The article says:
Mr Minter said: "Some of the plutonium particles lying on the sea bed have a half-life of 300 years. I want to ensure that future generations can enjoy the beach in safety and that they won't look back at us and ask why we did nothing while this beautiful landscape was being polluted."
The number of plutonium isotopes that have a half-life of 300 years is
zero.
The physics of every plutonium isotope is available on line:
http://atom.kaeri.re.kr/ton/nuc11.htmlThis is from the
Table of Nuclides, with which anyone interesting in nuclear engineering must be familiar.
Here is a typical entry, this for plutonium-240:
94-Pu-240
basic
n-XS summary
XS graphs
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element 94-plutonium-240
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Atomic Mass: 240.0538075 +- 0.0000021 amu
Excess Mass: 50121.319 +- 1.947 keV
Binding Energy: 1813454.935 +- 1.974 keV
Beta Decay Energy: B- -1378.952 +- 13.790 keV
"The 1995 update to the atomic mass evaluation" by G.Audi and A.H.Wapstra, Nuclear Physics A595 vol. 4 p.409-480, December 25, 1995.
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Spin: 0+
Half life: 6564 years
Mode of decay: Alpha to U-236
Decay energy: 5.256 MeV
Mode of decay: SF
Branch ratio: 5.7E-6 %
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Meta state at 2.800 Mev
Spin: (0+)
Half life: 3.7 ns
Mode of decay: SF
Branch ratio: >0.00 %
Possible parent nuclides:
Beta from Np-240
Electron capture from Am-240
Alpha from Cm-244
R.R.Kinsey, et al.,The NUDAT/PCNUDAT Program for Nuclear Data,paper submitted to the 9 th International Symposium of Capture-Gamma_raySpectroscopy and Related Topics, Budapest, Hungary, Octover 1996.Data extracted from NUDAT database (Jan. 14/1999)
The more you know, the better you can engage in critical thinking.