NeuLAND - FAIR

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We investigate this timing effect in a GEANT3 simulation for the LAND detector. In figure 4.7, the time difference between the first interaction of the primary neutron and the detection of the first light is displayed. The response of LAND (black line) is compared to an ideal LAND assuming a time resolution of σt=0 ps for the scintillator (red line). The time resolution of the scintillator was set to zero for the latter case in order to study the effect of the passive material solely. Overlayed is the time difference for a detector which has the same module size as LAND but no passive converter material (blue line) in the following denoted with LAND’. The width of the timing peak expanding to negative ∆t values stems from the timedelayed protons which have to escape from the passive converter material. Events in the far tails originate from neutrons where no light was created by the particles stemming from the first neutron interaction. e.g. protons which are absorbed in the iron sheets. This leads to a background caused by a wrong determination of the position and time. The entries in the region of positive ∆t stem from events, where more than one secondary particle contributes to the production of the light within one module at the same time. The reconstruction algorithm which calculates the time of an event from the mean-time of the two photomultiplier signals thus delivers smaller times than actually possible. In order to fulfill the design criteria for NeuLAND with respect to time resolution, the use of passive converters is problematic, as seen in figure 4.7. With inserted converter, even with ideal time resolution, the timing peak is broadened, and moreover, the fraction of events in the tails is increased drastically. In order to study the efficiency for low energy neutrons (≈ 200 MeV), again GEANT3 simulations for the same hypothetical detector as above (LAND’) were performed. Modules of the same dimensions were used but without iron converter. Instead, the depth of the detector was doubled, resulting in 20 layers of scintillator. In table 4.3 the comparison shows, that the efficiency without passive material is almost independent of the incident neutron energy, while for the LAND detector the efficiency decreases towards lower neutron energies. The efficiency at lower neutron energies will be important for the use of NeuLAND e.g. in quasi-free scattering experiments (see section 2.4), which need to use NeuLAND modules at large scattering angles from the target. Even for energies below the design limit of 200 MeV, a high efficiency is observed, which may be beneficial in quasi-free scattering experiments at large scattering angles, see section 2.4. In conclusion the use of passive converters has negative implications with respect to both resolution and efficiency. On a later stage of the simulation, we observe, that with respect to multi-neutron recognition, calorimetry plays a crucial role, see section 4.5. In consequence, the MRPC concept for NeuLAND (see appendix B), using inserted passive converters and a detection mechanism, which is rather insensitive to the deposited energy, is not competitive to the fully-active scintillator concept. In further design considerations for NeuLAND passive converters are omitted. 44
incident neutron fully active detector LAND converter-based detector energy [MeV] simulated efficiency [%] measured efficiency [%] 100 97 - 170 97 78(10) 270 94 85(7) 470 95 93(2) 600 96 94(1) 800 97 96(1) 1050 97 96(1) Table 4.3.: Comparison of efficiencies for neutron detection for LAND and a hypothetical LAND’ without passive material. The efficiency values for LAND stem from a calibration experiment using fast neutrons from deuteron-breakup [Bor-03]. The values for the fully-active detector were simulated using GEANT3. 4.3. Effect of Granularity and Timing Properties for a Fully-Active Detector In the present section, the required detector parameters regarding time and spatial resolution are determined in a physics-driven approach from the experimental cases listed in chapter 2. Amongst the design goals for NeuLAND is a relative energy resolution of σ ≤ 20 keV at small relative energies of neutrons and fragment; we refer to section 2.2. Simulations, assuming uniform phase-space distributions, have been performed with the aim to match the position and time resolution for given distances to the target. The two distances taken into account represent for the final detector design with a face-size of 250×250 cm 2 the distance of full-acceptance mode (15.5 m), and the highest-resolution mode (35 m), respectively. For the simulations, the breakup of 132 Sn at 600 AMeV into 131 Sn and one neutron was considered. Table 4.4 gives an overview of the resolution σ(Erel) achieved for Erel=100 keV. 15.5 m 35 m σt=0 ps σt=100 ps σt=150 ps σt=0 ps σt=100 ps σt=150 ps 3x3 cm 2 13 keV 25 keV 32 keV 7 keV 12 keV 16 keV 5x5 cm 2 19 keV 29 keV 35 keV 10 keV 14 keV 17 keV 10x10 cm 2 38 keV 44 keV 49 keV 18 keV 21 keV 23 keV Table 4.4.: Effect of target-detector distance, time resolution, and scintillator size on the relative energy resolution σ(Erel) at Erel=100 keV for 132 Sn decaying into 131 Sn and one neutron at beam energies of 600 AMeV. At first, for all simulations the time resolution of the scintillator was set to σt = 0 ps. We varied the cross section of the scintillator bars: 3 × 3, 5 × 5, and 10 × 10 cm 2 cross 45
Page 1 and 2: FAIR/NUSTAR/R 3 B/TDR NeuLAND Techn
Page 3 and 4: Germany EMMI and FIAS: Enrico Fiori
Page 5 and 6: INR Moscow: Alexander Botvina Russi
Page 7 and 8: Contents Executive Summary 11 1. In
Page 9: B.7. MRPC Solution using Glass as C
Page 12 and 13: Apart from the excellent energy res
Page 14 and 15: processes in the universe, such as
Page 16 and 17: decaying into 24 O plus 4 neutrons
Page 19 and 20: 2. Physics Scenarios: Requirements
Page 21 and 22: e studied at R 3 B at FAIR include
Page 23 and 24: all theoretical calculations predic
Page 25 and 26: at the surface of the nucleus. The
Page 27 and 28: the evolution of fission channels (
Page 29 and 30: 3. Summary of NeuLAND Prototype Res
Page 31 and 32: counts 70 60 50 40 30 20 10 0 15 15
Page 33 and 34: Figure 3.4.: Shown is the time reso
Page 35 and 36: 4. Monte Carlo Simulations Within t
Page 37 and 38: normalized counts normalized counts
Page 39 and 40: GEANT3 interface. Here, we compare
Page 41 and 42: Counts 1000 900 800 700 600 500 400
Page 43: counts 5 10 4 10 3 10 2 10 10 LAND
Page 47 and 48: investigated. Three values for the
Page 49 and 50: spectrum, absorption length, refrac
Page 51 and 52: Counts 600 500 400 300 200 100 with
Page 53 and 54: Since, as discussed above, several
Page 55 and 56: events 800 600 400 200 0 0 200 400
Page 57 and 58: clusters N 100 50 0 0 500 1000 1500
Page 59 and 60: In the following section we discuss
Page 61 and 62: events 15000 10000 5000 input outpu
Page 63 and 64: events 2000 1500 1000 500 σ = 15 k
Page 65 and 66: 5. Technical Specifications and Des
Page 67 and 68: construction, or for subsequent rep
Page 69 and 70: positioning of 50 submodules mounti
Page 71 and 72: Figure 5.6.: Detector frame with fi
Page 73 and 74: 5.4. Peripheral Systems 5.4.1. Read
Page 75 and 76: Figure 5.12.: The photo shows the T
Page 77: 6. Radiation Environment and Safety
Page 81 and 82: 8. Calibration 8.1. Calibration wit
Page 83 and 84: Figure 8.3.: ToF distribution in 10
Page 85: Figure 8.4.: Event display for seve
Page 89 and 90: 10. Installation procedure, its Tim
Page 91: 11. Cost and Funding 11.1. Cost Est
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The timeline for milestone 1 includ
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96 2. Sample Tests Random samples o
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PNPI St. Petersburg: G.D. Alkhazov,
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HV 1.$ mm 2$ mm 0+$1-2)-2'.%/ 5%4'.
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Beamline Be exit window P 6 P 3 P 4
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B.3. Design Issues Addressed with 4
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Time [ns] Counts 41 40 39 2200 2000
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Efficiency 100 80 60 40 20 0 7.5 8
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200 AMeV, Erel = 100 keV emitted %
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B.7. MRPC Solution using Glass as C
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114
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[Bot-04] S. Botvina andI.N. Mishust
Page 118 and 119:
[Lip-03] C. Lippmann, PhD Thesis, U
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