Question: How does the decay take place?
About the article "Magnetic resonance imaging", section "T1rho MRI".

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If the proton does not decay, stellar-mass objects will still become black holes, but more slowly.
The following timeline assumes that proton decay does not take place. 
The spontaneous decay of free protons has never been observed, and the proton is therefore considered a stable particle.
However, some grand unified theories of particle physics predict that proton decay should take place with lifetimes of the order of , and experimental searches have established lower bounds on the mean lifetime of the proton for various assumed decay products.
Experiments at the Super-Kamiokande detector in Japan gave lower limits for proton mean lifetime of for decay to an antimuon and a neutral pion, and for decay to a positron and a neutral pion.
Another experiment at the Sudbury Neutrino Observatory in Canada searched for gamma rays resulting from residual nuclei resulting from the decay of a proton from oxygen-16.
This experiment was designed to detect decay to any product, and established a lower limit to the proton lifetime of .
However, protons are known to transform into neutrons through the process of electron capture (also called inverse beta decay).
For free protons, this process does not occur spontaneously but only when energy is supplied.
The equation is:The process is reversible; neutrons can convert back to protons through beta decay, a common form of radioactive decay.
In fact, a free neutron decays this way, with a mean lifetime of about 15 minutes. 
In the 19th century, scientists used the idea of random motions of molecules in the development of statistical mechanics to explain phenomena in thermodynamics and the properties of gases.
According to several standard interpretations of quantum mechanics, microscopic phenomena are objectively random.
That is, in an experiment that controls all causally relevant parameters, some aspects of the outcome still vary randomly.
For example, if you place a single unstable atom in a controlled environment, you cannot predict how long it will take for the atom to decay—only the probability of decay in a given time.
Thus, quantum mechanics does not specify the outcome of individual experiments but only the probabilities.
Hidden variable theories are inconsistent with the view that nature contains irreducible randomness: such theories posit that in the processes that appear random, properties with a certain statistical distribution are somehow at work "behind the scenes" determining the outcome in each case. 
Some nuclei can undergo double beta decay (ββ decay) where the charge of the nucleus changes by two units.
Double beta decay is difficult to study in most practically interesting cases, because both β decay and ββ decay are possible, with probability favoring β decay; the rarer ββ decay process is masked by these events.
Thus, ββ decay is usually studied only for beta stable nuclei.
Like single beta decay, double beta decay does not change ; thus, at least one of the nuclides with some given has to be stable with regard to both single and double beta decay. 
  Bit decay, in computing  Software decay, in computing  Distance decay, in geography  Exponential decay, the decrease of a value in proportion to its value  Decay time (fall time), in electronics  Network decay (channel drift), in television programming  In music, how quickly the sound drops to the sustain level after the initial peak, see ADSR envelope