Table 1.
Typical uncertainty sources encountered in (n, xn) measurements at monoenergetic and white neutron source (WNS) facilities are listed with estimates of typical uncertainty ranges. There is great duplication between the last two columns, but we provide them both to serve as a checklist and to stimulate thoughtful comparison for evaluators and experimentalists reporting information.
| Uncertainty source | Monoenergetic | WNS | |
|---|---|---|---|
| Timing-spread concerns | |||
| Accelerator-beam-pulse width | < 1 ns | < 1 ns | |
| Spread induced by neutron-production target | ∼1 ns | ∼1 ns | |
| Spread due to sample size | ≪1 ns | ≪1 ns | |
| Spread due to n/γ-transit time through detector | 0.3 ns | 0.3 ns | |
| Response time of detector and timing electronics | ∼10–20 ns | ∼10–20 ns | |
| TOF determination | < 100 ps | < 100 ps | |
| Deadtimes | Varies | Varies | |
| Neutron-production target | |||
| Overall (need full descrip. includ. cooling) | 1% | ∼1% | |
| Neutron-flux monitoring | |||
| Fission chambers: deposit thickn. & uniform. | ∼1% (see [99]) | ∼1% (see [99]) | |
| Fission chambers: σU(n, f) | ∼1% (see [5]) | ∼1% (see [5]) | |
| Long counters | 1–2% | N/A | |
| Proton-recoil telescopes | 1–2% (see [126]) | 1–2% (see [126]) | |
| Liquid scintillators (For mono.) | 1% | N/A | |
| Scintillators (e.g., 6Li-glass) | 1% | < 1% | |
| Sample | |||
| Isotopic enrichment | < 1% | < 1% | |
| Contaminants/Secondary contents | ∼1% | ∼1% | |
| Chemical/Mechanical form and shape | ∼1% | ∼1% | |
| Mass | ≪1% | ≪1% | |
| Material uniformity | ∼1% | ∼1% | |
| Dimensional measurements | 0.3% | 0.3% | |
| Geometric effects | |||
| Source-sample geometry | < 3 % | ≪1% | |
| Sample-detector geometry | ∼2% | ∼2% | |
| Detector size & positioning | ∼2% | ∼2% | |
| Incident-neutron energy spread | 7Li(p, n) ∼1%, 3H(p, n) 2–5%, | ≪1% | |
| 2H(d,n) 2–6% | |||
| Attenuation & multiple scattering | |||
| Method used to perform corrections | < 5% | < 5% | |
| nσ (number density × cross-section) | 0.3% | 0.3% | |
| Monte Carlo unc. (statistics & methods) | ∼1% | ∼1% | |
| Atomic-data uncertainties | ∼1% | ∼1% | |
| Nuclear-data uncertainties | Varies | Varies | |
| Standard or reference cross sections | |||
| 1H(n, n), 56Fe(n, n′γ) (jitter), 48Ti(n, n′γ) | From nuclear- | From nuclear- | |
| 7Li(n, n′γ), 12C(n, n), 235U(n, f), 252Cf (sf) | data libraries | data libraries | |
| Detector efficiency (neutrons) | |||
| Scintillators, via direct-measurement methods | ∼3% | ∼3% | |
| Scintillators, via simulations | ∼3% | ∼3% | |
| Detector efficiency (γ rays) | |||
| < 0.2 MeV | 4% | 4% | |
| 0.2–2.6 MeV | 2% | 2% | |
| > 2.6 MeV | 5% | 5% | |
| Ability to extract yields from spectra | |||
| n-TOF spectra, elastic peak | < 2% | Limited by | |
| n-TOF spectra, inelastic peaks | 1–10% | Counting statistics | |
| Continuum-neutron-emission spectra | < 20% | ||
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