This data set represents the first step in a campaign of (t,3He) charge-exchange
experiments at the National Superconducting Cyclotron Laboratory
designed explicitly to measure
Gamow-Teller strength distributions in the electron capture direction
for stable medium-heavy atomic nuclei, with particular interest in reaching
the nuclei in the pf-shell or masses up to A=112.
The 115 MeV/nucleon secondary triton beam
with an average intensity
of 4×106 pps on 10 mg/cm2
thick target foils produces 3He that are
measured in the focal plane detectors of the S800
magnetic spectrometer. From these data, the scattering angle of the tritons
is reconstructed to within 7 mrad and the energy of the recoil nucleus is
reconstructed to better then 250 keV. Since there is no comprehensive study of the
(t,3He) probe for triton energies of 100-400 MeV/nucleon,
this data is the first step in evaluating the advantages of
extracting B(GT) from the (t,3He) probe over other hadronic probes.
The first target is a CD2 target used for calibrating cross section.
This is the third measurement for the (t,3He) probe
on 12C above 100 MeV/nucleon.
The present 12C(t,3He) cross section for the 12B ground state
(Jπ=1+) is lower than a previous measurement at the NSCL by more than
one standard deviation in uncertainty but agrees with 12C(3He,t)12N.
This (t,3He) measurement
for 24Mg, the second target, is the first above 100 MeV/nucleon.
The B(GT) distribution for 24Na
is extracted from differential cross sections as a
function of residual nucleus excitation energy up to 7 MeV.
For each peak in excitation energy, the differential cross section as
a function of reconstructed scattering angle is extrapolated to zero degrees
using angular distrubutions calculated with the distorted wave calculations
from the code FOLD
and transformed to q=0 zero momentum transfer.
Uncertainties in the B(GT) include a calculation of
interference to Jπ=1+ expected from ΔL=2, ΔS=1
Comparisons of B(GT) distributions of 24Na
with that of modern calculations using an improved interaction
for the sd-shell space are discussed. In particular,
a recently improved
hamiltonian for the sd-shell model space
is compared with the quarter-century-old USD
interaction. The experimental measurements, both the present data and those
of the competing charge-exchange probe (d,2He), are in good agreement
with theoretical calculations.
As a result of this work, the NSCL has dramatically improved the availability
of the secondary triton beam and the resolution
for charge-exchange experiments and completed
experiments for (t,3He) on several nuclei above A=45.