The following reaction occurs in a nuclear reactor: $$^{235}U + n \rightarrow $$\text{ }$$^{144}Ba + X + 3^{1}n + 202.5 \text{ MeV}$$ (i) Identify the element X - Leaving Cert Physics - Question b - 2010

To calculate the mass difference ( E = mc^2 ):

1. The energy released in the reaction is given as 202.5 MeV, converting to joules:

   $$E = 202.5 \times (1.6 \times 10^{-19}) \text{ J} = 3.24 \times 10^{-17} \text{ J}$$

2. The speed of light is approximately ( 3.0 \times 10^8 \text{ m/s} ): ( m = \frac{E}{c^2} = \frac{3.24 \times 10^{-17}}{(3.0 \times 10^8)^2} = 3.6 \times 10^{-34} \text{ kg} )

A chain reaction is a self-sustaining reaction where fission neutrons produced from one fission event cause further fission events, leading to a rapid increase in the number of fissions. This can be depicted through a diagram showing the process.

One condition necessary for a chain reaction to occur is that the mass of fuel present must exceed the critical mass. This ensures that at least one of the neutrons released from each fission event will cause fission of another nucleus.

One environmental impact associated with a nuclear reactor is the production of toxic or radioactive waste, which can expose the environment and living organisms to radiation.