The vp-process is a new nucleosynthetic scenario, proposed 2006, which supposed to take place at the very early epoch of type II supernova, involving nuclear reactions of proton-rich nuclei not only ...with protons and alphas, but also with neutrons due to the neutrino processes. The vp-process is one of the key processes for investigating the mechanism of type II supernovae, and the process could be possibly responsible for the anomalously abundant p-nuclei around mass 90-100. Specifically, the nuclear physics problems in the vp-process were discussed in this talk including our recent experimental results with low-energy RI beams and a simulation study. Alpha cluster resonances have been identified experimentally which play a crucial role for the stellar (α,p) and (α,γ) reactions just above the alpha threshold. Neutron induced reactions in the proton-rich nuclear regions in the vp-process are also suggested to play an important role, which will discard the waiting points, and accelerate the flow to heavier nuclei. This process involves nuclear structures of very high level density at high excitation energies in neutron deficient nuclei, and both of the projectile and the target are unstable, which is a quite difficult experimental challenge in nuclear astrophysics in the coming years. Some experimental challenges are discussed.
KOBRA (KOrea Broad acceptance Recoil spectrometer and Apparatus) facility being designed at Rare Isotope Science Project in Korea will be utilized to produce rare isotope beams by employing ...multi-nucleon transfer reactions at about 20MeV/nucleon for studies of nuclear structure. KOBRA will also provide high suppression of beam induced background for direct measurements of radiative-capture cross sections in the astrophysical energy range. The present design status of the KOBRA facility is reported along with a brief introduction to the facility. We have studied the feasibility of production of 44Ti based on the present design of KOBRA as an example, and calculated the intensity of 44Ti secondary beam, to be about 105 particles per second, for 1 pnA 46Ti primary beam with a carbon target for a beam energy of 25MeV/nucleon. A Monte Carlo simulation with a ray-tracing code has been performed to show that recoil products 66Se are well separated from a 65As beam by KOBRA for the 65As(p,γ)66Se reaction at a beam energy of 1MeV/nucleon.
The β-decay half-lives of 38 neutron-rich isotopes from (36)Kr to (43)Tc have been measured; the half-lives of (100)Kr, (103-105)Sr, (106-108)Y, (108-110)Zr, (111,112)Nb, (112-115)Mo, and (116,117)Tc ...are reported here. The results when compared with previous standard models indicate an overestimation in the predicted half-lives by a factor of 2 or more in the A≈110 region. A revised model based on the second generation gross theory of β decay better predicts the measured half-lives and suggests a more rapid flow of the rapid neutron-capture process (r-matter flow) through this region than previously predicted.
The triple alpha reaction is one of the most important reactions in the nuclear astrophysics. However, its reaction rate in high temperature environments at T9> 2 was still uncertain. One of the ...major origins of the uncertainty was that the radiative-decay probability of the 31− state in 12C was unknown. In the present work, we have determined the radiative-decay probability of the 31− state to be 1.3−1.1+1.2×10−6 by measuring the 1H(12C,12Cp) reaction for the first time, and derived the triple alpha reaction rate in high temperature environments from the measured radiative-decay probability. The present result suggests that the 31− state noticeably enhances the triple alpha reaction rate although the contribution from the 31− state had been assumed to be small.
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
7
Be+
n
reactions which may affect the primordial
7
Li abundance in the Big-Bang nucleosynthesis, and the other is for the
22
Mg(
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.
The cosmological lithium problem (CLP) stems from the outstanding discrepancy between theoretical predictions and astronomical observations of primordial lithium abundances. For the radiogenic ...production of 7Li, 7Be plays a pivotal role in the Big Bang nucleosynthesis (BBN). Nevertheless, the data for neutron-induced 7Be destruction processes were still sparse, and especially lacked information on the contributions of transitions to the 7Li excited states. In this work, we have determined the 7Be\({(n,{p}_{0})}^{7}\)Li, 7Be\({(n,{p}_{1})}^{7}\)Li*, and 7Be\({(n,\alpha )}^{4}\)He reaction cross sections by means of the Trojan Horse method. The present and the previous data were analyzed together by a multichannel R-matrix fit, providing an improved uncertainty evaluation of the \((n,{p}_{0})\) channel and the first-ever quantification of the \((n,{p}_{1})\) contribution in the BBN-relevant energy range. We implemented the revised total reaction rate summing both the \((n,{p}_{0})\) and \((n,{p}_{1})\) contributions in a state-of-the-art BBN code PRIMAT. As a consequence, the present nuclear-physics data offers a reduction of the predicted 7Li abundance by about one-tenth, which would impose a stricter constraint on BBN and head us in the correct direction to the CLP solution.
Low-energy radioisotope beam separator CRIB Yanagisawa, Y.; Kubono, S.; Teranishi, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
02/2005, Letnik:
539, Številka:
1
Journal Article
Recenzirano
Odprti dostop
A low-energy in-flight type RI beam separator, called CRIB, has been installed for nuclear physics and nuclear astrophysics by the Center for Nuclear Study, the University of Tokyo in the RIKEN ...Accelerator Research Facility. It consists of a double achromatic system and an Wien filter. It is capable of providing RI beams at 5–10
MeV/nucleon. Since CRIB has been developed in the end of 2000, many proton-rich RI beams were successfully produced via the (
p,
n), (
d,
t), and (
3
He
,
n) reactions in inverse kinematics. In this paper, the design of the separator and its performance are discussed including the method of RI-beam production at low energies.
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
7
Be in the Big-Bang nucleosynthesis, and the other is the study on the
22
Mg(
α
,
p
) reaction relevant in X-ray bursts, which was performed with the resonant scattering method from the inverse reaction channel.
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