International Topical Meeting on Nuclear Research Applications and Utilization of Accelerators

4-8 May 2009, Vienna

SM/EN-13

A Dual-Purpose Ion-Accelerator for Nuclear-Reaction-Based Explosives and SNM Detectionin Massive Cargo

M.B. Goldberg1, R. Böttger2, M. Brandis1, B. Bromberger2, V. Dangendorf2, E. Friedman3, D. Heflinger1, S. Löb2, P. Maier-Komor4, I. Mor1, K.H. Speidel5, K. Tittelmeier2, and D. Vartsky1

1Electro-Optics Division, Soreq Nuclear Research Cente Yavne, Israel
2Physikalisch-Technische Bundesanstalt (PTB), Braunschweig, Germany
3Racah Institute of Physics, the Hebrew University of Jerusalem, Jerusalem, Israel
4Physik-Department E12, Technische Universität München, Garching, Germany
5Helmholtz Institut für Strahlen- und Kernphysik, Nussallee, Bonn, Germany

Corresponding Author: mbgoldberg@hotmail.com

We present a dual-purpose ion-accelerator concept, to serve as radiation source for radiographic cargo inspection systems detecting Special Nuclear Materials (SNM: 239Pu & enriched-235U) and explosives. Such systems would be cost-effective, employing largely-common hardware, but different nuclear reactions and data acquisition modes. For SNM-detection, Dual-Energy Radiography (DER) using 15.11 & 4.43 MeV γ-rays from 11B(d, n) is envisaged [1]. Explosives are detected via Gamma Resonance Absorption (GRA) in 14N [2], the probe being 9.17 MeV γ rays produced at the Ep =1.747 MeV 13C(p, γ) resonance.

If the DER deuteron energy is selected to be precisely double the GRA proton capture resonance energy, namely 3.494 MeV, both reactions are accessible with an accelerator operating at this energy, by alternately bombarding 11B and 13C targets with mass-2 beams of d and H2+, respectively. Nitrogen-rich liquid scintillators could serve as common detectors, data acquisition modes alternating between γ-ray pulse-height spectra (DER) and internally-produced photo-proton spectra (GRA). Pulse-shape discrimination (PSD) is employed throughout, to reject undesired particlespecies events.

The viability of this dual-purpose system concept is non-trivial, since an appreciable contribution of proton-proton repulsion in H2+ ions to emission-line broadening of resonant 9.17 MeV γ rays at the resonant angle θR = 81.6° could prove detrimental to GRA-system performance characteristics. This contribution was hitherto unknown, but has recently been measured at the PTB Van-de-Graaff accelerator and found to be small compared to the emission-line broadening observed when the resonance is populated by protons. The latter was consistently measured as ~500 eV [3], the total nuclear level width being Γtot ~130 eV [3,4]. Presumably, the broadening is due to proton-induced inner-electron-shell excitation concomitant with nuclear capture [5].

The absence of appreciable emission-line broadening with H2+ ions is probably related to the wellknown “wake” effect [6], whereby the two correlated projectiles progressively align themselves along the beam direction while traversing the target medium. Thus, the Coulomb repulsion between them exhibits an appreciable longitudinal component, that manifests itself primarily by broadening the resonance excitation yield curve [7]. However, it does not exhibit a large transverse component and thus, produces little 9.17 MeV line-broadening.

1. M.B. Goldbert, U.S. Pat.# 7 381 962 (June 2008).
2. D. Vartsky et al., Proc. SPIE: Int. Soc. Opt. Eng. 5198 (2004) 243.
3. S.S. Hanna et al., Phys. Rev. 115 (1959) 986; W. Biesot et al., Phys. Rev. C 24 (1981) 808.
4. D. Vartsky et al., Nucl. Phys. A 505 (1989) 328.
5. W.H. Schulte et al., J. Phys. B: At. Mol. Opt.Phys. 27 (1994) 5271.
6. D.S. Gemmell et al., Phys. Rev. Lett. 34 (1975) 1420.
7. see, e.g., S.L. Andersen et al., Nucl. Phys. 7 (1958) 384.