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FLUENCE [ neutrons/cm‘

( € > 5 0 kev I]

Fig. 17.7. Helium Densities of Several Craphites After Irradiation at 715OC to the Indicated Fluence.

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30

I

0

I

I

I

I

2

I

I

I

I

I

I

I

I

I

1

I

I

I

I

I

I

4

6 8 IO INCIDENT NEUTRON ENERGY (MeV)

I

I

I

I

(2

I

I 44

Rg. 17.8. Specific Damage Energy Deposited in Various Materials by Fast Neutron Irradiation.

account anisotropic elastic and inelastic neutron scattering and using the semiempirical Lindhard formula9 for electronic excitation. In addition, where appropriate, the (n,2n) reaction has also been considered as an additional source Of disphmXntS. 'Ibis last does not occur in graphite.

The results of the calculation are shown in Figs. 17.8 and 17.9. We can defme a “damage efficiency” by the ratio ED/E,which is shown in Rg. 17.9 as a function of ’J. Lindhard et d,Kgf. Danske Videnskub.Sekkab, Mat.-Fys Medd 33, No. 10 (1963).

c-