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fig. 15. <A typical setup of ISOL-based unstable nuclear beam facility: the layout of the radioactive mee ewes: Wem eee ce is Bice Reg: ee acs Na ee el OE Vee: They include INS, University of Tokyo,“ Oak Ridge National Laboratory in th U.S.A, and GANIL in France.” Similar projects also have been approved recenth at TRIUMF™ and CERN-ISOLDE.*” The major concern here may be the absolut efficiency of ionization and acceleration of the radioactive products, which is current ly under development. There are several similar plans under discussion in Europ and Russia. Figure 15 displays the facility being constructed at INS, University o Tokyo. The whole system will be operational late in 1996. This is the first exten sive facility that includes a construction of secondary beam accelerators, a new typ RFQ, Split-Coaxial (SC)-RFQ linac and an interdigital H type linac, both of which ar now operational. Specifically, the SC-RFQ linac can accelerate ions of g/m=1/30 which will give a high absolute efficiency for radioactive nuclei. Because of th diverse applicability of radioactive nuclear beams in science, second generatio1 facilities are being planned by international collaborations. These include th: Isospin Laboratory planned for North America, a similar laboratory planned it Europe, and the Exotic Nuclei Arena of the Japanese Hadron Project in Japan.

Figure 15 <A typical setup of ISOL-based unstable nuclear beam facility: the layout of the radioactive mee ewes: Wem eee ce is Bice Reg: ee acs Na ee el OE Vee: They include INS, University of Tokyo,“ Oak Ridge National Laboratory in th U.S.A, and GANIL in France.” Similar projects also have been approved recenth at TRIUMF™ and CERN-ISOLDE.*” The major concern here may be the absolut efficiency of ionization and acceleration of the radioactive products, which is current ly under development. There are several similar plans under discussion in Europ and Russia. Figure 15 displays the facility being constructed at INS, University o Tokyo. The whole system will be operational late in 1996. This is the first exten sive facility that includes a construction of secondary beam accelerators, a new typ RFQ, Split-Coaxial (SC)-RFQ linac and an interdigital H type linac, both of which ar now operational. Specifically, the SC-RFQ linac can accelerate ions of g/m=1/30 which will give a high absolute efficiency for radioactive nuclei. Because of th diverse applicability of radioactive nuclear beams in science, second generatio1 facilities are being planned by international collaborations. These include th: Isospin Laboratory planned for North America, a similar laboratory planned it Europe, and the Exotic Nuclei Arena of the Japanese Hadron Project in Japan.

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Fig. 1. The solar abundance. The abundance of Si was normalized to 10°. This figure is borrowed from Ref. 20). Nuclear reactions are one of the key elements for the evolution of the universe The first stringent test for nuclear reactions is the so-called solar abundance, whiclt s of course the final result of various sequences of stellar events since the primordia jucleosynthesis just after the big bang. These included a variety of nuclear reaction: vhich produced almost all the elements from the light to the heavy mass region. [ ippears now possible to make a reasonable estimate of the solar abundance by taking nto account the evolution of our galaxy. Of course it is still very controversial tc nake a detailed model for the big bang and also for the evolution of our galaxy) ncluding various events. However, recent observations have been providing ver; nteresting and suggestive information for the chemical evolution of the galaxies Phe chemical abundance of stars in the bulge, the disk and the halo is clearly differen rom each other. The abundance suggests that stars in the bulge region were roduced mostly by Type II supernovae, whereas the ones in the disk like our sun ha: _considerable contribution of Type I supernovae, something like the frequency ratic f SNI/SNII=1/9. Totally different ratios are estimated for the Large Magellanic
Fig. 1. The solar abundance. The abundance of Si was normalized to 10°. This figure is borrowed from Ref. 20). Nuclear reactions are one of the key elements for the evolution of the universe The first stringent test for nuclear reactions is the so-called solar abundance, whiclt s of course the final result of various sequences of stellar events since the primordia jucleosynthesis just after the big bang. These included a variety of nuclear reaction: vhich produced almost all the elements from the light to the heavy mass region. [ ippears now possible to make a reasonable estimate of the solar abundance by taking nto account the evolution of our galaxy. Of course it is still very controversial tc nake a detailed model for the big bang and also for the evolution of our galaxy) ncluding various events. However, recent observations have been providing ver; nteresting and suggestive information for the chemical evolution of the galaxies Phe chemical abundance of stars in the bulge, the disk and the halo is clearly differen rom each other. The abundance suggests that stars in the bulge region were roduced mostly by Type II supernovae, whereas the ones in the disk like our sun ha: _considerable contribution of Type I supernovae, something like the frequency ratic f SNI/SNII=1/9. Totally different ratios are estimated for the Large Magellanic
Fig. 3.. Nucleosynthesis scenarios on a schematical nuclear chart. novae and the very early universe just after the big bang inevitably involve
Fig. 3.. Nucleosynthesis scenarios on a schematical nuclear chart. novae and the very early universe just after the big bang inevitably involve
Fig. 7. The S-factors of the ’Be(%, 7)8B reaction. The closed circles are from Ref. 66). WO UCLOLTIIICU PClicl. A possible problem with the nuclear physics side is the large cross section uncertainties of the reactions involved. The measured cross sections are not deter- mined better than 30 %, which is serious enough for the neutrino problem. They can be *He(*He, 2p)*He, ‘He(*He, 7)’Be and “Be(p, 7)*B. The first reaction is being inves- tigated at the underground laboratory at Gran Sasso,” where the experiment is almost free from the background due to cosmic rays. Among the three reactions, the “Be(d, 7)°B reaction, of which beta decay produces high energy neutrinos to be measured by the neutrino detectors underground, was investigated using a radioactive "Be target in the past. Here, the problem of the ’Be(, v)®B reaction is two-fold. One is to determine the S-factors with smaller uncertainties at Ecm.2100 keV, where the data so far obtained are scattered by more than 40%. The second is to measure cross sections at the energy as low as possible towards 10-20 keV, which gives more reliable extrapolation for the S-factor at 10-20 keV, which is the Gamow energy inside the core of the sun. The problem here is a non-resonant radiative proton capture reaction at extremely low energies. The reaction “Be(?, y)*B was reinvestigated recently at RIKEN by the Coulomb dissociation method mentioned in § 2. Before discussing the experimental result, we i lag | ng ol pee
Fig. 7. The S-factors of the ’Be(%, 7)8B reaction. The closed circles are from Ref. 66). WO UCLOLTIIICU PClicl. A possible problem with the nuclear physics side is the large cross section uncertainties of the reactions involved. The measured cross sections are not deter- mined better than 30 %, which is serious enough for the neutrino problem. They can be *He(*He, 2p)*He, ‘He(*He, 7)’Be and “Be(p, 7)*B. The first reaction is being inves- tigated at the underground laboratory at Gran Sasso,” where the experiment is almost free from the background due to cosmic rays. Among the three reactions, the “Be(d, 7)°B reaction, of which beta decay produces high energy neutrinos to be measured by the neutrino detectors underground, was investigated using a radioactive "Be target in the past. Here, the problem of the ’Be(, v)®B reaction is two-fold. One is to determine the S-factors with smaller uncertainties at Ecm.2100 keV, where the data so far obtained are scattered by more than 40%. The second is to measure cross sections at the energy as low as possible towards 10-20 keV, which gives more reliable extrapolation for the S-factor at 10-20 keV, which is the Gamow energy inside the core of the sun. The problem here is a non-resonant radiative proton capture reaction at extremely low energies. The reaction “Be(?, y)*B was reinvestigated recently at RIKEN by the Coulomb dissociation method mentioned in § 2. Before discussing the experimental result, we i lag | ng ol pee
Fig. 8. The Cluster Nucleosynthesis(CN) diagram.” Nucleosynthesis to heavy elements flows in the direction from top-left to bottom-right to Fe, releasing the energy to the stellar system.
Fig. 8. The Cluster Nucleosynthesis(CN) diagram.” Nucleosynthesis to heavy elements flows in the direction from top-left to bottom-right to Fe, releasing the energy to the stellar system.
Table I. The S-factors of the “C(a, y)'*O reaction in units of keV-b. determined by an interference of the tails of the resonances at higher energy and sub-threshold states nearby. Eee eee ee ee eee ee ee a ee Fe oe | ub-threshold states nearby. The astrophysical S-factors at 300 keV were estimated by extrapolation of the xperimental reaction cross section of ’C(a, y)'®O at Eem. 20.94 MeV, by measuring he singles gamma rays”™~””” or the gamma rays coincident with the recoil product yf °O. They are summarized in Table I. Here, the El and E2 strengths were eparated by measuring angular distributions. The extrapolation procedures, which vere made using K-matrix or R-matrix theory, have a large ambiguity. Recently, xtensive measurements were made for the #-delayed @ decay of ‘*N, which is ensitive predominantly to the El component” and has a large phase space to the ower energy in'®O. These facts give a better efficiency for deducing the S-factor(E1) it low energies. Buchmann et al.” and Zhao et al.” reported S-factors estimated rom their data, which are consistent with each other. Since these data were fitted ogether with other data of '’C(a, y) and ’C(a, a), the estimate of S(E1) is relatively vell determined. The results, shown in Table I, are slightly smaller than the previ- us data except for the one in Ref. 77). These are, however, roughly a factor of two maller than the values of 170—250 keV-b currently used for the stellar. models.” The E2 part is very poorly estimated yet, and the El part also needs more experimen- ation. Therefore, it should be concluded that the estimated values are still very incertain, and thus this is still one of the most important open problems to be solved yy experiment. "Thara ava anma nn ianing avnarimante ralatad ta thic anhtart Ona nnceihilitexr ic
Table I. The S-factors of the “C(a, y)'*O reaction in units of keV-b. determined by an interference of the tails of the resonances at higher energy and sub-threshold states nearby. Eee eee ee ee eee ee ee a ee Fe oe | ub-threshold states nearby. The astrophysical S-factors at 300 keV were estimated by extrapolation of the xperimental reaction cross section of ’C(a, y)'®O at Eem. 20.94 MeV, by measuring he singles gamma rays”™~””” or the gamma rays coincident with the recoil product yf °O. They are summarized in Table I. Here, the El and E2 strengths were eparated by measuring angular distributions. The extrapolation procedures, which vere made using K-matrix or R-matrix theory, have a large ambiguity. Recently, xtensive measurements were made for the #-delayed @ decay of ‘*N, which is ensitive predominantly to the El component” and has a large phase space to the ower energy in'®O. These facts give a better efficiency for deducing the S-factor(E1) it low energies. Buchmann et al.” and Zhao et al.” reported S-factors estimated rom their data, which are consistent with each other. Since these data were fitted ogether with other data of '’C(a, y) and ’C(a, a), the estimate of S(E1) is relatively vell determined. The results, shown in Table I, are slightly smaller than the previ- us data except for the one in Ref. 77). These are, however, roughly a factor of two maller than the values of 170—250 keV-b currently used for the stellar. models.” The E2 part is very poorly estimated yet, and the El part also needs more experimen- ation. Therefore, it should be concluded that the estimated values are still very incertain, and thus this is still one of the most important open problems to be solved yy experiment. "Thara ava anma nn ianing avnarimante ralatad ta thic anhtart Ona nnceihilitexr ic
Fig. 9. The HCNO cycle and the onset of the rp-process. The gray 6. Hot-CNO Cycle and the rapid-proton process ee Ee IRE Nae Nee et RE a BE NDEI IPE ae @ IIE TE Nel Ne NG ee EER IIE DEES Te ee IIE IE Another interesting nucleosynthesis problem along the main sequence of stars, as can be seen in the CN-diagram in Fig. 8, is the Carbon and Oxygen burning, which eventually lead to Si burning to reach the iron core formation just before the super- novae. These burning processes also play a crucial role in Type I supernovae. In the latter case, they take place even in higher temperature conditions (73= 1) since the burning processes are explosive. However, the nuclear data do not exist at the temperature region of interest. These also require devoted experimental efforts with very high intensity beams and a low-background detector system. These data will improve the supernova models.
Fig. 9. The HCNO cycle and the onset of the rp-process. The gray 6. Hot-CNO Cycle and the rapid-proton process ee Ee IRE Nae Nee et RE a BE NDEI IPE ae @ IIE TE Nel Ne NG ee EER IIE DEES Te ee IIE IE Another interesting nucleosynthesis problem along the main sequence of stars, as can be seen in the CN-diagram in Fig. 8, is the Carbon and Oxygen burning, which eventually lead to Si burning to reach the iron core formation just before the super- novae. These burning processes also play a crucial role in Type I supernovae. In the latter case, they take place even in higher temperature conditions (73= 1) since the burning processes are explosive. However, the nuclear data do not exist at the temperature region of interest. These also require devoted experimental efforts with very high intensity beams and a low-background detector system. These data will improve the supernova models.
Fig. 10. The reaction rates of the three successive
Fig. 10. The reaction rates of the three successive
nance at 2.521 MeV assumed before has been confirmed. There remains, however, a possibility of an alternative assignment to the analog states for the first two levels above the threshold. There are significantly large level shifts observed, compared to the mirror nucleus “Na. The reaction rate estimated based on the above experimen- tal result is about a factor of five larger than the previous estimate. This rate also suggests a reduction of the onset temperature of the "Mg(p, v)**A1 process roughly by 10%. Figure 12 shows the result of a simple model calculation of the nucleosynth- esis. Here, 100 % of "Mg was assumed, and the nucleosynthesis-flow was calculated with present reaction rate estimates till the final products after 1000 sec. The result clearly indicates that a sharp onset of the leakout from the NeNa cycle takes place through the “Mg(, y)*Al reaction at around 2.3X10°K. The critical physical parameters, the proton and gamma widths of the resonances just above the proton threshold should be determined. This is an interesting subject to be investigated with an unstable nuclear beam of “Mg. apes _ _ _ a _ _ - ne
nance at 2.521 MeV assumed before has been confirmed. There remains, however, a possibility of an alternative assignment to the analog states for the first two levels above the threshold. There are significantly large level shifts observed, compared to the mirror nucleus “Na. The reaction rate estimated based on the above experimen- tal result is about a factor of five larger than the previous estimate. This rate also suggests a reduction of the onset temperature of the "Mg(p, v)**A1 process roughly by 10%. Figure 12 shows the result of a simple model calculation of the nucleosynth- esis. Here, 100 % of "Mg was assumed, and the nucleosynthesis-flow was calculated with present reaction rate estimates till the final products after 1000 sec. The result clearly indicates that a sharp onset of the leakout from the NeNa cycle takes place through the “Mg(, y)*Al reaction at around 2.3X10°K. The critical physical parameters, the proton and gamma widths of the resonances just above the proton threshold should be determined. This is an interesting subject to be investigated with an unstable nuclear beam of “Mg. apes _ _ _ a _ _ - ne
‘ig. 14. a) The electric current of ‘Dy ** ions stored in the ring, and b) the rates of “Dy and Ho detected after time ¢s. This figure is borrowed from Ref. 134). The new developments in experimental technology open a new research field tha was not accessible before. Such new achievement was attained for bound-state bet: lecay measurements. Some nuclei become unstable against weak decay when all th: slectrons are removed when the Q-value is very small.'3” This was first demonstrat sd experimentally for the decay of '$%Dy%**—'*Ho. The half life of '@Dy%** wa: letermined to be 47 days. Here, the fully ionized *Dy*** has a slightly positiv 2-value for the weak decay. Such a condition of full ionization and storage of th ons was realized for the first time using the high energy heavy ion accelerator and the storage/cooler ring ESR at GSI. This enabled the half life measurement of **Dy*** *igure 14 displays change of number of ions of **Dy®* and '*Ho* in the storage ring ndicating the '‘“Dy®** > '"Ho® decay. The '?8’Re-8’QOs nair is a sood cosmochronometer since it is almost free from the
‘ig. 14. a) The electric current of ‘Dy ** ions stored in the ring, and b) the rates of “Dy and Ho detected after time ¢s. This figure is borrowed from Ref. 134). The new developments in experimental technology open a new research field tha was not accessible before. Such new achievement was attained for bound-state bet: lecay measurements. Some nuclei become unstable against weak decay when all th: slectrons are removed when the Q-value is very small.'3” This was first demonstrat sd experimentally for the decay of '$%Dy%**—'*Ho. The half life of '@Dy%** wa: letermined to be 47 days. Here, the fully ionized *Dy*** has a slightly positiv 2-value for the weak decay. Such a condition of full ionization and storage of th ons was realized for the first time using the high energy heavy ion accelerator and the storage/cooler ring ESR at GSI. This enabled the half life measurement of **Dy*** *igure 14 displays change of number of ions of **Dy®* and '*Ho* in the storage ring ndicating the '‘“Dy®** > '"Ho® decay. The '?8’Re-8’QOs nair is a sood cosmochronometer since it is almost free from the
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PhysicsStellar NucleosynthesisNuclear AstrophysicsNuclear ReactionsNuclear Reaction
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