Airborne activity

A more specific problem could be experienced when a detector is installed on a nuclear reactor site, particularly in a reactor hall. There, it may also detect Ar (half-life 1.827h, Ey = 1293.6keV) produced by thermal neutron activation of argon in the air within the voids in the 

Notwithstanding these reservations, it is routine practice in ultra-low background counting rooms to purge, not only the detector space, but also the whole laboratory of radon with filtered clean air. 

The earth s atmosphere receives a cosmic ray flux of about 70 % protons, 20 % alpha particles and 10 % other heavier ionized particles. Their energies are extremely high lO GeV to at least 10 GeV. In the upper atmosphere, at about 25 km above the surface, these particles interact to produce secondary radiations of many sorts, largely pions (ir-mesons). At surface levels, the pions interact further and about 70 % of the total flux generates 

The total cosmic ray flux giving events between 2 and 24MeV is about 0.015 particles per second per square centimetre. The peak at 13MeV corresponds to about 0.08 h keV , which diminishes to about 0.01 h keV at24MeV. 

The steep decline up to 2000 keV, the normal spectrometry range, is due to Compton events, backscatter and bremsstrahlung resulting from the decay of muons into high-energy electrons and positrons. On this are superimposed the 511 keV annihilation radiation and all the gamma-ray peaks from the background nuclides and the peaks from activations described below. 

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Because people everywhere tend to take their fun seriously, they spend freely on sports and recreational activities. The broad range of properties available from plastics has made them part of all types of sports and recreational equipment for land, water, and airborne activities. Roller-skate wheels are now abrasion- and wear-resistant polyurethane, tennis rackets are molded from specially reinforced plastics (using glass, aramid, graphite, or other fibers), skis are laminated with plastics, and so on. 

The sources of a-rays which produce the tracks on the bare CR-39 detectors are divided into airborne activity and activity deposited on the surface of the detectors. The relationship between time-averaged radon concentration (Cq) and the track density (T) on the bare track detector is represented by... 

It can be seen from this figure that whether a round track or a wedge-shaped track is produced is related to the incidence angle and the residual range of the a -ray at the incidence point on the surface of detector. It can be shown that for the tracks produced by the deposited Po-218 and Po-214, the ratios of the round track density and the wedge-shaped track density to the total track density are 0.60 and 0.40, respectively. If the respective ratios for airborne activities are denoted as a and b, the round track density (Tr) and the wedge-shaped track density (T ) are represented by... 

In these experiments, and those of Raabe (1968), the levels of airborne activity, and hence of ionisation in the chamber, were sufficient to ensure that decay products were neutralised, by collision with negative air ions, before entering the diffusion tube. 

It is likely that both the above mentioned effects - larger particle sizes and increase in airborne activity with height - contributed to the high values of W. At later times, the airborne activity from Chernobyl was mainly submicrometre in size and had equilibrated with the accumulation mode of natural nuclei. Over the period 10-90 d from the emission, 137Cs disappeared from the atmosphere with a half-life of 6 d, or mean life of 9 d (Fig. 2.8). The mass of air in the troposphere is 9000 kg per m2 of the earth s surface, and the average daily rainfall in the northern hemisphere is 3.1 mm. Using these data, it can be deduced that the washout ratio of 137Cs was... 

Lockhart, L.,B., Patterson, R.L. Saunders, A.W. (1965) Distribution of airborne activity with particle size. In Radioactive Fallout from Nuclear Weapon Tests, ed. A.W. Klement Jr. CONF 765. N.T.I.S. Springfield, Va. 

Location Major operations Mean airborne activity (Bqnr3) AAMD (am) °8... 

The resuspension of radioactive fallout can be related to the activity originally deposited. If 4 (Bq m-2) is the activity on the ground, xi (Bq m-3) the airborne activity, and Q (Bq m-2 s-1) the vertical flux, the resuspension factor is defined. 

Stewart (1966) has summarised values of Kr found by monitoring airborne activity a few days after fallout from the bomb tests at Maralinga and Monte Bello Island. A range of values from 10-4 to 10-7 m-1 was obtained, but where the ground was disturbed by vehicles, Kr reached 7 x 10-4 m 1. 

Concern about possible inhalation hazards was felt at an early stage in the development of the nuclear industry. Experiments were done with animals to study deposition of radioactivity in the lung, entry into the bloodstream and transfer to organs of concentration. Information has also been obtained from cases of accidental human exposure. The Task Group on Lung Dynamics (1966) reviewed these data and formulated recommendations on which are based the permissible levels of airborne activity. 

If airborne activity is a serious and troublesome problem for a laboratory, suggest ways to eliminate or minimize it. 

Most of the xenon isotopes that have a combination of high fission production cross section and are long-lived enough to be detected ( Xe, Xe, " Xe and Xe), still have half lives short enough that the airborne activity concentrations measured vary greatly with the distance from and the release rate from the source. For example, although... 

A. Types of Surveys. Various types of radiological surveys may be performed. Area surveys may involve the determination of fallout patterns on the ground, levels of airborne activity, or contamination patterns on ships or in buildings. Personnel surveys are performed to detect the presence of contaminated material on the body s surfaces, in body openings, e.g., nose and ears, or in the case of casualties with traumatic injury, contamination in wounds. The results of personnel surveys are used to evaluate health hazards and to establish decontamination requirements. Equipment/material surveys are conducted primarily to establish requirements for decontamination. Monitoring should be done with consistency (1-2 cm from surface for alpha and beta and 1 meter from surface for gamma). 

Contamination can result from a spiU during administration of a radiopharmaceutical and leakage of body fluids from the patient (urine, saliva and vomit). Contamination can also result from airborne activity released when opening a vial containing a solution of or from breathing exhaled activity from the patient. 

In a situation where the only problem is the generation ofairborne radioactivity, individuals should leave the space in which the airborne activity is present,closing the doors behind them and turning off any ventilation in the area, if the controls are in the room. If the ventilation controls are inaswitchroomorbreakerroomelsewhere, they can be turned off from this location. If the accident occurs in or near a fume hood that would vent the material from the laboratory, it may be appropriate to allow the hood to remain on to reduce the airborne concentration of activity within the room however, this would depend uponthe radioactive toxicity ofthe material involved. If it is one ofthe more toxic materials,it would usually be preferable to avoid dispersal into a public area even if the levels are low, because of the possible concerns of exposure to persons in theseareas.Even ifthe potential forexposure is minuscule,many persons will become very alarmed. The laboratory represents a controlled space that can be decontaminated and, in general, the best approach is to restrict the contaminated area as much as possible. 

Biofilm formation at the air-water interface. The bathtub ring often formed at the air-water interface around the sides of the basin is likely to be a biofilm due to microbial activity. This film acts like a trap and is known to concentrate caesium and other radioactive isotopes contained in the basin water. This biofilm should be removed mechanically by wet brushing, using water to hold down any airborne activity. A 35% solution of hydrogen peroxide has proven effective in suppressing microbial activity and could be used to assist in biofilm removal without corrosive attack on aluminium alloys. 

The ventilation system section is comprised of seven subsystems airborne activity confinement system (AACS), central control room habitability (CCRH), Assembly Area ventilation (AAV) system, Disassc ty Area ventilation (DAV) stem. Purification Area ventilation (PAV) system. Building 108-K ventilation (V108) system, and nuscellaneous ventilation tystem. 

Following a loss-of-coolant accident, a fraction of the radionuclides released from the primary circuit remains airborne in the containment atmosphere, as was discussed in the preceding sections. In order to reduce the airborne activity concentrations, standby filters are installed in the annulus of the German PWR plants, consisting of aerosol filters and iodine filters. In the German RSK Guidelines a retention efficiency of 99.9% for particulate iodine, of >99.99% for h and of >99% for organoiodides is required under accident conditions. In certain other countries, the specified iodine species as well as the required retention efficiencies differ somewhat from these values. 

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