The Yale Moving Tape Collector (MTC)
The Yale Moving Tape Collector is used to study beta-decay processes
and states populated in beta-decay daughter nuclei. Parent nuclei
are produced in heavy-ion reactions and then transported on a tape to
an
out-of-beam detector area, where beta energy measurements and
low-background
spectroscopy of the gamma-ray de-excitations of the daughter can be
performed.
Several research programs currently make use of the Yale Moving Tape
Collector:
-
Low-spin gamma-gamma spectroscopy: Beta decay provides
an
effective means of populating low-lying non-yrast states in the
daughter
nucleus. These states are of interest in the study of collective
phenomena, such as multi-phonon states. Gamma-gamma
spectroscopy
allows refinement of decay schemes and measurement of critical
branching
ratios, facilitating interpretation of the structure of these states. R.
F.
Casten, N. V. Zamfir, M.A. Caprio
(WNSL, Yale University)
-
Mass measurements: The mass difference between the
parent
nucleus and daughter nucleus in a beta-decay process can be determined
from the endpoint of the energy spectrum of emitted beta
particles.
If the mass of one of these nuclei is already known, measurement of the
mass difference establishes the mass of the other nucleus.
Beta-gamma
coincidence techniques allow beta-particles from different decay
channels
to be identified by their coincidence with specific de-excitation gamma
rays
from the daughter nucleus. D.S. Brenner (Clark University)
-
Angular correlation and g-factor measurements:
Feasibility studies are underway for use of the Yale Moving Tape
Collector in gamma-gamma
angular correlation measurements. In conjunction with a
superconducting
magnet, which induces spin precession of the daughter nucleus, these
measurements
would allow determination of nuclear magnetic g-factors.
Z. Berant,
A. Wolf (Nuclear Research Center Negev)
Production and detection
The beta decay parent nucleus is produced via a heavy-ion
fusion-evaporation
reaction, and its longitudinal momentum carries it out the back of the
target. The reaction involves the evaporation of several (~2-6)
energetic
nucleons, and each emission imparts a recoil momentum to the compound
nucleus.
Hence, the final product nucleus typically acquires a sizeable
transverse
component of momentum and is thus emitted at a substantial angle
relative
to the beam axis. For the reactions used with the Yale MTC, the
angular
distribution of product nuclei has its peak at an angle varying from 2
to 7 degrees away from the beam axis. This recoil deflection
effect
is exploited to separate the product nuclei from unscattered primary
beam:
The beam particles travel undeflected through the target and are
stopped
with a 3mm plug, while the majority of product nuclei are emitted at a
sufficient
angle to bypass the plug.
The product nuclei are embedded into a 16mm tape (aluminized motion
picture film leader). After a collection period, chosen based
upon
the involved half-lives, the tape is advanced to carry these nuclei to
the detector area.
The Moving Tape Collector makes use of a high-efficiency array of
segmented
Clover HPGe detectors for gamma-ray detection. The vacuum chamber
containing the moving tape is equipped with a beta-transparent window
(polypropylene
film) permitting the use of a beta detector as well. The detector
area accommodates up to four detectors on an angular correlation table.
[Nuclear Structure] [WNSL] [Physics Department] [Yale University]
Last modified 3 October 2000
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