Tuesday, October 16, 2007

What To Do With Those Neutrons? Part 2, Neutron Effects

Interesting citation here indicating that "[f]ew previous studies have shown measurable effects on the mechanical properties of HY-80 steel if irradiation levels are below 1x1017n/cm2." Nevertheless, it it would be useful to see what kind of radioactive changes the neutrons might induce in said steel. Using the wise-uranium.org calculator, for fast neutrons bombarding 1 kg stainless for a year, we get the following (slightly reformatted):
Neutron flux = 647.0e9  per cm2s
Irradiation = 1 a;  Delay = 0 h 
 
    Original      Reaction      Activation       Half-
    Nuclide                     & Decay (~>)     Life
                                Products

710.0 g Iron:
          Fe-54    (n,3n) ->           Fe-52    (8.275 h)
                                    ~> Mn-52m   (21.40 m)
                                    ~> Mn-52    (5.592 d)
          Fe-54    (n,p)  ->           Mn-54    (312.7 d)
          Fe-54    (n,t)  ->           Mn-52    (5.592 d)
          Fe-54    (n,A)  ->           Cr-51    (27.70 d)
          Fe-56    (n,2n) ->           Fe-55    (2.700 a)
          Fe-56    (n,p)  ->           Mn-56    (2.578 h)
          Fe-56    (n,t)  ->           Mn-54    (312.7 d)
          Fe-57    (n,3n) ->           Fe-55    (2.700 a)
          Fe-57    (n,p)  ->           Mn-57    (1.470 m)
          Fe-58    (n,t)  ->           Mn-56    (2.578 h)

190.0 g Chromium:
          Cr-50    (n,2n) ->           Cr-49    (42.09 m)
                                    ~> V-49     (330.0 d)
          Cr-50    (n,t)  ->           V-48     (15.97 d)
          Cr-52    (n,2n) ->           Cr-51    (27.70 d)
          Cr-52    (n,p)  ->           V-52     (3.750 m)
          Cr-53    (n,3n) ->           Cr-51    (27.70 d)
          Cr-54    (n,t)  ->           V-52     (3.750 m)
          Cr-54    (n,A)  ->           Ti-51    (5.750 m)

100.0 g Nickel:
          Ni-58    (n,2n) ->           Ni-57    (1.503 d)
                                    ~> Co-57    (270.9 d)
 
          Ni-58    (n,3n) ->           Ni-56    (6.099 d)
                                    ~> Co-56    (78.77 d)
          Ni-58    (n,p)  ->           Co-58    (70.81 d)
          Ni-58    (n,t)  ->           Co-56    (78.77 d)
          Ni-58    (n,A)  ->           Fe-55    (2.700 a)
          Ni-60    (n,2n) ->           Ni-59    (75.00e3 a)
          Ni-60    (n,p)  ->           Co-60    (5.271 a)
          Ni-60    (n,t)  ->           Co-58    (70.81 d)
          Ni-61    (n,3n) ->           Ni-59    (75.00e3 a)
          Ni-61    (n,p)  ->           Co-61    (1.650 h)
          Ni-62    (n,t)  ->           Co-60    (5.271 a)
          Ni-62    (n,A)  ->           Fe-59    (44.64 d)
          Ni-64    (n,2n) ->           Ni-63    (100.1 a)
There's a fair number of short-lived isotopes there, which usually means you'll end up with a mess of radioactivity. I'm still working on calculating all the decay products.

A very cranky, opinionated look at this was on talk-polywell, but I missed it earlier.

Update 10/18: Back to our 1 GW reference case, this means radiated power from fast neutrons (just the 11B + α reaction) ends up as

7.3x1017 neutrons/s * 2.7x106 MeV/neutron * 1.602x10-19 J/eV = 316 kW
M. Simon suggested that a 500 MW Polywell device would throw off 5 kW of neutrons. I'm not sure how he derives that figure, but I'll ask.

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