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How it worksThe ISOMAX detector, which was an order-of-magnitude evolutionary step up from its progenitor IMAX, is a balloon-borne mass-spectrometer, that was launched for the first time in summer 1998 to measure the abundances and energy spectra of the isotopes of light elements (Li through the CNO-group) in the crucial energy range around 1 GeV/nucleon. Mass- and Energy-resolution should be good enough such that even a one-day flight will significantly improve the statistics of known particles in that energy region (see Streitmatter et.al. 1996). ![]() The instrument employs the following components to measures the mass, charge and energy of a particle:
The mass of the particle is determined from the magnetic rigidity and velocity of the particle, and the kinetic energy then follows from the velocity. A charged particle in a homogeneous magnetic field will follow a circular orbit of radius r, where r is given by the magnetic rigidity R of the particle (and hence its mass A, charge Z and velocity, beta) and the strength of the magnetic field as r = R/B = p/ZB = beta * gamma * A /BZ. With Z determined by the TOF-scintillators and beta measured either by the TOF system or the Cherenkov counters, this can be solved for A if the radius of curvature r is sufficiently well measured. This provides all information about the particle species (A, |Z| and the sign of Z) and since E=gamma * m, this also provides all the necessary spectral information. For the short-duration flight of approximate one day, the expected statistics of high energy particles were too low to warrant a very low index of refraction (n) aerogel, therefore the system was equipped with an n=1.14 Cherenkov counter, which limited the useful energy range of the instrument to < 1.5 GeV/nucleon and the results will rest more heavily on the TOF system. For a longer duration flight attempted in 2000, an n=1.045 Cherenkov would have extended this range out to about 3 GeV/nucleon. Alternatively, the instrument could have been used to extend the range of measurement to heavier isotopes (5 < Z < 14) in the same energy range, and the isotopes of Hydrogen, Helium and even anti-protons to even higher energies. References:
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