43 research outputs found
Simultaneous spectroscopy of - rays and conversion electrons: Systematic study of 0 transitions and intruder states in close vicinity of mid-shell point in odd-Au isotopes
Experimental study of 1/2(+) isomers in At-199,At-201
Using fusion-evaporation reactions, a gas-filled recoil separator, and recoil-electron and recoil-electron-α
tagging techniques, a new isomeric 1
2
+ state [T1/2 = 45(3) ms] in 201At is identified, and an earlier reported
corresponding state [T1/2 = 273(9) ms] in 199At is confirmed. The 1
2
+ state is suggested to originate from an
intruder π(s1/2)
−1 configuration. In addition, nuclear structure of states below and above this 1
2
+ state are studied
in both nuclei. The isomer decays through a cascade of an E3 transition followed by a mixed M1/E2 transition
to the 9
2
− ground state, and it is interpreted to be fed from nearly spherical 3
2
+ and 5
2
+ states originating from
Ï€(d3/2)
−1 and π(d5/2)
−1 configurations, respectively.peerReviewe
Confirmation of the new isotope 178Pb
The extremely neutron-deficient isotope 178Pb has been produced. The GREAT spectrometer at the focal plane
position of the gas-filled separator RITU was used to study the α decay of 178Pb and its α-decay chain through
α-α correlations. The α decay was measured to have an energy and half-life of Eα= 7610(30) keV and t1/2 =
0.21+0.21
−0.08 ms, respectively. The half-life is consistent with recent theoretical calculations using the Coulomb
and proximity potential model. The α-decay reduced width and hindrance factor for 178Pb were deduced and
correspond to an unhindered l = 0 transition. In addition, the mass excess of 178Pb and the α-decay Q value
were calculated from the experimental results and compared to theoretical values.peerReviewe
Decay spectroscopy of 179 82 Pb 97 and evidence for a 9/2− intruder state in 179 81 Tl 98
The very neutron-deficient isobars 179Pb and 179Tl have been produced using the fusion-evaporation reactions 104Pd(78Kr,xpyn), where x≤1 and y≥2. The gas-filled separator RITU was employed to transport and separate the recoiling nuclei of interest from the scattered beam and unwanted products. The GREAT spectrometer was used to study the decay properties through α−α and α−γ correlations, which has allowed the ground state of 179Pb to be assigned as Iπ=9/2−. The decay of 179Pb was measured to have an α-particle energy and half-life of Eα=7348(5)keV and t1/2=2.7(2) ms, respectively. A search for a νi13/2 state in 179Pb was performed, but only a limit of excitation energy and half-life was obtained. In 179Tl a t1/2=114+18−10 ns isomeric state, likely at an excitation energy of 904.5(9) keV, was identified and is tentatively assigned to be a 9/2− proton intruder state.peerReviewe
Detailed spectroscopy of 193Bi
An experiment aiming to study shape coexistence in 193Bi has been performed. Due to its transitional character,
it has an exceptionally large number of structures identified close to the yrast line. Many new states have been
found, significantly extending the previously known level scheme of 193Bi, including several new rotational
bands. The π i13/2 band was extended to I π = 45/2+. The I π = 31/2+ member of the π i13/2 band was found
to de-excite also to a long-lived isomeric state. This isomeric state is located at 2350 keV and has a spin and
parity of 29/2+. The half-life of the isomeric state was measured to be 85(3) μs and it decays via the emission
of an 84 keV E2 transition. A level structure feeding this isomeric state was constructed. A low-energy, 49 keV
transition has been identified to depopulate the (29/2−) isomeric state, which places it at an energy 2405 keV
in the level scheme. This is the first time such a decay has been observed in the neutron-deficient Bi isotopes.
A superdeformed band almost identical to that present in the neighboring isotope 191Bi, based on the 1/2[651]
Nilsson orbital, has also been identified.peerReviewe
Detailed spectroscopy of 195Bi
An experiment focused on the study of shape coexistence and new high-spin structures in
195
Bi
has been performed. The nucleus is in a transitional region of the bismuth isotope chain. A large number of new states have been found, resulting in a significant extension of the previously known level scheme. Several new collective structures have been identified. A strongly coupled rotational band built upon the
13
/
2
+
isomeric state was extended up to
I
Ï€
=
(
49
/
2
+
)
and an energy of 5706 keV. The
I
Ï€
=
31
/
2
+
member of the
Ï€
i
13
/
2
band was also found to feed a new long-lived isomeric state with an excitation energy of 2616 keV and a spin and parity of
I
Ï€
=
29
/
2
+
. The half-life of the
29
/
2
+
isomeric state was determined to be
1.49
(
1
)
μ
s
. It decays via the emission of 457-keV
E
2
and 236-keV
E
1
transitions, respectively. A low-energy 46-keV
E
2
transition has been identified to depopulate the (
29
/
2
−
) isomeric state, with a measured half-life of
T
1
/
2
=
614
(
5
)
ns
. This transition allows the excitation energy of the isomeric state to be determined as 2381 keV. The feeding patterns of both
29
/
2
+
and (
29
/
2
−
) isomeric states have also been described. This is the first time collective structures have also been observed up to high spins and excitation energies in the neutron-deficient
195
Bi
nucleus. Evidence for the manifestation of shape coexistence in
195
Bi
is also discussed.peerReviewe
Experimental study of isomeric intruder ½+ states 197,203At
A newly observed isomeric intruder
½
+
state
[
T
½
=
3.5
(
6
)
ms
]
is identified in
203
At
using a gas-filled recoil separator and fusion-evaporation reactions. The isomer is depopulated through a cascade of
E
3
and mixed
M
1
/
E
2
transitions to the
9
/
2
−
ground state, and it is suggested to originate from the
Ï€
(
s
½
)
−
1
configuration. In addition, the structures above the
½
+
state in
203
At
and
197
At
are studied using in-beam
γ
-ray spectroscopy, recoil-decay tagging, and recoil-isomer decay tagging methods. The
½
+
state is fed from
3
/
2
+
and
5
/
2
+
states, and the origin of these states are discussed.peerReviewe
Spectroscopy of proton-rich 66Se up to: Isospin-breaking effect in the A = 66 isobaric triplet
Candidates for three excited states in the 66Se have been identified using the recoil-β tagging method together
with a veto detector for charged-particle evaporation channels. These results allow a comparison of mirror and
triplet energy differences between analog states across the A = 66 triplet as a function of angular momentum. The
extracted triplet energy differences follow the negative trend observed in the f7/2 shell. Shell-model calculations
indicate that the strength of the Coulomb isotensor part alone is not sufficient to account for this trend in the case
of the A = 66 triplet.peerReviewe
Identification of a dipole band above the IÏ€ = 31/2- isomeric state in 189Pb
A dipole band of six transitions built upon a firmly established I π = 31/2− isomeric state has been identified
in 189Pb using recoil-isomer tagging. This is the lightest odd-mass Pb nucleus in which a dipole band is known.
The dipole nature of the new transitions has been confirmed through angular-intensity arguments. The evolution
of the excitation energy and the aligned-angular momentum of the states in the new dipole band are compared
with those of dipole bands in heavier, odd-mass lead isotopes. This comparison suggests that the new band in
189Pb is based upon a π[s−2
1/2h9/2i13/2]11− ⊗ ν[i
−1
13/2+ ]13/2+ configuration. However, the increased aligned-angular
momentum in 189Pb may suggest evidence for a reduced repulsive proton/neutron-hole interaction compared to
dipole bands in the heavier mass isotopes.peerReviewe