First on-line detection of radioactive fission isotopes produced by laser-accelerated protons

Abstract

The on-going developments in laser acceleration of protons and light ions, as well as the production of strong bursts of neutrons and multi-$$\hbox {MeV}$$ MeV photons by secondary processes now provide a basis for novel high-flux nuclear physics experiments. While the maximum energy of protons resulting from Target Normal Sheath Acceleration is presently still limited to around $$100 \, \hbox {MeV}$$ 100 MeV , the generated proton peak flux within the short laser-accelerated bunches can already today exceed the values achievable at the most advanced conventional accelerators by orders of magnitude. This paper consists of two parts covering the scientific motivation and relevance of such experiments and a first proof-of-principle demonstration. In the presented experiment pulses of $$200 \, \hbox {J}$$ 200 J at $$\approx \, 500 \, \hbox {fs}$$ ≈ 500 fs duration from the PHELIX laser produced more than $$10^{12}$$ 10 12 protons with energies above $$15 \, \hbox {MeV}$$ 15 MeV in a bunch of sub-nanosecond duration. They were used to induce fission in foil targets made of natural uranium. To make use of the nonpareil flux, these targets have to be very close to the laser acceleration source, since the particle density within the bunch is strongly affected by Coulomb explosion and the velocity differences between ions of different energy. The main challenge for nuclear detection with high-purity germanium detectors is given by the strong electromagnetic pulse caused by the laser-matter interaction close to the laser acceleration source. This was mitigated by utilizing fast transport of the fission products by a gas flow to a carbon filter, where the $$\upgamma$$ γ -rays were registered. The identified nuclides include those that have half-lives down to $$39 \, \hbox {s}$$ 39 s . These results demonstrate the capability to produce, extract, and detect short-lived reaction products under the demanding experimental condition imposed by the high-power laser interaction. The approach promotes research towards relevant nuclear astrophysical studies at conditions currently only accessible at nuclear high energy density laser facilities.

Lasers for the observation of multiple order nuclear reactions

“…This has motivated the development of a gas transport and collection system in which nuclear reactions occur within a small, hermetically sealed chamber through which inert gas flows, carrying reaction products to a filter where gamma spectroscopy is performed (see Figure 6). A successful proofof-principle demonstration was conducted at the peta-watt PHELIX laser facility in 2020 [18] using 500 fs, ≈ 200 J laser pulses to accelerate bunches of protons via TNSA. The maximum proton fluence tested using this method at PHELIX is 2 × 10 11 protons/cm 2 , incident on 238 U targets.…”

Ion acceleration by an ultrashort laser pulse interacting with a near-critical-density gas jet

“…Radiolysis, the breaking of chemical bonds by radiation, is conducted with alpha projectiles with tens of MeV 60 and beam currents of 10 nA to 100 nA -parameters that can be achieved even with low repetition rate. Further optimization of the platform is of interest regarding short ion bunches for picosecond pulse radiolysis research 61 and may yield to high brilliance sources for not time averaged observations conducted with single shots 62 .…”

Defect engineering of silicon with ion pulses from laser acceleration

“…However, much shorter (sub-ns to ~10 ns) ion pulses can now be generated through the interaction of laser pulses with thin foils at intensities >10 18 W cm −214 . These short, intense ion pulses from laser-solid interactions are being explored for a broad range of applications 15 , including inertial fusion energy 16 , nuclear physics 17 , (flash) radiation biology 18 , studies of radiation effects in materials and materials analysis [19][20][21] . Most of these applications have focused on the use of high energy protons and (heavy) ions (>10 MeV).…”