Comparative measurement of prompt fission $\gamma$-ray emission from fast-neutron-induced fission of ${}^{235}\mathrm{U}$ and ${}^{238}\mathrm{U}$

Prompt fission $\gamma$-ray (PFG) spectra have been measured in a recent experiment with the novel directional fast-neutron source LICORNE at the ALTO facility of the IPN Orsay. These first results from the facility involve the comparative measurement of prompt $\gamma$ emission in fast-neutron-induced fission of ${}^{235}\mathrm{U}$ and ${}^{238}\mathrm{U}$. Characteristics such as $\gamma$ multiplicity and total and average radiation energy are determined in terms of ratios between the two systems. Additionally, the average photon energies were determined and compared with recent data on thermal-neutron-induced fission of ${}^{235}\mathrm{U}$. PFG spectra are shown to be similar within the precision of the present measurement, suggesting that the extra incident energy does not significantly impact the energy released by prompt $\gamma$ rays. The origins of some small differences, depending on either the incident energy or the target mass, are discussed. This study demonstrates the potential of the present approach, combining an innovative neutron source and new-generation detectors, for fundamental and applied research on fission in the near future.

Figure 1

Schematic view of the experimental setup used to measure prompt fission $\gamma$-ray characteristics drawn to scale. The ionization chamber to tag the fission is drawn in blue. The three lines at the center of the IC represent anode, target position, and anode, respectively, left to right. The arrows show schematically the opening of the neutron cone.

Figure 2

Comparison of the prompt fission $\gamma$-ray emission spectra, measured with ${\mathrm{BaF}}_2$, for fast-neutron-induced fission of ${}^{235}\mathrm{U}$ (red circles) and ${}^{238}\mathrm{U}$ (black squares).

Figure 3

Comparison of PFG emission spectra from fast-neutron-induced fission of ${}^{235}\mathrm{U}$ (red circles) from this experiment measured with ${\mathrm{BaF}}_2$ detectors with spectra from the thermal-induced fission of ${}^{235}\mathrm{U}$ (black line) from a previous experiment [4].