HW6-18 - 5-13 18. The averagemass of potassium in the human...

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Unformatted text preview: 5-13 18. The averagemass of potassium in the human body is about 140 g. From the abundance and half-life of 40K (seeTable 5.2), estimate the average activity (Bq) of 40K in the body. Solution: From Table 5.2, the atomic abundance of40K is 140= 0.000117. The number of potassium atoms in the body N K is NK = ~ = .(140)(6.022X 1023) = 2.156 X 1024atoms. 39.0983 The number of 4oK atoms is N40 = 0.000117NK = 2.523 X 1020atoms. This number of 4oK atoms has an activity A40 = A40N40.The decay constant for 40K is A40= T -In2 = 1.73 X 10-17 S-1 1/2 Thus the 40K activity in the body is A40 = A40N40= (1.73 x 10-17)(2.523 x 1020)= 4,360 Bq. 19. The naturally occurring radionuclides 222Rnand 220Rndecay by emitting a particles which have a range of only a few centimeters in air. Yet there is considerable concern about the presenceof these radioisotopes in interior spaces. Explain how these radioisotopesenter homesand workspacesand why they are consideredhazardous to the residents. Solution: Radon is a noble gas and, consequently,becomesairborne after escaping from the soil and seeping into houses through cracks in the basementfloors. The buildup of radon in homes can become severaltimes higher than that in the ambient outdoor air. Breathing radon itself is or little concern since it is almost immediately exhaled before it can decay. However, as it decays in the air, its radioactive daughters adhereto dust and aerosol particles, which when inhaled, become trapped in the surface lung tissues. The subsequentalpha decay of these daughters is thought to cause significant damage to the cells in these tissues, endowing the damaged cells with a predisposition for later turning cancerous. July 24, 2002 ...
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This note was uploaded on 02/01/2010 for the course ECE 4130 taught by Professor Cady during the Spring '06 term at Cornell University (Engineering School).

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