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Types of Radioactivity03:23

Types of Radioactivity

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The most common types of radioactivity are α decay, β decay, γ decay, neutron emission, and electron capture.
Alpha (α) decay is the emission of an α particle from the nucleus. For example, polonium-210 undergoes α decay:
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Nuclear Stability03:18

Nuclear Stability

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Protons and neutrons, collectively called nucleons, are packed together tightly in a nucleus. With a radius of about 10−15 meters, a nucleus is quite small compared to the radius of the entire atom, which is about 10−10 meters. Nuclei are extremely dense compared to bulk matter, averaging 1.8 × 1014 grams per cubic centimeter. If the earth’s density were equal to the average nuclear density, the earth’s radius would be only about 200 meters.
To hold positively charged protons together...
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Atomic Nuclei: Nuclear Spin State Population Distribution01:14

Atomic Nuclei: Nuclear Spin State Population Distribution

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Near absolute zero temperatures, in the presence of a magnetic field, the majority of nuclei prefer the lower energy spin-up state to the higher energy spin-down state. As temperatures increase, the energy from thermal collisions distributes the spins more equally between the two states. The Boltzmann distribution equation gives the ratio of the number of spins predicted in the spin −½ (N−) and spin +½ (N+) states.
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Radioactivity and Nuclear Equations03:18

Radioactivity and Nuclear Equations

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Nuclear chemistry is the study of reactions that involve changes in nuclear structure. The nucleus of an atom is composed of protons and, except for hydrogen, neutrons. The number of protons in the nucleus is called the atomic number (Z) of the element, and the sum of the number of protons and the number of neutrons is the mass number (A). Atoms with the same atomic number but different mass numbers are isotopes of the same element.
A nuclide of an element has a specific number of protons and...
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Nuclear Transmutation03:20

Nuclear Transmutation

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Nuclear transmutation is the conversion of one nuclide into another. It can occur by the radioactive decay of a nucleus, or the reaction of a nucleus with another particle. The first manmade nucleus was produced in Ernest Rutherford’s laboratory in 1919 by a transmutation reaction, the bombardment of one type of nuclei with other nuclei or with neutrons. Rutherford bombarded nitrogen-14 atoms with high-speed α particles from a natural radioactive isotope of radium and observed...
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Atomic Nuclei: Nuclear Relaxation Processes01:23

Atomic Nuclei: Nuclear Relaxation Processes

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In the absence of an external magnetic field, nuclear spin states are degenerate and randomly oriented. When a magnetic field is applied, the spins begin to precess and orient themselves along (lower energy) or against (higher energy) the direction of the field. At equilibrium, a slight excess population of spins exists in the lower energy state. Because the direction of the magnetic field is fixed as the z-axis,  the precessing magnetic moments are randomly oriented around the z-axis.
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Preparing an Isotopically Pure 229Th Ion Beam for Studies of 229mTh
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与波特-托马斯分布的偏差是由于非统计学 γ 衰变低于 ^{150}Nd 中子分离值.

O Papst1, J Isaak1, V Werner1

  • 1Technische Universität Darmstadt, Department of Physics, Institute for Nuclear Physics, 64289 Darmstadt, Germany.

Physical review letters
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概括

这项研究引入了一种使用核共振光的新方法,用于分析偶数核中的部分过渡宽度. 结果显示了波特-托马斯分布的偏差,表明Nd-150中的非统计性马衰变效应.

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科学领域:

  • 核物理 核物理 核物理
  • 量子力学就是量子力学.

背景情况:

  • 了解核衰变过程对于核结构物理学至关重要.
  • 波特-托马斯分布是部分过渡宽度的标准模型.

研究的目的:

  • 开发和应用一种用于研究部分过渡宽度波动的新方法.
  • 在特定的核系统中调查波特-托马斯分布的有效性.

主要方法:

  • 使用核共振光实验与近同色,线性极化光子束.
  • 分析玛衰变的平均分支比,从J=1状态到基态和2_{1}^{+}状态在偶偶的原子核中.
  • 将实验结果与基于奇平方分布的理论预测进行比较.

主要成果:

  • 观察到恒定的平均分支比为0.490{\displaystyle 0.490{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490{\displaystyle 0.490}{\displaystyle 0.490}{\displaystyle 0.490{\displaystyle 0.490}{\displaystyle 1.^{-}}}
  • 由此得出的自由度 (ν=1.93(12)) 与波特-托马斯分布 (ν=1) 所要求的值有显著的差异.
  • 量化了玛衰变行为的非统计效应,范围从9.4%~10%到94%~10%.

结论:

  • 该研究拒绝了波特-托马斯分布在所研究的能量范围中的部分过渡宽度的普遍有效性.
  • 观察到的偏差表明了核马衰变中非统计效应的存在和意义.
  • 开发的方法为探测核结构和反应动态提供了一个新的工具.