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Astrophysical reactions involving radioactive isotopes (RI) often play an important role in high-temperature stellar environments. The experimental studies on the reaction rates for those are still limited mainly due to the technical difficulties in producing high-quality RI beams. A direct measurement of those reactions would be still challenging in many cases, however, we can make a reliable evaluation of the reaction rates by an indirect method or by studying the resonance prorerties. Here we ntroduce recent examples of experimental studies on such RI-involving astrophysical reactions, performed at Center for Nuclear Study, the University of Tokyo, using the low-energy RI beam separator CRIB. One is for the neutron-induced destruction reactions of 7Be in the Big-Bang nucleosynthesis, and the other is the study on the 22Mg(α, p) reaction relevant in X-ray bursts, which was performed with the resonant scattering method from the inverse reaction channel.

Experimental studies on astrophysical reactions involving radioactive isotopes (RI) often accompany technical challenges. Studies on such nuclear reactions have been conducted at the low-energy RI beam separator CRIB, operated by Center for Nuclear Study, the University of Tokyo. We discuss two cases of astrophysical reaction studies at CRIB; one is for the 7Be+n reactions which may affect the primordial 7Li abundance in the Big-Bang nucleosynthesis, and the other is for the 22Mg(α, p) reaction relevantin X-raybursts.

Type I X-ray bursts (XRBs) are the most frequently observed thermonuclear explosions in nature. The 22Mg(α,p)25Al reaction plays a critical role in XRB models. However, experimental information is insufficient to deduce a precise 22Mg(α,p)25Al reaction rate for the respective XRB temperature range. A new measurement of 25Al+p resonant scattring was performed up to the astrophysically interested energy region of 22Mg(α,p)25Al. Several resonances were observed in the excitation functions, and their level properties have been determined based on an R-matrix analysis. In particular, proton widths and spin-parities of four natural-parity resonances above the α threshold of 26Si, which can contribute the reaction rate of 22Mg(α,p)25Al, were first experimentally determined.

Lateral migration radiography (LMR) is a new form of Compton backscatter imaging (CBI) that utilizes both multiple-scatter and single-scatter photons. The LMR imaging modality uses two pairs of detectors. Each set has a detector that is uncollimated to predominantly image single-scatter photons and the other collimated to image predominantly multiple-scattered photons. This allows generation of two separate images, one containing primarily surface features and the other containing primarily subsurface features. These two images make LMR useful for imaging and identifying objects to a depth of several X-ray photon mean free paths even in the presence of unknown surface clutter or surface imperfections. The principles of LMR are demonstrated through Monte Carlo simulation of the photon transport. The Monte Carlo simulation results are verified with experimental measurements from an LMR system used for landmine detection. The presented research demonstrates the methodology for designing an LMR system, identifies methods for restoring and enhancing LMR images, and lays the foundation for the development of other applications of LMR, including, for example, the nondestructive examination of welds, castings, and composites. [ABSTRACT FROM AUTHOR]