   Chapter 19, Problem 80CP

Chapter
Section
Textbook Problem

# The curie (Ci) is a commonly used unit for measuring nuclear radioactivity: 1 curie of radiation is equal to 3.7 × 1010 decay events per second (the number of decay events from l g radium in 1 s). A 1.7-mL sample of water containing tritium was injected into a 150-lb person. The total activity of radiation injected was 86.5 mCi. After some time to allow the tritium activity to equally distribute throughout the body, a sample of blood plasma containing 2.0 mL water at an activity of 3.6 μCi was removed. From these data, calculate the mass percent of water in this 150-lb person.

Interpretation Introduction

Interpretation: Total activity of radiation injected into a person is given. Removal of blood plasma after some time and its radioactivity is also given. The mass percent of water in the person is to be calculated.

Concept introduction: The average number of disintegration per second of a radioactive substance is known as its activity. The biological effects of radiation depends upon several factors such as, the energy of the radiation, ionization ability and penetrating ability of radiation and the chemical properties of the radiation source.

To determine: The mass percent of water in the 150lb person.

Explanation

Explanation

Given

Volume of sample drawn out is 2mL .

The total activity of radiation injected is 86.5mCi .

The activity in the water drawn out is 3.6μCi .

Mass of the person is 150lb .

The conversion of μCi to Ci is done as,

1μCi=106Ci

Therefore, the conversion of 3.6μCi to Ci is,

3.6μCi=3.6×106Ci

The conversion of mCi to Ci is done as,

1mCi=103Ci

Therefore, the conversion of 86.5mCi to Ci is,

86.5mCi=86.5×103Ci

The total volume is calculated by the formula,

VolumeofsampledrawnoutCountsinsampledrawnout=TotalvolumeTotalcounts

Substitute the value of volume of sample drawn out, counts in the volume drawn out and total counts in the above formula.

2mL3.6×10-6Ci=Totalvolume86.5×10-3CiTotalvolume=4.81×104mL_

Therefore, the total volume of water is 4

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