MAX, a Laue diffraction lens for nuclear astrophysics

Abstract

The next generation of instrumentation for nuclear astrophysics will have to achieve a factor of 10–100 improvement in sensitivity over present technologies. With the focusing gamma-ray telescope MAX we take up this challenge: combining unprecedented sensitivity with high spectral and angular resolution, and the capability of measuring the polarization of the incident photons. The feasibility of such a crystal diffraction gamma-ray lens has recently been demonstrated with the prototype lens CLAIRE. MAX is a proposed mission which will make use of satellite formation flight to achieve 86 m focal length, with the Laue lens being carried by one satellite and the detector by the other. In the current design, the Laue diffraction lens of MAX will consist of 13740 copper and germanium (Ge1−x Si x , x ∼ 0.02) crystal tiles arranged on 36 concentric rings. It simultaneously focuses in two energy bands, each centred on one of the main scientific objectives of the mission: the 800–900 keV band is dedicated to the study of nuclear gamma-ray lines from type Ia supernovae (e.g. 56 Co decay line at 847 keV) while the 450–530 keV band focuses on electron-positron annihilation (511 keV emission) from the Galactic centre region with the aim of resolving potential point sources. MAX promises a breakthrough in the study of point sources at gamma-ray energies by combining high narrow-line sensitivity (better than 10−6 cm−2 s−1) and high energy resolution (E/dE ∼ 500). The mission has successfully undergone a pre-phase A study with the French Space Agency CNES, and continues to evolve: new diffracting materials such as bent or composite crystals seem very promising

Copper Mosaic Crystals for Laue Lenses

“…A gamma-ray Laue lens for astrophysical applications based on mosaic copper single crystals requires crystals of high quality, with a homogeneous mosaic spread of less than 30 seconds of arc in order to achieve efficient focusing of high-energy gamma-rays (100 keV -1 MeV) onto a small detector volume [1]. The aim of the present work is to show the feasibility of making such a gamma Laue lens which is a real challenge.…”

Monte Carlo study of detector concepts for the MAX Laue lens gamma-ray telescope

“…The basic design of the MAX detector spacecraft and the mounting and cooling of the detector concepts assumed in this study emerged from the CNES pre phase A study of the MAX mission (Barrière et al, 2006;von Ballmoos et al, 2006). This basic design is identical for all three detector concepts, the only difference between the mass models is in the definition of the detectors.…”

“…For this study, both quantities were determined by Monte Carlo simulation. As described in more detail in Barrière et al (2006), for this study the lens crystals were assumed to have a geometrical size of 1.5 cm × 1.5 cm and a mosaicity of 30 . The focal length was assumed to be 86 m, and the source was assumed to be located on the optical axis (i.e.…”

“…MAX is a Laue lens telescope that has been proposed to the French Space Agency CNES in response to an announcement of opportunity for a formation flight demonstration mission (Barrière et al, 2006;von Ballmoos et al, 2006). The MAX gamma-ray Laue lens consists of Ge and Cu crystals and has a focal length of about 86 m. MAX is designed to concentrate gamma rays in two 100 keV wide energy bands centered on the two lines which constitute the prime astrophysical interest of the mission: the 511 keV positron annihilation line, and the broadened 847 keV line from the decay of 56 Co copiously produced in Type Ia supernovae.…”

Puzzles and potential for gamma-ray line observations of solar flare ion acceleration

“…With a collecting area averaging about 500 cm 2 over the two bands [20] and a likely photopeak efficiency in the detector plane on the order of 30-50%, MAX would have almost an order of magnitude more effective area. For the long-lived 847 keV line due to radioactive decay rather than de-excitation, the predicted fluxes of 1 − 10 × 10 −5 ph/cm 2 /s (see Figure 4) after major flares can be compared to the MAX 3σ narrow-line sensitivity of ∼10 −6 ph/cm 2 /s [20]. This is an opportunity to make an absolutely new measurement with, for once, a significance of more than 3σ .…”