WO2012025436A1

WO2012025436A1 - Method and device for generating free neutrons

Info

Publication number: WO2012025436A1
Application number: PCT/EP2011/064148
Authority: WO
Inventors: Dietrich Habs
Original assignee: Siemens Aktiengesellschaft; Ludwig-Maximilians-Universität
Priority date: 2010-08-23
Filing date: 2011-08-17
Publication date: 2012-03-01
Also published as: DE102010035132A1

Abstract

The invention relates to a method for generating free neutrons, wherein a sample is provided that at least partially comprises atoms, the neutrons of which can to be excited to a halo state, wherein in a first method energy is supplied to at least a portion of the atoms such that neutrons are excited to a halo state below the separation energy, wherein in a second method energy is supplied to the sample, such that neutrons in the halo state are released from the atom, wherein the energy supplied in the first method is greater than the energy supplied in the second method.

Description

description

The invention relates to a method for generating free low-energy neutrons according to claim 1 and a device for generating free neutrons according to claim 15. In the prior art, free neutrons, for example by means of nuclear reactors in a nuclear fission or using generated by spallation sources. Reactors that undergo nuclear fission require high investment and radioactive material is generated. Spallation sources are also very costly, since large and expensive particle accelerators are needed.

The object of the invention is to provide a simple and cost-effective method and a simple device for generating neutrons, in particular low-energy neutrons.

The object of the invention is achieved by the method according to claim 1 and by the device according to claim 15.

One advantage of the invention is that neutrons, in particular low-energy neutrons, are produced in a relatively simple manner.

The inventive method uses a target having we ^¬ nigstens partially atoms whose neutron can be excited in a Halo state. In a first method, a part of the atoms of at least energy is supplied in such a way that the neutron atoms are excited to a state Halo un ^¬ terhalb the separation energy. In a second method, the sample is energized ^¬ leads in such a way that the neutrons, which are located in the halo-state, be released from the atom. The energy supplied to a neutron in the first method is greater, preferably significantly greater, than the energy supplied in the second method. This pre ^¬ hens, offers the advantage that the energy distribution of the neutron has a narrow bandwidth due to the low energy which is supplied in the second method for solving a neutron from the atom. This is of particular advantage in order to use the free neutrons for investigations of samples.

Further advantageous embodiments of the invention are indicated in the dependent claims.

In one development of the method, the energy supplied in the first method is supplied by means of photon radiation, in particular gamma radiation. Photon radiation is a simple and reliable source for transferring energy to a neutron. In a further guide will form the supplied energy in the second process using a photon radiation is fed into ^¬ special laser radiation or undulator radiation. The photon radiation, in particular the laser radiation, is also very well suited to transfer the energy required to release the neutrons, which are in the halo state.

Experiments have shown that for the excitation of neutrons to a halo state one energy per neutron in the range of a few mega electron volts, in particular in the range of 5 to 15 MeV is sufficient.

Further experiments have shown that for the elevation of the neutrons from the halo state to the free state, energies per neutron in the order of magnitude of electron volts, in particular in the range of 1 to 500 eV, are sufficient. For the production of free neutrons, samples with atoms whose mass number A is between 50 and 60 Z = (Ti, V, Fe, Co, Ni, Cu) or between 140 and 180 Z = (Ba, Ca, Ce, Pr, Nd, Sm, Eu, Gal, Tb, Dy, Ho, Er, Tm, Yb, In, Hf, Ta). It is also possible to use atoms with other mass numbers, the atoms of the selected regions being particularly suitable as neutron source.

In a further embodiment, the second method is carried out within the half-life of the halo state of the neutrons. The state of the halo neutrons is statistically stable, so that due to interactions, the number of halo neutrons decreases with time, but is sufficiently stable. For a large yield of free neutrons, it is therefore advantageous to carry out the second ^method within the half-life of the halo state of the neutrons.

In a further embodiment, the first method and the second method are each carried out in a pulsed manner. In this way, temporally and spatially limited neutron beams can be generated, which can be used in particular for the investigation of dynamic processes.

In a further embodiment, in the second method, a linearly polarized photon radiation is used to detach the neutrons. The use of linearly polarized photon radiation generates magnetically polarized neutrons, which are particularly suitable for the investigation of magnetic states.

In a further disclosed embodiment, the polarization of the photon radiation is changed in the second method, in particular, the polarization of the photon radiation is changed in a pulsed operation of the photon radiation from pulse to pulse. In this way, pulsed neutron ^{bundles are generated} , whose magnetic polarization also varies from pulse to pulse is changed. This effect may be advantageous in investigations of dynamic magnetic processes.

In a further embodiment, the sample is cooled, in particular below a range of less than 50 K, preferably less than 10 K. In this way, a further reduction in the bandwidth of the energy distribution of the free neutrons is achieved. In another embodiment, a stack of spaced apart layers of atoms whose neutrons can be excited to a halo state is used as a sample. This geometrical arrangement free neutron beam can be generated by using a photon beam ^¬ while the second method, which have a fixed timing relationship to one another ^¬ and are spatially limited.

In another embodiment, neutron guides are used to guide the neutrons from the sample to an examination area having a bandpass mirror. Using the band-pass mirror to be directed in the neutron guide only Neutro ^¬ NEN having a predetermined wavelength range. As a result, the bandwidth of the energy of the neutrons conducted to the examination area can be further restricted.

In a further embodiment, a neutron guide is used, which has a polished metal substrate as a wall at least in an initial region, which faces the sample. The polished metal substrate, which may have particular aluminum ^¬ minium or iron, is suitable to to locate the initial portion of the neutron guide very close to the sample. The polished metal substrate shows a higher stability with respect to the radiation load than, for example, glass substrates.

The invention will be explained in more detail below with reference to FIGS. Show it 1 is a schematic representation of an atomic nucleus with egg ^¬ neem, which is in a halo state,

Fig. 2 shows a schematic representation of possible

Energy states of a neutron,

Fig. 3 shows a table of selected isotopes having a mass number between 40 and 60 and between 140 and 180 indicating the scattering length and the neutron binding energy ^¬, the neutron halo states entspre ^¬ Chen,

FIG. 4 shows a table of isotopes with a mass number between 140 and 180 which are particularly suitable for the generation of free neutrons.

Fig. 5 shows a simplified structure of the device for

Generation of neutrons,

FIG. 6 shows another structure of the neutron generating apparatus having a plurality of experimental areas, and FIG

Fig. 7 shows a target with layers of target material.

Fig. 1 shows a schematic representation of an atomic nucleus with neutrons N and protons P with a located in a halo state neutron Nl. Atoms consist of atomic nuclei and an electron shell. In the following, only the atomic nuclei are considered in detail. The atomic nuclei have protons P and neutrons N, Nl. Normally, the protons and neutrons are arranged very close together. However, there are also atomic nuclei that have a neutron in a certain energy state that is in a so-called halo state and is much farther from the hull than an ultimate proton. A corresponding nucleus is shown in FIG. 1, which has protons P and neutrons N, where a neutron Nl may have a clear distance to the other neutrons and protons of the hull core.

Experiments have shown that a neutron of a nucleus, as shown in Fig. 2 is an energetic Grundzu ^¬ stand G, but also excited states Hl, H2, H3 with an existing bond may have the nucleus. For example, the energy states H2, H3 correspond to a halo state of the neutron. The energy states Hl, H2, H3 are even lower than a separation energy S, from which the neutron dissolves from the atomic nucleus. Thus, a neutron can be released from an atomic nucleus when the energy of the neutron is above the separation energy S. A basic idea of the invention is to use neutrons from

To stimulate atoms in a first method in such a way that they have an increased energy below the separation energy S. Preferably, the distance to the separation ^¬ energy is as low as possible. In a second method, the neutrons are supplied with a further energy E2, so that the neutrons have an energy state which is greater than the separation energy S and therefore the neutrons separate from the atomic nuclei. In this way, preferably slow neutrons can be generated without the need for a deceleration of the neutrons or radioactive material is formed. Preferably, a pulsed neutron beam can be generated with high brilliance using the described Ver ^¬ driving. Preferably, the free neutrons have an energy of less than 1 eV.

It is advantageous, in the first method, the first Ener ^¬ energy El with a brilliant photon radiation, in particular a gamma ray with an energy range 1-15 MeV, preferably 6 to 8 MeV, to transmit to the neutrons to neutrons in a halo- To bring state. Preferably, the neutrons are excited to an energy state near the Se ^¬ paration energy-S. A neutron in a halo state represents a long-lived core state whereby the neutron is in an excited energy state be ^¬. In the halo state, the excited neutron is only slightly bound to the nucleus and can stay far away from the nucleus. In the first method, it is advantageous to transfer the first energy El with a small energy bandwidth ΔΕ to the neutrons. As a result, the neutrons of the atoms are raised to only a few energy states and thus have similar or identical energy states. The first energy may preferably be transmitted in one step to the neutrons with a gamma-ray pulse.

In the following second method, the neutrons in the halo state are supplied with a second energy E2 to release the neutrons from the atomic nuclei. The second energy 2 can preferably be supplied as a photon beam, for example as a laser beam. In this case too, a small energy bandwidth of the photon beam is advantageous in order to produce a brilliant neutron current which has a high energy sharpness. The photon beam can be chirped (with increasing energy) to produce particularly cold neutrons. For this purpose, the energy of the photons is increased during a pulse with increasing duration.

Gamma rays with a high degree of brilliance, which are produced, for example, by means of Compton backscattering of laser light on brilliant, high-energy electron bundles, are suitable as the energy source for the first method. Currently energy band widths are available for gamma rays with an energy of 10 MeV, which have an energy distribution in the range between 0.01 and 0.001 bandwidth, ie ΔΕ / Ε. ΔΕ is the energy interval of the gamma quanta and E is the maximum energy of the gamma quanta. Furthermore, the energy band ^¬ wide of the available gamma rays in the years up to a value of 0.0001 improve ΔΕ / Ε. In addition, the available gamma radiation sources at an energy of 10 MeV have a brilliance in the range of l ²⁰ (ph / mm ² mrad ² s 0.1% BW)). The brilliance is a measure of the quality of a radiation source, the To ^¬ number of photons (ph) per time interval (s) per outlet ^¬ area (mm ²⁾ per solid angle (mrad ²⁾ by relative energy ^¬ bandwidth (BW) describes. High brilliance means that a large number of photons are emitted in a very short time from a small exit surface to a small solid angle per relative energy band width. There are much more brilliant gamma rays built on the principle of Compton feedback and are advantageous to use.

For the calculation of the energy of the gamma quanta the following formula is used for the Compton backscatter:

Εγ = ((4 y ² -EL) / (1 + (γ θ) ² + 4 γ-EL / mc ² )),

where the γ-factor is the energy of the electron beam from E = γ-mc ² , Εγ is the energy of the photons, Θ is the angle the gamma ray occupies with the electron beam, EL is the energy of the photons. The energy of gamma radiation Εγ decreases with increasing angle Θ. A narrow bandwidth of the gamma beam requires a narrow energy distribution of the electric ^¬ nenbündel (Δγ / γ), a narrow bandwidth of the laser radiation (ÄEL / EL), a good Emittenz of the electron beam with a small opening and a small opening angle of the laser beam.

Detaching the neutrons with a single energization is very inefficient because the neutron picks up a high pulse of gamma radiation. For example, the momentum may be in the range of 500 meV for an atom of mass A = 180 and with a gamma radiation of 7 MeV. For the use of thermal neutrons whose energy is in the range of 25 meV, a small neutron energy, at which the momentum ^{momentum is} compensated, can be obtained only for a very narrow aperture angle. By using two separate methods, the first excitation into the halo state and a staggered separation of the halo neutrons by the introduction of a second energy, this problem can be avoided, since the halo nuclei after the lifting in the halo state within a few picoseconds deliver the impulse received via the gamma radiation to the outside world. Since the power transmitted to the neutron in the second process energy is low, the neutron receives only a small pulse from the photon radiation when sen from Loslö ^¬ atom.

Gamma radiation sources, which use the Compton backward scattering method, for example, in the HLys plant Duke Uni- sity, USA, installed in which the primary photon with- the aid of an FEL laser (free electron laser) produces ^¬ the eluting with Undulators a spatially periodic magnetic ^¬ field is generated and the electrons are generated by a storage ring. Then, in a second step, these FEL photons are backscattered on a circulating electron beam to generate the γ radiation. Furthermore, corresponding equipment from Lawrence Livermore National Laboratory under the name Plajades, T-REX and MEGa-Ray are known, which are based on a warm electron LINAC (linear accelerator) and a fiber laser for the backscatter.

According to our investigations, the target material is all atoms stable in the ground state for halo states whose energy states are in the vicinity of the separation energy, with atomic nuclei whose mass number A is between 140 and 180 or whose mass number A is between 40 and 60. A narrow bandwidth of energy distribution of the gamma radiation ensures that a sufficient number of neutrons of the atoms can be excited in halo states close to the separation energy. Atoms capable of being excited to a neutron-halo state of a mean lifetime of at least lps are suitable.

Fig. 3 shows a table of possible isotopes indicating the scattering length a and the binding energy S, which are suitable for the generation of free neutrons. However, these states were identifi ^ed with elastic scattering of thermal neutrons, that is, above the neutron ^binding energy. The table shows that the separations energy for the neutrons lies between 5.8 and 12.2 MeV. When the neutrons are excited into the halo state, the energy of the γ radiation must be chosen to be lower than the separation energy.

Figures 4A and 4B show tables of further isotopes suitable for the generation of halo states. With A the mass number, with Z the chemical element, with% the percentage of the isotope at the chemical element, with I g the spin of the ground state, with I core the spin of the nucleus without a neutron of the ground state, with E core the energy the excited core without a neutron with the Sn Se ^¬ para dissociation energy of a neutron.

In particular, atoms with halo-neutron states whose average life has a minimum length are suitable for the generation of free neutrons. The life of a halo neutron is a bond energy of 1 eV at ei ^¬ ner average life of typically 10 με and the binding energy of 1 keV at an average life of typically 300 ps. A sufficiently stable state of a halo-neutron is assumed for an average lifetime of at least 300 ps. From this lifetime, a free neutron can be generated using the described method. Preferably, a target has only atoms of a chemical element or preferably only atoms of an iso ^¬ tops of a chemical element.

Depending on the energy gap of the excited halo state of the separation energy is an appropriate photon ^¬ source of sufficient photon energy for the second Ver ^¬ drive required to stimulate the left in the halo-state Neut ^¬ ron on the separation energy. Thus, a La ^¬ serstrahl or X-ray radiation for the second method may be required.

The excitation of the neutron halo state using gamma and photon radiation can be estimated using the following Breit-Wigner formula for the cross section σ: σ (Εγ) = (λ ² γ / 4π) -g) · (Τγ · Τ ² ) / Εγ - Ετ) ² + Τ) ^2/4 ),

where g = (2 · ΙΑ + 1) / (2 · ΙΒ + 1) is a spin factor for the spin of the target and the photon beam and λγ (hc) / Εγ, where ^¬ at λγ the wavelength of the gamma radiation with the energy Εγ h

denotes, h = - = reduced Planck constant. This Re-

2π

sonanz is excited with a width Τγ and falls off with a width T2. The resonance has the total width T = Τγ + T2. The mean Τγ-width is known and a function of the mass number A and the separation energy S of the neutrons. For example, the average resonance width Τγ is about 100 meV for an atomic nucleus with the mass number A of 180.

Because of this situation, there may be a possibility for 60 different isotopes to generate halo states and halo isomers.

Due to the cooling of the target to low temperatures, for example, 50K, 10K can be achieved in particular with preference ^¬, a greater resonance cross-section for the interaction of the nuclei with the gamma and photon radiation during the first and the second method. In addition, with cooling, a thinner substrate may preferably be USAGE ^¬ det. As a radiation source for the first method embodiment ^¬ as gamma radiation source with 10 ¹³ photons per second with an energy of about 7 MeV per gamma quantum and a bandwidth (ΔΕ) at an energy of about 7 keV ⁽³ ΔΕ / Ε = 10 ^~) used , With this gamma radiation source, we excite atoms to neutron halo states with an energy width of about 100 meV, so that we get about 10 ⁸ excited atoms in a target in an area of 0.1 mm ² . After a corresponding excitation by photons, neutrons are emitted with an aperture angle of 100 mrad ² and a bandwidth (ΔΕ / Ε) better than 0.1%. In this way we obtain an average brilliance of 10 ⁶ neutrons / ((mm-mrad) ² · 0, 1% · BW · s), where BW is the energy bandwidth. te ΔΕ is designated. For further consideration, we can assume a brilliance of 10 ⁵ neutrons / ((mm-mrad) ² · 0, 1% · BW · s), since 0.1% BW is not always achieved. In this way, however, we are already two orders of magnitude better than the brilliance of reactors. Due to the target thickness of about 1 mm, which is required to absorb all resonant photons by the resonant atoms and due to the slow speed of the neutrons of about <2000 m / s, we preferentially pulse the monoenergetic neutron beam with a pulse duration of 1 με. In this way, the peak brilliance is improved by a factor of 10 ⁶ to a range of peak brilliance of about 10 ¹¹ neutrons / ((mm-mrad) ² x 0, 1% x BW x s).

For a halo state of a neutron of 1 keV distance to the separation energy S a correspondingly high-energy Pho ^¬ ton source for the second method is required, which must be available in the form of an X-ray source due to the high energy required of 1 keV. It can be generated with undulators with the existing electron beam.

The neutron pulse duration of approximately 1 με is essentially determined by the thickness of the target. A shortening of the neutron pulse duration can be achieved by using a thinner target. Preferably, a stack of multiple thin layers of atoms is used as a target, with which a set of microbatches of shorter duration neutrons can be generated in the range of nanoseconds rather than microseconds. However, then the sample to be examined should also have a small thickness in the nanometer range in order to avoid a longer time delay and an expansion of the neutron pulses.

Furthermore, a corresponding frequency modulation of the photon source during the second process may be used to increase the brilliance of the neutron beam.

Due to the frequency modulation, the bandwidth of the free Neutron improved as the cross section for the Lö ^¬ sen a neutron depends from the Halo state of the energy of the photons. In addition, the brilliance of the free neutrons can be improved if the photon radiation in the first method irradiates a different effective thickness of the target than the photon radiation of the second method. This may be it ^¬ ranges, for example, by different angle of incidence.

Also can Neut ^¬ Ronen beams are generated with a long period of time extremely monoenergetic and slow in the presence of neutrons with halo states that have a low energy gap for the separation energy ^¬, using a mono-energy laser beam in the second process. In a coherent photon field of the photon source for the second method, an improved alignment of the neutrons in the direction of the laser polarization can be achieved due to the collective alignment of the charged atomic nuclei with respect to the halo-state neutrons and due to the large dipole moment, so that one 10 ⁴ higher brilliance of the neutron beam is achieved. By adjusting the direction of the electromagnetic field of the photon radiation used for the second method to detach the neutrons from the nucleus, the direction in which the free neutrons are emitted can be restricted. In order for a neutron ^¬ conductor for receiving the free neutrons can be determined by a corresponding direction specification.

Preferably, fully polarized neutron beams can be obtained without significant loss of intensity. For this purpose, fully polarized gamma rays can be used in the first method, which are generated by a Compton backscattering process of a fully polarized laser beam on relativistic electron beams. If one excites an atom from a ground state to a fully po ^¬ larisierten Halo state, a fully polari ^¬ lized neutron beam is achieved, since the orbital angular momentum is equal to the 0th By switching the polarization of the First laser beam for the gamma radiation, the polarization of the neutron beam can be changed from pulse to pulse. Since the spin of the neutron is coupled to the magnetic dipole moment of the neutron, complete alignment of the neutron beam polarization is enabled.

The application of neutron beams, in particular neutron scattering, is currently experiencing a strong trend towards cold and thermal microneutron beams for studying structures and dynamic excitations of small samples under extreme conditions, e.g. in the field of solid state and soft body physics. Particularly in the field of reflectometry, narrow angle scattering (SANS) and diffraction, the highly brilliant and thin neutron beam can be used successfully. The new neutron source will open up a large area of research in basic and applied research.

The reasons for the great interest in a brilliant Neut ^¬ Ronen beam with a diameter on the order of less than 1 mm up to 30 μπι is for example the fact that new materials with unique features or characteristics, for example with respect to the magneto-resistive or magneto-electric coupling only can be produced in small quantities. For example, neutron scattering is a very useful tool for studying magnetic and lattice dynamics properties. Next ^¬ out is an application of the new neutron source in the field of study of quantum phase transitions or in the area of the geoscience, a pressure of 30 MPa are exposed in the sample. The application of high pressures requires a small sample size. To distinguish the signal of the sample and the signal of the printing system, an excellent focusing of the neutron beam with a high intensity is required. Also, biological samples and multi-layer structures can often only be prepared in small sizes. Thus, medical examinations with neutrons can be performed. Furthermore, the sensitivity sensitivity of the detectors with the help of a small neutron beam.

5 shows a schematic representation of the basic structure of a device for generating microneutron beams. It is a first radiation source 1 vorgese ^¬ hen, which emits a first photon beam 2 onto a target. 3 Opposite to the first radiation source 1 in Be ^¬ train on the target 3 is hen a collecting device 4 provided for. The collecting device 4 captures the part of the first photon radiation 2 that is not picked up or deflected by the target 3. Furthermore, a second radiation source 5 is provided, which holds a second photon beam 6 for the second method. Play in the illustrated exemplary embodiments, the second photon beam 6 of the second radiation source 5 is ge ^¬ via a deflection device 7 from above in the perpendicular angle to an observation plane 9 on the target. 3 The first and the second radiation source 1, 5 are connected to a control unit 12 in connection, which drives the first and the second radiation source 1, 5 according to stored control method. For cooling the target, a cooling device 20 may be provided, which is thermally conductively connected to the target 3 and the target cools, ^{insbesonde ¬} re below 50 Kelvin, preferably below 10 Kelvin.

Preferably, the second radiation source 5 provides a linearly polarized second photon beam 6. Due to the linear polarization, the neutrons 13 emitted by the target 3 are emitted in the observation plane 9. Furthermore, a diaphragm 10 with an opening 11 for focusing the first photon beam 2 between the first radiation source 1 and the target 3 is preferably arranged. The ers ^¬ te-ray source 1 adapted to deliver, for example, gamma rays with an energy in the range of 1 to 15 MeV. In addition, the gamma radiation may preferably be linearly polarized. Using gamma radiation excited atoms of the target 3 to ei ^¬ nem Halo state by a neutron of the atomic nucleus is excited into a halo state. The target 3 is irradiated with the second photon beam 6 then, in a second process, so that neutrons be found in the halo-state ^¬ be of the atoms, and thus released from the target 3 and fly away. The neutrons are emitted at a narrow angle, which depends on the polarization direction of the second photon beam 6. Neutron conductors are provided for guiding the neutrons, wherein the neutron conductors may have an elliptical or parabolic shape to guide the neutrons. The neutron guides are formed in such a manner that a high neutron flux does not damage the Neutronenlei ^¬ ter and that the neutron guide hochenerge- diagram neutrons do not conduct. For this purpose, the neutron ^{conductors may} preferably have a coating which provides a bandpass filter. Due to the bandpass filter, only neutrons with a certain wavelength range are guided along the neutron guide. Such neutron guides are an established technology.

Since the electric field of the second photon radiation 6 oscillates in opposite directions, the neutrons are emitted at the same time in opposite directions. Further preferably, chopper may be used to ^¬ to form the neutron beam on.

In addition to parabolic or elliptical neutron guides, even neutron guides can be used. The advantage of straight neutron guide is to avoid reflection losses, since only a reflection of a neutron over the entire line length occurs and the target is arranged in the ^focal point ^{¬ of} the guide system. A second focus of an elliptical neutron guide is located either at the site of a chopper or at the site of a sample to be examined. In addition, the second focus may be the virtual source of a focusing Monochrometer or the source for a conical picture.

A direct connection between the target and the sample to be examined may be blocked with glare elements within the neutron guide. In this way, all ande ren ^¬ radiations emitted for example from the target, such as gamma rays or other neutron suppressed. In addition, a temporal smearing of the time structure of the very short neutron beams is reduced since the flight path of the neutrons does not depend on the divergence.

For a small angle or a reflection of a shear paraboli ^¬ neutron guide is advantageous to widen the neutron beam brilliant micro- to a larger cross-sectional area and to reduce the divergence. In fact, the design of the neutron guide can be adapted in such a way that the phase space of the neutron is adapted to each beam size in the range of the size of the target of 100 μπι up to 1 mm. Using a Kirkpatrick-Baez geometry for the neutron guides, the neutron beams can be effectively focused to an area of a few tens of μm or less. Preferably, the neutron guides become efficient

Dissipation and conduction of the neutrons from the target to the sample as close as possible to the target. Radiation exposure is very high near the target and can damage glass neutron guides. This situation is improved by providing neutron guides used ^¬ the having highly polished metal surfaces, for example made of aluminum or iron and may be arranged with an initial portion close to the target. In the assumption that the target has a diameter of unge ^¬ ferry 0.1 mm, can use the described method, a neutron beam with a mean brilliance of 10 ⁵ neutrons / ((mm -mrad) ² · 0, 1% · BW · s) are generated. Of the Radiation angle for the neutrons can be in the range of 10 ⁴ mrad ² . Assuming an energy of 80 meV for the free neutrons, ie a wavelength λ of 1 λ, we assume that the neutron guides have a supermirror with an index of m = 7, where the total reflection angle of the supersymmetry is 0.7 ° is. Let us assume an elliptical neutron guide, which leads neutrons with a divergence of approximately 2 °, which corresponds to an aperture angle of 1200 mrad ² , the neutron ^beam having a band width of 2 meV and a region with a diameter of 0.1 mm, then we obtain a neutron flux of 3 × 10 ⁹ photons per mm ² and second with a divergence of 2 °. For a beam with a diameter of approximately 10 mm we obtain with the same estimate a neutron flux of 3 · 10 ⁵ neutrons per mm ² and second with a very narrow divergence angle of

0, 02 °.

The newly described type of neutron source can be ^¬ driven in a pulsed mode or in a pseudo-continuous wave mode. Due to the pulse structure and the repetition frequency of the electron and photon sources involved, adaptation to a wide range of parameters can be easily achieved. By switching the polarization plane of the electromagnetic field of the second radiation source during irradiation Neut ^¬ Ronen can be continuously produced with different energy levels. At a low pulse rate, the risk of overlapping can be reduced. Moreover, in particular a polarized gamma radiation without loss of brilliance can be obtained by the use of a completely polarized neutron beam by using egg ^¬ nes polarized first photon beam, it will be possible to examine magnetic materials and soft Materi ^¬ alien with highly incoherent scattering. By analyzing the polarization of the scattered neutrons, detailed information on the orientation of the magnetic moments in the sample and on the interaction of lattice structures can be investigated. Fig. 6 shows a further From guide form of plant for the production of free neutrons in which the first radiation source 1 winnung an electron linear accelerator with Energierückge- (ERLinac), which accelerates the electrons to an energy of 600 MeV ^¬ Ener. A third radiation source 23 in the form of a laser is provided in the arrangement for generating the first photon radiation in the form of gamma radiation by bombarding the electron packets by means of a third photon radiation 24. For this purpose, a corresponding mirror system 15 is provided in order to greatly increase the third photon beam 24 by the circulating intensity in the elevation activity of the four mirrors. The low-energy, second photon beam coming from above (FIG. 5), which is used in the second method for the solution of the neutrons from the halo states, is not shown in FIG. The second photon beam is directed perpendicular to the image plane from above onto the target. The second photon beam is generated by a second radiation source, as shown in FIG. At the target 3, a plurality of neutron guides 14 are arranged, which guide the generated neutrons to different examination areas. The neutrons can be used, for example, for imaging experiments, small angular scattering experiments or scattering experiments. In addition, the neu- can ronen over monochromatic filter of a sample supplied to the ^¬. Furthermore, the neutrons can be evaluated for the determination of the time of flight or the determination of the polarization of the neutrons. For this purpose, corresponding samples 8 to be examined, filters 16, choppers 17 and detectors 18 are provided.

The highly brilliant gamma source can be generated with an electron Line ^¬ arbeschleuniger. In this case, a high brilliance of typischerwei ^¬ se 8 pC and a frequency of 1.3 GHz can be generated with a flow of 10 ¹⁵ photons per second using a 100 mA electron stream. With such high electron currents is an energy recovery in the

Electrons (ERL) with a superconducting accelerator (see Figure 6) appropriate. Depending on the selected version approximate shape can also so-called warm linear accelerator Elektronenbe ^¬ (Linae) be used with a current of 3 μΑ. The normalized emittance of gamma radiation may range from 0.1 to 0.18 mm-mrad. The energy sharpness (ΔΕ / Ε) may be in the range of 10 ^{~ 3} to 5 · 10 ^{~ 5} . The pulse rate for the gamma radiation may range from 10 kHz up to a range of 5 GHz. The charge of an electron beam may be between 250 picocoulombs (pC) for the men was ^¬ electron linac and 8 picocoulombs (pC) are for a cold location th electron linac. The second photon source may have a repetition frequency of 120 Hz to 5 GHz. The pulse duration of the second photon source can be in the range of a few picoseconds. The pulse energy can be between 1.5 joules for the warm linear accelerator and 40 to 1 milliules for the cold linear accelerator. The stored energy can range from a few megawatts to a few 100 megawatts.

By means of the described linear accelerators, Compton backscattering can be used to generate gamma rays with an energy of 1 to 13 MeV, a gamma quantum flux of 10 ¹³ to 5 · 10 ¹⁵ gamma quanta / second with a bandwidth (ΔΕ / Ε) of 10 ^{~ 3} to 4 · 10 ^{~ 5} , a beam cross section of 15 to 25 μπι and a peak brilliance of 2 · 10 ²¹ to 6 · 10 ²⁴ photons / (mm ² -mmrad ² · s · 0, 1% bandwidth) can be achieved. In this way, an average brilliance of 3 × 10 ¹⁹ for a warm electron linear accelerator and 3 × 10 ²¹ for a cooled electron linear accelerator is achieved. Correspondingly structured first radiation sources 1 are in the

Report "Infrastructure producing high intensity gamma rays for ELI nucleophysics", Bucharest-Magorele, Romania, for ELI-gamma source working group, May 31, 2010, "High-flux and high-brightness gamma-ray source based on energy recovery linac "by R. Haitchima, Japan, Atomic Energy Agency, ELI NP, April 12-13, 2010. The use of gamma radiation to excite and study atoms, for example, in the article "Energy-recovery Latin for a high-flux quasi-monochromatic gamma-ray source", R. Haitchima, AccApp-07, Pocatello, Idaho, July 29 to August 2, 2007. Furthermore, the application of gamma radiation for the detection of a nuclear resonance fluorescence from the article "Proposal of non-destructive radionuclide assay using a high-flux gamma-ray source in nuclear resonance fluorescence", R. Haitchima et al. , Journal of nuclear science and technology, vol. 45, no. 5, pages 441-451, 2008.

The properties of a brilliant gamma source with a warm electron accelerator are described in F. Albert et al., Tics Letters, Vol. 35, 354 (2010).

The examples of gamma ray sources described are exemplary only. Preferably, sources are used which have a flux of gamma quanta greater than 5 x 10 ¹² quanta / s. The target for generating the neutrons may be less than 1 mm ³ . The energy sharpness (ΔΕ / Ε) can be better than 4 x 10 ^{~ 2} at energies in the range of 5-10 MeV.

The described method is not limited to the small-diameter ^¬ and high brilliance of the neutron radiation. Depending on the application, other values may be advantageous. In particular, applications in the field of materials science, life sciences and medical diagnostics, for example, for the study of tissue structures, in particular for the detection of cancer, possible.

FIG. 7 shows a target 3 which has parallel arranged first layers 21 of target material, which are connected to one another via second layers 22. The second layers 22 are composed of atoms that have no neutron halo states, e.g. For example carbon. But you can also consist of vacuum, so that the Compton electrons can leave well without heating the targets

Claims

claims

1. A method for generating free neutrons, wherein a sample is kept ready, which has at least partially atoms whose neutrons excited to a halo state ^¬ can,

wherein, in a first method, at least a portion of the atoms are first supplied with energy in such a way that neutrons are excited to a halo state below the separation energy,

wherein, in a second method, energy is subsequently supplied to the sample such that neutrons that are in the halo state are released from the atom, wherein the energy supplied in the first method is greater than the energy supplied in the second method.

2. The method of claim 1, wherein in the first method, the energy is supplied by means of gamma radiation.

3. The method of claim 1 or 2, wherein in the second method, the energy is supplied by means of a photon radiation.

4. The method according to any one of claims 1 to 3, wherein in the first method a neutron energy in the order of

MeV, in particular in the range between 1 and 13 MeV is supplied.

5. The method according to any one of claims 1 to 4, wherein in the second method a neutron energy in the order of eV, in particular in the range of 1 to 500 eV is supplied.

6. The method according to any one of claims 1 to 5, wherein the Pro ^¬ be at least partially atoms having a mass number between 50 and 60 and / or between 140 and 180.

7. The method according to any one of claims 1 to 6, wherein the second method is performed within a half-life of the halo state of the neutrons.

8. The method according to any one of claims 1 to 7, wherein the first and the second method is performed pulsed.

9. The method according to any one of claims 3 to 8, wherein in the first and / or in the second method, a linearly polarized photon radiation is used.

10. The method of claim 9, wherein the polarization of the photon radiation is changed, in particular in pulsed operation is changed from pulse to pulse.

11. The method according to any one of claims 1 to 10, wherein the sample is cooled, in particular in a range of less than 50 Kelvin, preferably less than 10 Kelvin.

12. The method according to any one of claims 1 to 11, wherein as

Sample a stack of spaced layers of atoms is used.

13. The method according to any one of claims 1 to 12, wherein a neutron guide is used with a band-pass ^mirror , where ^{¬ passes} in the bandpass mirror only neutrons with a fixed wavelength range.

14. The method according to any one of claims 1 to 13, wherein a neutron guide is used which has a polished metal substrate, in particular of aluminum or iron at least in an initial region.

15. Device for generating free neutrons, wherein a sample (8) is kept ready, which has at least partially Ato ^¬ me, whose neutrons can be excited to a halo state, a first radiation source (1) is provided with which in a first method, at least a portion of the atoms of energy can be supplied in such a way that neutrons are geregt a halo-state below the binding energy at ^¬,

wherein a second radiation source (5) is provided with which, in a second method, energy can be supplied to the sample in such a way that neutrons which are in the halo state are released from the atom,

wherein the first radiation source (1) can generate photons with a greater energy than the second radiation source (5).