TS2 on Target – view from the LOQ cabin

A brief overview of some neutron history

Since it carries no charge, one could not “weigh” a neutron directly in a mass spectrometer, but had to estimate its mass from the difference between deuterium and hydrogen. However in 1935, more accurate measurements allowed Chadwick to derive a neutron mass of between 1.0084 and 1.0090 units; the modern estimate lies almost exactly in the middle of this range, and so the neutron is appreciably heavier than the proton. Was Uncle Albert wrong? Chadwick immediately suggested (following Einstein again) that neutrons should have an excess of energy and be beta radioactive in common with other nuclei under like circumstances. It was not so easy, however, to verify this experimentally. But, partly owing to World War II, it was not until 1948 that neutron decay was verified – indeed, 12 minutes after they’ve been kicked out of the nucleus half of them will have split apart as Chadwick had suggested. So if you want to use neutrons, you can’t keep ’em in a bucket.

That last bit is a tad misleading — it’s no doubt referring to the decay, not the ability to confine. Since neutrons have a magnetic moment, they can be trapped. It’s a weird, shallow bucket, and it leaks, but you can keep ’em there until they decay.