WEBVTT 00:00:00.000 --> 00:00:02.840 This is College Physics Answers with Shaun Dychko. 00:00:03.177 --> 00:00:05.725 We are going to calculate the energy released 00:00:05.720 --> 00:00:07.451 in this neutron source 00:00:07.450 --> 00:00:10.582 when beryllium is bombarded by alpha particles. 00:00:11.737 --> 00:00:16.594 Now we need to know what the atomic mass of each of these isotopes are. 00:00:16.742 --> 00:00:19.211 So for helium-4, there's the atomic mass 00:00:19.210 --> 00:00:21.622 and here's beryllium-9 has that atomic mass 00:00:21.794 --> 00:00:25.600 carbon-12 is 12.00000 by definition 00:00:25.885 --> 00:00:27.862 and the mass of a neutron is this 00:00:28.045 --> 00:00:30.205 and to figure out the energy released, 00:00:30.200 --> 00:00:33.611 we have to find the difference in total mass 00:00:33.610 --> 00:00:36.457 between the two sides of this equation 00:00:37.120 --> 00:00:39.725 and then convert that into energy. 00:00:40.834 --> 00:00:45.074 So the energy released then is the mass defect is one way to put it 00:00:45.070 --> 00:00:47.988 or the change in mass times c squared. 00:00:48.217 --> 00:00:51.817 And so we have the mass of the alpha particle 00:00:52.034 --> 00:00:54.902 plus the mass of beryllium-9 00:00:55.085 --> 00:00:58.445 minus on the right-hand side, the mass of carbon 00:00:58.440 --> 00:01:00.948 and minus the mass of the neutron 00:01:01.405 --> 00:01:03.302 and that difference gets multiplied by 00:01:03.300 --> 00:01:07.942 931.5 megaelectron volts per c squared for every atomic mass unit 00:01:07.942 --> 00:01:09.940 and so the atomic mass units cancel 00:01:10.742 --> 00:01:15.428 and then we multiply by c squared because that's what this equation tells us to do 00:01:15.622 --> 00:01:18.297 and then these c squared's cancel leaving us with 00:01:18.468 --> 00:01:23.257 5.701 megaelectron volts of energy are released.