MadSci Network: Physics
Query:

Re: Further to the effects of electrons

Date: Tue Aug 21 22:40:20 2007
Posted By: Bart Broks, Quant/Strategist
Area of science: Physics
ID: 1187350576.Ph
Message:

Hello Steve,

Thank you for your question-and no, it is most certainly not infantile. A thorough and quantitative answer to this question would be extremely complicated indeed, and would in fact require more knowledge of general relativity than I possess.

The question about the ionizing radiation is interesting. Ionizing radiation consisting of electrons is called beta-rays, and it is a fairly common form of radioactive decay [1]. Now, even though they are quite energetic and few in number, as opposed to the electrons in a normal piece of wire, they are still moving electrons-and moving electrons means a current [2]! Just like any other current, a beam of electrons produces a magnetic field.

The reason the radiation is called ionizing is because it is capable of ripping apart atoms [3]. Atoms consist of a positive core and negative electrons. Kicking an outer electron of an atom requires an energy of between a few and 24 eV. An eV, or electron-volt, is the energy an electron gets when it is accelerated by a field of 1 V. Imagine a battery with a voltage of 1 volt, that is emitting electrons from its negative pole. These electrons gain an energy of 1 V traveling to the positive pole.

In ionizing radiation, the energy of the particles is more than 1 million eV, which is far more energy than the energy binding outer electrons to their core. If the electron hits a target (something that is maybe less likely than you would think at first hand, because the relativistic effects tend to reduce the interaction strength with other matter [4]), it might shoot away an electron, leaving the 2 free electrons and the positive core behind. The remaining positive core is called an ion; hence, the term ionizing radiation. You can imagine that if this core were in your DNA, you would not be very happy if this were to happen a lot-hence, the chief danger of ionizing radiation.

After a few collisions, the electrons have lost so much energy they can no longer ionize other particles. In this case, they will tend to accumulate to walls, because they repel each other, and if they stick to the walls of the room, they are apart as far as they can. This "charging" of our test chamber will mean the whole test chamber will start to repel electrons. A force that pushes away electrons like this is an electric force. Another way of looking at this is to consider that this braking of electrons is in essence the same as what the electric voltage of a battery is doing; hence, we might think of the room of being at a negative voltage with respect to our electron source. Now, if this negative voltage becomes large enough (by accumulation of charge), it becomes impossible for the electrons to overcome this force and they are pushed away. No further charge will accumulate.

Roughly the same thing will happen in the sugar cube example [5]: The first few extra electrons don't matter too much, but as charge accumulates, the repulsive force becomes larger, and the electrons will start to fly apart faster and faster, until an equilibrium is established between the speed at which electrons are ejected from the system and the rate of "production" from the sugar cubes.

I hope this answers your question.

Regards,

Bart Broks

  1. http://www.rdc.gov.lv/nucpedia/uk/beta_radiat.htm
  2. http://en.wikipedia.org/wiki/Electric_current
  3. http://en.wikipedia.org/wiki/Ionizing_radiation
  4. http://www-amdis.iaea.org/ALADDIN/
  5. http://www.madsci.org/posts/archives/2007-08/1187054157.Ph.r.html


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