Patent Number: 
Section: claims

1. Method performed by a computer and associated measuring equipment to determine the effective masses of N deposits of fissile matter respectively placed in N measurement fission chambers, N being an integer of 1 or more, the method comprising:A) a first measuring step (E1) during which N count rates are measured of N respective deposits of fissile matter of known effective masses, respectively placed in N calibration fission chambers respectively identical in their outer dimensions to the N measurement fission chambers, to form a matrix [C]0 of count rates of known deposits of fissile matter, each different measured count rate of said N respective deposits of fissile matter of known effective mass being a different coefficient of the matrix [C]0,B) a second measuring step (E2) during which N count rates are measured of N respective deposits of fissile matter placed in the N measurement fission chambers, to form a matrix [C] of count rates of deposits of fissile matter, the second measuring step being conducted under identical measuring conditions to the measuring conditions under which the first measuring step is conducted, each different measured count rate of said N respective deposits of fissile matter placed in the N measurement fission chambers being a different coefficient of the matrix [C], andC) a computing step (E3) to calculate and store, by operations performed within the computer, a data structure representing a column matrix [m] such that:[m]=[C]·I([a]>([a]01×[m]0−1×[C]0)),the coefficients of matrix [m] being the effective masses to be determined, the symbols “·I” and “x” respectively being the “matrix division” operator and the “matrix product” operator and the matrices [a], [a]0−1 and [m]0−1 respectively being:matrix [a], a known matrix of the isotopic analyses associated with the N deposits of fissile matter whose effective masses are to be determined,matrix [a]0−1, an inverse matrix of a known matrix [a]0 of the isotopic analyses associated with the N deposits of fissile matter of known effective masses,matrix [m]0−1, an inverse matrix of a known matrix [m]0 whose coefficients are the known effective masses of the N known deposits of fissile matter. 2. The method according to claim 1, further comprising the step of calculating and storing, by operations performed within the computer, a data structure representing a variance matrix var[m] of matrix [m] such that:var[m]={var[C]+[mij2]×(var[a]×[Xij2]+[aij2]×var[X])}·I{└([a]×[X])ij2┘},in which:var[C] is the variance matrix of matrix C,var[a] is the variance matrix of matrix [a],var[X] is the variance matrix of matrix [X] such that:[X]=[a]0−1×[m]0−1×[C]0,[mij2] is the matrix consisting of the terms mij to the power of 2, the terms mij being the coefficients of matrix [m], i being the index relating to the rows of the matrix and j being the index relating to the columns of the matrix,└aij2┘ is the matrix consisting of the terms aij to the power of 2, the terms aij being the coefficients of matrix [a], i being the index relating to the rows of the matrix and j being the index relating to the columns of the matrix,└Xij2┘ is the matrix consisting of the terms Xij to the power of 2, the terms Xij being the coefficients of matrix [X], i being the index relating to the rows of the matrix and j being the index relating to the columns of the matrix,[([a]×[X])ij2] is the matrix consisting of the terms ([a]×[X])ij to the power of 2, the terms ([a]×[X])ij being the coefficients of the product matrix [a]×[X], i being the index relating to the rows of the matrix and j being the index relating to the columns of the matrix. 3. The method according to claim 1, wherein N is 1. 4. The method according to claim 1, wherein N is greater than 1. 5. The method according to claim 2, wherein N is 1. 6. The method according to claim 2, wherein N is greater than 1.