Assessment of the Energy Resolution Function for the n_TOF target facility at CERN

1. Ongoing Work… C. Carrapiço, S. Andriamonje, E. Berthoumieux, I. F. Gonçalves, F. Gunsing, A. Mengoni, P. Vaz, V. Vlachoudis and the n-TOF collaboration Assessment of the Energy Resolution Function for the n_TOF target facility at CERN DAPNIA

2. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr List of Content • Motivation • Monte Carlo Geometry Implementation • Simulation Conditions • Monte Carlo Results • Energy Resolution Function Analysis • Parameterizations for Energy Resolution Functions • Energy Resolution Function Analysis FWHM and FWTM. • Conclusions

3. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr Motivation • The Energy Resolution Function plays an important role in the correction of resonance shape during the Sammy fit. • To know the correct parametrization of the resolution function is paramount for obtaining correct cross sections. • The n_TOF target system was planed with a moderation depth of 5 cm but during the implementation, an o-ring was introduced just behind the aluminum window. This expanded the moderation depth in 0.8 cm and now the target system is operating with moderator of 5.8 cm. • To know the real effect of the increased moderation depth it is crucial to compare realistic simulations.

4. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr Monte Carlo Geometry Implementation • The detailed geometry of the target was implemented. • The neutron beam line was implemented in a realistic way considering the effect of the collimator system and diameter reduction of beam line. • The neutron production is provoked by the interaction of 20GeV protons with the lead block. • The Monte Carlo code is able to make the transport of high energy hadrons and fragments and simulate nuclear reaction mechanisms up to a few tens of GeV.

5. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr State of the art • The simulations were performed using the preequilibrium and evaporation physics from the CEM2k model that has a number of improvements and refinements in the cascade and Fermi break-up models. • CEM2k is able to describe fission reactions and production of light fragments heavier than 4He (using the Generalized Evaporation Model code). This features permit to describe quite well a large variety of spallation, fission and fragmentation reactions.

6. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr Monte Carlo particle behavior Neutron tracks on the target Proton tracks on the target The protons impinge on the lead block with a 10° angle in respect to the neutron beam line.

7. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr Simulation Conditions • The spectrum is tallied at the end of the neutron beam line at a distance of 185m from the exit surface of the lead target. • To transport the neutrons in a such long flight path and to have a good statistics considering the very small solid angle, we recurred to deterministic particle transport inside the neutron beam line. • The simulation output is a 2D matrix with Delayed Distance vs Energy Bin. • There are 3600 bins for DD covering the range between -60cm to 300cm and 100 bins for Energy in the range of 1eV to 10MeV. • The simulations have been preformed for a moderation depth of 5 cm and 5.8 cm.

8. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr Monte Carlo Results counts Energy (MeV) Delayed Distance

9. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr Monte Carlo Results Energy (MeV)

10. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr Monte Carlo Summary • The use of Monte Carlo techniques to create a realistic neutron spectrum, coupled with a deterministic particle transport inside the neutron beam line, make possible to obtain results with reasonable statistics in a period of 2 days. • This allows to study different geometry configurations and different material compositions for the target system in a very short time period. • The simulations have been compared with other simulation made for the n_TOF target system and showed that the neutron fluence spectrum is reproduced.

11. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr Energy Resolution Function Analysis • The analysis routine consist in the fitting of the 1D projection of each individual energy bin. • The fit functions consists of a chi square distribution on top of two exponential functions.

12. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr Energy Resolution Function Analysis (continued) • The parameter extracted from the fit of each individual energy bin are then fitted as a energy dependent function. • This permits to reconstruct a 2D parametrization of the Energy Resolution Function.

13. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr Energy Resolution Function Analysis (FWHM) • In order to evaluate the differences between the different Energy Resolutions Functions we compared the Full With at Half Maximum. • The results show that the ERF for 5 cm follows the previous parametrization behavior. • The results for the ERF with 5.8 cm of moderator show significant differences. Old Parameterization 5.0 cm of water New Parameterization 5.0 cm of water New Parameterization 5.8 cm of water

14. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr Energy Resolution Function Analysis (FWTM) • The comparison at the Full With at a Tenth of Maximum showed a similar behavior between the ERF parametrization for 5 cm and the old parametrization • The FWTM for the ERF with 5.8 cm of moderator show significant differences in comparison with the old parametrization. Old Parameterization 5.0 cm of water New Parameterization 5.0 cm of water New Parameterization 5.8 cm of water

15. Carlos Carrapiço ccarrapico@itn.pt carlos.carrapico@cea.fr Conclusions • The results show that an increase in moderation depth can have an important effect above 1 keV. • For the energy range below 1 keV there isn't a significant deviation between the different moderation depths. • The numeric parametrization are being evaluated and will be released in a short time period.