The calculation of the neutron/gamma yield and the activation in the tungsten targets

I want to calculate the neutron and gamma yield of the tungsten after the electron bombardment, and the activation of the tungsten after a year of continuous exposure.

1、The result of the yield is showing in the next Fig. The gamma yield is 5 times of the neutron yield.

However, the gamma yield is about 2 orders of magnitude higher than the neutron yield in the calculation by MCNP. Therefore, is there any effect that has not been taken into account in the input file, resulting in such a big difference?

2、When calculating the activation of the tungsten target, all the outputs are zero, include the yield. Please help me to check the input file.
W2.inp (4.3 KB)


  1. In the first column (prompt radiation) you are looking at the particle yield from nuclear reactions (i.e. inelastic interactions) only, which does not include Bremsstrahlung photons.
    To get the full picture, you should for instance score photons on a region boundary with a dedicated card.

  2. As for the radioactive decays column, one should see there the particle yields from radioactive decays, namely electrons and photons. However, in the input file you uploaded, RADDECAY requests to kill the electromagnetic transport in the prompt stage, which is absurd with an electron beam. Moreover, you may want to bias (with LAM-BIAS) also photonuclear reactions by real PHOTONs, and not just ELECTRONs. There is no need to redefine TUNGSTEN and WATER materials.

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Thanks for your replay.

1、 The USRBDX is used to score the neutron and gamma yield . Ten TUNGSTEN targets is used in the simulation. Therefore, the boundary from regair1 to regair2 is used to score the neutron and gamma, which are escaped from the ten target. However, the neutron yield is as same as the result calculated by MCNP, the gamma yield is still much smaller than the result calculated by MCNP.

2、According to your suggestion. the RADDECAY is modified.

The modified input card is here.
W2.inp (5.4 KB)

Thanks again!

You did not modify the RADDECAY card according to my suggestion, since you keep multiplying the electromagnetic prompt cutoff by a factor 100 (999 in WHAT(5), interpreted as 999 * 0.1 = 99.9, see the manual), getting a photon transport threshold of 3.33 MeV as written in the output file.
Just remove the aforementioned 999 from RADDECAY and your photon population, extended down to 33 keV (its default PRECISIO threshold), will logically increase by more than one order of magnitude.

Thank you very much.
Yes, according to your suggestion, the gamma yield is increased from 0.8 p/e to 1.57 p/e and the neutron yield is still 0.0085 n/e. However, the gamma yield is still smaller than the results calculated by MCNP,which is 2.29 p/e socred by f1,fs and C card.

If the RADDECAY is not used in the calculation, the result is not changed.

W2.inp (8.7 KB)

Thanks again!

Note that 1.57 is the current result on your cylindrical surface, while you get there 2.15 when scoring photon fluence.