${}^{56,54}\mathrm{Fe}(n,\alpha ){}^{53,51}\mathrm{Cr}$ cross sections in the MeV region

${}^{56,54}\mathrm{Fe}(n,\alpha ){}^{53,51}\mathrm{Cr}$ cross sections were measured in the neutron energy region of 5–11 MeV using three neutron sources based on accelerators, a twin gridded ionization chamber, and highly enriched ${}^{56}\mathrm{Fe}$ and ${}^{54}\mathrm{Fe}$ foil samples. The ${}^{238}\mathrm{U}(n,f)$ reaction was used to monitor the neutron fluence, and the interferences from the low-energy neutrons were corrected according to the neutron energy spectra obtained through unfolding the pulse height spectra measured by a liquid scintillator. Both the measured cross sections show a “shoulder” structure in the 8–11 MeV region which may be caused by the level structure of the residual nuclei. The present paper aims to improve constraint of the ${}^{56,54}\mathrm{Fe}(n,\alpha ){}^{53,51}\mathrm{Cr}$ excitation functions in the MeV region where their neutron energy dependences are significant, while related measurements are nonexistent or scarce and the deviations among existing measurements and evaluations are significant. To obtain more precise excitation functions of the ${}^{56,54}\mathrm{Fe}(n,\alpha ){}^{53,51}\mathrm{Cr}$ reactions, further measurements and improved evaluations are required.

Figure 1

The sketch of the experimental setup: FC, fission cathode; PA, charge sensitive preamplifier; A, anode; G, grid; C, cathode; SE, shielding electrode; FIFO, fan in–fan out (CAEN N625); TCU, trigger control unit; SA, signal amplifier (ORTEC 572A); DA, delay amplifier (ORTEC 427A); LG, linear gate (ORTEC 542); SC, single channel analyzer (ORTEC 551); WFD, waveform digitizer (Signatec PDA14); DT5730, desktop digitizer (CAEN DT5730B); and PC, personal computer.

Figure 2

The measured neutron energy spectra.

Figure 3

The measured cathode-anode two-dimensional spectrum of the compound α source in the forward direction.

Figure 4

The cathode-anode two-dimensional spectrum after the background deduction in the forward direction for the measurement of the ${}^{54}\mathrm{Fe}(n,\alpha ){}^{51}\mathrm{Cr}$ reaction at $E_n=8.5\mathrm{MeV}$.

Figure 5

The measured anode spectra of the ${}^{54}\mathrm{Fe}(n,\alpha ){}^{51}\mathrm{Cr}$ reaction at $E_n=8.5\mathrm{MeV}$ in the forward direction compared with the simulated one.

Figure 6

The present ${}^{56}\mathrm{Fe}(n,\alpha ){}^{53}\mathrm{Cr}$ cross sections compared with the existing measurements and evaluations. Among the measured cross sections, only Saraf et al. and Wang et al. are included in the EXFOR library [5], and the others are the calculated results based on the measured ${}^{56}\mathrm{Fe}$($n$, xα) cross sections. In addition, the ($n$, α) cross sections of natural iron measured by Paulse et al. [5] and Wattecamos et al. [5], and the ($n$, xα) cross sections of natural iron measured by Baba et al. [25] and Kunieda et al. [26] are also presented.

Figure 7

The present ${}^{54}\mathrm{Fe}(n,\alpha ){}^{51}\mathrm{Cr}$ cross sections compared with the existing measurements and evaluations. All the measurements are included in the EXFOR library [5] except for Meadows et al. [27, 28] and Khryachkov et al. [29].