核言碎语（129）核的液滴模型（1）

　　109 核的液滴模型
　　Liquid Drop Model of Nucleus
　　（https://www.nuclear-power.com/）
　　核的液滴模型
　　One of the first models that could describe the behavior of the nuclear binding energies and therefore of nuclear masses was the mass formula of von Weizsaecker (also called the semi-empirical mass formula – SEMF) published in 1935 by German physicist Carl Friedrich von Weizsäcker. This theory is based on the liquid drop model proposed by George Gamow.
　　1935年，德国物理学家卡尔·弗里德里希·冯·魏茨泽克发表了冯·魏茨泽克的质量公式（也称为半经验质量公式——SEMF），这是最早能够描述核结合能以及核质量行为的模型之一。这个理论是基于乔治·伽莫夫 提出的液滴模型。
　　According to this model, the atomic nucleus behaves like the molecules in a drop of liquid. But in this nuclear scale, the fluid is made of nucleons (protons and neutrons), held together by the strong nuclear force. The liquid drop model of the nucleus considers that the nuclear forces on the nucleons on the surface are different from those on nucleons in the interior of the nucleus. Other attractive nucleons completely surround the interior nucleons. Here is the analogy with the forces that form a drop of liquid.
　　根据这个模型，原子核的行为就像一滴液体中的分子。但在这种核尺度下，流体是由核子（质子和中子）组成的，它们被强核力凝聚在一起。核的液滴模型认为，表面核子所受的核力与内部核子所受的核力不同。其他吸引核子完全包围内部核子。这是对形成液滴的力的类比。
　　In the ground state, the nucleus is spherical. If sufficient kinetic or binding energy is added, this spherical nucleus may be distorted into a dumbbell shape and then maybe split into two fragments. Since these fragments are more stable, the splitting of such heavy nuclei must be accompanied by energy release. This model does not explain all the properties of the atomic nucleus but does explain the predicted nuclear binding energies.
　　在基态，原子核是球形的。如果加入足够的动能或结合能，这个球形原子核可能扭曲成哑铃形状，然后可能分裂成两个碎片。由于这些碎片更加稳定，这些重原子核的分裂必然伴随着能量释放。这个模型并不能解释原子核的所有特性，但是可以解释所预测的原子核结合能。
　　The nuclear binding energy as a function of the mass number A and the number of protons Z based on the liquid drop model can be written as:
　　基于液滴模型，核结合能作为质量数A和质子数Z的函数可以写成:
　　This formula is called the Weizsaecker Formula (or the semi-empirical mass formula). The physical meaning of this equation can be discussed term by term.
　　该公式称为魏茨泽克公式（或半经验质量公式）。这个方程的物理意义可以逐项讨论。