User Guide for the Air Force Nuclear Weapons Center Dust Cloud Calculator V.1.0

Modeling Fallout from Nuclear Weapon Detonations: Efficient Activity and Dose Calculation of Radionuclides and Their Progeny

“…Here the bin border indicates the range in the formulae and the middle of the bin is the number used for dispersion calculation.Bin border (μm)Middle of bin (μm)In bin (%)Cumulative (%)<0.10.050.510.510.1 – 10.5525.8326.341 – 53.0023.1249.455 – 107.514.5263.9810 – 503027.5491.52>501008.48100We tested claims of activity distribution over particle size and particle size with height. However, we never could find satisfactory results to statements given in Harvey et al (1992), Ledger (2015) and Baker (1987), similarly as the conclusion of Arnold et al (2019). Therefore, we keep to a uniform approach for particles sizes with height and activity related to a certain particle size.…”

“…In air bursts, these ground particles are not present, which means that the average particles are likely to be small.Most sources in literature give a list of particle bins with a percentage of the radioactivity found therein. Others give a lognormal distribution for how the particles are formed, such as Baker (1987) and subsequent work by Ledger (2015). We will follow this approach, since this framework can approximate most statements about distributions.…”

“…For the ratio between these two groups, we follow Baker (1987), who indicated that if a stem is present, about 25% of the radioactivity will be on particle surfaces and the rest will be present within the volume of particles that did not have a condensation nucleus. For the calculation of the lognormal distribution, we follow Ledger (2015) as depicted in eqn (B1): F()r=1italicβr2πe−12ln()r−αnβ2,with α defined as: αn=ln()rmean+nβ2,and where r is the particle radius, r mean is the mean particle radius, and n indicates the type of activity distribution for the particle: n = 0 for radius, n = 2 for surface, and n = 3 for volume. The parameter β is defined as ln( σ ), where σ is the standard deviation of the particle radius.…”

“…Note that the quantity of radioactive gasses is not included in this table. Fractionation and changes of the distribution other than deposition are not considered, other than what is considered in the method by Baker (1987) and Ledger (2015). Seeing that Baker (1987) used data fly-through observations of only 20 min to 4 h after the explosion, we assume that fractionation was completed fairly shortly after the explosion.…”

“…For the ratio between these two groups, we follow Baker (1987), who indicated that if a stem is present, about 25% of the radioactivity will be on particle surfaces and the rest will be present within the volume of particles that did not have a condensation nucleus. For the calculation of the lognormal distribution, we follow Ledger (2015) as depicted in eqn (B1):…”