Annihilation peak

Fig. 3. Observed hyperfine splitting in the (n, L) = (37,35) —> (38,34) transition of antiprotonic helium. Plotted here is the area under the laser-induced annihilation peak normalized to the total delayed annihilations vs. the laser wavelength...

Figure 45. TOF spectrum transformed to energy transfer distribution for CO/Rh(lll). The top panel shows the single-phonon creation and annihilation peaks for the fmstrated translational motion of CO at 5.75 meV along with a difiuse elastic peak at zero energy transfer. In the lower panel, the shift in energy to 5.44 meV due to the heavier mass of the C 0 isotope is clearly discernible (dashed vertical line). (Reproduced fiom Fig. 3 of Ref. 130, with permission.)...

Figure 3 Schematic representation of a y-y coincidence spectrometer. 1=Nal(Ti) crystai detector 2 = irradiated sample 3 = spectroscopy amplifier plus single channel analyzer (adjusted to screen the 511 keV annihilation peak) 4 = coincidence unit 5 = recording instrument, e.g., multichannel analyzer.

A Annihilation peak at 511 keV, when an annihilation radiation produced in the... 

The positron has a short life it is rapidly slowed in matter until it reaches a very low, close to zero, kinetic energy. Positrons are anti-particles to electrons, and the slowed positron will inevitably find itself near an electron. The couple may exist for a short time as positro-nium - then the process of annihilation occurs. Both the positron and electron disappear and two photons are produced, each with energy equal to the electron mass, 511.00keV (Figure 1.9). These photons are called annihilation radiation and the annihilation peak is a common feature in gamma spectra, which is much enhanced when nuclides are present. To conserve momentum, the two 511keV photons will be emitted in exactly opposite directions. I will mention here, and treat the implications more fully later, that the annihilation peak in the spectrum will be considerably broader than a peak... 

It is not wise, therefore, automatically to dismiss the presence of an annihilation peak without considering its source. 

Annihilation peak (511 keV)-parrproduction withinthe detector surroundings, followed by escape of one of the annihilation gamma-rays in the direction of the detector. Be aware that many neutron-deficient nuclides may emit positrons, the annihilation of which will also give rise to counts in the annihilation peak. 

Figure 7.6 FWHM of full energy, single escape, double escape and annihilation peaks as a function of energy, demonstrating the anomalous width of single escape and annihilation peaks (the detector used had a FWHM at 1332.5 keV of 1.88 keV)...

Figure 7.7 Efficiency curve for a p-type closed coaxial detector. The point lying below the line is that representing the 511 keV annihilation peak...

In the QCYK spectrum, there are a number of potential problems due to the close proximity of extraneous peaks to those to be measured. Particularly difficult is the measurement of the 514.00 keV peak of Sr in the presence of the 511.00keV annihilation peak. Unfortunately, most commercial software does not recognize the fact that the annihilation peak is Doppler broadened and deconvolution of the doublet may be questionable. A similar problem could arise when measuring the 1332.49 keV peak of Co in the presence of the 1325.05 keV single escape peak of which will also be broadened. Fortunately, on any reasonable detector deconvolution will not be necessary. Attention can be drawn to the fact that the energy of the single escape peak of the Co 1173.23 keV peak, 662.23 keV, is very close to the 661.66 keV peak of Cs, although the intensity is very low and there is no problem in practice. 

The annihilation peak at 511 keV generated by pair-production events within the detector environment by high energy gamma-rays from the nuchdes above and cosmic ray events. 

The absorption vessels are measured with a Ge(Li) 7-spectrometer. The 7-spectra contain only the 511 keV annihilation peak, the decay of which corresponds to pure... 

As appears from the Ge(Li) r-spectrum given in Fig. VII-11, no peaks from radionuclides produced from copper appear in the spectrum of the final leadchlorofluoride precipitate. Besides the annihilation peak, there are only the 559 keV and 657 keV Br peaks and the keV peak. These radionuclides arise from arsenic, selenium and antimony impurities in the copper matrix. Only Sr ( 2 ) contributes to the annihilation... 

The positron lifetime experiments were carried out with a fast-slow coincidence ORTEC system with a time resolution of about 230 ps full width at half maximum. A 5mCi source of Na was sandwiched between two identical samples, and the total count was one million. The temperature-dependent Doppler broadening energy spectroscopic (DBES) spectra were measured using an HP Ge detector at a counting rate of approximately 800 cps. The energy resolution of the solid-state detector was 1.5 keV at 0.511 MeV (corresponding to positron 2y annihilation peak). The total... 

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