Gamow-Teller (GT) transitions in atomic nuclei are sensitive to both nuclear shell structure and effective residual interactions. The nuclear GT excitations were studied for the mass number A = 42, ...46, 50, and 54 "f-shell" nuclei in ((3)He, t) charge-exchange reactions. In the (42)Ca → (42)Sc reaction, most of the GT strength is concentrated in the lowest excited state at 0.6 MeV, suggesting the existence of a low-energy GT phonon excitation. As A increases, a high-energy GT phonon excitation develops in the 6-11 MeV region. In the (54)Fe → (54)Co reaction, the high-energy GT phonon excitation mainly carries the GT strength. The existence of these two GT phonon excitations are attributed to the 2 fermionic degrees of freedom in nuclei.
Differential cross sections of isoscalar and isovector spin-M1 (0(+)→1(+)) transitions are measured using high-energy-resolution proton inelastic scattering at E(p)=295 MeV on (24)Mg, (28)Si, (32)S, ...and (36)Ar at 0°-14°. The squared spin-M1 nuclear transition matrix elements are deduced from the measured differential cross sections by applying empirically determined unit cross sections based on the assumption of isospin symmetry. The ratios of the squared nuclear matrix elements accumulated up to E(x)=16 MeV compared to a shell-model prediction are 1.01(9) for isoscalar and 0.61(6) for isovector spin-M1 transitions, respectively. Thus, no quenching is observed for isoscalar spin-M1 transitions, while the matrix elements for isovector spin-M1 transitions are quenched by an amount comparable with the analogous Gamow-Teller transitions on those target nuclei.
Differential cross sections for transitions of known weak strength were measured with the (3He, t) reaction at 420 MeV on targets of 12C, 13C, 18O, 26Mg, 58Ni, 60Ni, 90Zr, 118Sn, 120Sn, and 208Pb. ...Using these data, it is shown that the proportionalities between strengths and cross sections for this probe follow simple trends as a function of mass number. These trends can be used to confidently determine Gamow-Teller strength distributions in nuclei for which the proportionality cannot be calibrated via beta-decay strengths. Although theoretical calculations in the distorted-wave Born approximation overestimate the data, they allow one to understand the main experimental features and to predict deviations from the simple trends observed in some of the transitions.
Measurements of inelastic proton scattering with high energy resolution at forward scattering angles including
0
∘
are described. High-resolution halo-free beams were accelerated by the cyclotron ...complex at the Research Center for Nuclear Physics. Instrumental background events were minimized using the high-quality beam. The remaining instrumental background events were eliminated by applying a background subtraction method. As a result, clean spectra were obtained even for a heavy target nucleus such as
Pb
208
. A high energy resolution of 20
keV (FWHM) and a scattering angle resolution of
±
0
.
6
∘
were achieved at an incident proton energy of 295
MeV.
.
The
18
F(
p
,
α
) reaction determines the rate of destruction of
18
F in novae. It represents the key nuclear physics uncertainty in modelling the calculated flux of annihilation radiation emitted ...following the radioactive decay of
18
F. The major uncertainties relate to states representing s-wave resonances in the compound system,
19
Ne. We report a first study of the
19
F(
3
He,
t
)
19
Ne reaction at intermediate energies and forward angles. This reaction has a simple, model-independent, mechanism that we use here to identify states near the proton threshold energy in
19
Ne corresponding to
Δ
L
=
0
transitions. In particular, we observe a
Δ
L
=
0
state at 6.13 MeV which could significantly affect the
18
F(
p
,
α
) astrophysical
S
-factor at nova burning temperatures.
The Low Energy Neutron Detector Array (LENDA) is a neutron time-of-flight (TOF) spectrometer developed at the National Superconducting Cyclotron Laboratory (NSCL) for use in inverse kinematics ...experiments with rare isotope beams. Its design has been motivated by the need to study the spin–isospin response of unstable nuclei using (p,n) charge-exchange reactions at intermediate energies (>100MeV/u). It can be used, however, for any reaction study that involves emission of low energy neutrons (150keV to 10MeV). The array consists of 24 plastic scintillator bars and is capable of registering the recoiling neutron energy and angle with high detection efficiency. The neutron energy is determined by the time-of-flight technique, while the position of interaction is deduced using the timing and energy information from the two photomultipliers of each bar. A simple test setup utilizing radioactive sources has been used to characterize the array. Results of test measurements are compared with simulations. A neutron energy threshold of <150keV, an intrinsic time (position) resolution of ∼ 400 ps (∼ 6cm) and an efficiency >20% for neutrons below 4MeV have been obtained.
Isospin symmetry is expected for the T(z)=+/-1-->0 isobaric analogous transitions in isobars with mass number A, where T(z) is the z component of isospin T. Assuming this symmetry, strengths of ...analogous Gamow-Teller (GT) transitions within A = 50 isobars were determined from a high energy-resolution study at 0 degrees in combination with the decay Q value and lifetime from the beta decay. This method can be applied to other pf-shell nuclei and can be used to study GT strengths of astrophysical interest.
Realization of matching conditions for high-resolution spectrometers Fujita, H; Fujita, Y; Berg, G.P.A ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
05/2002, Letnik:
484, Številka:
1
Journal Article
Recenzirano
For precise measurements of nuclear-reaction spectra using a beam from an accelerator, a high-resolution magnetic spectrometer is a powerful tool. The full capability of a magnetic spectrometer, ...however, can be achieved only if the characteristics of the beam coming from the accelerator are matched to those required by the spectrometer by properly adjusting the beam line conditions. The matching methods,
lateral dispersion matching,
focus matching and also the
kinematic correction compensate the spectrum line-broadening effects caused by the beam momentum spread and reaction kinematics. In addition,
angular dispersion matching should be performed if good resolution of the scattering angle is important. Diagnostic methods developed to realize these matching conditions for the spectrometers K600 at IUCF and Grand Raiden at RCNP are presented.
High resolution beam line for the Grand Raiden spectrometer Wakasa, T; Hatanaka, K; Fujita, Y ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
04/2002, Letnik:
482, Številka:
1-2
Journal Article
Recenzirano
We have designed and constructed a new beam line which can accomplish both lateral and angular dispersion matching with the Grand Raiden spectrometer. In dispersive mode, lateral and angular ...dispersions of the beam line are b16=37.1m and b26=−20.0rad, respectively, to satisfy matching conditions for Grand Raiden. In achromatic mode, the beam line satisfies the double achromatic condition of b16=b26=0. The magnifications of the beam line are (Mx,My)=(−0.98,0.89) and (−1.00,−0.99) for dispersive and achromatic modes, respectively. In the commissioning experiments, we have succeeded to separate the first excited 2+ state of 168Er with Ex=79.8keV clearly from the ground state in the (p,p′) reaction. We achieved energy resolutions of ΔE=13.0±0.3 and 16.7±0.3keV in full width at half-maximum for 295 and 392MeV protons, respectively. These energy resolutions agree with the resolving power of Grand Raiden for an object size of about 1mm.
The electric dipole strength distribution in 120Sn has been extracted from proton inelastic scattering experiments at Ep=295 MeV and at forward angles including 0°. It differs from the results of a ...Sn120(γ,γ′) experiment and peaks at an excitation energy of 8.3 MeV. The total strength corresponds to 2.3(2)% of the energy-weighted sum rule and is more than three times larger than what is observed with the (γ,γ′) reaction. This implies a strong fragmentation of the E1 strength and/or small ground state branching ratios of the excited 1− states.
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