The (3 decay of Na 20 proceeding to highly excited states of Ne 20 has been studied by measuring the delayed a particles which are subsequently emitted. Na 20 was produced by a (p,an) reaction on a natural magnesium target, in an external beam of 45-MeV protons from the UCLA cyclotron. A thin silicon detector and nanosecond electronics were used to suppress the large positron background usually present in this type of experiment. A method of measuring Q a directly is discussed, a transitions from states in Ne 20 at 7. 43, 7.84, 8.74, 9.48, 10.28, 10.86, and 11.28 MeV have been observed and their intensities measured.
Frequency distributions of the energy deposition by 600 MeV protons in small volumes as a result of their traversal of a tissue-equivalent gas have been measured after the beam's passage through various thicknesses of a tissue-equivalent plastic. The pathIength examined is equivalent to 1.75 , u of unit density tissue (muscle). Comparisons of the energy deposition distribution functions after passage through 0, 5 and 21 cm of tissue-equivalent plastic (muscle) are given. Through the use of a coincidence gate, spectra depicting energy deposition due only to direct proton ionization in the gas were compared with those combined with contributions due to the nuclear interaction products.
If the energy loss for a charged particle traversing a fixed pathlength were a single valued function of the parameters governing energy loss by charged particles, then the pathlength distribution through a given volume would completely describe the distribution of energy losses found for particles traversing that volume. This would be true for either parallel or isotropically incident beams. I n many instances of interest in micradosimetric measurement, statistical variations of energy losses by individual particles will play a significant role in determining the character of the resultant energy deposition distribution function obtained in a proportional counter. This has been investigated with an approximate analytical method for isotropically incident particle beams having various energies and masses traversing a number of differently shaped volumes, namely, the sphere and cylinders of different heightto-diameter ratios. Corrections for delta ray losses or contributions have not been considered.
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