Nuclear transitions on demand

TL;DR

The paper addresses the extreme suppression of nuclear photo-transitions and proposes a combinatorial enhancement strategy via nuclear multiphoton absorption (nPA) by overlapping intense laser-driven $\gamma$-flashes with optical photons. The core idea is to convert a tunable optical boost into an effective cross section $\sigma_{eff}^{2PA}=I_2\sigma^{2PA}_{if}$, enabling transitions up to $E4$ multipolarity and potentially revealing hidden nuclear states. A quantitative comparison suggests 2PA can dominate over stepwise pumping by up to $\sim10^5$ under realistic high-power laser conditions, with $\\mathcal{P}_2\sim10^{12}$ W cm$^{-2}$ and $\sigma_{eff}^{2PA}\approx10^{-25}$ cm$^2$, pointing toward the possibility of nuclear gamma-ray lasing. The proposed framework has broad implications for nuclear photonics, medical applications, energy technologies, and fundamental physics, but requires cross-disciplinary collaboration to overcome resonance and spectral-overlap challenges.

Abstract

I show a way to tune photo-nuclear cross section effectively and therefore achieve nuclear transitions "on demand". The method is based on combinatorial enhancement of multiphoton processes under intense conditions. Taking advantage of recent advances in high-power laser systems (HPLS) and nuclear structure calculations, efficient control of nuclear transitions up to E4 in multipolarity can be reached today. The same idea can be extended to the search for rare transitions and hidden states, which applies to the $γ$-beams generated from conventional sources as well.

Figures (5)

• Figure 1: Illustration of a photo-nuclear transition.
• Figure 2: The nPA yield for different intensity of incoming photons. Here data of atomic photonionization is presented, with photon intensity increases from top to bottom panel. The peak energy flux $\mathcal{P}\equiv IE_{\omega}\approx10^{13}$ W/cm$^2$ (where $E_{\omega}\approx1.2$ eV for Nd:YAG laser). The plot is extracted from Fig. 6 of Ref. Protopapas1997.
• Figure 3: Illustration of nPA processes (gaps between states are not to scale). Here nPA start at an initial state and goes through a series of virtual sates (denoted as red-dashed lines) to reach the final state.
• Figure 4: Illustration of stepwise pumping processes versus 2PA. Here the stepwise pumping start at state $|i\rangle$ and goes through an intermediate physical state $|m\rangle$ to the final state $|f\rangle$, while 2PA goes through the virtual sates (denoted as red-dashed lines) instead of $|m\rangle$ to reach the final state. Gaps between states are not to scale.
• Figure 5: Illustration of new opportunities opened via nPA.