Quasifree Reaction Research Articles

9B excited states and analysis of the 9Be(3He,t) spectra.

Inclusive spectra of ${(}^{3}$He,t) on $^{9}\mathrm{Be}$ have been measured and analyzed in a large energy range of emitted tritons at ${E}_{{\mathrm{}}^{3}\mathrm{He}=90}$ MeV in the angular range 7\ifmmode^\circ\else\textdegree\fi{}--27\ifmmode^\circ\else\textdegree\fi{}. The spectra have been analyzed in terms of a superposition of simultaneous breakups, quasifree reactions, and two-step-fragmentation plus pickup processes. The residual spectra correspond to excited states in $^{9}\mathrm{B}$. Confirmation for uncertain states was obtained. Some new states, possible analogs to $^{9}\mathrm{Be}$, were observed.

The 9Be(3He,2α)α reaction from 12 to 24 MeV and coherent sequential decay

Abstract Coincidence cross sections for 9 Be( 3 He, 2α)α were measured from E He = 102 to 24 MeV. Sequential decays of all known α-emitting 8 Be levels were observed with about equal cross section. Coherent analysis of 8 Be(11.4 MeV) sequential decay into two different α-particle pairs was required to fit the peaks from this state. Upper limits on the cross section for the possible 3 He + 5 He → 2α quasifree reaction on 5 He clusters in 9 Be are about 0.05 and 0.2 mb/sr 2 at E 0 = 12 and 24 MeV, respectively; these are much smaller than those reported for such a process at E 0 = 4 MeV.

3He break-up and quasi-free7Li(p, α)4He reaction at low energies

7Li(p, α)4He quasi-free reaction contributions in the7Li (3He, αα)2H reaction are examined at low incident3He energies.

High-resolution (e, e'p) experiments, spectroscopic factors and correlations

Recent experimental results obtained with the high-resolution quasi-free (e.e'p) reaction are presented. We address the issue of correlations in the nuclear many-body wave function, and the role of two-step processes and final state interactions. Data that may shed light on the hypothesis of medium-modified nucleons is discussed.

Two-step processes in the quasi-free (e,e'p) reaction.

The role of two-step processes in the $^{12}\mathrm{C}$(e,e,'p${)}^{11}$B reaction has been investigated by studying the transition to the ${(5/2)}^{\mathrm{\ensuremath{-}}}$ state at ${E}_{x}$=4.45 MeV. In a (1s${)}^{4}$(1p${)}^{8}$ shell-model space this state cannot be excited by a one-step process, and a secondary process is therefore required. Such processes are found to be sufficiently small to enable the study of small wave-function components with the (e,e'p) reaction.

Mass 2 and 3 cluster structure study with quasi-free reactions induced by 58 MeV protons on 9Be, 12C and 14N

Cross sections for (p, pd) and (p,p 3He) reactions at 58 MeV have been measured for 9Be, 12C and 14N targets. An energy resolution of about 400 keV permitted identification of several excited states in the different residual nuclei. The experimental results are presented and analysed in the framework of the distorted-wave impulse approximation. Spectroscopic and mechanism information is discussed. Some additional quasi-free reactions involving t, 3He and α structure of 9Be have been observed and are also reported.

Multiparticle break-up of 10B induced by fast neutrons

The reaction n + 10 B→ α + α + d + n induced by 14.4 MeV neutrons has been investigated in a kinematically complete experiment. Several final-state interactions have been observed in the sequential decay of the n + 10B system. The angular distribution of the 10B(n, 6Li 1) 5He 0 reaction, leading to two unstable particles and consequently measurable only in a kinematically complete experiment, has been measured. It has been analysed in the framework of DWBA as a pick-up process with the transfer of the five-nucleon cluster 5Li. The presence of quasifree scattering and quasifree reaction with the deuteron as spectator has also been observed.

Three-particle impulse approximation and d(N, 2N)N reactions

The three-particle impulse approximation with truncation (TIAT) has been applied to the investigation of d(p, 2p)n and d(p, pn)p quasi-free knock-out reactions (QFR) in the nonrelativistic scattering region (E<160 MeV). It is stated that the truncation procedure leads to the approximate restoration of the three-particle unitary relationships which are violated explicitly within the usual formulation of the single-collision mechanism. It is shown that the TIAT explains sufficiently well all the available experimental data for the value of the truncation parameter used by the authors in their earlier papers for the investigation of other QFR.

Inclusive pion single-charge-exchange reactions

The (${\ensuremath{\pi}}^{+}$,${\ensuremath{\pi}}^{0}$) and (${\ensuremath{\pi}}^{\ensuremath{-}}$,${\ensuremath{\pi}}^{0}$) reactions were studied on a variety of nuclei at a bombarding energy of 160 MeV. The full ${\ensuremath{\pi}}^{0}$ energy spectra were measured with a ${\ensuremath{\pi}}^{0}$ spectrometer at several detection angles. The energy spectra and angular distributions are characteristic of quasifree reactions. Effects due to multiple scattering, neutron screening, and Pauli blocking are clearly observed.

Interference effects in (π,πN) reactions

Contributions of quasifree and nonquasifree reaction processes to (..pi..,..pi..N) reactions have been investigated across the (3,3) resonance region. We demonstrate that the quantum mechanical interference between these two types of reaction processes significantly affects the calculated ..pi../sup -/- and ..pi../sup +/-induced cross sections, as well as their ratio. In the case of incident ..pi../sup -/, the contributions from the interference term even exceed those from the pure nonquasifree term. This investigation of the (..pi..,..pi..N) reaction thus indicates that the interpretations given to the parameter introduced into various published semiclassical models, in which interference effects were ignored, are incorrect.

Photoemission of Two Nucleons fromBe9in theΔ(1232)Resonance Region

Coincidence measurements of two nucleons from the reactions /sup 9/Be(..gamma..,pn)X and /sup 9/Be(..gamma..,pp)X have been made in the ..delta..(1232) resonance region with a tagged-photon beam. From the momentum and angular correlations between the two nucleons, two quasifree reactions, ..gamma..+''pnclzquo..-->..p+n and ..gamma..+''ppclzquo..-->..p+p, are clearly identified. The separation energy and the momentum distribution of the quasifree deuteron in /sup 9/Be are determined together with the ratio between cross sections of the two quasifree reactions.

Pion scattering and absorption contributions to proton emission from pion-nucleus collisions atTπ=50−295MeV

Proton spectra of /sup 3,4/He(..pi../sup + -/,p) and /sup 27/Al(..pi../sup + -/,p) have been measured at theta/sub p/ = 20/sup 0/ for T/sub ..pi../ = 50, 100, 150, 200, and 250 MeV, and at theta/sub p/ = 20/sup 0/ and 40/sup 0/ for T/sub ..pi../ = 295 MeV. A small contributor to these spectra is the exclusive pion absorption reaction for which the cross section of /sup 4/He(..pi../sup +/,p)/sup 3/He is reported. Major contributions are identified to come from quasifree ..pi..N..--> pi..p scattering and ..pi..NN..-->..Np absorption for which cross sections are also reported. The quasifree cross sections are compared with those of the free reactions ..pi..N..--> pi..p and ..pi..d..-->..pp. We use these results to assess the contribution of quasifree reactions to the total reaction cross section. The comparison of the quasifree ..pi..NN..-->..Np reaction relative to ..pi..d..-->..pp is discussed in terms of differences in the attenuation and the dynamics of the reactions. This information is of interest for the phenomenological interpretation of complex reactions such as the two-nucleon absorption model of /sup 3/He(..pi../sup -/, n)/sup 2/H, /sup 4/He(..pi../sup -/, n)/sup 3/H, and /sup 4/He(..pi../sup +/, p)/sup 3/He in which ..pi..d..-->..pp is assumed to be an elementary process. This experiment also providesmore » information on the cross section of ..pi../sup -/pp..-->..pn from which we determine the dependence of pion absorption on the isospin of the initial NN state.« less

Fragmentation spectra induced by light ions colliding with light nuclei

Inclusive energy spectra of light charged particles from the /sup 6/Li+/sup 3/He, /sup 9/Be+/b p/, and /sup 9/Be+/sup 3/He reactions have been measured using beams of 30 to 75 MeV. The continuum parts have been studied in the framework of phase space calculations. The influence of other reaction mechanisms, such as final state interactions, sequential processes, and quasifree reactions is evaluated. The authors deduce the nontrivial angular dependence of the various phase spaces.

The6Li(3He, pα)4He reaction at 13 MeV and the αd momentum distribution

The6Li(3He, pα)4He reaction has been studied at 13 MeV incident energy. The detection configuration was chosen in such a way to deduce within the impulse approximation the momentum distribution of the ad motion in6Li. The angular-correlation method has been used. The FWHM of the momentum distribution is (55 ± 6) MeV/c. This result has been compared with the trend of the experimental widths obtained in quasi-free reactions, as a function of the transferred momentum.

Study of the (α, 2α) reaction

An alternate treatment for the distorted waves in the distorted wave impulse approximation (DWIA) formalism for the quasi-free (α, 2α) reaction is proposed. The prescription is based on the surface localization of this reaction. It describes the distorted waves directly in terms of the measured α-nucleus phase shifts. The predictions based on this formalism are compared with the available data at 140 MeV and 90 MeV on 16O, 24Mg, 40Ca and 66Zn. They agree very well both in magnitude and shape.

The (p, dd) reaction on 6Li and 7Li nuclei at 670 MeV

The (p, dd) reaction was investigated for 6Li and 7Li nuclei at 670 MeV in a kinematically complete experiment. In transitions to the ground states evidence was found for the quasi-free pick-up process on quasi-tritons; the experimental data were analysed by quasi-free reaction theory. In other transitions the admixture of secondary processes cannot be excluded.

The quasi-free breakup of 3He

A DWBA formalism is presented for the quasi-free breakup of 3He into elastic, inelastic and particle-transfer channels. The model assumes that only a subset of the projectile interacts strongly with the target while the remaining fragment acts as a spectator. The full DWBA is reduced to a rather transparent quasi-free reaction mechanism. Distortion of the spectator wave function due to the Coulomb field of the target is included. Calculations of angular correlations and projected energy spectra resulting from processes involving the binary breakup of 3He on 28Si at E( 3 He) = 52 MeV are, apart from a normalization factor, in good agreement with the data.

Momentum distribution of alpha clusters in light nuclei from (α, 2α) reactions at high energy

The data of the (α, 2α) quasi-free reactions measured (5) on light nuclei at 700 MeV have been reanalysed and fitted with calculations performed in the PWIA. The results are in agreement with previous information on the momentum distribution of α-particles in light nuclei. The conditions for the validity of the PWIA in calculating quasifree cross-sections at high energy and the criteria concerning the proper choice of the wave function for the intercluster motion ar also discussed.

Do Quasifree Reaction Mechanisms Explain Reaction Cross Sections in Intermediate-Energy Proton-Nucleus Scattering?

The 800-MeV ($p, {p}^{\ensuremath{'}}$) inclusive proton spectra at forward angles are considered. A plane-wave impulse approximation is used to calculate quasifree nucleon knockout and quasifree isobar production. When the quasifree peaks are normalized to data, it is found that the integrated cross section for the two processes can account for the total reaction cross section.

Quasifree processes in the 3He+ 3Hand 3He+ 3He interactions

Quasifree scattering and quasifree reaction processes have been examined in ten 3H + 3He and 3He + 3He reactions with at least two of the three or more final state particles being charged. Beam energies of 50, 65 and 78 MeV were used. The experimental results are compared with PWIA predictions and Fourier transforms of the wave functions are extracted. The quasifree processes are described in a consistent, but qualitative, manner by the PWIA; distortion in the intial state appears to be the cause of the consistent deviation of the data from the PWIA predictions. Extracted values for the 3H(d, 3He)2n cross section are given.