Everything Science Grade 11

4.6 CHAPTER 4. ATOMICNUCLEI

(

1

2

)x=

1

8

Therefore, x = 3

Step 3 : Use the half-life of Po− 212 to calculate how long the sample was left to decay

The half-life of Po− 212 is 0.16 seconds. Therefore if there were three periods of

decay, then the total time is 0. 16 × 3. The time that the sample was left to decay

is 0.48 seconds.

Exercise 4 - 2

1. Imagine that you have 100 g of Na− 24.

(a) What is the half lifeof Na− 24?

(b) How much of this isotope will be left after 45 hours?

(c) What percentage ofthe original sample willbe left after 60 hours?

2. A sample of Sr− 90 is allowed to decay. After 84 days, 10 g of the sample remains.

(a) What is the half lifeof Sr− 90?

(b) How much Sr− 90 was in the original sample?

(c) How much Sr− 90 will be left after 112 days?

More practice video solutions or help at http://www.everythingscience.co.za

(1.) 00xd (2.) 00xe

4.6 The Dangers of Radiation ESBAN

Natural radiation comesfrom a variety of sources such as the rocks, sunand from space. However,

when we are exposedto large amounts of radiation, this can cause damage to cells. γ radiation

is particularly dangerous because it is able topenetrate the body, unlike α and β particles whose

penetration power is less. Some of the dangers of radiation are listed below:

• Damage to cells
  Radiation is able to penetrate the body, and alsoto penetrate the membranes of the cells within
  our bodies, causing massive damage. Radiation poisoning occurs when a personis exposed to
  large amounts of this type of radiation. Radiation poisoning damagestissues within the body,
  causing symptoms suchas diarrhoea, vomiting,loss of hair and convulsions.


• Genetic abnormalities
  When radiation penetrates cell membranes, it can damage chromosomes within the nucleus of
  the cell. The chromosomes contain all the genetic information for thatperson. If the chromo-
  somes are changed, thismay lead to genetic abnormalities in any children that are born to the
  person who has been exposed to radiation. Longafter the nuclear disasterof Chernobyl in Russia
  in 1986, babies were born with defects such as missing limbs and abnormal growths.