A first look to capture with fission tagging (TAC+MGAS) C. Guerrero (CERN)

1. A first look to capture with fission tagging (TAC+MGAS) C. Guerrero (CERN)

2. The Letter or Intent submitted to INTC (Nov. 2009) • The experimental set-up combines the use of the TAC (for capture) with a total of three MGAS (for fission) detectors loaded with 235U samples. • The detectors and samples were already used in 2009 (for monitoring purposes) • The long MGAS chamber has been designed and constructed at CERN. TAC HV (drift) MGAS Signal+Mesh 3 MGAS detectors each equipped with a 1 mg 235U sample

3. Design and construction of the fission tagging chamber The chamber has been designed and constructed at CERN in collaboration with Damien Grenier and Vincent Barozier. Gas entrance/exit Vacuum valve Connectors He at atmospheric pressure Kapton windows

4. Design and construction of the fission tagging chamber The chamber has been designed and constructed at CERN in collaboration with Damien Grenier and Vincent Barozier. Separators Sample assembly

5. Design and construction of the fission tagging chamber The samples are mounted in the Class-A lab of ISOLDE (B.179) The SAFETY FILE describing the detectors, the samples , risks and measures, usage procedures , etc. is available in EDMS: https://edms.cern.ch/document/1097338/1

6. Experimental set-up • The experiment was carried out after the 241Am with the TAC, thus the set-up for the BaF2 is that of the 241AM measurement (250 MSamples/s) • The MESH signals from the three MGAS detectors were preamplifier, amplified and the plugged into the DAQ (100 MSamples/s) named FTMG #1, #2 and #3.

7. Experimental set-up • The experiment was carried out after the 241Am with the TAC, thus the set-up for the BaF2 is that of the 241AM measurement (250 MSamples/s) • The MESH signals from the three MGAS detectors were preamplifier, amplified and the plugged into the DAQ (100 MSamples/s) named FTMG #1, #2 and #3.

8. Analysis of TAC and MGAS Time and energy calibration of the TAC modules using a 88Y source. Coincidence (Dcoinc=20 ns ) in the TAC to convert “signals” into “events” . Create ROOT files with “nt_baf2” and “nt_ftmg” for each run. Loop over each MGAS detector looking for coincidences (Dcoinc=50 ns ) in the TAC 25 ns Random coincidences?

9. Analysis of TAC and MGAS Time and energy calibration of the TAC modules using a 88Y source. Coincidence (Dcoinc=20 ns ) in the TAC to convert “signals” into “events” . Create ROOT files with “nt_baf2” and “nt_ftmg” for each run. Loop over each MGAS detector looking for coincidences (Dcoinc=50 ns ) in the TAC

10. Analysis of TAC and MGAS Time and energy calibration of the TAC modules using a 88Y source. Coincidence (Dcoinc=20 ns ) in the TAC to convert “signals” into “events” . Create ROOT files with “nt_baf2” and “nt_ftmg” for each run. Loop over each MGAS detector looking for coincidences (Dcoinc=50 ns ) in the TAC Questions at this stage: 1. There is a coincidence in the TAC for 85% of the MGAS fission signal (77% for conditions Esum>1 MeV and mcr>1). Is this figure reasonable? 2. It is known that ~7% of the prompt fission radiation is emitted with a delay of 20 to 100 ns. How can we take this into account ? (background events could trigger the coincidence before) 3. Shall we worry about the background from neutron emission? ( The travel time from the sample to the crystals (15 cm) is 10 ms for 1 eV and 100 ns for 10 keV)

11. Preliminary results from TAC+MGAS: Deposited Energy 235U(n,g) sum peak

12. Preliminary results from TAC+MGAS: Deposited Energy 235U(n,g) sum peak

13. Preliminary results from TAC+MGAS: Neutron Energy

14. Preliminary results from TAC+MGAS: Neutron Energy

15. Preliminary results from TAC+MGAS: Neutron Energy xX resonances Ba resonances

16. Preliminary results from TAC+MGAS: Neutron Energy xX resonances Ba resonances Very large neutron scattering background: where is it coming from?

17. Preliminary results from TAC+MGAS: Neutron Energy It was not possible to make a good vacuum in the chamber, and hence the “empty” measurement was not successful.

18. Conclusions We have measured for the first time at n_TOF simultaneous neutron capture and fission: (Design and construction of the fission chamber at CERN) The use of thin target has allowed to measure in “veto” mode, thus obtaining nice “fission-clean “ events in the TAC. Capture dominated resonances High fission contribution

19. Conclusions We have measured for the first time at n_TOF simultaneous neutron capture and fission: (Design and construction of the fission chamber at CERN) The use of thin target has allowed to measure in “veto” mode, thus obtaining nice “fission-clean “ events in the TAC. Following a very preliminary analysis, there are several open questions: There is a coincidence in the TAC for 85% of the MGAS fission signal (77% for conditions Esum>1 MeV and mcr>1). Is this “efficiency” reasonable? It is known that ~7% of the prompt fission radiation is emitted with a delay of 20 to 100 ns. How can we take this into account ? (background events could trigger the coincidence before) Shall we worry about the background from neutron emission? (The travel time from the sample to the crystals (15 cm) is 10 ms for 1 eV and 100 ns for 10 keV) Where is the high neutron scattering background coming from? Gas? Backings? Vacuum windows? Is it worth running with the neutron absorber? (available data to be analyzed) Shall we foresee any modification of the chamber and the set-up? […]