neutron sources in the world

Pulse reactors

The sources of neutron radiation with suitable examples and sketches are discuss here advanced. sources of neutron radiation is needed to read.

Types of neutron sources:

  1. Isotopic (ampoule) sources.
  2. The accelerator as a source of neutrons.
  3. Neutron generators.
  4. Reactors:
  5. industrial research: – continuous; – impulse.
  6. Plasma traps.

Pulse reactors

In pulsed reactors, a chain reaction develops on instant neutrons. Using the so-called reactivity modulators, the reactor is transferred to the supercritical state for a short period of time (from ~ 10-4 s to several seconds), when the neutron multiplication factor without taking into account delayed neutrons k> 1. A chain fission reaction quickly develops in the reactor. Then the reactor is transferred to a subcritical state and the process decays. As a result, pulsed neutron fluxes of high intensity are generated. Managing the criticality of a reactor using instant neutrons is a dangerous activity. “Carrying out such experiments is like tickling the tail of a sleeping dragon!” – said R. Feynman.

They say that in the 40s. The pulsed reactor in Los Alamos worked as follows. From above, a piece of plutonium or uranium, which flew past another piece of nuclear material, was thrown into a vertical pipe. For some time, the total mass exceeded the critical mass and a powerful neutron flux was generated. Modern pulse reactors are more complex systems and much attention is paid to the safety of their operation. Three types of impulse reactors are distinguished: self-extinguishing impulse reactors, periodic impulse reactors and boosters. In self-extinguishing pulse reactors, the fission chain reaction is quenched due to the negative feedback of various processes associated with the released heat, with the neutron multiplication factor.

One of the first pulsed reactors was the one-time Lady Godiva fast neutron reactor, created in 1951 at the Los Alamos Laboratory in the USA. The duration of neutron pulses in such reactors is from several tens of microseconds to several seconds. The pulse repetition rate is low (one pulse per hour, or even 2-3 times a day) and is determined by the time required to cool the reactor. In a pulse up to ∼1018 neutrons (JAGUAR at VNIITF, Snezhinsk). In periodic pulsed reactors, neutron pulses are initiated and quenched due to the periodic movement of part of the core, part of the reflector or moderator. In periodic – the power in each pulse is less than in a single one. The first IBR-1 batch reactor (pulsed fast reactor) was launched at JINR (Dubna) in 1960.

The idea of ​​IBR-1 was proposed by D.I. Blokhintsev: a disk with a uranium insert rotates between two parts of plutonium. When all three parts coincide, a powerful chain reaction arises, which quickly dies out. Regarding this reactor, N. Bohr said: “I admire the courage of people who decided to build such a wonderful installation!” DI. Blokhintsev believed that operating a pulsed reactor was the same as teasing a tiger in a cage (almost safe). Subsequently, a more powerful IBR-2 pulsed reactor was built at JINR (official operation since 1984). A diagram of this reactor is shown in Fig.

sources of neutron radiation reactor layout
reactor layout

IBR-2 reactor layout:

  1. core
  2. stationary reflector
  3. channel for the target of the accelerator and sample irradiation
  4. moderator-water
  5. main movable reflector
  6. additional movable reflector
  7. moderator-water

The 22-liter IBR-2 core contains 82 kg of plutonium dioxide and is cooled by liquid sodium. Reactivity is modulated using a movable reflector. From the moment of start-up, a steel reflector worked, which consisted of two parts: the main and auxiliary (the so-called “trident”). These two parts rotated at different speeds (1500 and 300 rpm) around the core. When they were simultaneously opposite the

In this case, a neutron pulse was generated. “Tridents” worked until 2003. In 2004, a new lattice reflector made of nickel alloy was launched, which consists of two parts rotating in opposite directions at a slow speed (600 rpm). The duration of the power pulse is preserved. This reflector will also work on the modernized IBR-2M reactor. The average power of IBR-2 is 2 MW; pulse power – 1500 MW. Thermal neutron pulses of duration ~ 300 μs are emitted with a period of 5 Hertz, and the neutron flux in the pulse on the moderator surface is 5 · 1015 neutrons / (cm2 · s). The IBR-2 research pulse reactor is one of the most efficient sources in the world for research on extracted beams of slow neutrons.

I must say that periodic pulsed reactors were built and operated only in the USSR and Russia, despite the fact that projects of such reactors were developed in other countries. This is primarily due to the problem of operational safety. Not in vain from the time of construction to the official launch of IBR-2 (1978-1984) almost as much time has passed as from the beginning of its design to construction (1966-1978). In the booster, the heavy metal converter target is placed in a subcritical assembly. A power pulse is initiated by a neutron pulse from an external source. As external sources, high-current electron accelerators (30 – 200 MeV) are used. Electrons from the accelerator give rise to inhibitory gamma rays in the target, which in turn cause photonuclear reactions (γ, xn). Photonuclear neutrons initiate a chain reaction in the assembly, which leads to an increase in the neutron flux by 10-30 times. After turning off the external source, neutron multiplication ceases. The superbuster has the ability to modulate reactivity in a breeding target. In the IREN booster (resonance neutron source) (JINR), the LUE-200 linear electron accelerator has a pulse duration of 250 ns, the electron current per pulse is ~ 1.5 A, the pulse repetition rate is 150 Hz, and the electron energy is ~ 200 MeV. The target converter is tungsten. Converter surrounds 239Pu shell in a state of deep subcriticality. The neutron pulse duration is 400 ns, and the integrated neutron yield is ∼9 · 1014 n / s.

The sources of neutron radiation with suitable examples and sketches are discuss here advanced. sources of neutron radiation is needed to read.

Reference sources of neutron radiation

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