Uranium -238 has a half life of 4.5 billion years. How long will it take a 2g sample of U-238 to contain just 0.4g of U-238?
Radioactive decay is a process where the nucleus of an unstable atom, such as Uranium-238 loses energy by emitting radiation.
The half life is the average time it take for half the nuclei in a sample to undergo radioactive decay.
Given an initial sample of x with mass N(0). After a time t the mass of x left in the sample N(t) is given by:
N(t) = N(0).2-t/t1/2 (1)
Where t1/2 is the halflife.
To answer the question we need to find t. Rearranging equation (1) we have:
- t1/2 log2[N(t)/N(0)] = t (2)
subbing the values from the question into (2)
-4.5x109 log2 [0.4/ 2] = 10.4 billion years
RE
Related Physics A Level answers
All answers ▸A pellet of mass 8.8 g embeds itself in a wooden block of 450 g which is suspended by a light in-extensible string. After the collision the block reaches a max height of 0.63 m. Calculate the initial velocity of the pellet.
A ball is thrown downwards from a height of 10m with speed of 5m/s, assuming g=10m/s^2, calculate the final velocity of the ball when it hits the ground
A ball is dropped from rest at a height of 2 metres. Assuming acceleration due to gravity (g) is 10m/s^2 calculate the velocity of the ball just before it hits the floor.
What does a negative velocity mean?