R.B. Galloway

The design and operation of a fast neutron polarimeter

Abstract A fast neutron polarimeter using neutron scattering from a high pressure He gas scintillator is described. Choice of scattering angle is considered with regard to the speed of data collection and the accuracy with which the analysing power of He is known. The importance of displaying the He recoil spectra for accurate polarization analysis is emphasised. A preliminary polarization measurement on the neutrons from the 2 H(d,n) 3 He reaction gave (−12.9±0.7)% for 390 keV deuterons and a reaction angle of 46° lab.

Neutron polarization studies with low-energy accelerators

Abstract The role of low-energy accelerators in fast-neutron polarization studies is assessed in the light of a review of the value of information on polarization, the techniques available for the measurement of the polarization of a fast neutron beam and of the available data on neutron polarization resulting from elastic scattering and from nuclear reactions. Data on the principal neutron producing reactions is summarised for incident particle energies of up to 10 MeV.

Criteria for evaluating background suppression techniques in nuclear spectroscopy based on consideration of statistical accuracy

Abstract A discussion is presented of the improvement possible in the statistical accuracy with which the intensity of a peak may be determined by improvement of the peak to background ratio when associated with a reduction in detection efficiency.

The polarization of neutrons from the 2H(d,n)3He reaction for deuteron energies less than 1 MeV

Abstract A series of measurements are reported of the polarization of neutrons emitted at a laboratory reaction angle of 46° from the 2H(d,n)3He reaction for deuterons from 0.3 to 0.9 MeV incident on a thin target. Particular attention is given to the collection and analysis of data from the 4He scattering polarimeter in a way which detects and corrects for spurious scattering effects, so as to give confidence that the polarization values reported here correctly chart the energy dependence through the scatter of previously published discrepant values. A possible origin of past discrepancies is discussed.

A voltage-dependent-resistor dynode chain to reduce the variation of photomultiplier gain with counting rate

Abstract A simple, compact dynode chain employing voltage-dependent-resistors to regulate the voltages applied to the dynodes of an EMI type 6262B photomultiplier is described. The use of this chain instead of a carbon resistor one enabled the range of counting rates over which a NaI (Tl) scintillation spectrometer could operate without excessive gain changes to be extended by a factor of 5.

The polarization of neutrons from the 2H(d, n)3He reaction for deuteron energies from 1 to 5.5 MeV

Abstract The dependence on deuteron energy of the polarization of the neutrons emitted at 45° from the 2H(d, n)3He reaction in the range 35 to 275 keV, was determined from the asymmetry in the scattering of the neutrons by 4He. There is no indication of the much discussed possible resonance at about 100 keV deuteron energy. The results are discussed in relation to the general theoretical treatment of the 2H-2H interaction put forward by Boersma.

A simple fast-neutron detector with pulse discrimination against gamma rays

Abstract The satisfactory neutron detection attainable with an NE213 liquid scintillator and a simple 11-stage photomultiplier employing the Owen technique of pulse-shape discrimination is demonstrated. Suitable circuitry for use with the detector is given and can be contained within a single-width NIM module, making the system particularly suitable for multi-detector experiments in which fast timing is not essential.

A polarimeter for studying the elastic scattering of polarized fast neutrons

Abstract The polarimeter described has been designed for use over a wide range of neutron energies to obtain the anglar dependence of polarization and the differential cross-section of elastically scattered neutrons. for good efficiency of data collection the asymmetry in the scattering of polarized neutrons is determined simultaneously at 3 scattering angles while adequate monitoring of the neutron flux is provided to enable the differential cross sections to be obtained also. The time-of-flight technique is employed. Examples are provided of the use of the instrument with 3 MeV neutrons from the 2 H(d,n) 3 He reaction and an associated particle time-of-flight system and with 16 MeV neutrons from the 3 H(d,n) 4 He reaction and a pulsed beam time-of-flight system.

Small angle scattering of fast neutrons

Abstract The reasons for interest in small angle scattering of fast neutrons are outlined. Apparatus developed for investigating small angle scattering of 3.5 MeV neutrons emitted in the 2H(d,n)3He reaction using a 1 MeV accelerator is described and its performance assessed. Preliminary measurements are presented of the differential cross sections for scattering by Cu and Pb at angles between 1.4° and 10°.

Scintillation counter stability

Abstract In view of the lack of available data on the stability over a period of days of a typical scintillation counter system with “standard” electronics, a brief report is presented on the performance of twelve scintillation counter systems over a period of six days. The gain fluctuations were characterized by a mean standard deviation of 0.25%, the best detector system showing only 0.13% and the worst 0.75%. A small but significant, 0.2%, gain change on movement between two test locations was also recorded.