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Annihilation of Positrons in Flight

Journal Article · · Physical Review
 [1];  [1];  [1]
  1. Princeton Univ., NJ (United States). Palmer Physical Lab.
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The weak continuous spectrum of hard γ rays resulting from the stopping of positrons in various materials has been investigated with a NaI(Tl) scintillation spectrometer. Measurements were made chiefly in the γ-ray energy interval from 0.511 Mev to 1.3 Mev, for the continuous β spectra of Ne19 and A35 (maximum positron energies of 2.2 Mev and 4.4 Mev, respectively). The experimental geometry was chosen to ensure averaging of the annihilation spectrum over all angles. Theoretical spectra were calculated for Lucite, brass, and lead as stopping materials. Comparison with experiment on an absolute basis was made possible by an experimental determination of the spectrometer efficiency as a function of γ-ray energy. The calculations included bremsstrahlung and single-quantum annihilation as well as two-quantum annihilation. In the case of Ne19 positrons annihilating in brass, the data are in satisfactory agreement with the calculations. However, the calculated spectra show a conspicuously stronger dependence on the atomic number of the stopping material than do the observed spectra. The experimental spectra from Ne19 positrons stopping in Lucite and brass are indistinguishable, while the calculated spectra show a brass to Lucite ratio of 1.3. In addition, the calculated intensities tend to be lower than the observed ones, particularly for A35 positrons and for stopping materials of low atomic number.
Research Organization:
Princeton Univ., NJ (United States). Palmer Physical Lab.
Sponsoring Organization:
US Atomic Energy Commission (AEC)
NSA Number:
NSA-08-003535
OSTI ID:
4410583
Report Number(s):
NYO--6415
Journal Information:
Physical Review, Journal Name: Physical Review Journal Issue: 4 Vol. 94; ISSN 0031-899X
Publisher:
American Physical Society (APS)Copyright Statement
Country of Publication:
United States
Language:
English

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Related Subjects

ABSORPTION-- ANNIHILATION-- ARGON 35-- BETA DECAY-- BREMSSTRAHLUNG-- COPPER ALLOYS-- ELECTRIC CHARGES-- ENERGY RANGE-- GAMMA RADIATION-- GAMMA SPECTROMETERS-- LEAD-- LUCITE-- MEASURED VALUES-- NEON 19-- NUMERICALS-- POLYMERS-- POSITRONS-- SCINTILLATION COUNTERS-- SODIUM IODIDES-- THALLIUM-- ZINC ALLOYS
ATOMS-- EFFICIENCY
PHYSICS