[mesa-users] ni56 beta decay rate is function of temperature? and goes to 0 for logT < 8?
Josiah Schwab
jwschwab at berkeley.edu
Wed Oct 23 14:39:22 EDT 2013
Hi Bill,
I'm pretty sure that your confusion is because these weak tables are
calculated for fully ionized Ni-56, but your intuition for Ni-decay is
from SNe ejecta where the nickel is only lightly ionized.
If I have a little free time later, I can give a more thorough answer,
but I don't think you should worry about this (not a bug).
Josiah
Bill Paxton writes:
> Hi,
>
> My turn to ask a question -- I have a model that manages to get ni56 up to regions of lower temperature compared to the usual places where it lives, i.e., where logT < 8 rather than the usual logT > 9. I was surprised to see the ni56 sticking around for a years when logT < 8.0, so I took a look at the weakreactions.tables in mesa/data/weaklib_data. You can find the table for ni56 beta decay by searching for "lbeta+ positron emission; ni56 co56". The values in the table are log10 of decay rate. The columns are temperatures in T9 = T*10^-9. Up at the high T9 end the rates are very large, while down at the low end, including my case of T9 = 0.1, they effectively go to zero.
>
> ni56 co56 by positron emission and electron capture; LMP
> T9 0.01 0.10 0.20 0.40 0.70 1.00 1.50 2.00 3.00 5.00 10.00 30.00
> lYeRho lbeta+ positron emission; ni56 co56
> 1 -99.999 -99.999 -69.740 -35.714 -21.132 -15.299 -10.760 -8.472 -6.021 -3.557 -1.373 -0.071
> 2 -99.999 -99.999 -69.740 -35.714 -21.132 -15.299 -10.760 -8.472 -6.021 -3.557 -1.373 -0.071
> 3 -99.999 -99.999 -69.740 -35.714 -21.132 -15.299 -10.760 -8.472 -6.021 -3.557 -1.373 -0.071
> 4 -99.999 -99.999 -69.740 -35.714 -21.132 -15.299 -10.760 -8.472 -6.021 -3.557 -1.373 -0.071
> 5 -99.999 -99.999 -69.740 -35.714 -21.132 -15.299 -10.760 -8.472 -6.021 -3.557 -1.373 -0.071
> 6 -99.999 -99.999 -69.740 -35.714 -21.132 -15.299 -10.760 -8.472 -6.020 -3.556 -1.373 -0.071
> 7 -99.999 -99.999 -69.740 -35.714 -21.132 -15.299 -10.760 -8.472 -6.019 -3.553 -1.370 -0.071
> 8 -99.999 -99.999 -69.740 -35.714 -21.132 -15.299 -10.760 -8.472 -6.019 -3.551 -1.358 -0.068
> 9 -99.999 -99.999 -69.740 -35.714 -21.132 -15.299 -10.760 -8.472 -6.019 -3.551 -1.354 -0.049
> 10 -99.999 -99.999 -69.740 -35.714 -21.132 -15.299 -10.760 -8.472 -6.019 -3.551 -1.354 -0.028
> 11 -99.999 -99.999 -69.740 -35.714 -21.132 -15.299 -10.760 -8.472 -6.019 -3.551 -1.354 -0.027
>
>
>
> I had expected to find something more like what I find for mg20 beta decay where the rates are (almost) independent of T.
>
> mg20 na20 by positron emission and electron capture; OHMT
> T9 0.01 0.10 0.20 0.40 0.70 1.00 1.50 2.00 3.00 5.00 10.00 30.00
> lYeRho lbeta+ positron emission; mg20 na20
> 1 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.765 0.766 0.799 1.382
> 2 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.765 0.766 0.799 1.382
> 3 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.765 0.766 0.799 1.382
> 4 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.765 0.766 0.799 1.382
> 5 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.799 1.382
> 6 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.800 1.382
> 7 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.768 0.802 1.382
> 8 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.769 0.811 1.385
> 9 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.769 0.814 1.406
> 10 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.766 0.769 0.814 1.429
>
>
> I thought this might be a bug in the preprocessor that builds the weakreactions.tables file from the separate sources. The ni56 => co56 reaction rates come from "LMP",
> LMP: K. Langanke, G. Martínez-Pinedo / Nuclear Physics A 673 (2000) 481–508
> so I checked that input file (mesa/weaklib/preprocessor/input_data/lmp.data). But I found the "-99.999" entries for beta decay rates there too.
>
> neg. daughter ni56 z=28 n=28 a=56 q= -1.6240
> pos. daughter co56 z=27 n=29 a=56 q= 1.6240
> +++ ni56 --> co56 +++ --- co56 --> ni56 ---
> t9 lrho uf lbeta+ leps- lrnu lbeta- leps+ lrnubar
> 0.01 1.0 -0.003 -99.999 -8.684 -9.066 -99.999 -99.999 -99.999
> 0.10 1.0 -0.058 -99.999 -9.164 -9.537 -99.999 -99.999 -99.999
> 0.20 1.0 -0.134 -69.740 -9.291 -9.652 -69.759 -74.128 -70.327
> 0.40 1.0 -0.306 -35.714 -9.387 -9.722 -37.930 -38.276 -38.162
> 0.70 1.0 -0.503 -21.132 -8.777 -9.063 -24.300 -23.078 -23.182
> 1.00 1.0 -0.511 -15.299 -7.439 -7.669 -18.824 -17.809 -17.866
>
>
> What's the story here? Is ni56 stable to beta decay at logT < 8? ;p Curiouser and curiouser.
>
> Thanks,
> Bill
>
>
>
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