When it comes to radioactive decay, what is the difference between random and spontaneous?

For example, when the count rate of a radioactive isotope is measured, the readings fluctuate. Is this a demonstration of the randomness of the process, or of its spontaneous nature?

  • $\begingroup$ The introductory Wikipedia entry on Radioactive decay touches on these two terms. $\endgroup$
    – BMS
    Commented Mar 25, 2014 at 20:11
  • $\begingroup$ Where in the entry does it explain the difference? $\endgroup$ Commented Mar 25, 2014 at 20:13
  • $\begingroup$ When you randomly scatter points on a surface or volume, you'll get a lot of variation in local point density. I'm assuming something similar (random events result in relative large differences) happens there as well. $\endgroup$
    – Kvothe
    Commented Mar 25, 2014 at 20:13
  • 1
    $\begingroup$ I think you are a victim of the "learn the precise phrase in the textbook and repeat it" school of education. Sorry to hear that it has spread outside the USA $\endgroup$ Commented May 19, 2014 at 15:43
  • $\begingroup$ Spontaneous means it is unaffected by temperature, pressure e.t.c $\endgroup$
    – user113855
    Commented Apr 9, 2016 at 10:57

4 Answers 4


I believe spontaneous means it happens on its own. You don't need any outside influence to get the isotope to decay. This term is sometimes used in contrast to stimulated.

Random means one cannot know precisely when the next decay will happen, though one can predict the probability of such events occurring in some time interval.

A decay process can be both spontaneous and random, but only one of these two options touches on the statistical nature of decay.

There's a small bit in the introductory paragraph of the Wikipedia page on radioactive decay.

  • $\begingroup$ It should also be pointed out that spontaneity is usually discussed in the context of chemistry rather than physics. The concept of spontaneity in physics more often than not is expressed in terms of presence or absence of external forces. $\endgroup$
    – mhp
    Commented Jan 20, 2016 at 12:05

Spontaneous means unpredictable process which is governed from within rather than by external conditions like temperature and pressure.

Random implies any time, it may happen without any pattern.


The best way to differentiate is to look at the count-rate vs time graph. Random nature of radioactivity is indicated by the fluctuation of the count-rate. Whereas, spontaneous means that the process of radioactivity is not dependent upon any external environmental conditions like temperature, pressure, magnetic/electric field. For example: Plot a count rate graph at 100 degrees and then at 200 degrees. Graph of the shape will be the same and also half life in both the cases will be same indicating the spontaneous nature of the process of radioactivity.


Spontaneous means to me as anything that takes place on its own without any inflience of any external factor e.g Temperature Pressure Magnetic field Electric field.etc ........... Radioactivity or radioactive decay is a spontaneous process. It is because the radioactive elements continuously emit radiation from them as a result of reactions taking place within them. It can be understood easily by the following experiment. Once henry bacquerel(a physicist) accidently observed that the uranium salt crystal emitted some radiations that turned the photographic plate black. It was seen that he did nothing during this observation but still these radiations were emitted. This shows that radioactivite ie. The emission of radiations by particles is a spontaneous process.


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