Providing information

1. A method for determining a dispersion format of a radioactive material within a matrix, wherein said radioactive material is potentially present in a dispersion format which is self-shielding against emissions arising from said radioactive material, the method comprising:

measuring emissions from said radioactive material within said matrix at three or more energies selected from energies about 143.8 keV, about 163.3 keV, about 185.7 keV, about 205.3 keV, about 766.4 keV, about 1001.0 keV;

determining a ratio of emissions at one said energy to emissions at another said energy in respect of at least two different pairs of said energies;

obtaining a ratio value of said ratio of the emissions at the two energies for each of said pairs of energies;

comparing one said ratio value to a first threshold value, wherein when one said ratio value is to one side of said first threshold value said dispersion format for said radioactive material in said matrix is determined to be a dispersion format which is self-shielding against emissions arising from said radioactive material; and

comparing second said ratio value to a second threshold value, wherein when second said ratio value is to one side of said second threshold value said dispersion format for said radioactive material in said matrix is determined to be a dispersion format which is self-shielding against emissions arising from said radioactive material.

2. A method for providing information on the dispersion format of a radioactive material within a matrix, the method comprising:

measuring the emissions from the radioactive material within the matrix at two or more energies;

determining the ratio of the emissions at one of the energies to the emissions at another of the energies; and

comparing the ratio value for the ratio of the emissions at the two energies to a value, the value having one side and the value having another side; and

wherein when said ratio value is to the one side of said value said dispersion format for said radioactive material in said matrix is determined to be a dispersion format which is self shielding against emissions arising from said radioactive material; and

wherein when said ratio value is to one side of said value said dispersion format for said radioactive material in said matrix is determined to be a dispersion format which is not self shielding against emissions arising from said radioactive material.

3. A method according to claim 2 in which the value is a threshold value.

4. A method according to claim 2 in which one or more of the energies at which emissions are measured are selected from amongst the following: 143.8 keV; 163.3 keV; 185.7 keV; 205.3 keV; 766.4 keV; 1001.0 keV.

5. A method according to claim 2 in which the pair of energies for which the ratio of the emissions at one of the energies to the emissions at another of the energies is determined is provided by any two from amongst the energies: 143.8 keV; 163.3 keV; 185.7 keV; 205.3 keV; 766.4 keV; 1001.0 keV.

6. A method according to claim 2 in which the pairs for which the ratio of the emissions at one of the energies to the emissions at another of the energies is determined are provided by one or more of the following pairs of energies: 143.8 keV and 185.7 keV; 163.3 keV and 185.7 keV; 205.3 keV and 187.5 keV.

7. A method according to claim 2 in which the threshold value is the boundary between a first dispersion format and a second dispersion format.

8. A method according to claim 7 in which the first dispersion format is a format not giving self-shielding and/or a dispersed format.

9. A method according to claim 7 in which the second dispersion format is a format giving self-shielding and/or a non-dispersed format.

10. A method according to claim 2 in which one or more of the following pairs of energies and threshold value therefore is used:

in respect of the ratio 143.8 keV to 185.7 keV a threshold value of 0.14±0.02;

in respect of the ratio 163.3 keV to 185.7 keV a threshold value of 0.07 +0.01 or −0.005; and

in respect of the ratio 205.3 keV to 187.5keV a threshold value of 0.10−0.01 or +0.005.

11. A method according to claim 2 in which one or more of the following pairs of energies and threshold value therefore is used:

in respect of the ratio 185.7 keV to 143.8 keV a threshold value of 7.2±0.4;

in respect of the ratio 185.7 keV to 163.3keV a threshold value of 14.3±2;

in respect of the ratio 187.5 keV to 205.3 keV a threshold value of 10.0±2.4.

12. A method according to claim 2 in which a further threshold value is provided.

13. A method according to claim 12 in which one or more of the following pairs of energies and further threshold values is used:

in respect of the ratio 143.8 keV to 185.7 keV a further threshold value of 0.24±0.05;

in respect of the ratio 163.3 keV to 185.7 keV a further threshold value of 0.11±0.02; and

in respect of the ratio 205.3 keV to 187.5 keV a further threshold value of 0.07±0.02.

14. A method according to claim 12 in which one or more of the following pairs of energies and further threshold values is used:

in respect of the ratio 185.7 keV to 143.8 keV a further threshold value of 4.17±0.4;

in respect of the ratio 185.7 keV to 163.3 keV a further threshold value of 9.1±2; and

in respect of the ratio 187.5 keV to 205.3 keV a further threshold value of 14.3±2.4.

15. A method according to claim 2 in which in the comparison, where the ratio value is closer to the zero diameter ratio value than the threshold value, the indication is that the radioactive material is dispersed in the matrix.

16. A method according to claim 12 in which in the comparison, where the ratio value is between the threshold value and the further threshold value the indication is that the radioactive material is dispersed in the matrix.

17. A method according to claim 2 in which in the comparison, where the ratio value is on the other side of the threshold value compared with the zero diameter ratio value, the indication is that the radioactive material is not dispersed within the matrix.

18. A method according to claim 12 in which in the comparison, where the ratio value is on the other side of the further threshold value compared with the zero diameter ratio value, the indication is that the measurement is not reliable and/or that further investigation is required.

19. A method according to claim 2 in which the measured emissions are corrected to remove emissions from one or more one or more of plutonium, americium or radium within the matrix.

20. A method according to claim 19 in which the measured emissions are corrected to remove one or more of

Pu 239 emitted gammas at 143.3 keV;

Pu 239 emitted gammas at 161.5 keV;

Pu 239 emitted gammas at 203.6 keV;

Am 241 emitted gammas at 146.6 keV;

Am 241 emitted gammas 164.5 keV;

Am 241 emitted gammas 203.8keV;

Ra 226 emitted gammas at 186 keV.

21. A method according to claim 2 in which the measured emissions are corrected for matrix attenuation by considering the effect of the matrix on a transmission source.

22. A method for providing information on the self shielding of a radioactive material within a matrix, the method comprising:

measuring the emissions from the radioactive material within the matrix at two or more energies;

determining the ratio of the emissions at one of the energies to the emissions at another of the energies; and

comparing the ratio value for the ratio of the emissions at the two energies to a threshold value, a ratio value to one side of the threshold value indicating no self-shielding for the radioactive material in the matrix.

23. A method according to claim 22 in which an indication of no self-shielding for the radioactive material is provided where the self-shielding is below a given level.

24. A method according to claim 22 in which a ratio value to the other side of the threshold value is taken to indicate self-shielding for the radioactive material.