Coulombwall

Coulombwall

As Coulombwall or Coulomb barrier is potential denoted against which a positively charged particle must start to in the likewise positively charged nucleus to arrive. This potential is based on the Coulomb force (named after Charles Augustin de Coulomb ), which acts repulsively between two electrical charges with the same sign.

According to classical mechanics , the particle needs a minimum energy to overcome the barrier . According to quantum mechanics , on the other hand, there is a certain chance of tunneling through such a barrier even with lower particle energy .

Ernest Rutherford was the first to observe that alpha radiation - which consists of positively charged particles - can overcome the barrier of atomic nuclei and thus trigger nuclear reactions. Such experiments gave first indications of the components and structure of atomic nuclei.

To discover the quarks and postulate the gluons, it was necessary to overcome the Coulomb barrier of the proton .

The potential in the atomic nucleus and in its vicinity is determined by the electromagnetic and the " strong " interaction. The long-range electromagnetic interaction causes (here in the form of the Coulomb force mentioned) a repulsive potential at large distances. At small distances, on the other hand, the short-range strong interaction ensures an attractive nuclear potential and thus determines the size of the atomic nucleus. The summation of both effects results in a binding or quasi-binding potential.

The potential barrier with its finite height is referred to as the “Coulomb” wall, although it only comes about through the interaction of the two different basic forces. Their effective height depends not only on the charge of the atomic nucleus and the charge of the incoming particle, but also on the angular momentum of the incoming particle.

The finite height of the Coulomb Wall also explains the alpha decay of some atomic nuclei and plays a role in many nuclear reactions , because a charged particle has to either overcome the barrier or “tunnel through” it when it leaves the nucleus.

calculation

The height of the coulomb wall is:

${\displaystyle V_{c}={\frac {1}{4\pi \varepsilon _{0}}}{\frac {Z_{1}\,Z_{2}\,e^{2}}{r}}}$

It can be approximately determined in MeV using the following rule of thumb:

${\displaystyle V_{C}\approx {\frac {Z_{1}\cdot Z_{2}}{A^{\frac {1}{3}}}}}$

It contains and the atomic numbers of the projectile and target core as well as the mass number of the target core . ${\displaystyle Z_{1}}$ ${\displaystyle Z_{2}}$ ${\displaystyle A}$

Trivia

The street "Am Coulombwall" in Garching near Munich was named after the Coulombwall.

In the movie Marvel's The Avengers , Bruce Banner / Hulk (comic) suspects that 120 million Kelvin are enough to break through the "Coulomb Barrier" and create a wormhole.

See also

• Potential well

Individual evidence

1. ↑ K. Bethge, G. Walter, B. Wiedemann: Kernphysik , 2nd edition, Springer 2001, p. 228