐射有哪几种类型？
What types of nuclear radiation exist?
常见的核辐射有 alpha 粒子、beta 粒子和 gamma 射线三种。alpha 穿透力最弱、一张纸就能挡住，gamma 穿透力最强、需要厚铅板防护。
Common nuclear radiation includes alpha particles, beta particles, and gamma rays. Alpha is weakest and stopped by paper, while gamma is strongest and needs thick lead shielding.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#核辐射 #alpha #gamma
什么是放射性？
What is radioactivity?
放射性是不稳定原子核自发释放粒子或电磁波（如 alpha、beta、gamma 射线）而变成另一种核的过程。这种现象由贝克勒尔发现，广泛应用于医学和能源。
Radioactivity is the spontaneous emission of particles or electromagnetic rays, such as alpha, beta, and gamma, by unstable nuclei as they change into other nuclei. Discovered by Becquerel, it is widely used in medicine and energy.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#放射性 #衰变 #射线
考古学家凭什么能算出古生物死了多少年？半衰期是什么？
How can archaeologists date an ancient organism, and what is a half-life?
生物活着时，体内碳-14（放射性碳同位素）的比例保持稳定；死后不再补充，碳-14只能不断衰变减少。半衰期就是一半原子衰变掉所需的时间，碳-14的约为5730年。测出残存的碳-14比例，就能反推死亡时间，这就是碳-14测年法。
While an organism lives, its body keeps a steady ratio of carbon-14, a radioactive isotope; after death the supply stops and the isotope slowly decays away. Half-life is the time for half the atoms to decay — about 5,730 years for carbon-14. Measuring the leftover carbon-14 reveals when the organism died: radiocarbon dating.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#半衰期 #碳-14 #测年法
太阳为什么能一直发光发热，它的燃料会用完吗？
Why does the Sun keep shining, and will its fuel ever run out?
太阳核心温度约1500万摄氏度，氢核在极高的压力和温度下聚变成氦核，同时释放巨大能量，这就是核聚变。太阳每秒把约6亿吨氢变成氦，其中约400万吨的质量按E=mc²转化成能量。按这个消耗速度，它大约还能再燃烧50亿年。
At the Sun's core, about 15 million degrees, hydrogen nuclei fuse into helium under enormous pressure, releasing vast energy — nuclear fusion. Every second the Sun turns about 600 million tonnes of hydrogen into helium, converting roughly 4 million tonnes of mass into energy via E=mc². At that rate it can shine for another 5 billion years.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#核聚变 #质能方程 #太阳
为什么说香蕉和我们自己都带有微弱放射性？
Why are bananas — and even our own bodies — slightly radioactive?
天然钾里含约0.012%的钾-40，它有放射性：其中约11%通过电子俘获变成氩-40并放出γ射线，其余大部分变成钙-40并放出β射线。香蕉富含钾，所以有微弱放射性；人体同样含钾-40，体内每秒都发生几千次衰变。但这些剂量极其微小，远低于任何已知的健康影响水平。
Natural potassium contains about 0.012% potassium-40, which is radioactive: roughly 11% of it decays to argon-40 by electron capture, emitting gamma rays, and the rest becomes calcium-40 with a beta ray. Bananas are rich in potassium, so they are faintly radioactive, and your body holds potassium-40 too, with thousands of decays each second. The doses are minuscule, far below any known health effect.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#钾-40 #天然放射性 #本底辐射
家里的烟雾报警器里为什么含一点点放射性物质？
Why is there a tiny amount of radioactive material inside a home smoke detector?
这类报警器内含微量的镅-241，它持续放出α粒子，把探测室内的空气电离，使两片电极之间维持微弱电流。烟雾颗粒飘进来会吸附离子、减弱电流，报警器就响了。镅-241的用量极小，放出的辐射剂量远低于自然本底辐射，正常使用是安全的。
These alarms hold a speck of americium-241 whose alpha particles continuously ionize the air in a sensing chamber, keeping a weak current flowing between two electrodes. Smoke particles grab the ions, drop the current, and trigger the alarm. The amount is so tiny that the dose is far below natural background radiation, so it is safe in normal use.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04 · 2 条独立证据
来源 · Source
K. S. Krane,《Introductory Nuclear Physics》(Wiley,1987),第13章(核裂变)
K. S. Krane, 'Introductory Nuclear Physics' (Wiley, 1987), Ch.13 (Nuclear Fission)
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780471805533 (1987) · 核验依据 2 ISBN 9780471805533 (1988)
#镅-241 #电离 #烟雾报警器
放射性物质放出的射线有哪几种，为什么穿透力差别那么大？
What types of radiation do radioactive materials emit, and why do they differ so much in penetration?
主要有三种。α射线是氦原子核，质量大、带正电，穿透力最弱，一张纸就能挡住；β射线是高速电子，穿透力中等，几毫米铝板可以挡住；γ射线是能量极高的电磁波，穿透力最强，要用厚铅板或混凝土防护。穿透力越强的射线，越难阻挡，也越需要注意防护。
Three main kinds. Alpha rays are helium nuclei — heavy and charged, they stop on a sheet of paper; beta rays are fast electrons stopped by a few millimeters of aluminum; gamma rays are ultra-energetic electromagnetic waves that demand thick lead or concrete. The more penetrating the radiation, the harder it is to shield against.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#α射线 #β射线 #γ射线
核电站靠什么反应发电，和原子弹一样吗？
What reaction powers a nuclear plant, and is it like a bomb?
电站用受控的核裂变：铀-235 吸收中子裂成两半并放出能量与新中子，靠控制棒调节链式反应平稳发热。原子弹则是让反应在极短时间内失控爆发。
Plants use controlled fission: uranium-235 absorbs a neutron, splits, and releases energy plus new neutrons; control rods keep the chain reaction steady and warm. A bomb lets it run away in an instant.
难度 进阶 · 适合 小学高段(9-12)
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#核裂变 #链式反应 #控制棒
为什么原子核的比结合能在铁-56附近达到极大?这条曲线如何决定核聚变与核裂变各自在哪个质量区释放能量?
Why does the binding energy per nucleon of atomic nuclei peak near iron-56, and how does this curve decide which mass regions release energy through fusion versus fission?
轻核聚变时比结合能沿曲线上升,重核裂变成中等质量碎片时同样向峰值靠拢,两者都因此释放能量。在铁-56附近核力的吸引与质子间的库仑排斥达到最优平衡,继续聚合或分裂都只能吸能。所以恒星的热核燃烧终止于铁族元素,更重的核要依靠超新星等过程合成。
Fusing light nuclei raises the binding energy per nucleon along the curve, and splitting heavy nuclei into mid-mass fragments moves them up the same curve, so both processes release energy. Around iron-56 the attractive nuclear force and the Coulomb repulsion between protons reach their best balance, and neither further fusion nor further fission pays. Stellar thermonuclear burning therefore terminates at iron-group elements, while heavier nuclei must be synthesized in supernova-related processes.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-04 · 2 条独立证据
来源 · Source
Audi, Kondev, Wang & Huang,《The NUBASE2016 evaluation of nuclear properties》,Chinese Physics C,2017 (DOI: 10.1088/1674-1137/41/3/030001)；M. Wang 等,《The AME2016 atomic mass evaluation (II). Tables, graphs and references》,Chinese Physics C,2017 (DOI: 10.1088/1674-1137/41/3/030003)
Audi, Kondev, Wang & Huang, 'The NUBASE2016 evaluation of nuclear properties', Chinese Physics C, 2017, DOI: 10.1088/1674-1137/41/3/030001; M. Wang et al., 'The AME2016 atomic mass evaluation (II). Tables, graphs and references', Chinese Physics C, 2017, DOI: 10.1088/1674-1137/41/3/030003
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1088/1674-1137/41/3/030001 · 核验依据 2 Crossref DOI 10.1088/1674-1137/41/3/030003
#比结合能 #铁峰
放射性衰变的半衰期是什么含义?碳-14 测年的上限为什么停在五万年附近,而不能覆盖更久远的样品?
What does the half-life of radioactive decay mean, and why does radiocarbon dating top out near fifty thousand years rather than cover older samples?
半衰期指核素数目减少一半所需的时间,满足 N = N0·(1/2)^(t/T),碳-14 的 T 为 5730 年。生物存活期间通过呼吸与进食不断与大气交换碳,死亡之后交换停止,体内的碳-14 便按指数规律单纯衰减。经过八到九个半衰期,残余放射性已接近仪器本底,统计涨落会淹没年龄信号,因此常规方法的可靠上限约为五万年。
The half-life T is the time for a nuclide population to fall by half, following N = N0*(1/2)^(t/T), and carbon-14 has T = 5730 years. While an organism lives it exchanges carbon with the atmosphere through respiration and feeding; once it dies the exchange stops and its carbon-14 simply decays away exponentially. After eight to nine half-lives the residual activity approaches instrument background and statistical noise buries the age signal, so routine dating caps out near fifty thousand years.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-11-04 · 2 条独立证据
来源 · Source
Libby W. F., Science 109, 227 (1949);Arnold J. R. 与 Libby W. F., Science 110, 678 (1949)
Libby W. F., Science 109, 227 (1949); Arnold J. R. & Libby W. F., Science 110, 678 (1949)
独立核验依据 · Independent verification: 核验依据 1 Crossref DOI 10.1126/science.109.2827.227（本条出处含多部著作，按段登记 · 核验依据 2 Crossref DOI 10.1126/science.110.2869.678（本条出处含多部著作，按段登记
#原子核物理 #半衰期与碳-14 测年
为什么重核裂变和轻核聚变都释放能量?比结合能曲线怎样把两者统一解释?
Why do heavy-nucleus fission and light-nucleus fusion both release energy, and how does the binding-energy-per-nucleon curve explain both in one picture?
比结合能在铁-56附近达到约8.8 MeV每核子的极大值,位于曲线两侧的核素都可以靠向峰顶移动而放出能量。重核裂变的碎片比母核更接近峰顶,平均每个核子释放约1 MeV;氘氚聚变则受益于轻核区曲线的陡升,每次反应释放17.6 MeV,约合每核子3.5 MeV。这条曲线先陡升后缓降:上升段主要由表面项占比随核子数增多而迅速减小驱动,下降段则由库仑排斥主导,从而同时解释了两类放能途径。
Binding energy per nucleon peaks near iron-56 at roughly 8.8 MeV per nucleon, so nuclides on either side of the curve gain energy by moving toward the peak. Fission fragments lie closer to the peak than the parent nucleus, releasing about 1 MeV per nucleon, while deuteron-triton fusion benefits from the steep rise of the light-nucleus branch, yielding 17.6 MeV per reaction or about 3.5 MeV per nucleon. The curve rises steeply then falls gently: the rise is driven mainly by the rapidly shrinking surface-term share as nucleon number grows, while the fall is governed by Coulomb repulsion, explaining both exothermic routes at once.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-10-04 · 2 条独立证据
来源 · Source
Krane《Introductory Nuclear Physics》Wiley 1988,半经验质量公式与比结合能曲线章节
Krane, Introductory Nuclear Physics, Wiley 1988, chapters on the semi-empirical mass formula and the binding-energy curve
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780471805533 (1987) · 核验依据 2 ISBN 9780471805533 (1988)
#核物理 #结合能
核电站是怎么发电的？
How does a nuclear power plant generate electricity?
核电站利用铀等燃料的受控核裂变产生大量热，把水加热成高温高压蒸汽推动汽轮机发电。它不排放二氧化碳，但会产生需要妥善处理的放射性废料。
A nuclear plant uses controlled fission of fuel like uranium to produce heat, turning water into high-pressure steam that drives turbines to generate electricity. It emits no carbon dioxide but produces radioactive waste needing careful handling.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#核电站 #裂变 #发电
什么是半衰期？
What is a half-life?
半衰期是指放射性物质衰变掉一半所需的时间，是每种核素固定的特征量。比如某物质半衰期是 10 年，10 年后就只剩原来的一半。
Half-life is the time for half of a radioactive substance to decay, a fixed property of each nuclide. If a substance's half-life is 10 years, only half remains after 10 years.
难度 入门 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23 · 2 条独立证据
来源 · Source
程守洙 江之永,《普通物理学》第七版,高等教育出版社,2016
Cheng Shouzhu and Jiang Zhiyong, General Physics, 7th ed., Higher Education Press, 2016
独立核验依据 · Independent verification: 核验依据 2 ISBN 9787040429190（豆瓣书目条目: 普通物理学．上册）
#半衰期 #衰变 #放射性