K.C.S.E Physics Q & A - MODEL 2015PP2QN16

K.C.S.E Physics Q & A - MODEL 2015PP2QN16

​(a) It is observed that alpha  particles have a lower penetrating power than beta particles. Explain this observation. 
(b) A radioactive substance has a half life of 12 years. Determine the time it would take to decay to 12.5% of its original value. 

​(c) A Geiger Müller (GM) tube is used for detecting radiations from a radioactive source.
State the function of:
(i) the mica window;
(ii) bromine gas in the tube. 
(d) (i) In a diffusion chamber, explain why some of the tracks formed are observed to be;
(I) Short, 
(II) Straight. 
(ii) State two advantages of using a GM tube instead of a diffusion cloud chamber to detect radiations from radioactive substances.

answers

(a) Alpha particles are heavier and move at lower speeds hence less penetrating power than
Beta particles which are lighter and move faster

​(c) (i) allows the radiations into the tube 
(ii) absorbs kinetic energy of positive ions so that they do not cause secondary ionization in the tube 
(d) (i) Short - They ionize heavily loosing most of the energy hence cannot travel far.
Straight - They are massive compared to air molecules hence collision with air molecules cannot change their path.
(ii) GM is easily portable than a cloud chamber. 
GM is more sensitive.
GM tube detects radiation at very low intensity and cloud chamber cannot detect radiation at very low intensity.