The ICRP Publication 101 "Assessing Dose of the Representative Person for the Purpose of Radiation Protection of the Public" defines the deterministic and probabilistic approaches to find the dose of the Representative Person from doses incurred by population members. Are results for members of the group of different ages included in forming the average or the 95th percentile of the dose distribution, or shall they be treated separately? I am not sure, although the example for the probabilistic approach in B.7.2 of ICRP 101 would suggest the first case. Simply put, at the end of the analysis, is there only one Representative Person with one Dose to the Representative Person, or are there Representative Persons for each age group, e.g. Representative Infant (1 y), Representative Child (10 y), Representative Adults (adult).
Article Assessing Dose of the Representative Person for the Purpose ...
A short answer:
It depends on the situation but for long lasting exposure such as for a facility operated for 50 years or more, or for disposal of long lived radioactive waste the Commission suggests the use of life averaged coefficients.
See setion 3.4 paragraph (77).
In the preceding paragraph the Commission states that “The Commission continues to believe that the precision implied by using the full set of [age specific/MJ] dose coefficients is not warranted in the estimation of prospective dose to the public because of the uncertainties involved”.
In special situation where age specific information is wanted one may use the references ICRP 1966a or b, where dose coefficients are given for six age ranges.
Strangely enough, those references seems to be missing in the list of references to ICRP 101, but the commission is probably referring to publication 72, published 1996:
"Age-dependent Doses to the Members of the Public from Intake of Radionuclides Part 5, Compilation of Ingestion and Inhalation Coefficients".
Now I can follow it. If I was studying the radiological impact of an NPP for which the operation time is 50 years, I could use one age group with age-averaged doses because children would turn to adults and adults would have children in turn. Using one number is convenient from the practical point of view. If I study the impact of an emergency with short lasting effect, I should look at every age group, embryo/fetus, breast fed infants included. If I looked at a facility with the lifetime, say 5 years, such as an experiment at CERN, I should investigate doses to the three groups (1 y, 10 y, adults). Do I understand it correctly?
You are on the right track but you need to understand the logic of the situation.
The need to involve various groups depends on the expected exposure situation. If you e.g. are dealing with staff > 20 years from a minor local onsite release, you limit your group accordingly. Observe that if you are concerned with releases to the general public you might still be OK with the average groups.
You can check it yourself by making your own parallel calculations. You might find that one infant + one adult etc. for all the groups, exposed at one situation may give you the same detriment/person as one individual receiving the same dose distributed over a lifetime.