Search

A low-background gamma-ray detector of NaI(Tl) comprising a core surrounded by an annulus was developed for nuclear astrophysics experiments with radioactive ion beams, mostly for detailed studies of low-energy radiative capture reactions that involve proton and alpha particles. Monte Carlo simulations using EGS4 were performed to calculate the full-energy detection efficiency. The background was satisfactorily reduced as designed. The best S / N ratio for very low-event rate was obtained using the annulus in anticoincidence with the core. A consideration of an experiment of astrophysical interest, the 19 Ne(p,γ) 20 Na reaction, is also briefly discussed.

A search for {sigma} hypernuclear states in p -shell hypernuclei has been performed with the Moby Dick spectrometer and the low energy separated beam (LESB-2) at the Brookhaven Alternating Gradient Synchrotron (BNL AGS). Unlike some previously published reports, no narrow states have been observed for targets of {sup 6}Li and {sup 9}Be in (K{sup -}, {pi}{sup {+-}}) reactions, either for bound state or continuum regions. Together with the previously reported J=0 , T=1/2 bound state in {sup 4}{sub {sigma}} He , these results demonstrate the crucial role of isospin in {sigma} hypernuclei. (c) 1999 The American Physical Society.

We have observed a clear peak below the {Sigma}{sup +} -production threshold in the {sup 4}He( K{sup {minus}},{pi}{sup {minus}}) reaction at 600 MeV/c and {theta}{sub K{pi}}=4{sup {circ}} . This is confirmation of the existence of the bound state of {sup 4}{sub {Sigma}}He , which was reported in the {sup 4}He(stopped K{sup {minus}},{pi}{sup {minus}}) reaction. As in the case of stopped kaons, no such peak was found in the {sup 4}He(K{sup {minus}} ,{pi}{sup +}) spectrum. Quantitatively reliable parameters for this level have been established. The binding energy and the width of the bound state are 4.4{plus_minus}0.3(stat){plus_minus}1(syst ) MeV and 7.0{plus_minus}0.7(stat){sup +1.2}{sub {minus}0.0}(syst) MeV, respectively. {copyright} {ital 1998} {ital The American Physical Society}

A series of experiments were made to investigate the early stage of the rapid-proton process. Specifically, the nuclear reaction chain at N=11 was discussed, including a recent result on 25 Si. A discussion with nova model calculations using the present experimental results is also made.

An ISOL-based radioactive nuclear beam facility is just about to come into operation at INS. The present status of the INS radioactive nuclear beam project is reported. The capability of the facility and possible experiments are also discussed, including research programs of nuclear physics and nuclear astrophysics.

Hypernuclear mass spectra of ${\mathrm{}}_{\mathrm{\ensuremath{\Lambda}}}^{10}$B, ${\mathrm{}}_{\mathrm{\ensuremath{\Lambda}}}^{12}$C, ${\mathrm{}}_{\mathrm{\ensuremath{\Lambda}}}^{28}$Si, ${\mathrm{}}_{\mathrm{\ensuremath{\Lambda}}}^{89}$Y, ${\mathrm{}}_{\mathrm{\ensuremath{\Lambda}}}^{139}$La, and ${\mathrm{}}_{\mathrm{\ensuremath{\Lambda}}}^{208}$Pb were measured by the (${\mathrm{\ensuremath{\pi}}}^{+}$,${\mathit{K}}^{+}$) reaction with an energy resolution of 2 MeV (FWHM). The experiment was carried out with a 1.06 GeV/c ${\mathrm{\ensuremath{\pi}}}^{+}$ beam from the KEK 12-GeV PS and with the superconducting kaon spectrometer (SKS). For light hypernuclei, core-excited states were resolved for the first time. For heavy hypernuclei, peak structure reflecting \ensuremath{\Lambda} shell structure was observed. \textcopyright{} 1996 The American Physical Society.

Experimental studies on bottled neutrons have been carried out using a supermirror turbine facility and are compared with the results of numerical simulations. The gravity effects for 1 m elevation and fall with guides are observed. Measured exhausting and storage lifetimes agree with the numerical results, which indicate the collision loss probability of about 10 −4 to be expected in the bottle studied.

A superconducting kaon spectrometer has been installed in the north experimental hall of the KEK 12-GeV proton synchrotron. The spectrometer was designed to serve for nuclear physics experiments with meson beams in the 1 GeV/c region, particular emphasis being laid on study of Λ-hypernuclei via (π+, K+) reactions. In order to obtain Λ-hypernuclear data with better statistics and energy resolution, it was designed to have a good momentum resolution of 0.1% FWHM and a large acceptance of 100 msr. It consists of a large superconducting dipole magnet, tracking chambers, and trigger counters that can efficiently select kaons from large background of pions and protons. The overall energy resolution for scattering is realized together with a beam-line spectrometer in the K6 beam line, the momentum resolution of which was also designed to be better than 0.1% FWHM. A good energy resolution of better than 2 MeV FWHM has been confirmed in π−-12C elastic scattering and in the (π+,K+) reaction on 12C.

A spectroscopic study of Λ hypernuclei by the ( π + , K + ) reaction has been performed for the wide hypernuclear mass range using a new superconducting kaon spectrometer (INS-SKS) at the KEK 12 GeV PS. A Λ 12 C spectrum with 2 MeV (FWHM) energy resolution was measured and core excited states of Λ 12 C were clearly identified for the first time. It is discussed that the excitation energies and cross sections of these states will be closely related with the choice of ΛN interaction models as well as hypernuclear structure. Hypernuclear spectra of Λ 10 B, Λ 28 Si, Λ 89 Y, Λ 139 La and Λ 208 Pb were also obtained and binding energies of a Λ hyperon were deduced for each Λ orbital. The mass number dependence of the Λ binding energies is, within the present experimental errors, consistent with a calculation based on the Woods-Saxon potential.

A spectroscopic study of the $_{\ensuremath{\Lambda}}^{12}\mathrm{C}$ hypernucleus by the (${\ensuremath{\pi}}^{+}, {K}^{+}$) reaction has been performed using a new superconducting kaon spectrometer (INS-SKS) at the KEK 12 GeV Proton Synchrotron with an energy resolution of 2 MeV (FWHM). In addition to two prominent peaks which correspond to the $s$ and $p$ orbitals of a $\ensuremath{\Lambda}$ hyperon, for the first time two smaller peaks were clearly observed at excitation energies of 2.6 and 6.9 MeV. These two peaks are interpreted as states where the $^{11}\mathrm{C}$ excited core and a $\ensuremath{\Lambda}$ hyperon in the $s$ orbit are weakly coupled. The excitation energies and the cross sections of these peaks provide information on the $\ensuremath{\Lambda}N$ interaction.

Generation of the compression wave by a train entering a tunnel is investigated by model experiments. In the model experiments, the train and the tunnel are represented by an axisymmetric model, a three-dimensional mirror image model and a three-dimensional model. The experimental results indicate that the effect of the three-dimensionality of the train nose shape is approximately 2 % for the pressure gradient of the compression wavefront when the train nose is streamlined, hence without large flow separation around the train nose. Furthermore, the relationship between the pressure gradient of the compression wavefront and the train position in a cross-section at the tunnel portal is clarified.

The first measurement of two-nucleon pion absorption in 4 He at 1 GeV/ c has been performed at the KEK 12 GeV proton synchroton. Both the (π + , pp) and (π + , pn) modes were measured and clearly identified, even at this energy. An isospin dependence was obtained which was different from that in the Δ-energy region.

The computer-controlled instrument for the magnetic measurement of the SKS sector-type superconductivity magnet at KEK is described. The sector-shaped field is measured to a precision on the order of 10/sup -4/ of the maximum field by assemblies of Hall elements. The authors discuss the field measuring instrument, the concept of how to control the instrument and read data, and preliminary results on field mapping. >

A sector-type superconducting spectrometer magnet, called SKS, for nuclear physics experiments in the 1-GeV/c region has been constructed and installed at KEK. It has a maximum central magnetic field of 3 T in a magnet gap of 50 cm, required by properties of high resolution and large acceptance. From another requirement to be movable around a target at a cold state, a flexible transfer line is adopted. The maximum rated current of 500 A is selected to make the heat losses as as small as possible. A small refrigerator is used for thermal insulations at 80 and 20 K in combination with a medium one at 4 K. >

The {sup 20}Ne(p,t)h{sup 18}Ne reaction has been studied in order to investigate the properties of {sup 18}Ne excited states. A missing 3{sup +} state of {sup 18}Ne, which could have a great influence on the {sup 17}F(p,{gamma})h{sup 18}Ne reaction rate, was searched for, but the existence of this state was not clearly verified. The spins and parities of the 5.11- and 5.15-MeV states were assigned tentatively by angular distribution measurements, as 2{sup +} and 3{sup {minus}}, respectively. We were able to resolve the doublets at 4.5, 5.1, and 6.3 MeV clearly for the first time due to our high precision system, which allowed us to determine the widths of some critical states above the proton threshold of {sup 18}Ne more precisely. {copyright} {ital 1999} {ital The American Physical Society}

The atomic mass excess of {sup 187}Ir is determined to be {minus}39.725{plus minus}0.007 MeV from the measured {ital Q} value of {minus}1.521{plus minus}0.006 MeV for the {sup 187}Os({sup 3}He,{ital t}){sup 187}Ir reaction. The result is compared with some predicted values.

The atomic mass excesses of {sup 181}Re and {sup 181}Os were determined to be {minus}46.519{plus minus}0.016 and {minus}43.49{plus minus}0.20 MeV from the measured {ital Q} value of {minus}26.480{plus minus}0.014 MeV for the {sup 185}Re({alpha},{sup 8}He){sup 181}Re(g.s.) reaction and the known beta-decay {ital Q} value. The results were compared with some predicted values.

Thermal properties of PZT detectors were studied in a temperature range from 5 to 50 degrees. The sensitivity of a disk-shaped detector was flat in sensitivity, where as we found an anomalous sensitivity at 44 degree in spherical shaped one. The detectors of both disk-shaped and spherical forms were warmed up in water, into which an electron beam was irradiated. By applying corrections for the thermal properties, we have obtained experimental results consistent with previous data.

The ground state and low-lying levels of the unbound ${}^{11}\mathrm{N}$ nucleus were investigated with the three-neutron pickup reaction ${}^{14}\mathrm{N}{(}^{3}\mathrm{He}{,}^{6}\mathrm{He}{)}^{11}\mathrm{N}.$ The energies and widths of these, experimentally observed, levels are compared with other measurements and calculations. Angular distributions were measured for the first time for this reaction. The distorted-wave Born approximation analysis confirms the spin assignments for the lowest levels.

Superlattice type photodiodes of a GaAs-Al/sub x/Ga/sub 1-x/As structure were studied at room temperature. A combination of potential-well width and barrier width was sensitive to the charge multiplication factor. Using a diode with a 10 nm well and a 15 nm barrier, the detector characteristics were investigated from a point of view of achieving a high gain. This type of photodiode was confirmed to be sensitive to Cherenkov light generated in water. Effects of carrier doping up to 10/sup 18/ cm/sup -3/ at room temperature on the multiplication rate is discussed.

An experiment demonstrating the production of double-Lambda hypernuclei in (K(-),K(+)) reactions on (9)Be was carried out at the D6 line in the BNL alternating-gradient synchrotron. The technique was the observation of pions produced in sequential mesonic weak decay, each pion associated with one unit of strangeness change. The results indicate the production of a significant number of the double hypernucleus (4)(double Lambda)H and the twin hypernuclei (4)(Lambda)H and (3)(Lambda)H. The relevant decay chains are discussed and a simple model of the production mechanism is presented. An implication of this experiment is that the existence of an S = -2 dibaryon more than a few MeV below the double Lambda mass is unlikely.

We have developed a Multiple-Sampling and Tracking Proportional Chamber (MSTPC) for the measurement of reactions involving unstable nuclei. We have measured the 8Li(α, n)11B reaction directly and exclusively by using the MSTPC, and obtained a new data of the total cross section.

The atomic mass excesses of $^{86}\mathrm{Zr}$ and $^{88}\mathrm{Mo}$ were determined to be -77.807\ifmmode\pm\else\textpm\fi{}0.031 and -72.703\ifmmode\pm\else\textpm\fi{}0.021 MeV from the measured Q values of -40.136\ifmmode\pm\else\textpm\fi{}0.030 and -43.278\ifmmode\pm\else\textpm\fi{}0.020 MeV for the $^{90}\mathrm{Zr}$(\ensuremath{\alpha}${,}^{8}$He${)}^{86}$Zr(g.s.) and $^{92}\mathrm{Mo}$(\ensuremath{\alpha}${,}^{8}$He${)}^{88}$Mo(g.s.) reactions. The results were compared with some predicted values.

Experimental investigation of critical nuclear reactions for the breakout off the Hot-CNO cycle are in progress. One is the 15O(α,γ)19Ne reaction, which could be the limiting reaction of the breakout at relatively low temperature (T

This report discusses the following topics on the Soleoidal Detector Collaboration: Summary and overview of the detector; physics and detector requirements; central tracking system; superconducting magnet; calorimetry; muon system; electronics; online computing; offline computing; safety; experimental facilities; installation; test and calibration beam plan; and cost and schedule summary.

Measurements of the semileptonic weak neutral-current reactions ..nu../sub ..mu../p..--> nu../sub ..mu../p and nu-bar/sub ..mu../p..-->..nu-bar/sub ..mu../p which yield the absolute differential cross sections dsigma(..nu../sub ..mu../p)/dQ/sup 2/ and dsigma(nu-bar/sub ..mu../p)/dQ/sup 2/ described. The weak-neutral-current parameter, sin/sup 2/theta/sub W/, is determined to be sin/sup 2/theta/sub W/ = 0.220 +- 0.016 (stat)/sub -0.031//sup +0.023/(syst).

Coherent pion photoproduction from deuteron is studied by measuring the differential cross-sections at c.m. angles between 90° and 130° in a photon energy range from 500 to 1000 MeV. The experimental data are compared with a model calculation which takes into account two kinds of contributions, the nonresonant contribution consisting of pion photoproduction from single nucleons and pion rescattering and that from the dibaryon resonances3F3(2.26) and1G4(2.51). The model predictions for the photon asymmetry σ and the deuteron polarizationiT11 are also presented.

Yields of 24 radioactive nuclides formed by the interaction of bremsstrahlung with maximum end-point energies of 100 MeV--1 GeV with Cu have been measured by direct ..gamma..-ray counting of irradiated targets. The yields in the mass range of 42 to 60 (except for /sup 60/Cu) were analyzed by a nonlinear least-squares fit to obtain the mass yield and charge dispersion curves in spallation reactions. From the parameter values obtained, the energy dependence of the slope of the mass yield curve and the relationship between target N/Z and the most probable product N/Z were investigated and compared with the results of proton, ..cap alpha.., and heavy-ion-induced spallation of Cu. The characteristics of photon-induced spallation are discussed.

A hierarchical, distributed intelligence data acquisition system which has been used for the past two years in neutrino experiments at Brookhaven National Laboratory is described. Performance characteristics and the nature of problems encountered in bringing the system to maturity are discussed and some generalizations of the experience are suggested.

The atomic mass excess of /sup 193/Au was determined to be -33.419 +- 0.011 MeV for the first time from the measured Q value of -26.919 +- 0.009 MeV for the /sup 197/Au(..cap alpha..,/sup 8/He)/sup 193/Au reaction. The atomic mass excess of /sup 193/Hg was also determined to be -31.080 +- 0.032 MeV by using the known Q value of /sup 193/Hg beta decay to /sup 193/Au. These results were compared with some predicted values.

The linear polarization of the coherent bremsstrahlung from a single crystal of silicon was measured by observing the one-dimensionally projected angles of electron and positron pairs. The coherent bremsstrahlung was produced by injecting the 1153 MeV electrons to the silicon crystal nearly along the [110] axis. The emission angles, η + and η − , of pair particles were determined event by observing their tracks with a set of four wire spark chambers. From the ( η + , η − ) distribution of events, the polarization of photons was evaluated. The obtained polarization was consistent with the calculated values, and the technique gives a new approach to the measurement of the linear polarization of photons.

An experimental investigation of the reaction γ p → p p p at photon energies 4.7 ⩽ E γ ⩽ 6.6 GeV is described. The main results are the measurement of the cross section as a function of energy, a discussion of the main dynamical features of the reaction and the observation of a narrow p p mass state at 2.024 ± 0.005 GeV with a width of 29 ± 13 MeV.

The result of a measurement of sigma(..nu../sub ..mu../+e/sup -/..--> nu../sub ..mu../+e/sup -/) is presented. With use of neutrinos of mean energy 1.5 GeV from the Brookhaven National Laboratory alternating gradient synchrotron and a massive, active, high-resolution detector, a signal of 51 +- 9 events with a average signal-to-background ratio greater than 2:1 is observed. sigma(..nu../sub ..mu../e/sup -/..--> nu../sub ..mu../+e/sup -/) = (1.60 +- 0.29(stat) +- 0.26(sys)) E/sub ..nu../ (GeV) x 10/sup -42/ cm/sup 2/ is obtained.

The differential cross section of the reaction ( γ p → p φ ) has been measured in the t range 0 ⩽ t ⩽ 0.4 GeV 2 and for photon energies from 3.0 to 6.7 GeV. In particular for the small t region the measurement accuracy was better than 10%. We obtained for the slope parameter B in an exponential parametrization of the differential cross section d σ /d t = A e − Bt values of B ⋍ 6 ± 0.5 GeV −2 which are significantly larger than the slopes obtained by most other experiments at higher t values. This indicates a t dependence of B particularly in the small t region. An energy dependence of the optical point (d σ /d t ) t =0 , observed in our measurements, has been explained as a kinematic effect due to the VDM relation. A fit of our measurements is in excellent agreement with all other published values of (d σ /d t ) t =0 ( γ p → φ p), this implies that σ tot (φp) must be essentially energy independent in this energy range. Spin density matrix elements of the φ have been evaluated and an analysis of the helicity amplitudes has been carried out. This analysis confirmed s -channel helicity conservation. Moments of spherical harmonics of the K K angular decay distribution have been computed for 10 MeV K K mass-bins from threshold to 1.3 GeV. The mass dependence of the normalized moments is generally smooth. Contributing amplitudes have essentially only even moments. The moment 〈 Y 2 0 〉/〈 Y 0 0 〉 changes sign above the φ mass. Differential cross sections for the inelastic φ production γ p → φ X have been evaluated for the first time both with respect to t − t min and M K . The integrated inelastic cross sections are comparable in size with the elastic ones. The slopes of the differential cross sections d σ /d t appear to become flatter with increasing M X .

A mass-dependent asymmetry was observed in the decay angular distribution of a photoproduced K+K− system near the K+K− threshold. The corresponding moments 〈Y10〉 have been evaluated. Interpreting the asymmetry as an S-P wave interface due to the states S993∗(0+) and o1019(1−) one can compute the moments 〈Y10〉 through an amplitude analysis. The theoretical calculation reproduces the experimental results well, if one assumes a real S-wave amplitude for the S993∗. The data cannot be explained by a non-resonant real S-wave. Other possibilities have been discussed. An estimate of the photoproduction cross section of the S∗ → K+K− can be given on the basis of the above hypothesis.

A Si single crystal has been mounted on the conventional internal target holder of the 1.3 GeV electron synchrotron at the Institute for Nuclear Study, Tokyo. The energy spectrum measured with the pair spectrometer has a clear enhancement due to the coherent bremsstrahlung process. The linear polarization of the photon beam thus obtained is estimated to be 27% and 10% at the photon energy of 200 and 540 MeV, respectively.

Differential cross sections of proton Compton scattering have been measured in the energy range between 375 MeV and 1150 MeV in steps of 25 MeV at c.m. angles of 130°, 100° and 70°. The recoil proton was detected with a magnetic spectrometer. In coincidence with the proton, the scattered photon was detected with a lead-glass Cerenkov counter of the total absorption type. Theoretical calculations based on an isobar model with two components, that is, the resonance plus the background, were practiced. The photon couplings of the second resonance region were determined from the proton Compton data for the firs time. The results were that the helicity 1 2 photon couplings of P11(1470) and S11(1535), and the helicity 3 2 photon coupling of D13(1520) were consistent with those determined from the single-pion photoproduction data; however, the helicity 1 2 photon coupling of D13(1520) required a somewhat larger value than that from the single-pion photoproduction data.

A search for K + → π + γ, π + γγ, π + γγγ was made detecting pions from stopped kaons in the kinetic energy region between 117 MeV and 127 MeV. New Limits of 1.4 ×10 −6 , 8.4 × 10 −6 and 1.0 × 10 −4 for the branching ratio were obtained assuming a phase-space spectrum on the pion energy. The first limit also aplies to another process K + → π + + a, where a is a light meson with mass smaller than 100 MeV/ c 2 and decays into n γ's with lifetime less than 10 −9 s.

The π + and π − momentum spectrum of the reaction γ p → ππ N have been measured at lab angles 20°, 40°, 60° and 90° and photon energies 0.744, 0.844, 0.944 and 1.044 GeV with a magnetic spectrometer using the photon subtraction method. Both spectra show a peak corresponding to the production of the πΔ(1236) state. The analysis has been carried out with amplitudes for the quasi two-body process γ p → πΔ (1236) and a phase-space background so as to reproduce both π + and π − spectra. The ratio of cross sections σ ( γ p → π + Δ 0 )/ ( γ p → π − Δ ++ ) is found to vary 0.0 to 1.8, depending on kinematical conditions.

The recoil proton polarization of proton Compton scattering (γp→γp) was measured in the photon energy range from 500 MeV to 1000 MeV atθ ∗=100° and from 400MeV to 800 MeV atθ ∗=130°. A recoil proton and a scattered photon were detected in coincidence with a magnetic spectrometer and a photon detector. The recoil proton polarization was measured with a carbon polarimeter. The results are compared with a phenomenological analysis based on an isobar model and a dynamical analysis based on the dispersion relation.

The recoil proton polarization of the reaction γp → π0p was measured at a c.m. angle of 100° for incident photon energies between 451 and 1106 MeV, and at an angle of 130° for energies from 400 to 1142 MeV. One photon, decayed from a π0 meson, and a recoil proton were detected in coincidence. Two kinds of polarization analyzer were employed. In the range of proton kinetic energy less than 420 MeV and higher than 346 MeV, carbon plates and liquid hydrogen were used for determining the polarization, respectively. The data given by the two polarimeter systems are in good agreement. Results are compared with recent phenomenological analyses. From the comparison between the present data and the polarized target data, the invariant amplitude A3 can be estimated to be small.

Using stopped kaons, rare decay modes K + → π + ν v and K + → π + a 0 is the light pseudoscalar meson (axion), have been measured. The upper bound of the branching ratio was found to be 1.4 × 10 −7 for K + → π + ν v and 3.8 × 10 −8 for K + → π + a 0 .

The differential cross section for $^{2}\mathrm{H}$(\ensuremath{\gamma}, ${\ensuremath{\pi}}^{0}$${)\mathrm{}}^{2}$H for photon energies from 500 to 800 MeV is calculated based on elementary processes. A comparison between calculated results and the experimental data at large angles demonstrates that double scattering becomes dominant in this region and that dibaryon resonances make no contribution to within the experimental accuracy.

Momentum distributions for inclusive photoemission of deuterons from nitrogen have been measured at laboratory angles of 43° and 50°, and for maximum energies of the bremsstrahlung photon beam of 725, 775 and 825 MeV. The double differential cross sections of deuterons emitted from nitrogen are obtained for photon energies of 750 and 800 MeV and for laboratory angles of 43° and 50°. The photon energy is determined by the photon subtraction method. Results are examined by a π 0 photoproduction process off a quasi-deuteron in nitrogen ( γ ″d″→ π 0 d) and by a two-step process. The two-step process means the following: first, a nucleon is produced by a photo-pion production process from a quasi-free nucleon in the nitrogen nucleus ( γ ″N″→ π N); second, the nucleon produced at the first step picks up another nucleon in the nucleus and then a deuteron is emitted (N+A→d+anything).

The muon range spectrum in the stopped K+ decay has been measured in order to search for a discrete line associated with heavy-neutrino emission in Kμ2 decay. An upper bound of 0.5 ∼ 2 × 10−5 for the mixing ratio between νμ and a massive neutrino has been obtained for a mass range of 160–230 MeV/c2.

The differential cross sections for the reactions γ d → π 0 d have been measured for photons from 500 to 1000 MeV. We discuss the effect of the double scattering term and suggest no indication for the dibaryon resonances of the mass around 2.5 GeV.