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ANITA neutron source. Characteristic measurements with activation detectors. Measurement requests. The homogeneity of the neutron beam Low-energy neutrons in the neutron beam Protons in the neutron beam Positions “user2” and “user3” (positions 6 and 12 m from the target). Activation method.
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ANITA neutron source Characteristic measurements with activation detectors
Measurement requests • The homogeneity of the neutron beam • Low-energy neutrons in the neutron beam • Protons in the neutron beam • Positions “user2” and “user3” (positions 6 and 12 m from the target)
Activation method • Monoisotopic materials • Al, Au, Bi, Ta, natCu • ca. 1g of material – 10^8 neutrons • Irradiation (8h of 350 nA beam) • Gamma spectra measurements (days after) • Analysis of spectra
Detectors positions cross of detectors + Cu detector user2, user3 positions (6m, 12m) collimator for LE neutrons concrete wall
Results • Neutron beam uniformity: • No non-homogeneity out of the limits of statistical error ~ 5% • Low-energy neutrons: • Present in all foils, less near the wall ? • Spectrum cannot be determined from our data • Extra positions: • “user2” - 6 m : 4x less LE neutrons than at “user1”, 7x less 196Au, 3x less 194Au (196Au, 194Au not reliable, close to detectable limits) • “user3” - 12 m : 8x less LE neutrons, others not detected, upper limit for 196Au ~ 7x less
Protons in neutron beam I • Protons are monitored by the reactions in natCu: • 63Cu(p,n)63Zn • 63Cu(p,2n)62Zn • No traces of Zn isotopes were found in the Cu detector • The amount of 63Zn and 62Zn ca. 10x lower than the amount of 61Cu would be detected • 61Cu was well detected • 63Zn and 62Zn lines should have more that 3s*resolution counts ~ 200 counts • 200 counts corresponds to 10x lower amount of Zn comparing to 61Cu
Calculations • Neutron (and proton) spectra can be simulated: • MCNPX • FLUKA (can simulate also in magnetic field) • Simplified target was used in simulations • Cross-sections are taken from TALYS and verified against values from EXFOR (agreement is good enough for our estimations) • The spectrum multiplied with appropriate cross-sections = the amount of produced radioisotope • Absolute and relative comparison
Simulated spectra • Shapes (FLUKA, MCNPX and preliminary spectrum – same shape, but different absolute values, because of simplified target, distance-detector target) • Relations between n and p spectra (there is in total 1000x less p than n) • Magnetic field - no noticeable difference
Protons in neutron beam II • Simulated p and n spectra (MCNPX) are convoluted with xs for 62Zn and 61Cu • Result: 100x less 62Zn than 61Cu, this is 10x lower than our detection limit (10x, slide Protons – part 1) • We experimentally set the upper limit for the proton spectrum to 10x higher values than was simulated (1 proton per 100 neutrons):
Experiment / calculation • Average value of exp/sim : 1.64 • Causes of discrepancies are: • Simplified simulation • Cross-sections • Systematic errors
Conclusion • Measurements with activation detectors showed that ANITA neutron source meets all requirements for a good neutron source: • Homogenous neutron beam • LE neutron background measured (simulations for understanding) • Low proton background (at least 100x less protons than neutrons) • Relative neutron intensities in positions at 6 m and 12 m were measured (LE neutrons measure reliably, for 196Au and 194Au some upper estimations were set) • Calculated spectra convoluted with cross-sections give acceptable production rates – the shape of the real spectrum (10-100 MeV) is determined • Magnetic field in simulation does not change the results (codes MCNPX and FLUKA are both usable)