Question

Consider the 500-Watt heat source in the previous problem. Assuming that at launch the 500-Watt source was pure plutonium 238, what was the mass of the plutonium 238 at launch (closest answer in kg)? The alpha particles emitted by the plutonium have energy 5.6 MeV.

(Previous Problem: Plutonium 238 is used as a heat source to generate electricity in space probes. It is an alpha-emitter with a half life of 88 years. If the plutonium heat source on a probe produces 500 Watts of power when it is launched, how much is it producing 28 years after launch)

Answer 1

500 Watt source means , it produce 500 J per sec at launch.

1 alpha particle has 5.6 * 106 eV = 5.6* 106 *1.6022 * 10-19 J =8.9722 *10-13 J

To produce 500 watt ,no. of alpha particles produced in 1 sec= 500/8.9722 *10-13

=55.727*1013

no. of alpha particles produced in 1 sec = no. of plutonium atom decayed in 1 sec

and   

at t=1 sec  

no. of plutonium atom decayed in 1 sec=

= ==55.727*1013

Mass in grams =3.7 * 238 =880.6 g

Mass in kg =0.88 kg