The Joy of CEX: Sharpening the (t,^3He) probe at 345 MeV for the charge-exchange knife drawer
This data set represents the first step in a campaign of
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 4×10^6 pps on 10 mg/cm^2
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
(J?=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 J?=1^+ expected from ?L=2, ?S=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.
School:The Ohio State University
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:charge exchange nuclear physics astrophysics experimental cex gamow teller gt strength nscl intermediate energy
Date of Publication:01/01/2008