Two weeks ago we talked about a note that Ed Storms and Brian Scanlan were passing around [1]. They are conducting an experiment using GM counters and have identified two signals for unknown species that are decaying. The half-lives are calculated to be 58 minutes and 109 minutes, respectively, and there is a question about whether the signals are for the same species. The note uses a process of elimination to suggest that the decaying species could be potassium-40. Normally potassium-40 has a half-life of 1.24E9 years, so something unusual would have to happen to cause it to decay more quickly.
At the time I was wondering what species had half-lives in nature on the order of 58 to 109 minutes. There is a Wikipedia page that mentions nobelium-259 (58 minutes) and fluorine-18 (109 minutes) [2]. It turns out this page is quite incomplete. Using Mathematica, I was able to come up with a more complete list: Isotope Atomic Number Decay Modes Half-life (m.) Fluorine18 9 β+ 109.771 Chlorine39 17 β- 56.2 Argon41 18 β- 109.61 Scandium49 21 β- 57.17 Cobalt61 27 β- 99. Zinc69 30 β- 56.33 Gallium68 31 β+ 67.72 Germanium75 32 β- 82.78 Germanium78 32 β- 88. Arsenic70 33 β+ 52.67 Arsenic78 33 β- 90.67 Bromine75 35 β+ 97. Krypton77 36 β+ 74.33 Krypton87 36 β- 76.33 Strontium80 38 β+ 106.3 Zirconium87 40 β+ 100.8 Niobium97 41 β- 72.17 Ruthenium94 44 β+ 51.83 Ruthenium95 44 β+ 98.58 Silver103 47 β+ 65.67 Silver104 47 β+ 69.17 Cadmium104 48 β+ 57.67 Cadmium105 48 β+ 55.5 Cadmium118 48 β- 50.33 Indium108 49 β+ 58. Tin128 50 β- 59.07 Tellurium117 52 β+, PE 62. Tellurium129 52 β- 69.67 Iodine120 53 β+ 82. Iodine134 53 β- 52.5 Barium126 56 β+ 1.e2 Barium139 56 β- 83.06 Lanthanum131 57 β+ 58. Lanthanum142 57 β- 91.17 Cerium133 58 β+ 97. Praseodymium137 59 β+ 76.83 Neodymium136 60 β+ 50.67 Neodymium149 60 β- 103.7 Samarium142 62 β+ 72.48 Terbium147 65 β+ 1.e2 Terbium148 65 β+ 60. Holmium156 67 β+ 57. Erbium163 68 β+ 75. Thulium163 69 β+ 108.6 Ytterbium164 70 EC 75.83 Ytterbium177 70 β- 114.7 Ytterbium178 70 β- 73. Lutetium167 71 β+ 51.5 Hafnium183 72 β- 64.02 Tantalum174 73 β+ 68. Osmium181 76 β+ 1.1e2 Iridium183 77 β+, α 57. Platinum185 78 β+, α 70.83 Thallium195 81 β+ 69.67 Thallium196 81 β+ 110.3 Lead199 82 β+ 90. Bismuth201 83 β+, α 103. Bismuth202 83 β+, α 103. Bismuth212 83 β-, α, β-+α 60.55 Polonium205 84 β+, α 104. Astatine207 85 β+, α 1.1e2 Astatine208 85 β+, α 97.83 Radon224 86 β- 107. Radium230 88 β- 93. Actinium229 89 β- 62.67 Protactinium239 91 β- 1.1e2 Uranium229 92 β+, α 58. Neptunium240 93 β- 61.83 Americium237 95 β+, α 73. Americium238 95 β+, α 98. Curium249 96 β- 64.15 Berkelium251 97 β- 55.67 Californium255 98 β-, F, α 85. Einsteinium249 99 β+, α 102.2 Mendelevium256 101 β+, α, F 77. Mendelevium259 101 F, α 97. Nobelium259 102 α, EC, F 58. Lawrencium266 103 α, F 67. Rutherfordium264 104 α 67. Rutherfordium268 104 α, F 67. Dubnium270 105 α, F 67. Seaborgium272 106 α, F 67. Bohrium273 107 α, F 90. Bohrium274 107 α, F 90. Hassium276 108 α, F 67. The lighter elements, up to Gallium, are particularly interesting. Note that radon-224 is in the list and has a half-life of 107 minutes. I am not sure of this, but it looks like radon-224 is not a daughter of the usual radium decay and only exists as a synthetic isotope, so even if the 109-minute half-life went back to radon-224, there would appear to be something unusual going on. In the note by Storms and Scanlan, C, O, Si, Al, K, Fe, Mg, Ti, Na, Ni, Cu and Cr are mentioned at different points in connection with materials in the GM detector and in the samples, and all but one of these elements are not favored as the source of the unidentified decaying species. The experiment itself involves subjecting samples of Pd and Ni sputtered with various metals to H2. Three different materials were prepared in this way, and they all displayed the same behavior once activated. I have found few exothermic proton or deuteron capture reactions starting from stable isotopes that will lead to the light elements in the table above, up to and including Gallium; they are: 20Ne + d -> 18F + α 17O + p -> 18F + γ 40Ar + d -> 41Ar + p 68Zn + d -> 69Zn + p 70Ge + d -> 68Ga + α One interesting detail about these reactions is that there is that the only overlap with the elements mentioned in a previous paragraph is oxygen; in this case, 17O, which exists in small amounts in the environment. Eric [1] http://lenr-canr.org/acrobat/StormsEnatureofen.pdf [2] http://en.wikipedia.org/wiki/List_of_radioactive_isotopes_by_half-life#103_seconds
