Evidence of heavy-ion reactions from intense pulsed warm, dense plasmas

摘要

Nuclear reactions in pulsed-power ion-diodes are usually induced by proton- or deuteron-projectiles accelerated to high energy by the voltage across the anode-cathode (A-K) gap. Reactions for which the incident projectile has a larger atomic number (Z > 2) are inhibited by the Coulomb barrier and are not usually detected. This work documents the detection of several heavy-ion nuclear reactions in the operation of a plasma-filled rod-pinch (PFRP) diode fielded on the 2-MV Gamble II generator¹ in which the required Q-value is larger than the A-K potential difference. By injecting a cable-gun plasma between an anode-cathode gap, this PFRP diode has been shown to concentrate a 500-kA, 2-MeV, 60-ns electron beam onto the pointed end of a 1-mm diameter tapered tungsten rod, generating a warm-dense tungsten plasma (up to W⁺¹², ∼20 g/cm³, 25 eV, and 2.4 MJ/cm³). To utilize the PFRP diode as a source of highly-charged ions, high-intensity electron beams impinge upon a ∼l-mm diameter Al anode rod charged to high-voltage. After an experimental discharge, anode material debris is collected in a 3-in diameter Al cup (at ground potential) and gamma-ray emissions are measured using a high-purity Ge spectroscopy system over several days. By measuring the gamma-ray energies and half-lives, the production of a variety of radioisotopes were identified, including ³⁸K, ^34mCl, ⁴³Sc, ^44mSc, ⁴⁸V, and ⁵²Mn (up to 10⁸ per discharge). Weak evidence for ²⁴Na, ⁶⁹Ge, and ⁷⁹As was also observed. Heavy-ion nuclear reactions with Q-values exceeding the accelerating potential of the diode are proposed to explain the presence of several observed radioisotopes, suggesting a novel acceleration mechanism. Although the production of these isotopes in sub-10-MeV accelerators has been observed before²''^{3, this is the first demonstration of their production using a PFRP diode.}