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For many nuclei beyond the proton drip line in the Z > 72, N > 82 region, both proton and α emission are energetically allowed. In the case of some proton emitters, there are α-decay chains emanating from both parent and daughter nuclei. This means that if the mass excess of one member of an α-decay chain is known, then the mass excesses for all members of both chains can be obtained. In addition, proton separation energies may be derived for nuclei in the α-decay chain of the proton emitter. The method of time- and space-correlations also allows the identification of isomeric states in these nuclei. As an example, a large number of mass excesses and proton separation energies for ground and metastable states have been derived from Q α and Q p values obtained from the proton emitters 165,166,167Ir, 171Au, 177Tl and their daughters.

Ground and isomeric proton and alpha decay branches are reported for the new isotope ${}^{177}\mathrm{Tl},$ produced by bombarding a ${}^{102}\mathrm{Pd}$ target with a 370 MeV beam of ${}^{78}\mathrm{Kr}$ ions. The ground state is assigned as a $\ensuremath{\pi}{s}_{1/2}$ configuration and the high spin isomer is assigned as a $(\ensuremath{\pi}{h}_{11/2}{)}^{\ensuremath{-}1}$ configuration. The ground-state proton decay of ${}^{171}\mathrm{Au}$ has been identified for the first time, produced by bombarding a ${}^{96}\mathrm{Ru}$ target with ${}^{78}\mathrm{Kr}$ ions. The ${}^{171}\mathrm{Au}$ ground state is also assigned as a $\ensuremath{\pi}{s}_{1/2}$ configuration. Spectroscopic factors, masses, and proton separation energies are derived using these new proton decay measurements. New ground-state $\ensuremath{\alpha}$ decays for ${}^{169}\mathrm{Ir}$ and ${}^{173}\mathrm{Au}$ are also reported.

In-beam \ensuremath{\gamma} rays have been observed in the neutron-deficient isotopes ${}^{170,171,172}\mathrm{Pt}$ using the recoil-decay tagging technique. The yrast transition sequence proposed for ${}^{172}\mathrm{Pt}$ indicates that the ${0}^{+}$ bandhead of the deformed intruder band is situated about 900 keV above the weakly deformed ground state, i.e., its excitation energy has risen by about 300 keV compared to ${}^{174}\mathrm{Pt}.$ The measured energy of the ${2}^{+}\ensuremath{\rightarrow}{0}^{+}$ transition in ${}^{170}\mathrm{Pt}$ supports an even larger increase in the excitation energy of the intruder configuration with the departure from the middle of the 82--126 major neutron shell. Furthermore, a band with transition energies almost identical to those found in ${}^{172}\mathrm{Pt}$ has been assigned to ${}^{171}\mathrm{Pt}$ and was interpreted as corresponding to a rotationally aligned ${i}_{13/2}$ neutron orbital coupled to the core excitations.

With the use of a fragment mass analyzer, the $\ensuremath{\alpha}$ decay of ${}^{180}\mathrm{Tl}$ was identified in ${}^{92}\mathrm{Mo}$ bombardments of ${}^{90}\mathrm{Zr}.$ At least three \ensuremath{\alpha} transitions were observed but on the basis of the data obtained it was not possible to conclude if they originate from one or more levels in ${}^{180}\mathrm{Tl}.$ In the same irradiations a new \ensuremath{\alpha} group was also identified in ${}^{179}{\mathrm{Tl}}^{m}$ decay. Based on energy and half-life systematics, it appears that ${}^{179}{\mathrm{Tl}}^{m},$ in contrast to the isomers in heavier odd-A Tl nuclei, is not the ${h}_{9/2}$ intruder level but rather the ${h}_{11/2}$ proton state.

The $\ensuremath{\alpha}$-decay properties of ${}^{190}$Po were investigated through the use of a fragment mass analyzer in conjunction with a double-sided Si strip detector. The isotope was produced via the ${}^{96}\mathrm{Mo}{(}^{96}\mathrm{Mo},2n)$ reaction, and its $\ensuremath{\alpha}$-decay energy and ${T}_{1/2}$ were measured as 7529(10) keV and ${2.4}_{\ensuremath{-}0.3}^{+0.4}$ ms, respectively. The resulting reduced width is nearly identical to that of the ${}^{192,194}\mathrm{Po}$ isotopes. This is believed to result from significant mixing between the ground state $\ensuremath{\pi}(2p)$ and the low-lying ${0}^{+}\ensuremath{\pi}(4p\ensuremath{-}2h)$ intruder state in the Po parent. The result provides further evidence for shape coexistence in the light Po isotopes. In addition, ${}^{191}\mathrm{Po}$ was unambiguously identified, and the ${}^{186}\mathrm{Pb}$ $\ensuremath{\alpha}$-decay branch was determined experimentally for the first time.

The new proton radioactivities ${}^{165,166,167}\mathrm{Ir}$ and ${}^{171}\mathrm{Au}$ have been observed. The Ir isotopes were produced via the ${}^{92}\mathrm{Mo}{(}^{78}\mathrm{Kr}{,pxn)}^{165,166,167}\mathrm{Ir}$ reactions at 357 and 384 MeV. ${}^{171}\mathrm{Au}$ was produced via the ${}^{96}\mathrm{Ru}{(}^{78}\mathrm{Kr}{,p2n)}^{171}\mathrm{Au}$ reaction at 389 MeV. The proton emitters were each identified by position, time, and energy correlations between the implantation of a residual nucleus into a double-sided silicon strip detector, the observation of a decay proton, and the subsequent observation of a decay alpha particle from the daughter nucleus (${}^{164,165,166}$Os and ${}^{170}\mathrm{Pt},$ respectively). Both ${}^{166}\mathrm{Ir}$ and ${}^{167}\mathrm{Ir}$ have proton-emitting ground and isomeric states, which also decay by alpha emission. The proton-decay rates have been reproduced by calculations using the WKB barrier penetration approximation and a low-seniority shell-model calculation of the spectroscopic factors. The alpha decays of the four nuclei are followed by chains of alpha decays, allowing the determination of single-particle orbital orderings. Mass information has also been obtained from the alpha-decay chains because a connection to a known mass can be obtained for one of the nuclei. Ground-state mass excesses are reported for ${}^{151}\mathrm{Tm},$ ${}^{154}\mathrm{Yb},$ ${}^{155}\mathrm{Lu},$ ${}^{158}\mathrm{Hf},$ ${}^{159}\mathrm{Ta},$ ${}^{162}\mathrm{W},$ ${}^{163}\mathrm{Re},$ ${}^{166}\mathrm{Os},$ ${}^{167}\mathrm{Ir},$ and ${}^{170}\mathrm{Pt}.$ The mass excess for ${}^{171m}\mathrm{Au}$ is also given. Proton separation energies are also deduced for the odd-$Z$ alpha daughter nuclei of the Ir proton emitters.

Proton radioactivities from {sup 157}Ta and {sup 161}Re are reported. Fusion-evaporation residues from the reaction of 270 MeV {sup 58}Ni ions on {sup 102}Pd and {sup 106}Cd targets were separated according to M/Q and implanted into a double-sided silicon strip detector. One line from {sup 157}Ta was observed with a proton energy of 927(7) keV [t{sub 1/2}=10.1(4) ms, b{sub p}=3.4(12){percent}] from the {pi}s{sub 1/2} ground state. A new alpha decay transition with energy 6117(4) keV was also observed from this state. Two proton lines from {sup 161}Re were observed with energies 1192(6) keV [t{sub 1/2}=0.37(4) ms, b{sub p}=100(7){percent}] and 1315(7) keV [t{sub 1/2}=16(1) ms, b{sub p}=4.8(6){percent}] from the {pi}s{sub 1/2} and {pi}h{sub 11/2} states, respectively. {copyright} {ital 1997} {ital The American Physical Society}

Excitations in {sup 192}Po have been studied via in-beam {gamma}-ray spectroscopy following the {sup 164}Er + 164 MeV {sup 32}S reaction. The experiment was performed at the ATLAS facility using ten Compton-suppressed Ge detectors and the Fragment Mass Analyzer. The {alpha} decay of {sup 192}Po has been used to identify prompt {gamma}-ray transitions by means of the recoil decay tagging technique. The first three excited states of {sup 192}Po were established. The particle-core model has been successfully used to model these excitations and the quasiparticle random phase approximation has been applied to extract microscopic wave functions of the 2{sub 1}{sup +} states. {copyright} {ital 1997} {ital The American Physical Society}

In a series of $^{78}\mathrm{Kr}$ bombardments of $^{92}\mathrm{Mo}$ the new isotopes $^{166}\mathrm{Pt}$ and $^{167}\mathrm{Pt}$ were identified via their $\ensuremath{\alpha}$-decay properties. The $\ensuremath{\alpha}$-decay energies and half-lives of these two nuclides are as follows. (1) $^{166}\mathrm{Pt}$, ${E}_{\ensuremath{\alpha}}=7110(15)$ keV, ${T}_{\frac{1}{2}}=0.3(1)$ ms, and (2) $^{167}\mathrm{Pt}$, ${E}_{\ensuremath{\alpha}}=6988(10)$ keV, ${T}_{\frac{1}{2}}=0.7(2)$ ms. Also, the half-life of $^{168}\mathrm{Pt}$, which was previously unknown, was determined to be 2.0(4) ms. In a separate but concurrent experiment involving $^{78}\mathrm{Kr}$ + $^{96}\mathrm{Ru}$ reactions, $^{170}\mathrm{Pt}$ was made and a half-life of 14.7(5) ms was measured for it; the one published value is ${6}_{\ensuremath{-}2}^{+5}$ ms. Results for $^{162\ensuremath{-}164}\mathrm{Os}$ contained in the same data sets were also analyzed and by using mother-daughter correlations, the $\ensuremath{\alpha}$ branches of $^{162,163,164}\mathrm{Os}$ were established to be near 100%.

The new proton radioactivity ${}^{185m}\mathrm{Bi}$ has been observed, produced via the ${}^{95}\mathrm{Mo}{(}^{92}\mathrm{Mo},pn{)}^{185}\mathrm{Bi}$ reaction. Its decay proceeds from the low-lying ${\frac{1}{2}}^{+}$ intruder state in ${}^{185}\mathrm{Bi}$ to the ${}^{184}\mathrm{Pb}$ ground state with the emission of a proton of energy $1.585\ifmmode\pm\else\textpm\fi{}0.009\mathrm{MeV}$ and a half-life of $44\ifmmode\pm\else\textpm\fi{}16\ensuremath{\mu}\mathrm{s}$. This marks the first observation of proton radioactivity above the $Z\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}82$ closed shell, and it has been used to obtain the admixture of a ${0}^{+}$ intruder state in ${}^{184}\mathrm{Pb}$ into the ${}^{184}\mathrm{Pb}$ ground-state wave function.

The isotope {sup 181}Pb was produced in {sup 92}Mo bombardments of {sup 90}Zr and, together with other reaction products, was passed through a recoil mass separator and implanted in a double-sided silicon strip detector for {alpha}-particle assay. The half-life and energy of the main {sup 181}Pb {alpha} transition were determined to be 45 (20) ms and 7065 (20) keV, respectively. This {sup 181}Pb {ital E}{sub {alpha}} agrees with one previously measured value [7044 (15) keV], but not with the one [7211 (10) keV] used as input to the 1993 Atomic Mass Evaluation. The 6180-keV {alpha} transition assigned to {sup 181}Tl by Bolshakov {ital et} {ital al}. was observed, but the 6566-keV {alpha} particles ascribed to a 2.7-ms level in {sup 181}Tl by Schneider were not. {copyright} {ital 1996 The American Physical Society.}

The $\ensuremath{\alpha}$ decays of the two neutron-deficient nuclei ${}^{172}\mathrm{Hg}$ and ${}^{173}\mathrm{Hg}$ were observed for the first time using the ${}^{78}\mathrm{Kr}{(}^{96}\mathrm{Ru},2n)$ and ${}^{80}\mathrm{Kr}{(}^{96}\mathrm{Ru},3n)$ reactions, respectively. The reaction products were dispersed according to their mass-to-charge state ratios in the Argonne Fragment Mass Analyzer and implanted in a double-sided silicon strip detector, where their subsequent decays were studied using spatial and time correlations between implants and decays. A half-life of ${250(}_{\ensuremath{-}90}^{+350}) \ensuremath{\mu}\mathrm{s}$ and an energy of 7350(12) keV were deduced for the $\ensuremath{\alpha}$ decay of ${}^{172}\mathrm{Hg}$. In ${}^{173}\mathrm{Hg}$ the half-life was measured to be ${0.93(}_{\ensuremath{-}0.26}^{+0.57}) \mathrm{ms}$ and the corresponding energy is 7211(11) keV. In addition, the half-life and energy of the $\ensuremath{\alpha}$ decay of ${}^{174}\mathrm{Hg}$ were measured more precisely. The reduced widths deduced for these Hg isotopes indicate that the observed decays correspond to unhindered $\ensuremath{\Delta}l=0$ transitions. The $\ensuremath{\alpha}$-decay Q values are compared with the values calculated using mass tables by M\"oller and Nix, and by Liran and Zeldes. The latter mass tables show better agreement with the data.

The proton-rich isotopes ${}^{180}\mathrm{Pb},$ ${}^{182}\mathrm{Pb}$, and ${}^{184}\mathrm{Pb}$ were produced in ${}^{92}\mathrm{Mo}$ bombardments of ${}^{90}\mathrm{Zr},$ ${}^{92}\mathrm{Zr}$, and ${}^{94}\mathrm{Zr}$, respectively, and their $\ensuremath{\alpha}$-decay properties were investigated with the use of a fragment mass analyzer and a double-sided Si strip detector. These data yielded unambiguous identifications of ${}^{180}\mathrm{Pb}$ and ${}^{182}\mathrm{Pb}$ and half-lives for all three Pb nuclei that are more precise than previously available values. An examination of $\ensuremath{\alpha}$ reduced widths in the Pb mass region leads to the conclusion that the $Z=82$ shell gap is greatly reduced for neutron numbers midway between 82 and 126. Available mass data, manifested in $\ensuremath{\Delta}{Q}_{\ensuremath{\alpha}}$ values and two-proton separation energies of even-even nuclei with the same neutron numbers, support this conclusion.

Fine structure in the α decay of 192Po has been studied in the reaction of 36Ar on 160Dy at 176 MeV. Evaporation residues were selected in-flight using the Argonne Mass Analyzer and implanted into a double sided silicon strip detector. The correlation technique between implants and subsequent decays was used to observe fine structure in the α decay of 192Po leading to the identification of an excited 0+ state in 188Pb at 571(31) keV. The half-life of 192Po has been determined to be 33.2(14) ms. The observation of a low-lying 0+ state is discussed in terms of proton particle-hole pair excitations across the Z=82 shell gap. The small hindrance factor to the excited 0+ state relative to the ground state supports the picture of shape coexistence in light even-even Po isotopes.

Intruder state excitation energies in odd-mass nuclei just outside a closed proton shell plotted versus neutron number generally exhibit parabola-shaped curves with minima near neutron mid-shells. The Bi isotopes, however, do not seem to follow this trend. Recent experiments performed at Argonne National Laboratory have identified the previously unobserved {sup 187}Bi ground state (h{sub 9/2}) to {sup 183}TI ground state s{sub 1/2} {alpha} transition. Its energy when combined with those of two earlier known transitions, namely {sup 187}Bi (h{sub 9/2}) {yields} {sup 183m}Tl (h{sub 9/2}) and {sup 187m}Bi (s{sub 1/2}) {yields} {sup 183}Tl(s{sub 1/2}), establishes the excitation energies of the {sup 183m}Tl and {sup 187m}Bi to be 620(20) keV and 110(20) keV, respectively. This value for {sup 187m}Bi is 80 keV lower than the excitation energy of the same intruder level in {sup 189}Bi. Implications of this result with respect to intruder-state systematics are discussed.

In a series of experiments at the Argonne ATLAS Accelerator Facility, several α emitters near the proton drip line were produced with fusion evaporation reactions, separated from the beam and dispersed in M/Q with a recoil mass spectrometer, and implanted and studied in a double-sided silicon strip detector. In 78Kr bombardments of 92Mo and 96Ru, the new isotopes 166Pt and 167Pt were identified via their α-decay properties and more accurate half-lives were measured for 168Pt and 170Pt. The light isotopes of lead, 180Pb, 182Pb, and 184Pb were produced in Mo bombardments of Zr target nuclei. The α-decay energies and half-lives of the new isotopes are as follows: 1) 166Pt, Eα=7110(15) keV, T1/2=0.3(1) ms; and 2) 167Pt, Eα=6988(10) keV, T1/2=0.7(2) ms. Also, the half-life of 168Pt, which was previously unknown, was determined to be 2.0(4) ms and that of 170Pt was observed to be 14.7(5) ms. The tentative α-decay energies and half-lives of the even Pb isotopes are: 1) 184Pb, Eα=6625(10) keV, T1/2=500(25) ms; 2)...

The α decay of 186Bi was investigated via the 97Mo(92Mo, p2n) reaction and the use of a fragment mass analyzer with a double-sided Si strip detector. In contrast to an earlier work wherein only one α transition was reported, we observed two transitions arising from two isomers in 186Bi with energies and half-lives of: 7158(20) keV, T1/2 = 15.0(17) ms; and 7261(20) keV, T1/2 = 9.8(13) ms.

Fine structure in theα decay of192Po has been observed leading to the identification of an excited 0+ state in188Pb at 571 (31) keV. The half-life of192Po has been determined precisely to be 33.2 (14) ms and theα-branching ratio of the daughter188Pb has been deduced to be 0.085 (13).