David E. Alburger

A Single arm spectrometer detector system for high-energy heavy ion experiments

The recent availability of 14.6 GeV/c per nucleon 16O and 28Si ions from the Brookhaven National Laboratory Tandem-AGS accelerator facility has prompted the design, construction and operation of a large-solid-angle (25 msr) magnetic spectrometer with particle identification from ∼0.5 to ∼4.7 GeV/c. A small-solid-angle Cherenkov counter complex views the target through the magnet and extends the particle identification up to ∼15 GeV/c. This experiment (E-802) employs event characterization detectors, a charged-particle multiplicity array, a highly segmented lead-glass detector, and a zero degree calorimeter. The facility measures momentum spectra of identified heavy-ion-produced hadrons with high resolution (Δp/p≤0.005) as a function of collision centrality given by triggers from the event characterization detectors. Construction and performance details of the spectrometer components and auxiliary detectors are described.

γ-ray spectroscopy in Λ hypernuclei

Abstract The present status of hypernuclear γ -ray spectroscopy with Hyperball is summarized. We observed two γ transitions of 16 Λ O( 1 − → 1 − , 0 − ) and obtained the strength of the ΛN tensor force. In 10 B( K − , π − γ ) data, we did not observe the spin-flip M1 transition of 10 Λ B( 2 − → 1 − ), but γ rays from hyperfragments such as 7 Λ Li( 7 / 2 + → 5 / 2 + ) and 9 Λ Be( 3 / 2 + → 1 / 2 + ) were observed. In 11 B( π + , K + γ ) data, we observed six γ transitions of 11 Λ B. We also attempted an inclusive γ -ray measurement with a stopped K − beam.

Intermediate‐Image Pair Spectrometer

An iron‐free intermediate‐image beta‐ray spectrometer has been constructed having a momentum spread (full width at half‐maximum) for a point source of conversion electrons continuously variable between limits of 0.5% and 4% with corresponding transmissions of 1% and 8% of 4π, respectively. The line half‐width contribution due to source size is 0.3% per mm of diameter. At a power dissipation of 100 kw the spectrometer focuses electrons of 9‐Mev energy allowing positron‐electron pair lines corresponding to transitions of up to 19 Mev to be measured using a double‐crystal statistical‐separation detector together with a fast coincidence circuit. In tests with the 6‐Mev nuclear transition in O16 using a Van de Graaff beam spot 1 mm in diameter the momentum half‐width of the pair line can be varied from 0.56% to 2.5% with corresponding absolute transmissions of 0.07 to 6.3 pair counts per 105 source transitions, respectively. The energy of this transition has been determined as 6.065±0.009 Mev. Electron‐gamma a...

Properties of 13B and 20Na: The second-class current problem

Abstract The half-lives of 13 B and 20 Na are measured: t 1 2 ( 13 B ) = 17.33 ± 0.17 ms ; t 1 2 ( 20 Na ) = 442 ± 5 ms . The mass difference is measured: 20 Na− 20 Ne = 13.892 ± 0.007 MeV. Combined with other data these measurements lead to ( ft ) + /( ft ) − = 1.166 ± 0.026 for A = 13 and 1.054 ± 0.023 for A = 20. If these numbers were to be directly interpreted in terms of secondclass currents we should find for the induced tensor coupling constant: g IT (13) = (2.6 ± 0.5) × 10 −3 ; g IT (20) = (1.5 ± 0.6) × 10 −3 .

Search for double-Λ hypernuclei and the H-dibaryon in the (K−,K+) reaction on 12C

Abstract A search for double- Λ hypernuclei ( 12 ΛΛ Be) and H -dibaryons using the 12 C( K − , K + ) reaction was performed at the BNL-AGS using a high-intensity 1.8 GeV/ c K − beam. A missing-mass analysis below the end point of the quasi-free Ξ − production was used to investigate these S =−2 systems. The upper limit obtained for the forward-angle cross section of 12 ΛΛ Be production is 6 to 10 nb/sr. This is the first search for the direct production of double- Λ hypernuclei to reach the sensitivity required to observe the signal predicted by theoretical calculations. For the H -production cross section, we have obtained an upper limit in the range of a few nb/sr to 10 nb/sr for the H mass below 2100 MeV/ c 2 . This upper limit is the most sensitive H search result to date for a tightly bound H .

Results from the BNL E802 spectrometer for 14.5 GeV/c per nucleon silicon beams

We present selected results of measurements of inclusive ..pi.., K, proton, and deuteron spectra from 14.5 A GeV/c Si collisions with various targets. Results of neutral energy and charged particle dN/d/eta/ measurements are also discussed. Large K to ..pi.. ratios are observed in Si + Au collisions. Results are compared to the Lund-Fritiof model. 11 refs., 11 figs.

The beta decay of 18N and T = 2 states of mass 18

Abstract The 18 N(β − ) 18 O decay was observed via the 9 Be( 18 O, p2α) 18 N reaction, utilizing helium-transport techniques and Ge(Li) spectroscopy. In addition to the previously reported β-decay to the 18 O 4456 keV level ( J π = 1 − ) branches were observed to levels at excitation energies (in keV) of 1982 ( J π = 2 + ). 5530(2 − ), 6198(1 − ). 6350(2 − or 1 + ), 6880(0 − ), and 7771(2 − ). The percentage β-branches, in order of increasing excitation energy, are 3.9 ± 1.5, 54.6 ± 1.0, 3.1 ± 0.4, 1.4 ± 0.2, 2.2 ± 0.3, 14.8 ± 0.8 and 5.0 ± 0.5. respectively, with 15 % assumed on the basis of calculations to proceed to non-γ-emitting states. These measurements allow definite assignments J π = 1 − for the 18 N ground state and J π = 0 − for the 18 O 6880 keV state. Additional measurements determine the 18 N half-life to be T 1 2 = 624 ± 12 ms. A shell-model calculation for mass 18 was carried out in a full 1ħω basis. The predictions for the T = 2 energy level spectrum and for 18 N β-decay are discussed.

New isotopeY80, and the decays ofSr79,Y81, andY82

The helium-jet recoil transfer technique has been used to study the decays of /sup 79/Sr, /sup 80/Y, /sup 81/Y, and /sup 82/Y, produced by /sup 58/Ni(/sup 24/Mg,2pn), /sup 58/Ni(/sup 24/Mg,pn), /sup 58/Ni(/sup 25/Mg,pn), and /sup 60/Ni(/sup 24/Mg,pn) reactions, respectively. Decay properties of these four radioactivities have been deduced from the analysis of extensive singles and multiparameter spectroscopic measurements. The low lying level structure of /sup 80/Sr, as revealed by the decay of /sup 80/Y, can be reproduced through calculations of the interacting-boson-approximation model which place /sup 80/Sr at or near the O(6) limit. Positron end-point measurements (deduced from (..beta..,..gamma..) coincidence studies) have been used to determine decay energies for each of these nuclides. Nuclidic mass excesses inferred from these data show progressively larger deviations from the predictions of currently available mass models for the more neutron-deficient Y isotopes as the N = Z line is approached. It is suggested that this may reflect the influence of nuclear deformation of these isotopes on the mass surface in the vicinity of N = Z = 40.

Precision measurements of gamma-ray energies from 13.3 a 152Eu decay

Abstract The energies of 29 γ rays from the decay of 152 Eu have been determined in order to provide calibration energies for Ge γ-ray spectrometers. Particular emphasis is placed on those γ transitions resulting from the decay of the 152 Sm 1530 keV level. A least-squares adjustment to these 152 Sm γ transitions results in a set of recommended calibration lines.

Precision energy determinations of gamma transitions from 56Co decay

Abstract The energies of 16 γ-rays from 56 Co decay were determined with a Ge(Li) Compton suppression spectrometer. The mixed source technique was used with γ-ray energy standards provided by 110m Ag, 124 Sb, 182 Ta, and 144 Ce β-decay. The main motive for these measurements was to obtain more precise energies for transitions with energies in the 2500–3500 keV range. A least-squares adjustment was made to the present and previous γ-ray energy measurements, resulting in a set of recommended γ-ray calibration lines.