# 10eV neutron shielding

Dear experts,
I am studying the radiation shielding of a material against 10eV neutron. The running file is as follows.

2022.3.22(GZ)10eV.flair (3.2 KB)
2022.3.22(GZ)10eV.inp (2.6 KB)

When I got the running results, I found that many positions in the cloud map were blank without particles, and most of the points in the numerical results were also 0, with a very large statistical error.

What is the cause of this situation?
Is it because the neutron energy is too low?
How can I solve this problem to get an accurate simulation?

Dear @Junjie_Zhang,
You don’t have enough statistics. You need to run more primary to obtain a statistically relevant result.

Dear amario,

I’ve increased the number of particles by a factor of 10, The statistical error is still large.

2022.3.23(GZ)10eV.flair (3.3 KB)
2022.3.23(GZ)10eV.inp (2.7 KB)

When I increase the energy of the particle, the statistical error decreases. Is it because after low energy particles pass through the material shielding, only a few particles reach the detection area, while high energy neutrons have stronger penetration and more particles can reach the detection area?

In addition, can I reduce the number of detection intervals（bins） to reduce the statistical error?

Dear @Junjie_Zhang,

Let’s first recall that the statistical uncertainty is related to the number of simulated primaries N and that the uncertainty goes with \sqrt{N}. Therefore, increasing by 10 the number of primaries, will reduce the uncertainty by a factor \sqrt{10} \simeq 3.

Nevertheless, what is more important is that the energy of the neutrons is quite low and the shielding region GZHNT is quite thick: 101 cm. Therefore, there is a very limited amount of neutrons that reach your detection area R3.
Additionally, since there is nothing in your geometry beyond the detection area, there is no chance that an escaping neutron would be backscattered inside the detection area and contribute more than once to the dose equivalent.

You can of course reduce the number of bins to reduce the uncertainty. It seems to me that your binning is very fine.

I cannot give you more advice as I don’t know what’s your goal and what you want to achieve.