Answer:
Here's what I get.
Explanation:
James Chadwick is best known for his discovery of the neutron in 1932.
Earlier research
Before 1932, the only subatomic particles known were the electron and the proton. Scientists thought that the nucleus contained both protons and electrons.
For example, they thought a helium atom contained four protons and two electrons, with two electrons orbiting the nucleus.
In 1928, German physicists discovered that beryllium nuclei, when bombarded with α particles, emitted a strange type of extremely energetic radiation. It had no charge, because it wasn't deflected by electric or magnetic fields. Neither was it γ-rays, because it did not discharge an electroscope.
In 1932 Irène and Frédéric Joliot-Curie discovered that the radiation knocked protons loose from paraffin, and they could be detected by a Geiger counter. They, too, thought the radiation was some type of strange γ-rays
.
Chadwick's work
Chadwick did not believe their explanation.
He quickly repeated their experiments with paraffin and also used other substances as targets.
He couldn't observe the uncharged radiation directly, but he could count the protons and measure their energies as they were ejected from the targets.
By working backwards and using the laws of conservation of energy and momentum, Chadwick concluded that the radiation must consist of neutral particles with a mass 1.0067 times that of a proton.
He had discovered the neutron.
