During the Manhattan Project, a pile of fissile material accidentally achieve supercriticality on two separate occasions, killing Harry Daghlian and Louis Slotin, respectfully.
when a nuclear reactor in Tokaimura, Japan had an accident, technicians Hisashi Ouchi and Masato Shinohara received toxic doses of radiation. They also died from radiation poisoning.
The toxic radiation was the flash of Neutrons released from an uncontrolled fission reaction.
If neutrons are neutral, how do they interact and destroy living tissue?
Neutrons can still impart energy to a nucleus. This can ionize the atom, and that leads to all kinds of unpleasant chemical effect. Also, neutrons can be absorbed by an nucleus, and “activate” it - turning it into a radioactive isotope.
Just so. Loose neutrons essentially slam into the hydrogen atoms of living tissue and send the H nucleus flying free of its electron. Plenty of hydrogen atoms in water, of course – but also in proteins (e.g. collagen), lipids, and carbohydrates. Neutron radiation can do a number to a living thing.
One mechanism is that they can be absorbed by stable isotopes to create radioactive ones.
Which then decay emitting ionising radiation which breaks chemical bonds leading to radiation poisoning.
Elastic scattering, a.k.a. proton recoil. Neutron detection - Wikipedia goes into it.
ETA: this is why substances containing lots of hydrogen are better neutron shields than materials of higher atomic number. Because protons weigh about the same amount as neutrons the energy of the impacting neutron is likely to be about halved, whereas with a heavy nucleus the neutron is more likely to “ricochet” with most of its energy retained.
Because they’re not charged, neutrons don’t interact electromagnetically with the matter in your body. Instead they interact via the strong force with your atomic nuclei. Nuclei are very small. A single neutron is unlikely to interact with a single nuclei. But you have a lot of nuclei and a fission reaction that’s near critical produces a lot of neutrons.
Just to add a simplifying note to the good answers already given, the dangerous type of radiation is ionizing radiation. And while charged particles like electrons can ionize atoms due to their electric charge, electrically neutral particles like photons and neutrons can do the same just due to their kinetic energy if that energy is high enough. Incidentally, even though photons theoretically have zero rest mass, they do have kinetic energy due to energy-mass equivalence, and a photon’s energy is a direct function of its frequency (or, inversely proportional to wavelength). That’s why X-rays and gamma rays are potentially dangerous, while radio waves and microwaves are not (except insofar as they can cause heating, but they’re not ionizing).
There are four different basic physiological interactions with neutron radiation: elastic scattering, inelastic scattering, neutron capture, and spallation. (Technically there is also fission induced by neutron bombardment but the human body doesn’t have any fissile or fissionable isotopes unless the person has been eating nuclear fuel elements or smoke detectors.) Each of these modes has different types of interactions and products with living tissue, and are characterized by a neutron kerma factor. (“kerma” is actually an acronym meaning “kinetic energy released per unit mass” but is rarely capitalized and just used as a general metric for what different energies of neutron radiation do.)
Although neutrons are not themselves charged particles, they are considered indirectly (or secondarily) ionizing radiation because they will react with nuclei which can then produce energetic ironizing radiation. The primary interactions in tissue with neutron capture by normal hydrogen producing deuterium and an energetic gamma ray, 14N which produces 14N and a free proton. The kerma that is actually deposited in tissue per neutron fluence by thermal (slow) neutrons is primarily by capture and is dependent upon the neutron capture cross section, the density of interacting nuclei and the average energy transfer per reaction (a quasi-empirically defined statistical measure). There can be interactions with intermediate and fast neutrons, primarily by elastic scattering which transfers energy through kinetic interactions (basically heating). Fast neutron exposure can present as thermal damage but do very little actual damage, so counterintuitively the faster the neutrons the less serious damage it does.
To complete the picture. What kills you varies with the damage. Enough random damage just cooks you and you die before you hit the ground. This is the far end. At the other end, where people dies weeks after is more insidious.
Cells that’s dividing unravel their DNA so that it can be replicated. In this state the DNA is much more vulnerable to oxidation by radicals created by oxidising radiation. Enough damage and the cell machinery will trigger apoptosis. The cell kills itself. Usually a beneficial action, clearing out misbehaving cells, too much of anything is not good.
Fast dividing cell lines are found in blood production, gut lining, skin, liver. And radiation poisoning occurs when these cell lines are damaged. Which accounts for the symptoms. Enough damage and your body won’t be able to continue to function. You will survive until the cessation of renewal of these cells catches up with you. Survival is quite possible, if you have not lost the entire capacity of cell renewal. But there is a continuum of long term effects. High incidence of cancer being an obvious one. Degradation of immune system another- which likely accounts for a significant part of the cancer incidence.
More extreme cell chemistry damage, will shut down cellular processes, and you die quickly. But you don’t need anything like the dose to trigger the cascade from DNA damage.
The Nuclear Regulatory Commission and International Commission on Radiological Protection actually publish weighting factors to estimate the effects of absorbing different types of radiation. If your basic beta and gamma rays are assigned a weight of 1, then absorbing 1 Gy of alpha particles, for example, will result in an equivalent dose of 20 Sv. “Neutrons of unknown energy” and high-energy protons have a weight of about 10. The ICRP report breaks it down by energy, too, so you can see that 1 MeV neutrons have a factor of about 20 while 50 MeV neutrons only hit you for 5.5.
14N is the main (99.6%) isotope of natural nitrogen. Perhaps Carbon-14 is meant as the product if a proton is kicked out. Otherwise you get 15N and a gamma ray: CapGam - 14N(N,G) E=THERMAL
A proton emitted in a thermal neutron reaction like that can deposit its kinetic energy in the body and dose you.
Sorry, that was a cut and paste error; that sentence should read:
The primary interactions in tissue with neutron capture by normal hydrogen producing deuterium and an energetic gamma ray or14N which produces 14C and a free proton.
14N is the primary stable isotope of nitrogen (99.6% of all nitrogen), and 14C is the unstable isotope of carbon used in radiocarbon dating.
@Francis_Vaughan gave an overall summary of what ionizing radiation does. For the most part, the concern is about gamma/X-ray radiation (very high energy photos), with less concern about energetic beta radiation (electrons or positrons), which can only penetrate a fraction of an inch into tissue which can result in desquamation (death and shedding of skin) through the entire epithelial layer, and very little about external exposure to alpha radiation (essentially an ionized helium nucleus that can’t penetrate the layer of ‘dead’ epithelial tissue). However, beta and alpha radiation are of much more concern if they are ingested within the body or are produced by elements already in the body through the neutron interactions described above. There are a variety of mechanisms that result in the various signs and symptoms of acute radiation exposure but the primary are chromosomal damage (disruption of the chromatin structure which contains DNA) as well as damage to the DNA itself via both direct impingement and free radicals which oxidize cellular structures. Note that this doesn’t just apply to the nuclear DNA in your chromosomes but also the extrachromosomal DNA and DNA in the mitochondria, which can result in a multitude of metabolic dysfunctions and essentially will cause the cell to proceed into apoptosis (cell death), and the patient essentially disintegrating from within. With massive whole body radiation exposure it will also cause a shutdown of the adaptive immune system, rendering the patient unable to fight off even normally innocuous infections as the epidermis also breaks down, allowing pathogens to enter through the skin. The number of incidents of whole body neutron radiation exposure are small because this can basically only occur in a criticality accident, so case studies in medical literature are limited all cases unshielded exposure to high levels of neutron radiation frequently result in death, although people who were far enough away or shielded by equipment or metal cabinets have survived without apparent long term harm.
