Fxperiments with High velocity Positive Ions
Fxperiments with High velocity Positive Ions
复制标题
高速正离子实验
DOI：
--
复制
发表时间：
--
期刊：
影响因子：
--
通讯作者：
E. T. S. Walton
中科院分区：
文献类型：
--
作者：
J. Cockcroft;E. T. S. Walton
发展一条针对原子核问题的新的攻击路线似乎是非常重要的。我们关于原子核结构的大部分信息来自α粒子的实验，如果我们能用高电位加速的正离子源来补充这些信息，我们就应该有一种实验武器，它比α粒子有许多优点。首先，它的强度要比α粒子源大得多，因为就粒子数而言，1微安的正离子相当于180克镭当量。此外，它还具有不受穿透β和γ射线影响的优点，这在许多实验中是一个复杂问题，同时速度可以随意变化。当然，获得这样的源的主要困难在于，如果要获得接近α粒子的速度，那么加速粒子所必需的非常高的势的产生和应用。例如，来自钋的α粒子的能量相当于520万电子伏特，而给予氦核等量的能量则需要260万伏特的电势。因此，我们必须决定什么是我们可以有效工作的最小加速电压，因为实验难度随着电压的增加而迅速增加。在作出这一决定时，我们自然受到伽莫夫最近关于“人工解体理论”的理论工作的指导。在伽莫夫理论中，速度为v的α粒子进入原子序数为Z的原子核的有效半径内的几率为W = e-16 π e2 Z/hvJk，其中Jk是随v和Z缓慢变化的函数。因此，很明显，对于能量相等的粒子，较轻的粒子有更大的机会穿透进入原子核，因此，我们应该选择质子作为正离子的来源。
It would appear to be very important to develop an additional line of attack on problems of the atomic nucleus. The greater part of our information on the structure of the nucleus has come from experiments with α-particles and if we can supplement these with sources of positive ions accelerated by high potentials we should have an experimental weapon which would have many advantages over the α-particle. It would, in the first place, be much greater in intensity than α-particle sources, since one microampere of positive ions is equivalent, so far as numbers of particles is concerned, to 180 grams of radium equivalent. It would in addition have the advantage of being free from penetrating β and γ rays which are a complication in many experiments, whilst the velocity would be variable at will. The main difficulty in obtaining such sources lies of course in the production and application of the very high potentials necessary to accelerate the particles if velocities approaching that of the α-particle are to be obtained. For example, α-particle from polonium have an energy corresponding to 5.2 million electron volts and a potential of 2.6 million volts would be required to give a helium nucleus an equal amount of energy. We have therefore to decide what is the minimum acceleration voltage at which we can usefully work, since the experimental difficulties increase very rapidly with increasing voltage. In making this decision we are naturally guided by the recent theoretical work of Gamow on the “ Theory of Artificial Disintegration.” On Gamow’s theory the probability of an α-particle of velocity v entering a nucleus of atomic number Z, after coming within the effective radius of the nucleus, is W = e -16π e 2Z/ hv Jk, Where Jk is a function varying slowly with v and Z. It is clear, therefore, that for particles of equal energy the lighter particle has the greater chance of penetration into the nucleus, so that we should choose protons as our source of positive ions for this reason.