DEVELOPMENT OF A 4$pi$ SCINTILLATION POSITRON SPECTROMETER AND APPLICATION TO THE MEASUREMENT OF THE POSITRON SPECTRUM IN Y$sup 8$$sup 8$
A 4 pi scintillation spectrometer applicable to the measurement of positron spectra was developed. The operation of the system was evaluated in measurements of the positron spectra of Zn/sup 65/, Na/sup 22/, and Co/sup 58/ and the negatron spectra of W/sup 185/ and Pm/sup 147/. It was applied to the measurement of the weak positron transition arising in the decay of Y/sup 88/. The spectrometer system consists of a 4 pi beta detector with auxiliary gamma detectors and associated coincidence circuitry. It is necessary to eliminate distortion in the positron spectrum arising from Compton scattered electrons due to the annihilation radiation and to any coincident nuclear garima radiation. This is accomplished by gating the data-recording device (a multichannel analyzer) to accept and store pulses from the beta detector only when two coincident 511-kev quanta (and perhaps also a nuclear gamma quantum) have been detected. Satisfactory performance of the system was established in measurements of the positron spectra of Zn/sup 65/, Na/sup 22/, and Co/sup 58/, as well as the simple ground-state-to-ground-state negatron transitions in W/sup 185/ and Pm/sup 147/. In the case of the shapes of the spectra of Zn/sup 65/, Pm/sup 147/, and W/ sup 185/ good agreement was obtained with previously reported results using magnetic spectrometer systems. The end-point energies for all beta spectrum measurements presented appear to be from 1 to 3% low compared with averages of other reported values. A discussion is presented of certain systematic errors in energy assignments for the calibration lines (arising from summing effects in the 4 pi geometry), which might account for the low end-point energies. It is pointed out that this problem is connected with the question of the scintillation response of Pilot-B scintillator. The significance of a 20 plus or minus 5-kev positive energy intercept at zero pulse-height for the experimental calibration line is considered in relation to this question. In the measurement of the positron spectrum in Y/sup 88/ as undistorted distribution is obtained by requiring simultaneous detection of the two annihilation quanta and the 1840-kev nuclear gamma radiation that deexcites the level in Sr/sup 88/ to which the positron decay leads. Two measurements of the spectrum yielded experimental shape factors that are consistent with a unique onceforbidden character for the transition. The average endpoint energy for the two measurements is 761 plus or minus 9 kev. The results are in good agreement with values of 757 plus or minus 7 and 761 plus or minus 10 kev derived from recent (p,n) threshold measurements. The positron branching was measured and found to be 0.20 plus or minus 0.01%. The log ft is 9.4 and log fitis 8.7. From recent gamma intensity measurements in the Y/sup 88/ decay the electron-capture branching to the 1840- kev level was determined to be 5.8 plus or minus 0.7%, which yields an electron capture to positron ratio of 29 plus or minus 4. The log fit and electron capture to positron ratio are both in excellent agreement with values that might be expected for unique once-forbidden transitions on the basis of beta-decay theory and nuclear systematics. (TCO)
- Research Organization:
- Originating Research Org. not identified
- NSA Number:
- NSA-18-004125
- OSTI ID:
- 4126726
- Resource Relation:
- Other Information: Thesis. Orig. Receipt Date: 31-DEC-64
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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Related Subjects
ANNIHILATION
BETA SPECTROMETERS
CAPTURE
CIRCUITS
COBALT 58
COINCIDENCE METHODS
COMPTON EFFECT
DECAY
DISTRIBUTION
ELECTRONS
ENERGY
ERRORS
GAMMA DETECTION
GAMMA RADIATION
MAGNETIC FIELDS
OPERATION
PHOSPHORS
POSITRONS
PROMETHIUM 147
PULSE ANALYZERS
PULSES
RADIATION DETECTORS
SCATTERING
SODIUM 22
SPECTRA
SPECTROMETERS
STRONTIUM 88
TUNGSTEN 185
YTTRIUM 88
ZINC 65