Search

Precise measurements of the intensities of superallowed Fermi 0+ → 0+β-decays have provided a powerful test of the CVC hypothesis at the level of 3×10-4 and also led to a result in disagreement with unitarity for the CKM matrix at the 98% confidence level. It is essential to address possible trivial explanations for the apparent non-unitarity such as uncertainties in the isospin symmetry-breaking corrections. We have carefully studied the 74Rb →74Kr β-decay in order to measure the non-analog β-decay branching to the 0+ state at 508 keV in 74Kr. We have determined that this branching is < 3×10-4, far smaller than any published theoretical estimate. We also show that high-precision, complete spectroscopy, measuring the major β-branches to excited 0+ and 1+ states, must be performed if one is to obtain a meaningful branching ratio to the excited 0+ state and concomitantly deal, in a substantial way, with the possibility of β feeding to an array of 1+ states.

We report results on the ratio of mid-rapidity anti-proton to proton yields in Au+Au collisions at $\rts = 130$ GeV per nucleon pair as measured by the STAR experiment at RHIC. Within the rapidity and transverse momentum range of $|y

Presently, the world data for superallowed {beta} decay leads to a result in disagreement (at the 98% confidence level) with the predictions of the minimal standard model for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. Precise data for the superallowed 0{sup +}{yields}0{sup +} {beta} decay of {sup 74}Rb would provide a critical test of the nucleus-dependent isospin symmetry-breaking corrections that must be calculated for these superallowed Fermi {beta} decays. The present work reports the first precise measurement of the half-life for {sup 74}Rb (t{sub 1/2}=64.761{+-}0.031 ms ). The data were obtained at the radioactive beam facility (ISAC) at TRIUMF using a beam of {approx}4000 {sup 74}Rb ionss{sup -1} .

Elliptic flow from nuclear collisions is a hadronic observable sensitive to the early stages of system evolution. We report first results on elliptic flow of charged particles at midrapidity in Au+Au collisions at √(sNN) = 130 GeV using the STAR Time Projection Chamber at the Relativistic Heavy Ion Collider. The elliptic flow signal, v₂, averaged over transverse momentum, reaches values of about 6% for relatively peripheral collisions and decreases for the more central collisions. This can be interpreted as the observation of a higher degree of thermalization than at lower collision energies. Pseudorapidity and transverse momentum dependence of elliptic flow are also presented.

A light-isotope radioactive ion-beam capability has been added to the 88-in. Cyclotron at Lawrence Berkeley National Laboratory by coupling to the production cyclotron of the Berkeley Isotope Facility. The connection required the development and construction of a 350 m gas transport system between the two accelerators as well as automated cryogenic separation of the produced activity. The "rst beam developed, 11C, has been successfully accelerated with an on-target intensity of 1]108 ions/s at energies of around 10 MeV/u. ( 2000 Elsevier Science B.V. All rights reserved.

An axion detector consisting of a tunable high-Q cavity, a superconducting magnet, and a superheterodyne receiver with an ultra-low noise pre-ampli"er has been built to search for galactic halo axions in the mass range of 1.3}13 leV. The detector instrumentation, search process, and data analysis are described. For the "rst time, this class of detector has reached su$cient sensitivity to detect halo axions with high con"dence. ( 2000 Elsevier Science B.V. All rights reserved.

A search for proton decay from a predicted (19) /(2) {sup {minus}} isomer of {sup 77}Rb has been performed. Products of the {sup 40}Ca+{sup 40}Ca reaction at average laboratory bombardment energies of 145 and 160 MeV were transported by a helium jet to an array of particle-identification telescopes. No evidence of proton emission from the predicted isomer was observed. In a second measurement, mass 77 residues of the {sup 40}Ca+{sup nat}Ca reaction at an average laboratory bombardment energy of 132 MeV were separated using the on-line mass separator RAMA. The yields of {sup 77}Rb and {sup 77}Sr were monitored by observation of beta-delayed gamma rays; 1.6{times}10{sup 6} atoms of {sup 77}Rb were transported to the detectors. A single particle-identification telescope subtending 23{percent} of 4{pi} sr again showed no evidence of proton emission from the predicted isomer. {copyright} {ital 1998} {ital The American Physical Society}

Six improved low-energy gas- ΔE /gas- ΔE /Si- E particle-identification telescopes have been incorporated into an array. Calibration experiments have shown that these telescopes are capable of detecting and identifying protons with energies as low as ∼180 keV and alpha particles with energies as low as ∼450 keV, even when operating in a high-radiation environment. Methods of calibration at very low energies have been developed and tested. A survey of the beta-delayed proton emitters 21 Mg, 29 S, 40 Sc and 41 Ti revealed no new intense proton groups at low energies.

\ensuremath{\beta}-delayed proton decays of the nuclides $^{27}\mathrm{P}$ and $^{31}\mathrm{Cl}$ were measured using the helium-jet recoil collection technique and low-energy particle identification detector telescopes. In $^{27}\mathrm{P}$, two new proton groups at 466\ifmmode\pm\else\textpm\fi{}3 keV and 612\ifmmode\pm\else\textpm\fi{}2 keV, with intensities of 9\ifmmode\pm\else\textpm\fi{}2% and 97\ifmmode\pm\else\textpm\fi{}3% relative to the main (100%) group at 731\ifmmode\pm\else\textpm\fi{}2 keV, were discovered. Additionally, during the $^{27}\mathrm{P}$ experiments, a new proton transition was identified following the \ensuremath{\beta} decay of $^{28}\mathrm{P}$. This group, at a proton energy of 1452\ifmmode\pm\else\textpm\fi{}4 keV, had a 2\ifmmode\pm\else\textpm\fi{}1% intensity relative to the 100% group at 679\ifmmode\pm\else\textpm\fi{}1 keV. A total $^{27}\mathrm{P}$ \ensuremath{\beta}-delayed proton branch of 0.07% was estimated. The experimental Gamow-Teller \ensuremath{\beta}-decay strengths of the observed transitions from $^{27}\mathrm{P}$ were compared to results from shell model calculations. A search for new proton transitions in $^{31}\mathrm{Cl}$, the next member of this A=4n+3, ${\mathit{T}}_{\mathit{z}}$=-3/2 series, was unsuccessful. However, several proton peaks that had been previously assigned to $^{31}\mathrm{Cl}$ decay were shown to be from the decay of $^{25}\mathrm{Si}$. \textcopyright{} 1996 The American Physical Society.

Utilizing the [sup 24]Mg([ital p],[ital n]) reaction and a low-energy proton detector ball, beta-delayed proton emission from [sup 24]Al has been observed in the form of a quasicontinuum of protons from [similar to]300 to 1100 keV. By making a comparsion with a previously known [sup 24]Al beta-delayed alpha branching ratio, a branching ratio for beta-delayed proton emission of (1.2[plus minus]0.3)[times]10[sup [minus]5] has been determined.

We propose a large-scale experimental search for dark-matter axions which may constitute an important fraction of our own galactic halo. As shown by Sikivie,1 dark-matter axions may be detected by their stimulated conversion into monochromatic microwave photons in a tunable high-Q cavity inside a strong magnetic field. The principal improvement in power sensitivity over two earlier pilot experiments (×25) derives from the large-volume high field superconducting magnet (the NASA SUMMA coils). The improvement in mass range (1.5 to 12.6 μeV) will result from the use of several microwave cavity arrays, of 2n cavities each, over the course of the experimental program, rather than a single cavity. We are participating in a joint venture with the Institute for Nuclear Research of the Russian Academy of Sciences to do R&D on metalized precision-formed ceramic microwave cavities for the axion search.

The ${\mathit{T}}_{\mathit{z}}$=-3/2, A=4n+1 nuclide $^{73}\mathrm{Sr}$ produced in the $^{40}\mathrm{Ca}$${(}^{36}$Ar,3n) reaction has been observed via beta-delayed proton emission. A single proton group at a laboratory energy of 3.75\ifmmode\pm\else\textpm\fi{}0.04 MeV has been observed, corresponding to decay of the T=3/2 isobaric analog state in $^{73}\mathrm{Rb}$ to the ground state of $^{72}\mathrm{Kr}$. Combining this measurement with a Coulomb displacement energy calculation yields a mass excess for $^{73}\mathrm{Sr}$ of -31.82\ifmmode\pm\else\textpm\fi{}0.24 MeV based on a predicted mass for $^{72}\mathrm{Kr}$ of -53.94\ifmmode\pm\else\textpm\fi{}0.24 MeV.

We have used the 40 Ca( 36 Ar, 2pn) reaction to study the low-lying level structure of 73 Kr. By utilizing a bombarding energy at the Coulomb barrier, the relative cross section for this channel was enhanced to a few percent of the total reaction cross section. Levels in 73 Kr were assigned based primarily upon observed neutron-gamma-gamma coincidences and upon comparisons of these newly assigned transition cross sections with those from known nuclei.

We have measured the electron-capture decay branch of $^{100}\mathrm{Tc}$ to be (1.8\ifmmode\pm\else\textpm\fi{}0.9)\ifmmode\times\else\texttimes\fi{}${10}^{\mathrm{\ensuremath{-}}3}$%, from which we deduce logft=4.${45}_{\mathrm{\ensuremath{-}}0.30}^{+0.18}$. This indicates that a two-step process connecting only the ground states of $^{100}\mathrm{\ensuremath{-}}^{100}$Tc${\mathrm{\ensuremath{-}}}^{100}$Ru can account for the measured 2\ensuremath{\nu} double-\ensuremath{\beta}-decay rate of $^{100}\mathrm{Mo}$.

The [ital T][sub [ital Z]]=[minus]3/2, [ital A]=4[ital n]+1 nuclide [sup 65]Se produced in the [sup 40]Ca([sup 28]Si,3[ital n]) reaction has been observed via beta-delayed proton emission. A single proton group at 3.55[plus minus]0.03 MeV has been observed, corresponding to the decay of the [ital T]=3/3 isobaric analog state in [sup 65]As to the ground state of [sup 64]Ge. Combining this measurement with a Coulomb displacement energy calculation yields a mass excess for [sup 65]Se of [minus]33.41[plus minus]0.26 MeV.

We have measured the beta-delayed proton spectrum arising from $^{25}\mathrm{Si}$ produced in the $^{24}\mathrm{Mg}$${(}^{3}$He,2n) reaction. Utilization of a new low-energy proton detector has permitted the observation of protons from 250 to 6000 keV. Most proton groups have been placed into a decay scheme by using penetrability calculations and transitions from the mirror beta decay, $^{25}\ensuremath{\rightarrow}^{25}$Mg. This placement permits the construction of the Gamow-Teller strength function which we compare to a beta strength function calculated from complete-space s-d shell model wave functions.

The beta-delayed two-proton decay of theT z =−5/2 nuclide39Ti has been observed. The39Sc isobaric analog state has been calculated to lie at 8.82 MeV using the measured two-proton sum energy of 4750±40 keV for its decay to the37K ground state. Combining this excitation energy with a Coulomb displacement energy calculation has lowered the energy available for ground state two-proton emission of39Ti from 760 to 530 keV.

An attempt to confirm the reported direct one-proton and two-proton decays of the (21+) isomer at 6.7(5) MeV in 94Ag has been made. The 0.39(4) s half-life of the isomer permitted use of a helium-jet system to transport reaction products from the 40Ca + (nat)Ni reaction at 197 MeV to a low-background area; 24 gas DeltaE-(Si)E detector telescopes were used to identify emitted protons down to 0.4 MeV. No evidence was obtained for two-proton radioactivity with a summed energy of 1.9(1) MeV and a branching ratio of 0.5(3)%. Two groups of one-proton radioactivity from this isomer had also been reported; our data confirm the lower energy group at 0.79(3) MeV with its branching ratio of 1.9(5)%.

The ground state proton decays of {sup 65}As and {sup 69}Br have been searched for in {sup 28}Si and {sup 32}S bombardments of a natural calcium target. These studies employed a newly developed rapidly rotating recoil-catcher wheel and a low-energy particle-identification telescope. No proton groups that could be assigned to either of these nuclides were observed. The minimum detectable limits indicate that {sup 65}As and {sup 69}Br either decay predominantly by beta emission or have half-lives less than 100 {mu}s. The overall evidence strongly indicates that {sup 65}As predominantly beta decays.

There is a qualitative disagreement between the Gamow-Teller strength function extracted from the \ensuremath{\beta}-delayed proton decay of $^{37}\mathrm{Ca}$ and that estimated using the $^{37}\mathrm{Cl}$(p,n) reaction. Adelberger and Haxton have shown that this could be explained by the strong tendency of high energy states in $^{37}\mathrm{K}$ to proton decay to $^{36}\mathrm{Ar}$ in its first excited state. We present the results of an experiment confirming this idea. By detecting proton-\ensuremath{\gamma} coincidences we determined that the fraction of $^{37}\mathrm{Ca}$ decays that feed the first excited state of $^{36}\mathrm{Ar}$ is 2.9\ifmmode\pm\else\textpm\fi{}0.8 %. This should be compared to a shell model prediction of 1.80\ifmmode\pm\else\textpm\fi{}0.20 %. We also present some information on the \ensuremath{\beta} decay of $^{25}\mathrm{Si}$ obtained as a by- product of our experiment.

With the use of mass-separated sources, the \ensuremath{\beta}-decay properties of $^{151}\mathrm{Yb}$ and $^{151}\mathrm{Tm}$ were investigated. The ${\mathit{h}}_{11/2}$, ${\mathit{s}}_{1/2}$, ${\mathit{d}}_{3/2}$, ${\mathit{d}}_{5/2}$, and ${\mathit{g}}_{7/2}$ single-proton states in $^{151}\mathrm{Tm}$ and the ${\mathit{f}}_{7/2}$, ${\mathit{h}}_{9/2}$, ${\mathit{p}}_{3/2}$, ${\mathit{i}}_{13/2}$, and probably the ${\mathit{p}}_{1/2}$ single-neutron states in $^{151}\mathrm{Er}$ were identified. Systematics of neutron states in even-Z N=83 isotones are compared with predictions of spherical Hartree-Fock-Bogoliubov calculations.

A 120 MeV $^{15}\mathrm{O}$ radioactive ion beam with an intensity on target of $4.5\ifmmode\times\else\texttimes\fi{}{10}^{4}$ pps has been developed at the 88-Inch Cyclotron at the Lawrence Berkeley National Laboratory. This beam has been used to study the level structure of $^{16}\mathrm{F}$ at low energies via the $p$($^{15}\mathrm{O}$, $p$) reaction using the thick target inverse kinematics method on a polyethylene target. The experimental excitation function was analyzed using $R$-matrix calculations. Significantly improved values for the level widths of the four low-lying states in $^{16}\mathrm{F}$ are reported. Good agreement with the theoretical spectroscopic factors is also obtained.

The level structure of {sup 12}N has been investigated from 2.2 to 11.0 MeV in excitation energy using a {sup 11}C + p resonance interaction with thick targets and inverse kinematics. Excitation functions were fitted using an R-matrix approach. Sixteen levels in {sup 12}N were included in the analysis, several of them are new. Spin-parity assignments, excitation energies and widths are proposed for these levels. To fit the high energy part of the excitation function, imaginary phase shifts had to be added to the phase shifts generated by the hard sphere scattering.

The isotope {sup 190}Po was produced in the {sup 144}Sm({sup 48}Ti,2{ital n}) reaction and its {alpha}-decay energy and half-life were measured to be 7.49(4) MeV and 2.0{sub {minus}1.0}{sup +0.5} ms, respectively. These data compare as follows with preliminary values reported by Quint {ital et} {ital al}.: {ital E}{sub {alpha}}=7482(20) keV and a {ital T}{sub 1/2}=9.6{sub {minus}4.4}{sup +47} ms. While the two energies agree, the half-lives differ by a factor of almost 5. The earlier data yield an {alpha} reduced width which is much smaller than those of neighboring nuclides; our {sup 190}Po energy and half-life result in a width that fits the overall {alpha}-decay-rate systematics in the mass region above the {ital Z}=82 closed shell. {copyright} {ital 1996 The American Physical Society.}

In a series of {sup 48}Ti bombardments of {sup 144}Sm the decay energy of the {sup 189}Bi{sup {ital m}} ({pi}{ital s}{sub 1/2}) {alpha} transition that proceeds to the ({pi}{ital s}{sub 1/2}) ground state of {sup 185}Tl was measured to be 7.30(4) MeV. This result establishes the excitation energy of {sup 189}Bi{sup {ital m}} as 190(40) keV rather than the adopted 92(10)-keV value. Our data indicate a leveling off in excitation energy at {ital N}{approx}106 for the {ital s}{sub 1/2} intruder state in the odd-{ital A} Bi isotopes rather than a continued drop at that neutron number as inferred by Coenen {ital et} {ital al}. in their discussion of intruder state systematics in the Pb region. Consequences of this discrepancy for the adopted excitation energy of the {pi}{ital s}{sub 1/2} isomer in {sup 187}Bi are discussed.

An experiment proposed to search for dark-matter axions in the mass range 0.6-16 mu eV is described. The method is based on the Primakoff conversion of axions into monochromatic microwave photons inside a tunable microwave cavity in a large-volume high-field magnet. This proposal capitalizes on the availability of two Axicell magnets from the MFTF-B fusion machine at Lawrence Livermore National Laboratory. Assuming a local dark-matter density in axions of rho /sub a/=0.3 GeV/cm/sup 3/, the axion would be found or ruled out at the 97% c.l. in the above mass range in 48 months. >

We present the first measurement of midrapidity vector meson phi production in Au+Au collisions at RHIC (roots(NN)=130 GeV) from the STAR detector. For the 11% highest multiplicity collisions, the slope parameter from an exponential fit to the transverse mass distribution is T=379+/-50(stat)+/-45(syst) MeV, the yield dN/dy=5.73+/-0.37(stat)+/-0.69(syst) per event, and the ratio N-phi/Nh- is found to be 0.021+/-0.001(stat)+/-0.004(syst). The measured ratio N-phi/N-h(-) and T for the phi meson at midrapidity do not change for the selected multiplicity bins.

We report first results on elliptic flow of identified particles at midrapidity in Au+Au collisions at √(sNN)= 130 GeV using the STAR TPC at RHIC. The elliptic flow as a function of transverse momentum and centrality differs significantly for particles of different masses. This dependence can be accounted for in hydrodynamic models, indicating that the system created shows a behavior consistent with collective hydrodynamical flow. The fit to the data with a simple model gives information on the temperature and flow velocities at freeze-out.

We have built and operated a large-scale axion detector, based on a method originally proposed by Sikivie, to search for halo axions. The apparatus consists of a cylindrical tunable high-Q microwave cavity threaded axially by a static high magnetic field. This field stimulates axions that enter the cavity to convert into single microwave photons. The conversion is resonantly enhanced when the cavity resonant frequency is near the axion rest mass energy. The experiment is cooled to 1.5 K and the electromagnetic power spectrum emitted by the cavity is measured by an ultra-low-noise microwave receiver. The axion would be detected as excess power in a narrow line within the cavity resonance. The apparatus has achieved a power sensitivity better than ${10}^{\ensuremath{-}23} \mathrm{W}$ in the mass range $2.9--3.3 \ensuremath{\mu}\mathrm{eV}.$ For the first time the rf cavity technique has explored plausible axion models, assuming axions make up a significant fraction of the local halo density. The experiment continues to operate and will explore a large part of the mass in the range of $1--10 \ensuremath{\mu}\mathrm{eV}$ in the near future. An upgrade of the experiment is planned with dc superconducting quantum interference device microwave amplifiers operating at a lower physical temperature. This next generation detector would be sensitive to even more weakly coupled axions contributing only fractionally to the local halo density.

The minimum-bias multiplicity distribution and the transverse momentum and pseudorapidity distributions for central collisions have been measured for negative hadrons (h{sup -}) in Au+Au interactions at s{sub NN}=130 GeV . The multiplicity density at midrapidity for the 5% most central interactions is dN{sub h{sup -}}/d{eta}|{sub {eta}=0} =280{+-}1(stat){+-}20(syst) , an increase per participant of 38% relative to p{bar p} collisions at the same energy. The mean transverse momentum is 0.508{+-}0.012 GeV/c and is larger than in central Pb+Pb collisions at lower energies. The scaling of the h{sup -} yield per participant is a strong function of p{sub {perpendicular}} . The pseudorapidity distribution is almost constant within |{eta}

Most of the mass of the Milky Way galaxy is contributed by its halo, presumably in the form of non-interacting cold dark matter. The axion is a compelling cold dark matter candidate. We report results from a search which probes the local galactic halo axion density using the Sikivie RF cavity technique. Candidates over the frequency range 550$$ $\le$ f $\le$$$ 810 MHz (2.3$$ $\mu$eV $\le$$$ m$_{a}$ $\le$ 3.4 $\mu$eV) were investigated. The absence of a signal suggests that KSVZ axions contribute no more than 0.45 GeV/cm$^3$ of mass density to the local dark matter halo over this mass range., Comment: 10 pages (includes 3 figures)

Presently, the world data for superallowed beta decay leads to a result in disagreement (at the 98% confidence level) with the predictions of the minimal standard model for the unitarity of the Cabibbo-Kobayashi-Maskawa matrix. Precise data for the superallowed 0(+)--0(+) beta decay of (74)Rb would provide a critical test of the nucleus-dependent isospin symmetry-breaking corrections that must be calculated for these superallowed Fermi beta decays. The present work reports the first precise measurement of the half-life for (74)Rb ( t(1/2) = 64.761+/-0.031 ms). The data were obtained at the radioactive beam facility (ISAC) at TRIUMF using a beam of approximately 4000 (74)Rb ions s(-1).

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.

BEARS is an initiative to develop a radioactive ion-beam capability at Lawrence Berkeley National Laboratory. The aim is to produce isotopes at an existing medical cyclotron and to accelerate them at the 88″ Cyclotron. To overcome the 300-meter physical separation of these two accelerators, a carrier-gas transport system will be used. At the terminus of the capillary, the carrier gas will be separated and the isotopes will be injected into the 88″ Cyclotron’s Advanced Electron Cyclotron Resonance ion source. The first radioactive beams to be developed will include 20-min 11C and 70-sec 14O, produced by (p, n) and (p, α) reactions on low-Z targets. Tests at the 88″ Cyclotron lead to projections of initial 11C beams of 2×108 ions/sec 14O beams of 1×106 ions/sec. Construction of BEARS is expected to be completed in the spring of 1999.

BEARS (Berkeley Experiments with Accelerated Radioactive Species) is an initiative to develop a radioactive ion-beam capability at Lawrence Berkeley National Laboratory. The aim is to produce isotopes at an existing medical cyclotron and to accelerate them at the 88 inch Cyclotron. To overcome the 300-meter physical separation of these two accelerators, a carrier-gas transport system will be used. At the terminus of the capillary, the carrier gas will be separated and the isotopes will be injected into the 88 inch Cyclotron`s Electron Cyclotron Resonance (ECR) ion source. The first radioactive beams to be developed will include 20-min {sup 11}C and 70-sec {sup 14}O, produced by (p,n) and (p,{alpha}) reactions on low-Z targets. A test program is currently being conducted at the 88 inch Cyclotron to develop the parts of the BEARS system. Preliminary results of these tests lead to projections of initial {sup 11}C beams of up to 2.5 {times} 10{sup 7} ions/sec and {sup 14}O beams of 3 {times} 10{sup 5} ions/sec.

We report the first results of a high-sensitivity (10^{-23} Watt) search for light halo axions through their conversion to microwave photons. At 90 percent confidence we exclude a KSVZ axion of mass 2.9 x 10^{-6} eV to 3.3 x 10^{-6} eV as the dark matter in the halo of our Galaxy., Comment: 11 text pages, 4 figures (figures 2 and 3 combined), to be published in Physical Review Letters

Aluminum-23 was produced in two 40 MeV proton bombardments of Mg targets at LBNL’s 88-Inch Cyclotron. Reaction products were transported by helium jet to a detection chamber. They were observed by two low-energy particle-identification telescopes; each consisted of two gas-ΔE detectors, a thin (

The experimental investigation of the decays of proton-rich light nuclei has provided a wealth of spectroscopic information. This includes details of energy levels, spins, isospins, masses, half-lives and other decay properties. In light nuclei, total beta decay energies rapidly increase as one moves away from the valley of beta-stable nuclides towards the proton drip line. This opens up decay modes, such as beta-delayed proton and beta-delayed alpha emission, which are very sensitive probes of nuclear structure. There have been several recent articles that review the decay properties of proton drip-line nuclei. The beta decays of proton-rich light nuclei (with T{sub z} {le} -1/2) are characterized by two general features. The first is a fast superallowed Fermi transition to the isobaric analog state (IAS) in the beta daughter. If the IAS is above the proton separation energy, the beta-decaying precursor nuclide is classified as a strong beta-delayed proton emitter. The A = 4n+1, T{sub z}=-3/2 series of nuclei from {sup 17}Ne to {sup 73}Sr (with the exception of the unobserved member {sup 69}Kr), are all strong {Beta}p emitters. In contrast, the A = 4n, T{sub z}=-1 series of nuclei, from {sup 24}Al to {sup 48}Mn are designated as weak {Beta}p emitters since the IAS in the beta daughters is bound with respect to proton emission.

The efficiency of the Homestake Mine 37Cl solar v-detector is calibrated[1] using transition rates measured in the β+ decay of 37Ca.

We have investigated nuclei close to the proton drip line by using heavy‐ion fusion reactions to produce extremely neutron‐deficient nuclides. Their nuclear decay properties were studied by using on‐line isotope separators at Oak Ridge (UNISOR) and Berkeley (OASIS), the Oak Ridge National Laboratory velocity filter, and a fast helium‐gas‐jet transport system at Lawrence Berkeley Laboratory 88‐inch Cyclotron. Many isotopes, isomers, and β‐delayed‐proton and α‐particle emitters were discovered. This contribution summarizes three topics that are part of our overall program: (a) decay rates of even‐even α‐particle emitters, (b) mass excesses of 181Pb, 182Pb, and 183Pb, and (c) β‐delayed proton emitters near N=82.

In this paper we review the general physics learned at the proton drip line. The extraordinary experimental problems which must be overcome are discussed in addition to several novel solutions. Finally, results of several recent experiments to look for ground state one-and two-proton emission are discussed.

Theα decay of the new isotope180Pb was observed in40Ca bombardments of144Sm:Eα = 7.23(4)MeV, and,T1/2=(4−2+4)ms. With this decay energy and the known mass of176Hg, the mass excess of180Pb was calculated to be −1.98(5)MeV.

The α decay of the new isotope 180Pb was observed in 40Ca bombardments of 144Sm: E α = 7.23(4) MeV, and, \({T_{1/2}} = \left( {4_{ - 2}^{ + 4}} \right){\text{ ms}}\). With this decay energy and the known mass of 176Hg, the mass excess of 180Pb was calculated to be −1.98(5) MeV.

With the aid of an on-line isotope separator the decay of /sup 147/Dy to levels in /sup 147/Tb was investigated in a series of heavy-ion bombardments of rare earth targets. These data allows us to identify the s/sub 1/2/, d/sub 3/2/, d/sub 5/2/, and g/sub 7/2/ proton orbitals in /sup 147/Tb, a nucleus with one proton beyond the /sup 146//sub 64/Gd/sub 82/ core.

The decay of the $T=\frac{5}{2}$ isobaric analog state in $^{35}\mathrm{K}$ at 9053 \ifmmode\pm\else\textpm\fi{} 45 keV, fed by the superallowed $\ensuremath{\beta}$ decay of 50 \ifmmode\pm\else\textpm\fi{} 30-ms $^{35}\mathrm{Ca}$, results in two-proton emission to both the ground and the first excited states of $^{33}\mathrm{Cl}$. The measured energy correlations between the two decay protons indicate a sequential-decay mechanism. From the isobaric-multiplet mass equation, a mass excess of 4453 \ifmmode\pm\else\textpm\fi{} 60 keV can be predicted for the ground state of $^{35}\mathrm{Ca}$.

The masses of /sup 76/Kr and /sup 74/Kr were measured utilizing the /sup 78/Kr(/sup 4/He,/sup 6/He) and /sup 78/Kr(/sup 4/He,/sup 8/He) reactions. Mass excesses of -68971 +- 13 and -62210 +- 75 keV were obtained for /sup 76/Kr and /sup 74/Kr, respectively, and found to compare favorably with some mass formulae predictions, but not with others. Speculations about shape differences in light krypton and rubidium isotopes are presented as they relate to various mass formulae.