The point spread function of electrons in a magnetic field, and the decay of the free neutron

Experiments in nuclear and particle physics often use magnetic fields to guide charged reaction products to a detector. Due to their gyration in the guide field, the particles hit the detector within an area that can be considerably larger than the diameter of the source where the particles are produced. This blurring of the image of the particle source on the detector surface is described by a suitable point spread function (PSF), which is defined as the image of a point source. We derive simple analytical expressions for such magnetic PSFs, valid for any angular distribution of the emitted particles that can be developed in Legendre polynomials. We investigate this rather general problem in the context of neutron beta decay spectrometers and study the effect of limited detector size on measured neutron decay correlation parameters. To our surprise, insufficient detector size does not affect much the accuracy of such measurements, even for rather large radii of gyration. This finding can considerably simplify the layout of the respective spectrometers.Comment: 24 pages, 12 figure

Impact of climate induced glacial melting on coastal marine systems in the Western Antarctic Peninsula region

IMCOAST is an international research program that features a multidisciplinary approach involving geo and biological sciences, field investigations, remote sensing and modeling and knowledge into the hydrographical and biological history of the marine coastal ecosystems of the Western Antarctic Peninsula region

Migratory Stories: Building Ethical Immigration Policy

Yorki J. Encalada Egúsquiza, an academic who studies border issues, discusses the reality that Child Migrants (CM) face, “They are minors traveling alone, then they have to appear in immigration courts, regardless of age. We\u27re talking about children, in some cases, toddlers, without lawyers, who have to face a court that wants to deport them.” United States immigration policy fails to aid CMs who arrive at the U.S.-Mexico border; in a practice of exclusionary policy, it further traumatizes children who have journeyed to the U.S. alone. Using interviews I have conducted, memoirs, political theory, and scholarly literature, my research scrutinizes U.S. immigration policy surrounding CMs and the ethics behind policy making. This thesis examines the CM experience through three stakeholders\u27 eyes: CMs, policy organizations, and provider organizations. Their viewpoint develops an understanding of the unethical practices of current policy while examining the everyday work that stakeholders do to aid in the CM experience. Through theoretical conceptions of cosmopolitanism and ethics, this thesis develops a framework on ethics, creating a standard for ethical policy making founded on a mutual understanding that stakeholders must be involved in policy making for CMs. This thesis calls attention to the inherent unethical nature of and sheer lack of policy for CMs and the ethical reasoning behind why the U.S. must approach this crisis in an informed and ethical way

The Efficiency-Equity Tradeoffs in Agricultural Research Priority Setting: The Potential Impacts of Agricultural Research on Economic Surplus and Poverty Reduction in Nigeria

Public agricultural research has come under increasing pressure to redefine its strategic priorities to contribute to poverty alleviation goals. However, the issue of whether the poor benefit more from agricultural research that pursues efficiency or equity objectives remains unresolved, largely due to lack of empirical evidence on the nature and magnitude of the efficiencyequity tradeoffs. This paper estimates the potential impacts of agricultural research on economic surplus and poverty reduction in Nigeria, identifies strategic priorities according to both efficiency and equity criteria, and examines the nature and magnitude of the efficiencyequity tradeoffs. The results show that there are no significant efficiencyequity tradeoffs because the rural poor in Nigeria depend mainly on the production of food staples for both consumption and household income. Although introducing a poverty dimension does not result in a significant shift in strategic priorities, greater benefits to the poor are possible through poverty-based targeting without compromising total benefits. However, efforts made towards the realization of potential benefits to the poor from pursuing either efficiency or equity objectives would be more important than mere targeting of research. Therefore, both agricultural research and support services, including extension, credit, input supply, and infrastructure, should be targeted to the poor to achieve poverty alleviation goals through agricultural research.poverty reduction, economic surplus, research priority setting, Nigeria, Research and Development/Tech Change/Emerging Technologies, I32, I38, O13, O32, Q16,

A solenoidal electron spectrometer for a precision measurement of the neutron β\beta-asymmetry with ultracold neutrons

We describe an electron spectrometer designed for a precision measurement of the neutron $\beta$-asymmetry with spin-polarized ultracold neutrons. The spectrometer consists of a 1.0-Tesla solenoidal field with two identical multiwire proportional chamber and plastic scintillator electron detector packages situated within 0.6-Tesla field-expansion regions. Select results from performance studies of the spectrometer with calibration sources are reported.Comment: 30 pages, 19 figures, 1 table, submitted to NIM

The influence of the chameleon field potential on transition frequencies of gravitationally bound quantum states of ultra-cold neutrons

We calculate the chameleon field potential for ultracold neutrons, bouncing on top of one or between two neutron mirrors in the gravitational field of the Earth. For the resulting non--linear equations of motion we give approximate analytical solutions and compare them with exact numerical ones for which we propose the analytical fit. The obtained solutions may be used for the quantitative analysis of contributions of a chameleon field to the transition frequencies of quantum states of ultra-cold neutrons bound in the gravitational field of the Earth.Comment: 11 pages, 4 figure

Light Hadron Spectroscopy: Theory and Experiment

Rapporteur talk at the Lepton-Photon Conference, Rome, July 2001: reviewing the evidence and strategies for understanding scalar mesons, glueballs and hybrids, the gluonic Pomeron and the interplay of heavy flavours and light hadron dynamics. Dedicated to the memory of Nathan Isgur, long-time collaborator and friend, whose original ideas in hadron spectroscopy formed the basis for much of the talk.Comment: to be published in "Lepton Photon 2001 Conference Proceedings" (World Scientific Publishing), 19 pages with 6 figure

Determination of the Weak Axial Vector Coupling from a Measurement of the Beta-Asymmetry Parameter A in Neutron Beta Decay

We report on a new measurement of the neutron beta-asymmetry parameter $A$ with the instrument \perkeo. Main advancements are the high neutron polarization of $P = 99.7(1)$ from a novel arrangement of super mirror polarizers and reduced background from improvements in beam line and shielding. Leading corrections were thus reduced by a factor of 4, pushing them below the level of statistical error and resulting in a significant reduction of systematic uncertainty compared to our previous experiments. From the result $A_0 = -0.11996(58)$, we derive the ratio of the axial-vector to the vector coupling constant $\lambda = g_\mathrm{A}/g_\mathrm{V} = -1.2767(16)$Comment: 5 pages, 4 figure

Measurement of the Neutrino Asymmetry Parameter B in Neutron Decay

A new measurement of the neutrino asymmetry parameter B in neutron decay, the angular correlation between neutron spin and anti-neutrino momentum, is presented. The result, B=0.9802(50), agrees with the Standard Model expectation and earlier measurements, and permits improved tests on ``new physics'' in neutron decay.Comment: 4 pages, 2 figures; v2: revised PRL versio