High sensitivity analysis of deuterium in solids by 15N-induced nuclear reactions

Cross section of 15N-2D nuclear reactions from 3.3 to 7.0 MeV for simultaneous hydrogen and deuterium quantitation in surface layers with 15N ion beams

“…Figure 2 indicates that the relative 15 N-2 D cross section increases by two orders of magnitude between 3.3 and 7.0 MeV. The energy dependence of the relative cross section obtained here connects well with data in the range from 5 to 16 MeV reported by Hayashi et al [19] (see Supplementary Material S1), which show that the cross section increases further (about 2.5 times) between 7 and 16 MeV. Certain step-like variations of the cross-section appear around ~4.8 and ~6.6 MeV, which may correspond to excited nuclear states encountered in the 15 N-2 D reactions, but no pronounced resonances are seen in the entire range from 3.3 to 7.0 MeV.…”

“…Spectrum (a), recorded with a dose of 7.2 C of 15 N 2+ at 6.54 MeV on Kapton, only shows the familiar -emission at 4.3 MeV (from the excited 12 C* state produced in the 1 H( 15 N,) 12 C reaction) and the associated weaker single escape (SE) peak at 0.511 MeV lower energy [4,25]. The 2 D-induced -emissions at 2.75, 6.13 and 7.12 MeV seen in spectrum (b), obtained with 8.7 C of 15 N 2+ at 6.385 MeV on a thicker (275 nm) film of a-C:D/Si, originate from 16 O* excited states produced in the 2 D( 15 N,p) 16 N and 2 D( 15 N,n) 16 O reactions, which occur simultaneously [19]. The 16 N nucleus formed in the 2 D( 15 N,p) 16 N reaction is unstable and decays with a half-life of 7.1 s into the same 16 O* states as those directly produced by 2 D( 15 N,n) 16 O.…”

“…By measuring the -yield at 6.13 and 7.12 MeV while the 15 N beam irradiates the target, a combined cross section for the 2 D( 15 N,p) 16 N and 2 D( 15 N,n) 16 O reactions is thus determined. Evaluating the 2 D( 15 N,p) 16 N reaction cross section separately (from the delayed -emission due to -decay of 16 N after shutting off the 15 N beam [19]) was not of practical interest to our present purpose and hence not pursued. The additional -emissions at 3.09 and 3.68 MeV seen in spectrum (b) originate from 13 C* excited nuclear states formed in the 2 D( 15 N,) 13 C reaction that also occurs in parallel with 2 D( 15 N,p) 16 N and 2 D( 15 N,n) 16 O [19].…”

“…The 15 N ions of energies above 6.385 MeV used as projectiles in 1 H( 15 N,) 12 C NRA also induce the 2 D( 15 N,p) 16 N and 2 D( 15 N,n) 16 O reactions with 2 D in the target. The latter reactions release -rays of 6.13 and 7.12 MeV [19] that are well-separated from the 4.3-MeV -emission from 1 H( 15 N,) 12 C and easily detectable with virtually no background from natural radiation (see Figure 1 below). In contrast to the sharp energy resonance of 1 H( 15 N,) 12 C at 6.385 MeV, the 15 N-2 D reactions are non-resonant, hence their -reaction cross section varies only little within the narrow scan range (~100 keV) of incident 15 N energies required to obtain 1 H profiles within several 10 nm below a target surface with 1 H( 15 N,) 12 C NRA.…”

“…Thus, although the 15 N-2 D reactions cannot deliver information on the 2 D depth location, it should be possible to perform 1 H depth profiling in the near-surface region with 1 H( 15 N,) 12 C NRA while simultaneously quantifying the integral 2 D content in a sample from the -yield at 6.13 and 7.12 MeV. Although proposed as early as 1986 by Hayashi et al [19], who reported the relative cross section of the 2 D( 15 N,p) 16 N and 2 D( 15 N,n) 16 O reactions for 15 N energies from 5 to 16 MeV, this approach did not attract notable applications so far. This is likely the case because only very scarce data were reported for the 15 N + 2 D reaction cross section at 15 N energies below ~6.4 MeV.…”