正电子发射断层扫描（PET）利用了什么核化学原理实现体内成像？
What nuclear-chemistry principle does positron emission tomography (PET) exploit for in vivo imaging?
PET 使用发射正电子的放射性核素（如 ¹⁸F、¹¹C）标记生物分子注入体内。正电子行进极短距离后与电子发生湮灭，产生一对方向相反的 511 keV γ 光子；符合探测这两个光子的共线事件即可重建示踪剂在体内的三维分布，反映代谢与受体活动。
PET uses positron-emitting radionuclides such as ¹⁸F or ¹¹C to label biomolecules injected into the body. The positron travels a very short distance before annihilating with an electron, producing a pair of 511 keV gamma photons emitted in opposite directions; coincidence detection of these collinear photons reconstructs the tracer's 3D distribution, reflecting metabolism and receptor activity.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
Brown, LeMay 等,《Chemistry: The Central Science》第14版,Pearson,2017
T. L. Brown et al., Chemistry: The Central Science, 14th ed., Pearson, 2017
#PET #正电子 #湮灭 #符合探测
碳-14 测年法的原理是什么？它的适用年代范围和局限有哪些？
What is the principle of carbon-14 dating, and what are its applicable range and limitations?
宇宙射线产生的大气 ¹⁴C 被生物通过碳循环固定，活着时体内 ¹⁴C/¹²C 比保持恒定；死亡后 ¹⁴C 按 5730 年半衰期衰变而不再补充。测残留 ¹⁴C 比例即可反推死亡年代，常规适用范围约 5 万年以内。局限包括需校正大气 ¹⁴C 波动、样品须含足够碳且未受现代碳污染。
Cosmic rays produce atmospheric ¹⁴C, which living organisms fix via the carbon cycle so their ¹⁴C/¹²C ratio stays constant; after death ¹⁴C decays with a 5730-year half-life and is no longer replenished. Measuring the remaining ¹⁴C fraction back-calculates the death date, typically up to about 50,000 years. Limits include calibrating atmospheric ¹⁴C fluctuations and ensuring samples contain enough carbon and no modern contamination.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
Brown, LeMay 等,《Chemistry: The Central Science》第14版,Pearson,2017
T. L. Brown et al., Chemistry: The Central Science, 14th ed., Pearson, 2017
#碳14测年 #放射性碳 #半衰期 #校正
锝-99m为什么是医学影像中最重要的放射性同位素？
Why is technetium-99m the most important radioisotope in medical imaging?
99mTc半衰期仅约6小时，发射140千电子伏的伽马射线，穿透力适中、组织吸收少，适合SPECT相机成像；它衰变后很快变成半衰期很长、只发软β射线的99Tc，对患者的剂量负担低。99mTc由钼-99衰变产生，可标记到多种配体上靶向不同器官，用于心脏灌注显像、骨扫描等。
99mTc has a half-life of only about 6 hours and emits 140-keV gamma rays that penetrate well with little tissue absorption, ideal for SPECT imaging; after decay it quickly becomes 99Tc, which has a long half-life and emits only soft beta radiation, keeping the patient dose low. Produced from molybdenum-99 decay, 99mTc can be tagged onto many ligands to target different organs, such as cardiac perfusion imaging and bone scans.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
Brown, LeMay 等,《Chemistry: The Central Science》第14版,Pearson,2017
T. L. Brown et al., Chemistry: The Central Science, 14th ed., Pearson, 2017
#放射性同位素 #锝-99m #医学影像
核裂变释放能量的物理化学本质是什么？链式反应如何维持？
What is the physico-chemical essence of energy release in nuclear fission, and how is a chain reaction sustained?
重核（如 ²³⁵U）吸收中子裂变为两个中等质量碎片，由于中等核每个核子平均结合能更高，质量亏损按 E=mc² 转化为巨大能量。裂变同时放出 2–3 个中子，若其中至少一个引发新的裂变并使增殖系数 k ≥ 1，链式反应即可自持。临界质量与几何、反射层共同决定能否达到临界。
A heavy nucleus such as ²³⁵U captures a neutron and splits into two medium-mass fragments; because medium nuclei have higher binding energy per nucleon, the mass defect converts to huge energy via E=mc². Fission also emits 2–3 neutrons, and if at least one induces another fission so the multiplication factor k ≥ 1, the chain reaction sustains itself. Critical mass and geometry, with reflectors, determine whether criticality is reached.
难度 专业 · 适合 高中(15-18)
CC BY 4.0 · 已核验 · Verified 2026-10-04
来源 · Source
《原子核物理》(卢希庭)；国际原子能机构(IAEA)核技术报告
IAEA nuclear technology reports; Krane, Introductory Nuclear Physics
独立核验依据 · Independent verification: 核验依据 1 ISBN 9780471805533 (1987)
#核裂变 #结合能 #链式反应 #临界
同位素示踪技术在化学与生物医学研究中有哪些典型应用？
What are typical applications of isotope tracing in chemical and biomedical research?
同位素示踪利用同一元素不同核素（如 ²H、¹³C、¹⁵N、¹⁸O）化学行为相同但可被检测的特性，追踪原子在反应或代谢中的去向。典型应用包括用 ¹³C 标记底物研究代谢通路、用 ¹⁵N 追踪肥料在土壤-植物中的迁移、以及用 ¹⁸F 标记示踪剂进行 PET 成像。
Isotope tracing exploits that different nuclides of an element (e.g., ²H, ¹³C, ¹⁵N, ¹⁸O) behave chemically identically yet are detectable, letting researchers follow atoms through reactions or metabolism. Typical uses include ¹³C-labeled substrates to map metabolic pathways, ¹⁵N to track fertilizer movement in soil–plant systems, and ¹⁸F tracers for PET imaging.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
Brown, LeMay 等,《Chemistry: The Central Science》第14版,Pearson,2017
T. L. Brown et al., Chemistry: The Central Science, 14th ed., Pearson, 2017
#同位素示踪 #标记 #代谢通路 #PET
α、β、γ 三种射线各有什么特性？它们的穿透能力有何差异？
What are the characteristics of alpha, beta, and gamma radiation, and how do their penetrating powers differ?
α 粒子是氦核（⁴₂He），带正电、质量大，电离强但一张纸即可阻挡；β 粒子是高速电子，穿透力中等，需几毫米铝板屏蔽；γ 是高频电磁波（光子），电离弱但穿透极强，需厚铅或混凝土防护。三者电离与穿透能力呈反向关系。
Alpha particles are helium nuclei (⁴₂He), positively charged and massive, with strong ionization but stopped by paper; beta particles are fast electrons of moderate penetration needing a few millimeters of aluminum; gamma rays are high-frequency photons, weakly ionizing but highly penetrating, requiring thick lead or concrete. Their ionizing and penetrating powers are inversely related.
难度 进阶 · 适合 初中(12-15)
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
Brown, LeMay 等,《Chemistry: The Central Science》第14版,Pearson,2017
T. L. Brown et al., Chemistry: The Central Science, 14th ed., Pearson, 2017
#α射线 #β射线 #γ射线 #电离
放射性衰变主要有哪几种类型？各伴随什么粒子或辐射？
What are the main types of radioactive decay, and what particles or radiation accompany each?
主要衰变类型包括 α 衰变（放出氦核，原子序数减 2）、β⁻ 衰变（中子转质子放出电子与反中微子）、β⁺ 衰变（质子转中子放出正电子与中微子）以及 γ 衰变（激发核退激放出光子）。此外还有电子俘获等过程。衰变类型由核的中子-质子比与能量状态决定。
Main decay types are alpha decay (emits a helium nucleus, atomic number drops by 2), beta-minus decay (a neutron becomes a proton, emitting an electron and antineutrino), beta-plus decay (a proton becomes a neutron, emitting a positron and neutrino), and gamma decay (an excited nucleus de-excites, emitting a photon). Electron capture also occurs. The type depends on the neutron–proton ratio and the nucleus's energy state.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
Brown, LeMay 等,《Chemistry: The Central Science》第14版,Pearson,2017
T. L. Brown et al., Chemistry: The Central Science, 14th ed., Pearson, 2017
#放射性衰变 #α衰变 #β衰变 #γ衰变
放射性衰变的半衰期是什么意思？它能用来做什么？
What does the half-life of radioactive decay mean, and what is it used for?
半衰期是放射性核素数量衰变到原来一半所需的时间，由核种本身决定、不受温度压力等外界条件影响。衰变遵循一级动力学 N = N₀·(1/2)^(t/T₁/₂)，因此可用剩余活度推算样品年代或计算辐照剂量衰减。常见如 ¹⁴C 半衰期约 5730 年、¹³¹I 约 8 天。
The half-life is the time for a radioactive nuclide's amount to fall to half its initial value; it is intrinsic to the nuclide and independent of temperature, pressure, and chemical state. Decay follows first-order kinetics N = N₀·(1/2)^(t/T₁/₂), so remaining activity can date samples or compute dose decay. Examples include ¹⁴C at about 5730 years and ¹³¹I at about 8 days.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-08-23
来源 · Source
Brown, LeMay 等,《Chemistry: The Central Science》第14版,Pearson,2017
T. L. Brown et al., Chemistry: The Central Science, 14th ed., Pearson, 2017
#半衰期 #放射性衰变 #一级动力学 #核素
商品化的锝[99mTc]药盒都预装了氯化亚锡，注入淋洗液后室温摇匀即可完成标记。亚锡离子在其中起什么关键作用？
Commercial 99mTc radiopharmaceutical kits come preloaded with stannous chloride, so adding the generator eluate and shaking finishes labeling at room temperature. What key role does Sn(II) play here?
从发生器淋洗出的高锝酸钠中锝为+7价，对配体几乎呈惰性。亚锡离子把Tc(VII)还原到+4/+5等较低氧化态，形成能被DTPA、MDP或HMPAO等螯合剂迅速捕获的活性物种；过量锡还可清除溶解氧并维持合适pH，从而保障标记率和制剂稳定性。
Pertechnetate eluted from the generator carries Tc(VII), which is almost inert toward ligands. Stannous ion reduces Tc(VII) to lower oxidation states such as +4/+5, forming reactive species promptly captured by chelators like DTPA, MDP or HMPAO; surplus tin also scavenges dissolved oxygen and keeps the pH suitable, safeguarding labeling yield and formulation stability.
难度 进阶 · 适合 大众
CC BY 4.0 · 已核验 · Verified 2026-11-03
来源 · Source
S.S. Jurisson & J.D. Lydon, Chemical Reviews, 1999, 99, 2205-2218
S.S. Jurisson and J.D. Lydon, Chem. Rev., 1999, 99, 2205-2218, DOI: 10.1021/cr980435t
独立核验依据 · Independent verification: 核验依据 1 CROSSREF 标识 10.1021/cr980435t：Potential Technetium Small
#锝99m #亚锡还原 #药盒标记