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UMON - 235 U(n,f) flux monitor? A rough idea...

This article discusses the design and evaluation parameters of the UMON - 235U(n,f) flux monitor for measuring neutron flux and detection efficiency. The article includes details on the detector size, target specifications, activity level, and relevant cross-section data. It also discusses the expected amplifier performance and the need for lab tests to verify the electronics. The pros and cons of different design options are also presented.

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UMON - 235 U(n,f) flux monitor? A rough idea...

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  1. UMON - 235U(n,f) flux monitor? A rough idea...

  2. detection efficiency ≈ geometrical efficiency 1 detector: e ≈ 32 / (4π x 42) ≈ 4.5% 2 detectors: e ≈ 9% 4 detectors: e ≈ 18% 3 cm 6 cm 4 cm 2.1 cm (3s) Si detector U target

  3. Evaluation parameters thickness 1.45µm (10x 235U(n,f) experiment) BIF according to flux specifications H2O2U (99.9% enriched in 235U) 5 cm diameter H2O2U (0.1% 238U) total activity: 3.7 kBq 15 days @ 70000 pulses/day

  4. 2 detectors (3cm x 3cm) folded the flux with cross section and the relevant parameters resulting counts and stat uncertainty worst case: < 5% • EAR1 flux from M.Barbagallo • (n,f) cross section from ENDF/B-VIII (25meV-30MeV) • (n,f) cross section IAEA 2015 (30MeV-1GeV)

  5. max energy loss in the target ≈ 40 MeV

  6. Si detector with fast voltage amplifier (LNS) 5 MeV alpha + strong gamma background ≈ 20 mV, S/N ≈ 5 (from previous test for 7Be) 20-30 ns duration 100 MeV fragment: expected 400 mV max neutron energy: 100 MeV 5-20 ns additional flight time (target-to-detector in 45°config) expected amplifier dead time after g-flash: 800ns to be verified with lab test (laser)

  7. conclusions • UMON - 235U(n,f) flux monitor seems feasible • 3.7 kBq activity sounds promising from RP point of view • lab tests needed to prove that the electronics is appropriate, i.e.: • withstands the g-flash • provides the expected signal for fragments pros: compact, simpler mechanics pros: single U layer, smaller ∆t for fragments cons: 2xU layers or extra thin backing cons: bigger, more complex mechanics

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