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marcello pisani
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not easy to add something to ..

such a perfect work but .. in order to add further salt  .. here is an extract from a document made in the 70's by the US  NRC ( discovered by our special agent Fatboyharris ) about modifcations on half-life of radioemitting materials by binders : 

''It is generally accepted that zinc sulfide (ZnS) is damaged by the action of ionizing radiation, the very radiation that produces light. Wallhausen (1956) suggested a half-life of 10 years for ZnS, a value which is also accepted by the IAEA (1967) expert group. This decay must be considered in evaluating the useful luminosity of the radioluminous materials. Due to the long physical half-life of radium, the effective half-life of radiumactivated paint will be about 10 years.
The effective half-life of Pm-147 activated paint is calculated by combining the physical half-life of Pm-147 of 2.62 years with the 10-year half-life of ZnS resulting in an effective half-life of 2.1 years.
Using the same procedure, the effective half-life for tritium gas in tubes can be calculated to be 5.5 years. The actual value is rarely that long because of tritium release from the tubes.
A calculation of effective half-life for tritiated paint is somewhat more difficult because of differences in the decomposition rate of various tritiated polymers. The IAEA (1967) report assumes no tritium release and thus obtains the 5.5-year value calculated for tritium gas. This assumption is obviously invalid in view of many recent measurements both with paint and with users of luminous paints. It is well known that tritium release is elevated during the first few weeks subsequent to application. Chollet (1968) suggests an annual tritium release of 10-20%. Lorenzer and Born (1968) report 16% release per year, whereas, Guent (1974) suggests a 25% release rate. Coenen (1963) reports tritium release rates of 0.08-0.35 ACi/mCi-d with an average of 0.1 pCi/mCiWd. If the highest value is disregarded, this average corresponds to 3.6% per year, whereas his highest value relates to about 13%. From these data, an average tritium release half-life of 4 years can be estimated. The effective luminosity half-life can thus be calculated from the physical half-life of tritium of 12.3 years, the stability half-life of ZnS of 10 years, and the tritium release half-life of 4 years to be 2.3 years.''