# Laser Wakefield Photoneutron Generation with Few-Cycle High-Repetition-Rate Laser Systems

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## Abstract

**:**

## 1. Introduction

^{12}n/s) neutron sources is using an RF LINAC electron accelerator, where the electron beam is absorbed in a high-Z target, and the generated bremsstrahlung interacts with the same target, generating photoneutrons. Experimental demonstrations and characterizations have been carried out earlier at the nELBE facility [10], utilizing a 1 mA 40 MeV electron beam. In an alternative configuration, electrons are converted to gamma in a first-stage converter and transported to a neutron generator. This configuration has been employed in the PARRNe experiment [11,12] with a W-converter and uranium carbide (UC

_{x}) neutron generator that can produce ${\mathbf{10}}^{\mathbf{13}}$ fissions/s using a 100 kW beam of 30 MeV electrons as part of the ALTO project. Another facility [13] is already under implementation, using a 100 MeV, 100 kW electron beam driver, with a maximum-predicted neutron current of 1–4 × 10

^{14}n/s. The high-Z target can be liquid lead [10], tungsten, or even enriched uranium [14,15]. High-intensity electron beams with currents exceeding 10 A can generate a peak neutron yield of ${\mathbf{10}}^{\mathbf{10}}$ n/pulse, as demonstrated at the GELINA facility [16], and ${\mathbf{10}}^{\mathbf{12}}$ neutron/pulse at ORELA [17], with both facilities able to achieve a repetition rate of 100 Hz. An overview of the present and upcoming neutron generator facilities leveraging particle beams was presented in [18].

## 2. Laser Electron Acceleration

^{9}electrons). While the broadband nature of the electron spectrum might not be suitable for some applications, in the generation of photoneutrons, the spectral quality of the beam is of secondary importance.

## 3. Photoneutron Generation

^{−1/3}MeV for A > 40, where A is the atomic mass number, e.g., 208 for lead, which corresponds to 13.5 MeV. The width of the resonance is 3 MeV for lead, as shown in Figure 2. The neutron binding energy for Pb-208 is 7.8 MeV, indicating a threshold energy for the photon. This fact is also reflected in Figure 2 as the threshold energy.

^{−}

^{4}n/e/MeV. In contrast the DT fusion yield is $1\times {10}^{-5}$ n/d. The yield improves for spallation to 30 n/p; however, a proton with energy over 1 GeV is needed.

^{3}He fusion reactions using 200 mJ and a 160 fs laser.

## 4. Photoneutron Applications

- (a)
- Medical radio-isotope production (Moly-99 to Tc-99 precursor);
- (b)
- Incineration of spent nuclear fuel;
- (c)
- Neutron radiography/imaging.

#### 4.1. Medical Radioisotope Production

^{4}s for a 1 kHz laser. An improvement factor of 10 could be achieved if we use electron irradiation of an enriched U-235 assembly directly together with a double-stage multiplier, a possibility we intend to explore in our proposed experiment. Considerations of such duty-cycle were not taken into account in this study).

#### 4.2. Transmutation of Spent Nuclear Fuel

- (1)
- Fission products such as iodine, strontium, molybdenum, etc.
- (2)
- Actinides such as plutonium and isotopes of uranium and thorium and minor actinides (americium, curium and neptunium).

^{240}Pu (24,000 years) ->

^{134}Cs (2 years) +

^{104}Ru (stable) + 2 n + energy

#### 4.3. Neutron Radiography/Imaging and Neutron Spectroscopy

## 5. Conclusions

^{9}Be is proposed to leverage the (n, 2n) reaction.

## Author Contributions

## Funding

## Institutional Review Board Statement

## Informed Consent Statement

## Data Availability Statement

## Acknowledgments

## Conflicts of Interest

## Dedication

## References

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**Figure 1.**Electron density at the center of the density plateau (

**a**), electron distribution function and spectrum after the plasma (

**b**), spectrum on a log-lin plot (

**c**).

**Figure 2.**Photonuclear cross-section for two isotopes of lead, obtained from the END-F and TENDL cross-sectional libraries.

**Figure 3.**Neutron yield per electron for various electron energies and radius of a lead sphere (

**a**), with electrons that are sourced at the sphere origin. The efficiency of neutron generation as a function of electron energy (

**b**), for selected lead sphere radii.

**Figure 4.**Photon energy spectrum resulting from injecting mono-energetic 20 MeV (red), 50 MeV (green) electrons and LWFA electrons (blue) at a center of a 10 cm lead sphere.

**Figure 5.**Neutron energy spectra for 20 MeV (red), 50 MeV (green) electron beams and LWFA electrons (blue) sampled at r = 0.5 cm (solid), r = 10 cm (dashed) and Watt fission spectrum (gray) for U-235.

**Figure 6.**Fission product yield for various neutron energy bombardment.

^{99}Mo yield from fission is 6% of all the fission products. Adapted from data from T.R. England and B.F. Rider, LA-UR-94-3106 (1994).

**Figure 7.**Motivation for transmutation adapted from [40]. Comparison of the radiotoxicity of nuclear waste from uranium-based PWR to that produced by the naturally occurring uranium needed to generate 1 metric ton of enriched uranium. Permission to reuse figure granted from Elsevier.

Energy (MeV) | $\u2329{\mathit{E}}_{\mathsf{\gamma}}\u232a\phantom{\rule{0ex}{0ex}}\left(\mathbf{MeV}\right)$ | $<{\mathit{E}}_{\mathit{n}}>\left(\mathbf{MeV}\right)$ | ${Y}_{e}$ | ${Y}_{y}$ | ${Y}_{n}$ | |
---|---|---|---|---|---|---|

0.5 cm | 5 cm | |||||

20 | 2.6 | 2.0 | 1.7 | 6.3 | 5 | 0.003 |

50 | 4.9 | 2.0 | 1.7 | 16 | 15 | 0.01 |

LWFA (<${E}_{e}$> = 71 MeV) | 11.3 | 2.0 | 1.7 | 23 | 23 | 0.02 |

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**MDPI and ACS Style**

Papp, D.; Necas, A.; Hafz, N.; Tajima, T.; Gales, S.; Mourou, G.; Szabo, G.; Kamperidis, C.
Laser Wakefield Photoneutron Generation with Few-Cycle High-Repetition-Rate Laser Systems. *Photonics* **2022**, *9*, 826.
https://doi.org/10.3390/photonics9110826

**AMA Style**

Papp D, Necas A, Hafz N, Tajima T, Gales S, Mourou G, Szabo G, Kamperidis C.
Laser Wakefield Photoneutron Generation with Few-Cycle High-Repetition-Rate Laser Systems. *Photonics*. 2022; 9(11):826.
https://doi.org/10.3390/photonics9110826

**Chicago/Turabian Style**

Papp, Daniel, Ales Necas, Nasr Hafz, Toshiki Tajima, Sydney Gales, Gerard Mourou, Gabor Szabo, and Christos Kamperidis.
2022. "Laser Wakefield Photoneutron Generation with Few-Cycle High-Repetition-Rate Laser Systems" *Photonics* 9, no. 11: 826.
https://doi.org/10.3390/photonics9110826