Nuclear Instruments and Methods最新文献

The energy compression system at the Glasgow 170 MeV electron linac is described. A system of three magnets plus a radio-frequency cavity is used to compress the linac energy spectrum by a factor of 5 to 15, depending on energy. Examples of compressed spectra are shown, and the effect of a phase shift in the compression cavity is demonstrated.

A comparison between the absolute efficiency values of HgI₂ and NaI detectors has been carried out for six different source-to-detector arrangements. The HgI₂ and NaI detectors have been cansidered as equal in volume. Six different detector sizes and sources sizes have been used in the calculations. The calculations have been performed in the γ-ray energy region 60–1500 keV with the Monte Carlo method using a Univac 1100 computer. Water has been used as the source medium.

The final design features of the extraction system for the K-500 cyclotron under construction at MSU are presented. The resulting cyclotron performance for a number of typical ions are reviewed and the expected extracted beam phase space characteristics are also discussed.

The isothermal decay of the thermoluminescence output of Li₂B₄O₇ : Mn (0.1% by weight of Mn) was studied as a function of dose and found to be dose dependent in the range 3–10⁵ Gy.

A forward-scattering and a transmission-type polarimeter have been constructed to measure the circular polarization of γ-rays in heavy-ion reactions. The polarimeters were designed to provide large counting efficiencies necessary for particle-γ coincidence experiments. A doubly symmetric detector arrangement was used in-beam to minimize systematic errors. The polarization sensitivity of the forward-scattering polarimeter was determined from Monte Carlo calculations and by using a ⁹⁰Sr–⁹⁰Y source of polarized bremsstrahlung. The applicability of the transmission-type polarimeter in the case of continuous γ-ray spectra is discussed.

Saturation capture probabilities for neutrons, impinging onto thick samples at resonance energies, are proposed as a standard for capture probability, in the energy region of a few hundred eV. Capture probabilities for the 132 eV resonance of cobalt, are examined.

A non-destructive method has been developed for the determination of sub-pCi levels of thorium in solutions by β-α coincidence measurement of daughter activity from purged thoron (²²⁰Rn).

A photon transmission gauge applied for integral water content measurement in a soil layer was analyzed. The gauge may be used as a control unit for automatic irrigation in a field, or as a scanner employed for establishing an irrigation policy. The characteristic functions of the gauge; response and relative resolving power were developed. The functions provide parameter study at the design stage and interpretational ability at the operational stage. The model led to a design which eliminates sensitivity to water distribution in the examined soil. It is shown that a resolving power of 2% was obtained for a 2.3 mCi ¹³⁷Cs source at 53 cm below surface, in measuring water content of 0.2 g water/cm³ soil during 1000 s.

High purity Ar and mixtures of Ar with 1% CH₄, 3% CH₄, CO₂ and N₂, respectively, have been applied for fission fragment detection in a gridded ionization chamber. Gas scintillation has been observed simultaneously with a photomultiplier VALVO-XP2041. Whereas all mixtures work equally well as an ionization gas, only Ar + 3% N₂ shows a primary scintillation yield sufficient for fast timing.

The large vertical Van de Graaff in the Nuclear Physics Laboratory at Oxford University has been converted to a folded tandem with a rated terminal voltage of 10 MV. The new parts were designed and largely manufactured within the Laboratory and included the terminal, two negative ion sources, low energy and high energy beam transport and vacuum systems and a new control system. The conversion began in July 1977 and progressed so that experiments with the folded tandem began in January 1979. Excluding the value of manufacture and installation by Laboratory staff, the total cost of the conversion was £100 000, the major items of outside manufacture being the 180° magnet, the accelerator tubes and the serial data links. The main design features of the new accelerator are discussed as well as its performance during the first 18 months of operation.