Nuclear Reactions

核反应

Many kinds of nuclear reactions occur in response to the absorption of particles such as neutrons or protons. Other types of reactions may involve the absorption of gamma rays or the scattering of gamma rays. Of particular note is the resonant absorption of gamma rays in the Mossbauer effect. Specific nuclear reactions can be written down in a manner similar to chemical reaction equations. If a target nucleus X is bombarded by a particle a and results in a nucleus Y with emitted particle b, this is commonly written in one of two ways.

许多类型的核反应是在吸收粒子（如中子或质子）时发生的。其他类型的反应可能涉及吸收伽马射线或散射伽马射线。特别值得注意的是，莫塞莱效应中伽马射线的共振吸收。特定的核反应可以像化学反应方程式一样进行书写。如果靶核X被粒子a轰击后产生核Y并发射出粒子b，这通常可以以两种方式之一来书写。

a + X -> Y + b or X(a,b)Y

We can characterize the energetics of the reaction with a reaction energy Q, defined as the energy released in the reaction. The Q is positive if the total mass of the products is less than that of the projectile and target, indicating that the total nuclear binding energy has increased. The probability of a given type of nuclear reaction taking place is often stated as a "cross section".

我们可以用反应能Q来表征反应的能变，定义为反应中释放的能量。如果产物的总质量小于弹靶的总质量，Q为正，表明总核结合能已增加。某种核反应发生的可能性通常表述为“截面”。

Table of examples

示例表格

a + X → Y + b 或 X(a,b)Y

Index

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HyperPhysics***** Nuclear

HyperPhysics ***** 核物理

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Some Nuclear Reactions

某些核反应

反应

9Be(p,α) 6Li

Reaction 反应	Measured Q (MeV) 测得的Q值（MeV）	Reaction	Measured Q (MeV) 测得的Q值（MeV）
²H(n,γ)³H	6.257 +/- 0.004	⁹Be(p,α)⁶Li	2.132 +/- 0.006
²H(d,p)³H	4.032 +/- 0.004	¹⁰B(n,α)⁷Li	2.793 +/- 0.003
⁶Li(p,α)³H 6Li(p,α) 3H	4.016 +/- 0.005	¹⁰B(p,α)⁷Be	1.148 +/- 0.003
⁶Li(d,p)⁷Li 6Li(d,p) 7Li	5.020 +/- 0.006	¹²C(n,γ)¹³C	4.948 +/- 0.004
⁷Li(p,n)⁷Be 7Li(p,n) 7Be	-1.645 +/- 0.001	¹³C(p,n)¹³N	-3.003 +/- 0.002
⁷Li(p,α)⁴He 7Li(p,α) 4He	17.337 +/- 0.007	*¹⁴N(p,n)¹⁴C	-0.627 +/- 0.001
⁹Be(n,γ)¹⁰Be 9Be(n,γ) 10Be	6.810 +/- 0.006	¹⁴N(n,γ)¹⁵N	10.833 +/- 0.007
⁹Be(γ,n)⁸Be	-1.666 +/- 0.002	¹⁸O(p,n)¹⁸F	-2.453 +/- 0.002
⁹Be(d,p)¹⁰Be 9Be(d,p) 10Be	4.585 +/- 0.005	¹⁹F(p,α)¹⁶O	8.124 +/- 0.007

* The nuclear reaction in the atmosphere which produces carbon-14 for radiocarbon dating.

大气中的核反应产生碳-14，用于放射性碳测定。

Data from C. W. Li, W. Whaling, W. A. Fowler, and C. C. Lauritson, Physical Review 83:512 (1951)

数据来自C. W. Li, W. Whaling, W. A. Fowler和C. C. Lauritson，发表于Physical Review 83:512 (1951)

Index

索引

HyperPhysics***** Nuclear

HyperPhysics ***** 核物理

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Nuclear Cross Section

核截面

To characterize the probability that a certain nuclear reaction will take place, it is customary to define an effective size of the nucleus for that reaction, called a cross section. The cross section is defined by

为了表征某种核反应发生的可能性，通常会定义该反应的核有效尺寸，称为截面。截面定义为

The cross section has the units of area and is on the order of the square of the nuclear radius. A commonly used unit is the barn:

截面的单位是面积，其数量级与核半径的平方相当。常用的单位是巴恩：

1 barn = 10^-28m²

A standard old story was that in the early days of the field, a particular cross section turned out to be much bigger than expected. An experimenter exclaimed "Why, that's as big as a barn!" and a unit name was born.

一个标准的老故事是，在该领域早期阶段，某个截面被发现比预期大得多。实验者 exclaimed '为什么，那大得像一个谷仓！'，于是一个单位名称由此诞生。

Scattering Cross Section

散射截面

1 次郎 = 10 -28 m²

Index

索引

HyperPhysics***** Nuclear

HyperPhysics ***** 核物理

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