Nuclear Instruments最新文献

A 1-meter bent crystal gamma-ray spectrometer is described. The gamma lines are registered on Ilford G5 nuclear emulsions. By counting with a microscope the electron tracks forming a line, it is possible to determine gamma intensities. Corrections have to be made for emulsion efficiency, crystal reflectivity and the geometry of the spectrometer. The accuracy of this method is controlled by the measurements of some known lines in Ta¹⁸². In addition the energies and intensities of two lines in Sm¹⁵³ are given: 69.66±0.02 keV and 103.18±0.04 keV; intensity ratio 9 to 100.

Equations allowing determination of the electric and magnetic f fields at each point within a gap-excited metallic duct are derived. With the application to accelerators in mind, formulas are established for the energy and lateral momentum kicks to which a particle is subjected upon crossing the gap region. The configuration where the gap is in a plane perpendicular to the duct's axis is given some special attention.

Proton and gamma-ray responses of the alkali halide scintillators, NaI, KI, CsI, LiI and Li⁶I have been obtained and the response of a 5-MeV proton was found to be approximately equivalent to the response of a 7-MeV electron for all five scintillators.

Special emphasis was given to the responses of LiI and Li⁶I in an attempt to clarify various anomalies which have arisen in the course of neutron energy measurements with LiI by means of the Li⁶(n,α) reaction. From an estimate of the triton response of LiI and Li⁶I, which was derived from the proton and gamma-ray data in conjuntion with the alpha-particle response and measurements of the pulse height of the Li⁶(n,α) group, it has been shown that energy calibration of the Li⁶(n,α) group with gamma rays is unsatisfactory.

Applications of photographic techniques as a tool in measuring pulse amplitude (PA) distributions fall into 3 general groups:

• 1.

  (1) Recording of individual events as they arrive from the nuclear radiation detector, with subsequent analysis based on visual or photoelectric inspection of the record.

• 2.

  (2) Time exposures of a large series of events, the distribution analysis being provided by the exposure-density correspondence in the photographic process.

• 3.

  (3) Use for permanent storage of results from counting equipment, after the pulse sorting has been performed electronically.

The first and third groups will be reviewed in sections 2 and 5, and some improvements of existing techniques suggested. Quantization of variables is discussed in §§ 2.5 and 2.6 as a simple means for removing ambiguities in automatic scanning of individual event records.

For the second group a thorough presentation of design problems and evaluation procedures is attempted (sections 3 and 4). Gray wedge (GW) techniques lead to a straight-forward quantitative interpretation of photographed PA spectra.

The simplest version of a fast GW spectrometer consists of a commercial oscilloscope and a special plug-in adaptor unit. The adaptor described in § 3.3 provides double rectangular pulse shaping, various shape corrections, overload protection, and generates an exponential sawtooth voltage derived from the linear oscilloscope sweep. This simple GW spectrometer is particularly useful at high counting rates (up to 10⁵ counts/sec).

For a more general use (at both high and low intensities) additional parts such as pulse stretches, gating circuits and various sweep or wedge arrangements are needed (§ 3.4). Stretching and gating requirements will be discussed from a general point of view, and details of circuits used at the ETH will be presented in §§ 3.5 through 3.7. Various methods of producing GW effects are reviewed and the calculated wedge characteristics and light efficiencies compared (§ 3.8). Advantages of the electronic type of GW are the freedom from light losses, simplicity of construction, and versatility in selecting different wedge characteristics. Photographic procedures (§ 3.10) include the use of a printing process to obtain easy-to-read graphs of the PA spectra. Empirical calibration is described in §§ 3.11 and 3.12, and the sources of deviations from the calculated behaviour are discussed.

Absolute intensity evaluation from GW pictures is made possible, as shown in section 4, if the spectrometer is equipped with a few electronic counting channels and an automatic channel limit marker to establish the correspondence between the photographic curve and the channel counts. In coincidence measurements both individual dot recording and density recording of two-dimensional distributions are foun