[Chemist_Geek]

Lead will stop the gammas--but you need lots of low-density material (hydrogen, et cetera) to stop the neutrons.

Really dumb question here: What instrument does one use to detect neutron radiation, how does it work, and how portable and fragile is it?

[spunkets]

Neutrons are not usually found from a decay process. They are produced commonly by reactions. neutrons and detection of same

A geiger counter, or geiger tube is used to detect alpha, beta and gamma rad. geiger tube

Thermal (slow moving) neutrons from reactions are collected by metals like cadmium and nonmetals like carbon(carbon pile reactor(Chernobyl)). Those are the control rod materials.

[MrNeutron1962]

We use fission chambers in nuclear power. Vacuum filled chambers that have a plating of special nuclear material, usually Pu-239. A high voltage is impressed between the shell of the device and an inner screen, kinda like a vacuum tube, but instead of a cathode to emit electrons the SNM does if for you. When struck by a fast neutron, the Pu breaks down into ionized particles, causing a leakage current between the sheel and the pin. This can be measured, and using a conversion factor, the neutron flux can be estimated. The neat part about these devices is most ions will not penitrate the outer casing, just not enough zoomies eV wise.

These devices are very robust, and will survive the post-Lose of Coolant Accident (LOCA) environment inside containment for hundreds of hours. The sensitivity is adjusted two way, one, more dense SNM is used, like Pu-243, and second, the area of the detector can be increased. Figures a guy call mr neutron whould know this.

[j_tull]

AN/PDR 70 is carried on USN ships. Size of 2 stacked cases of beer, weighs 60lbs, probe is pretty fragile. I retired in '95, they may have something newer.