166 research outputs found
Magnetic guidance of charged particles
Many experiments and devices in physics use static magnetic fields to guide
charged particles from a source onto a detector, and we ask the innocent
question: What is the distribution of particle intensity over the detector
surface? One should think that the solution to this seemingly simple problem is
well known. We show that, even for uniform guide fields, this is not the case
and present analytical point spread functions (PSF) for magnetic transport that
deviate strongly from previous results. The "magnetic" PSF shows unexpected
singularities, which were recently also observed experimentally, and which make
detector response very sensitive to minute changes of position, field
amplitude, or particle energy. In the field of low-energy particle physics,
these singularities may become a source of error in modern high precision
experiments, or may be used for instrument tests, for instance in neutrino mass
retardation spectrometers.Comment: 16 pages, 5 figures, version 2: improved approximation metho
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
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