Alpha recoil distribution

It has been reported for many years that condensation nuclei can be produced by ionizing radiation. Recent studies have improved the measurement of the activity size distribution of these ultrafine particles produced by radon and its daughters (Reineking, et al., 1985 Knutson, et al., 1985). It seems that the Po-218 ion is formed by the radon decay, is neutralized within a few tens of milliseconds, and then attached to an ultrafine particle formed by the radiolysis generated by the polonium ion recoil. Although there will be radiolysis along the alpha track, those reactions will be very far away (several centimeters) from the polonium nucleus when it reaches thermal velocity. The recoil path radiolysis therefore seems to be the more likely source of the ultrafine particles near enough to the polonium atom to rapidly incorporate it. 

Since the subsequent B-decays of Pb-212 and Pb-214 4- Bi-214 do not result in significant recoil (Mercer, 1976), the alpha measurement of Po-214 and the Pb-212 daughters is in reality tracing the aerosol distribution of a Rn-220 daughter atom (Pb-212) which has condensed only once and a Rn-222 daughter atom (Pb-214) that has probably condensed more than once. This stability of the Pb isotopes is the basis for our generic reference to Pb-212 and Pb-214 distributions. 

The aerodynamic size distributions of Pb-214, Pb-212, Pb-210, Be-7, P-32, S-35-SoJ , and stable SO4 were measured using cascade impactors. Pb-212 and Pb-214, measured by alpha spectroscopy, were largely associated with aerosols small than 0.52 11m. Based on over 46 low-pressure impactor measurements, the mean activity median aerodynamic diameter (AMAD) of Pb-212 was found to be 0.13 11m, while for Pb-214 the AMAD was larger—0.16 lim. The slightly larger size of Pb-214, confirmed with operationally different impactors, was attributed to a-recoil-driven redistribution of Pb-214 following decay of aerosol-associated Po-218. A recoil model was presented that explained this redistribution. Low-pressure impactor measurements indicated that the mass median aerodynamic diameter of SoJ ... 

Because the momentum and energy evolved in the decay must be conserved, they are distributed between the product nucleus (sometimes called the recoil nucleus) and the emittedg alpha particle. The unit of energy commonly used in describing nuclear decay and radiation is the electron volt and its multiples. One electronvolt equals 1.6 x 10 J, which is numerically equal to the electron charge e in coulombs. 

The alpha particle spectrum at all resonances is complicated by the fact that the transitions aj leading to the broad excited state of Be are accompanied by particles aj2 due to the break-up in flight of the recoil Be nuclei these form a continuous distribution between certain limits. The analysis of this distribution by Dee and Gilbert to prove the existence of an excited state of Be , was the first successful treatment of a three-body reaction. The ground state of Be is also unstable to break-up into alpha particles angular correlations in the alpha particle reactions have confirmed previous assignments for the Be levels. 

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