1. Prompt dose upstream the 12-ft concrete shielding blocks Igor Rakhno May 4, 2007

2. The calculations The 3-ft steel beam stop with a 8" poly front tip is placed to cover the opening 3.25" in diameter. The beam stop is 6.5" in diameter. 400 MeV protons. Neutron cut-off energy was 300 keV. Gammas from reactions (n,γ) induced by thermal neutrons were, therefore, ignored. Normalization here is per 2×10 14 p/s. 2

3. 3 Model

4. 4 Prompt dose

5. 5 Residual dose

6. Conclusions At full Linac intensity the integral dose for a human phantom upstream the 12-ft concrete shielding blocks is about 190 mrem/hr. One has about 10 3 neutron/cm2*sec averaged over the phantom volume. A steel plate (1-2 inches thick) and poly blocks (≈1-2 ft thick) next to the shielding blocks in the MTA hall could help. 6