A. Honig

Measurements of HD (gamma, pi) and Implications for the Convergence of the Gerasimov-Drell-Hern Integral

We report new measurements of inclusive pion production from frozen-spin HD for polarized photon beams covering the Delta(1232) resonance. These provide data simultaneously on both H and D with nearly complete angular distributions of the spin-difference cross sections entering the Gerasimov-Drell-Hearn (GDH) sum rule. Recent results from Mainz and Bonn exceed the GDH prediction for the proton by 22 microbarns, suggesting as yet unmeasured high-energy components. Our pi0 data reveal a different angular dependence than assumed in Mainz analyses and integrate to a value that is 18 microbarns lower, suggesting a more rapid convergence. Our results for deuterium are somewhat lower than published data, considerably more precise and generally lower than available calculations.

New investigations of polarized solid HD targets

Abstract Polarized solid HD targets in a frozen-spin mode, with superior nuclear physics characteristics and simple operational configurations, have previously been restricted in their deployment due to a disproportionate target production time with respect to utilization time. Recent investigations have yielded frozen-spin polarization lifetimes, at a convenient target temperature of 1.5 K, of nearly a year for both H and D at high holding fields, and of more than a week at sub-Tesla holding fields. These results, taken together with the advent of new interesting spin-physics using relatively weakly ionizing beams, such as polarized photon beams, remove the above impediment and open up the use of polarized solid HD to long duration nuclear spin-physics experiments. Large, multiple targets can be produced, retrieved from the polarization-production apparatus with a cold-transport (4 K) device, stored for very long times in inexpensive (1.5 K, 7 T) cryostats, and introduced “off-the-shelf” into in-beam cryostats via the portable cold-transport apparatus. Various modes for achieving polarized H and/or D, as well as already achieved and expected polarization values, are reported. Experimental results are given on Kapitza resistance between the solid HD and the cooling wires necessary to obtain low temperatures during the heat-evolving polarization process. 15 mK is achievable using gold-plated aluminum wires, which constitute 15% extraneous nucleons over the number of polarizable H or D nucleons. Application to more highly ionizing beams is also given consideration.

Large, mobile frozen-spin polarized solid HD

Abstract A completed system for producing large quantities of highly spin-polarized H and D in solid HD is described. It is of the relaxation-switched frozen-spin type, in which relaxation is turned off after polarization at high B (17 T) and low T (15 mK), and the polarization is retained at high T (4 K) and low B (fractional Tesla). The first application is as targets for polarized gammas at BNL. Presently, three targets of 1.3 mol each are produced in a single run at Syracuse, cold transferred to a mobile storage cryostat with high field, transported to BNL, and cold-transferred there into an in-beam cryostat.

Polarization of hydrogen molecules HD, D2 and DT

Abstract Highly polarized Hydrogen molecules in the solid phase are of primary interest as “polarized targets” for Nuclear Physics and “polarized fuel” for Inertial Confinement Fusion (ICF). We are developing new techniques to polarize Hydrogen molecules. There are 2 objectives: production of polarized HD targets by static polarization, in order to perform nuclear physics experiments; and investigation of dynamic polarization processes for HD, D 2 and DT, for fusion research. These approaches are described and the results already obtained for the static polarization of HD are given. The possibility to investigate dynamic polarization methods for HD and apply them to DT in order to produce polarized DT fuel for fusion is discussed.

Solid HD polarized target: conceptual design of transport and in-beam cryostat

Abstract A description of a cold transport/retrieval Dewar for the removal and insertion of a polarized solid HD target is given. The procedure for removing such a target from the production dilution refrigerator, storing the target for long periods of time until needed, inserting it into the in-beam cryostat, and finally disengaging it will be discussed. This apparatus considerably reduces the complexity of the in-beam cryostat at both the LEGS and GRAAL Compton Laser Backscattering facilities, where the new HD polarized target will have its first use.

First beam-target double-polarization measurements using polarized HD at legs

A new polarized target using HD in the solid phase has been developed for studies of the nucleon spin structure at Q(2) = 0 using pion photo-production. In combination with the high quality LEGS photon beam and a large solid angle spectrometer this target allows practically background-free measurements on the proton and on the neutron. The first beam-target double-polarization data taken with this target are reported here.

Recent Polarization Experiments and the GDH Sum Rule

Measurements of the spin‐difference cross sections entering the Gerasimov‐Drell‐Hearn (GDH) sum rule are reviewed. Results on the proton from Mainz and Bonn exceeded the GDH prediction by 22 μb, requiring as yet unmeasured canceling high‐energy components. Recent experiments with frozen‐spin HD at BNL reveal a different angular dependence for π0 production than what was assumed in Mainz analyses in lieu of direct measurements and integrate to a value that is 18 μb lower, suggesting a rapid convergence. Results for deuterium over limited energy ranges are consistent with large canceling contributions but differ from existing state of the art calculations.

Large, accessible, highly polarized frozen‐spin solid HD targets

New advances in frozen‐spin polarized solid HD make practical the use of large targets of independently polarizable H and D for experiments in fusion, photonuclear and particle physics. Long polarization‐retention times of about a year at 1.5 K and 7.5 Tesla allow multiple target production and long term storage in economical cryostats, for off‐the‐shelf availability of polarized HD material and targets. Polarization‐retention times at sub‐Tesla fields, which exceed a week, provide a fair match between polarization‐production time and target‐utilization time in moderate fields, for weakly ionizing beam fluxes in which radiation damage to the target is small. Because of the convenient 1.5–4 K frozen‐spin temperature range, cold‐transfer (4 K) portable apparatuses, which have already been constructed and used, can move the targets readily from polarization‐production systems to storage or in‐beam cryostats with negligible polarization loss. This permits total separation of polarization‐production and target...

Measurements of the spin structure of the nucleon using SPHICE: A strongly polarized hydrogen and deuterium ice target

Frozen‐spin HD polarized targets operating between 0.4 and 4K, used with cold‐transfer (4K) techniques, provide great configurational flexibility. Their long depolarization times under target usage conditions assure reasonable match between polarization production and usage times, for weakly ionizing beam fluxes, and the very long relaxation times at fields above 7T (∼1 yr.) provide an economical storage mode and ‘‘off‐the‐shelf’’ availability.

Status of the legs polarized HD target

A solid, polarized HD target has been developed for the measurement of double-polarization observables in the Delta resonance region. Since the use of the first target in-beam in November 2001, dramatic improvements have been made to the in-beam and transfer cryostats and the NMR circuit has been redesigned and is well understood.