Worldwide Open Proficiency Test: Determination of ... - Nucleus - IAEA

Isotope Decay mode Branching ratio, % Progeny, T(1/2)
40
30
20
10
0
114 223
177 270 46 86 113
81 39 61 257 95
246 295 296 6240 264 82 191 144 185
220 12 214 234 294
218 77 159 260
269 143 111 90 54
71 91 168 125 153
253 255 297 83 279
26 17 178 299 300
124 76 36 41 112
120 170 175 210
221 84 93 242 217
173 89 182 132 60
70 154 45 289 65
288 136 134 290 11
219 88 94 292 293
200 99 238 274
166 277 275 160 72
92 133 73 40 127
199 37 63 57 190
233 31 58 241 171
27 47 51 87
201
34
163
101
207 131 119 55 78
15 265 110 115 272
244 13 52 165 109
267 43 141 122 237
254 16 20 18
22 179 258 24 130
7283 32 236 278
64 284 169 285 239
161 44 123
263
19 53 5138
273
155 194 195 216
252 211 56 140 227
10 62 251 174 157
172 192 123 42 261
150 25 193 268 59
235 164 79 121 206
197 142
Bi-212
Draft, page 34
Tl-208 in moss-soil
[Bq/kg] TABLE 6. DECAY BRANCHING RATIOS OF Bi-212
Alpha 35.93 Tl-208, 3.06 min
T(1/2)=60.54 min Beta 64.07 Po-212, 300 ns
Tl-208 is a well detectable gamma-emitter and several old databases and gamma-libraries
(very often provided by the manufacturers of the spectrum evaluation software) are containing
the Tl-208 gamma lines with a corrected abundance by the branching ratio. Using this type of
library, the software calculates the activity back to the mother element to facilitate the
comparison with other gamma-emitters of this series. However, the physical activity of Tl-
208 is less in proportion with the branching ratio which is equal to 0.3593. In case of the
moss-soil, the analyst task was to determine the massic activity of Tl-208.
Considering the reported results, most of the participating laboratories were using the correct
gamma-abundance values for this isotope.
Laboratory code
Figure 21: S-shape presentation of the Tl-208 results, two splited results population due to wrong
calculation
However, up to 40% of the laboratories reported unacceptable overestimated results due the
use of wrong gamma-abundance values for Tl-208, which means that the applied gamma
library should be revised accordingly.
Generally speaking, nuclear data library in a gamma-spectrometry laboratory should be a
controlled document within the frame of the laboratory quality system and the master file of
the library should be stored in a safe manner to preserve its integrity and it should be updated
according to a written procedure. Gamma spectroscopists might modify the library content to
meet specific needs, but these modifications and their technical justification should be
documented and known to the system. Nuclear data library should be protected from
unauthorised use or technically unjustified modification.