Four-body Breakup Reactions Research Articles

Study of n-n correlations in d + 2H → p + p + n + n reaction

A kinematically complete measurement of the four-body breakup reaction d+2H→2pS+2nS→p +p +n +n has been performed at 15 MeV deuteron beam of the SINP MSU. The two protons and neutron were detected at angles close to those of emission of 2pS and 2nS systems. The energy of singlet dineutron state was determined by comparing experimental TOF spectrum of breakup neutrons with simulated spectra depending on this energy. A low value Enn = 0.076 ± 0.006 keV obtained by fitting procedure apparently indicates an effective enhancement of nn-interaction in the intermediate state of studied reaction.

New description of the four-body breakup reaction

We present a novel method of smoothing discrete breakup cross sections calculated by the method of continuum-discretized coupled-channels. The method based on the complex scaling method is tested with success for $^{58}$Ni($d$, $pn$) reaction at 80 MeV as an example of a three-body breakup reaction, and applied to $^{12}$C($^6$He, $nn^4$He) reaction at 229.8 MeV as a typical example of a four-body breakup reaction. The new method does not need to derive continuum states of the projectile in order to evaluate the breakup cross section as a smooth factor of the excitation energy of the projectile. Fast convergence of the breakup cross section with respect to extending the modelspace is confirmed. For the $^6$He breakup cross section, the resonant component is separated from the non-resonant one.

CALCULATION OF BREAKUP CROSS SECTION FOR FOUR-BODY BREAKUP REACTION SYSTEMS

We present a new method of smoothing discrete breakup cross sections calculated by the method of continuum-discretized coupled-channels. In the four-body breakup reaction of 12 C (6 He , nn4 He ) at E in = 229.8 MeV , the continuous breakup cross section is evaluated as a function of the excitation energy of 6 He . Convergence of the cross section with respect to extending the modelspace is also confirmed.

Description of Four-Body Breakup Reaction with the Method of Continuum-Discretized Coupled-Channels

We present a method of smoothing discrete breakup S-matrix elements calculated by the method of continuum-discretized coupled-channels (CDCC). This smoothing method makes it possible to apply CDCC to four-body breakup reactions. The reliability of the smoothing method is confirmed for two cases, 58 Ni(d, pn) at 80 MeV and the E1 transition of 6 He. We apply CDCC with the smoothing method to a 6 He breakup reaction at 22.5 MeV. Multistep breakup processes are found to be important. Subject Index: 221, 223, 227

THREE AND FOUR-BODY BREAKUP REACTIONS

Breakup reactions provide spectroscopic information on exotic nuclei. Coulomb breakup indirectly measures the astrophysical S factor for radiative-capture reactions. The validity of first-order perturbation theory is limited for extended systems such as halo nuclei. More elaborate reaction models are necessary: semi-classical time-dependent Schrödinger equation, eikonal and dynamical eikonal approximations, continuum-discretized coupled-channel method. Breakup experiments do not provide much information on the structure of a two-cluster halo nucleus but accurate exclusive experiments should be more interesting for three-cluster nuclei.

Full coupled-channel description of three-body and four-body breakup reactions

Recent development of the continuum-discretized coupled-channels method (CDCC) is reported with introducing the eikonal CDCC method (E-CDCC) and four-body CDCC. The former is applied to analysis of 8B breakup by 208Pb at 52 A MeV and the astrophysical factor S 17 ( 0 ) for the 7Be( p , γ ) 8B reaction is extracted with the asymptotic normalization coefficient method. We obtain S 17 ( 0 ) = 20.9 −1.9 +2.0 eV b , which is significantly larger than the previous one, S 17 ( 0 ) = 18.9 ± 1.8 eV b , determined from an analysis with the virtual photon theory. The difference between the two values is found to be due to the contributions from nuclear breakup and higher-order processes. The latter, four-body CDCC, is applied to 6He+ 209Bi scattering near the Coulomb barrier energy and found to reproduce the elastic cross sections well, in contrast to the standard three-body CDCC. Accurate treatment of the three-body continuum states of 6He turns out to be essential to correctly describe the 6He+ 209Bi scattering.

Breakup energy spectrum of singlet deuterons measured using d+d-->d*+d* four-body reaction at 15.7 MeV.

A kinematically complete measurement of the four-body breakup reaction d+d\ensuremath{\rightarrow}${\mathit{d}}^{\mathrm{*}}$+${\mathit{d}}^{\mathrm{*}}$\ensuremath{\rightarrow}p+n+p+n has been performed at 15.7 MeV bombarding energy. A ring-detector system consisting of a charged-particle detector and a neutron detector is used to define a singlet deuteron, i.e., ${\mathit{d}}^{\mathrm{*}}$; a charged-particle detector is used to measure spectra of products produced by another ${\mathit{d}}^{\mathrm{*}}$ at five angles. A velocity-distribution diagram has first been obtained, and by performing a fit the most probable breakup energy of the singlet deuteron in the laboratory system is obtained, 0.054\ifmmode\pm\else\textpm\fi{}0.012 MeV. A final state interaction calculation using known p-n singlet phase shifts predicts the expected proton spectra.

Study of the Reactions 9Be(n,α)6He and 9Be(n,αα)nn at 14.1 MeV

The differential cross sections for the reactions 9 Be(n, α 0 ) 6 He(g.s.) and 9 Be(n, α 1 ) 6 He * and the α-α particle-correlation spectrum from the 9 Be(n, αα)nn reaction have been measured using 14.1 MeV neutrons. The measured angular distributions of α-particles were in good agreement with those of Perroud and Sellem at 13.99 MeV, and were compared with DWBA calculations. The spectroscopic factors for the cluster transfer reactions on 9 Be have been deduced. The observed correlation spectrum implies that this four-body breakup reaction is dominated by a sequential decay process in the measured α-particle energy region. The second and third excited states in 6 He have been confirmed to be located at around 3.4 MeV and 6.0 MeV, respectively.

Study of the reaction 12C(n, 3α)n from threshold to En = 35 MeV

The four-body breakup reaction 12C(n, 3α)n induced by 10–35 MeV neutrons has been studied in a kinematically complete experiment. The reaction cross section for the n + 12C → 3α + n breakup and the partial cross section for sequential processes via 12C 9.63 and 8Be g.s. intermediate states have been determined after several corrections due to the detection cutoff of low-energy α-particles have been performed. The analysis of the three α-correlation spectra yields information on the contribution of different reaction mechanisms to the total cross section.

D+dfour-body breakup reaction at 80 MeV

The $d+d$ four-body breakup reaction has been studied in a geometry chosen to emphasize the double spectator process. Data were obtained at a bombarding energy of 80 MeV for the coincident detection of both emitted protons at several equal angle pairs. Comparison with simple plane wave Born approximation calculations suggests that, in addition to the double spectator process, another process, more strongly localized in phase space, is important. It is suggested that such a process is the double spin-flip excitation of both deuterons to the singlet state.[NUCLEAR REACTIONS $d+d\ensuremath{\rightarrow}2p+2n$, ${E}_{0}=80$ MeV; measured $\frac{{d}^{4}\ensuremath{\sigma}}{d{\ensuremath{\Omega}}_{{p}_{1}}d{\ensuremath{\Omega}}_{{p}_{2}}d{E}_{{p}_{1}}d{E}_{{p}_{2}}}({\ensuremath{\theta}}_{{p}_{1}},{\ensuremath{\theta}}_{{p}_{2}},{E}_{{p}_{1}},{E}_{{p}_{2}})$; coplanar geometry; PWBA analysis.]

Neutrons fromBe9(α,n)Reaction forEαbetween 6 and 10 MeV

Absolute differential cross sections have been measured as a function of angle and $\ensuremath{\alpha}$ bombarding energy for the reaction $^{9}\mathrm{Be}(\ensuremath{\alpha},n)^{12}\mathrm{C}$ leaving $^{12}\mathrm{C}$ in its ground, first excited, and second excited states. The angular distribution for the ground-state (0+ state) transition changed from a fore-aft peaking at ${E}_{\ensuremath{\alpha}}=6.8$ MeV to a three-peaked angular distribution at ${E}_{\ensuremath{\alpha}}=9.9$ MeV. Similar behavior was observed for the second-excited-state transition (0+). The angular distribution for the first-excited-state transition (2+) displayed fore-aft peaking and was not sensitive to bombarding energy. A strong, low-energy component, present at forward angles at all bombarding energies, can be accounted for by three- and four-body breakup reactions.