D. Seiler

Position sensitive measurement of lithium traces in brain tissue with neutrons.

PURPOSE The application of lithium is well known to have an antimanic-depressive effect, however, the influence it has on the human brain is still insufficiently known. The aim of our work is to develop a method to investigate the lithium concentration in the human brain with a very high sensitivity and a submillimeter resolution. Present methods either do not provide spatial resolution or are not sensitive enough to measure the naturally occurring lithium content in the human brain. Our method provides the opportunity to perform postmortem series measurements and obtain a detailed map of the lithium distribution in the human brain. This way possible correlations of the lithium distribution in the human brain and biological reasons for affective disorder can be clarified. METHODS To study the lithium distribution in different regions of the human brain the authors developed a method to measure lithium traces postmortem with a submillimeter spatial resolution using the neutron capture reaction (6)Li(n, α)(3)H. The lithium is measured by coincident detection of the alpha particles and tritons, emitted in opposite directions. The general concept, the preparation of the brain samples, the experimental setup at the measurement station of the Forschungs-Neutronenquelle Heinz Maier-Leibnitz, and a first measurement on human brain tissue are presented. RESULTS A first measurement on a brain tissue sample nicely showed a spatial distribution of lithium down to a few hundreds of pg∕cm(3) with a maximal resolution of about σ(x) = σ(y) ≈ 200 μm. Also a direct correlation of lithium and optical tissue structure is observable. Typical measurement times of a few minutes allow for series measurements of up to 20 × 20 mm(2) large samples with a thickness of w = 10-20 μm in medical studies. CONCLUSIONS The combination of a very high lithium sensitivity with position resolving measurement makes this method well suited for postmortem studies of the microscopic lithium distribution in the human brain and thus to form a microscopic picture of the impact of lithium in different areas of the human brain.

Isotopic 32 S/ 33 S ratio as a diagnostic of presolar grains from novae

Abstract Measurements of sulphur isotopes in presolar grains can help to identify the astrophysical sites in which these grains were formed. A more precise thermonuclear rate of the 33S( p , γ )34Cl reaction is required, however, to assess the diagnostic ability of sulphur isotopic ratios. We have studied the 33S(3He,d)34Cl proton-transfer reaction at 25 MeV using a high-resolution quadrupole–dipole–dipole–dipole magnetic spectrograph. Deuteron spectra were measured at ten scattering angles between 10° and 55°. Twenty-four levels in 34Cl over E x = 4.6 – 5.9 MeV were observed, including three levels for the first time. Proton spectroscopic factors were extracted for the first time for levels above the 33S + p threshold, spanning the energy range required for calculations of the thermonuclear 33S( p , γ )34Cl rate in classical nova explosions. We have determined a new 33S( p , γ )34Cl rate using a Monte Carlo method and have performed new hydrodynamic nova simulations to determine the impact on nova nucleosynthesis of remaining nuclear physics uncertainties in the reaction rate. We find that these uncertainties lead to a factor of ≤5 variation in the 33S( p , γ )34Cl rate over typical nova peak temperatures, and variation in the ejected nova yields of S Ca isotopes by ≤ 20 % . In particular, the predicted 32S/33S ratio is 110–130 for the nova model considered, compared to 110–440 with previous rate uncertainties. As recent type II supernova models predict ratios of 130–200, the 32S/33S ratio may be used to distinguish between grains of nova and supernova origin.

Nuclear structure of 30 S and its implications for nucleosynthesis in classical novae

The uncertainty in the 29P(p,gamma)30S reaction rate over the temperature range of 0.1 - 1.3 GK was previously determined to span ~4 orders of magnitude due to the uncertain location of two previously unobserved 3+ and 2+ resonances in the 4.7 - 4.8 MeV excitation region in 30S. Therefore, the abundances of silicon isotopes synthesized in novae, which are relevant for the identification of presolar grains of putative nova origin, were uncertain by a factor of 3. To investigate the level structure of 30S above the proton threshold (4394.9(7) keV), a charged-particle spectroscopy and an in-beam gamma-ray spectroscopy experiments were performed. Differential cross sections of the 32S(p,t)30S reaction were measured at 34.5 MeV. Distorted wave Born approximation calculations were performed to constrain the spin-parity assignments of the observed levels. An energy level scheme was deduced from gamma-gamma coincidence measurements using the 28Si(3He,n-gamma)30S reaction. Spin-parity assignments based on measurements of gamma-ray angular distributions and gamma-gamma directional correlation from oriented nuclei were made for most of the observed levels of 30S. As a result, the resonance energies corresponding to the excited states in 4.5 MeV - 6 MeV region, including the two astrophysically important states predicted previously, are measured with significantly better precision than before. The uncertainty in the rate of the 29P(p,gamma)30S reaction is substantially reduced over the temperature range of interest. Finally, the influence of this rate on the abundance ratios of silicon isotopes synthesized in novae are obtained via 1D hydrodynamic nova simulations.

New 34CI proton-threshold states and the thermonuclear 33S(p,γ)34Cl rate in ONe novae

Analysis of presolar grains in primitive meteorites has shown isotopic ratios largely characteristic of the conditions thought to prevail in various astrophysical environments. A possible indicator for a grain of ONe nova origin is a large 33 S abundance: nucleosynthesis calculations predict as much as 150 times the solar abundance of 33 S in the ejecta of nova explosions on massive ONe white dwarfs. This overproduction factor may, however, vary by factors of at least 0.01-3 because of uncertainties of several orders of magnitude in the 33 S(p,γ) 34 Cl reaction rate at nova peak temperatures (T peak ~ 0.1-0.4 GK). These uncertainties arise due to the lack of nuclear physics information for states within ~600 keV of the 33 S + p threshold in 34 Cl (S p ( 34 Cl) = 5143 keV). To better constrain this rate we have measured, for the first time, the 34 S( 3 He,t) 34 Cl reaction over the region E x ( 34 CI) = 4.9-6 MeV. We confirm previous states and find 15 new states in this energy region. New 33 S(p,γ) 34 Cl resonances at E R = 281(2), 301(2), and 342(2) keV may dominate this rate at relevant nova temperatures. Our results could affect predictions of sulphur isotopic ratios in nova ejecta (e.g., 32 S/ 33 S) that may be used as diagnostic tools for the nova paternity of grains.

Proton‐Rich Sulphur and Nucleosynthesis in Classical Novae

The structure of proton-unbound states in {sup 30}{sub S} and {sup 31}{sub S} is important for determining the {sup 29}P(p,{gamma}){sup 30}S and {sup 30}P(p,{gamma}){sup 31}S reaction rates, which influence explosive hydrogen burning in classical novae. The former reaction rate in this temperature regime had been previously predicted to be dominated by two low-lying, unobserved, J{sup {pi}} = 3{sup +} and 2{sup +} resonances in {sup 30}S. To search for evidence for these levels, the structure of {sup 30}{sub S} was studied using the {sup 32}S(p,t){sup 30}S reaction with a magnetic spectrograph. We provide an update on the status of the ongoing analysis and some preliminary results.

Structure of {sup 30}S with {sup 32}S(p,t){sup 30}S and the thermonuclear {sup 29}P(p,{gamma}){sup 30}S reaction rate

The structure of proton unbound

Development of a novel macrostructured cathode for large-area neutron detectors based on the B-10-containing solid converter

^{30}\mathrm{S}

Evidence for the existence of the astrophysically important 6.40-MeV state of 31S

states is important for determining the

Ultracold neutron detectors based on 10B converters used in the qBounce experiments

^{29}\mathrm{P}

Structure of S 30 with S 32 ( p , t ) S 30 and the thermonuclear P 29 ( p , γ ) S 30 reaction rate

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