Relativistic effects authentication
Early 20th century. Basic concepts of physics through three far-reaching revolution; as a sign of these three revolutions and results, that is, special relativity, general relativity and quantum mechanics established. The physical sciences there are two very important experiment that has plagued people. One is the 1887 Michelson and Morley made by the speed of light experiment and the other is the so-called blackbody radiation. Special theory of relativity changed the concept of time and space: from Newton's absolute space-time becomes four-dimensional concept of time and space, which is Einstein in 1905 proposed his principle of relativity and the speed of light the same principle. Special theory of relativity space-time concept. Einstein's special theory of relativity has been confirmed for a large number of experiments, and applied to all areas of modern physics. Special theory of relativity is the basis for the design of all particle accelerators.
This experiment also measured close to the speed of light c, high-speed electronic (particle) momentum and kinetic energy to prove the correctness of special relativity. Energy 1mev particle velocity 0.94c. Experimental energy of the particles used in the 0.4 ~ 2.27mev range. Very close to the speed of light c. They are able to verify the relativistic mass-energy relationship dynamic. Study magnetic spectrometer measurement principles and other nuclear physics experimental methods and techniques. γ-ray decay or nuclear fission is the radiation, in essence, it is a kind of energy than visible light and x-ray of electromagnetic radiation is much higher. The use of γ-rays and physical laws of interaction, people design and manufacture a variety of types of radiation detectors. Scintillation detector is one of them. It is the use of certain substances under the action of the light rays to detect radiation characteristics of the instruments, both measuring the intensity of radiation, can also measure the energy of radiation, and radioactive isotopes in nuclear physics research in widely used measure. This study describes a common γ-ray measuring instruments: sodium iodide crystal detector and γ-ray particle's momentum and kinetic energy relativistic effects.
[Experimental purposes]
1, to understand the structure of scintillation detectors, principle.
2, master nai (tl) single crystal γ scintillation spectrometer several performance indicators and testing methods.
3, measuring the electron kinetic energy and momentum quickly.
4, verify the fast electron momentum and kinetic energy relations relativistic effects.
[Experimental principles]
Interaction between nuclear radiation and some of the material will make ionization, excitation and fluorescence, scintillation detector is to use this feature to work. The figure is a diagram consisting of scintillation detectors. Scintillation detector with scintillator, photomultiplier tubes and the corresponding three major components of electronic equipment. The figure above the front of a detector sensitive to radiation and can produce flashes of light scintillator, when the rays (such as γ, ) into the scintillator, the secondary electrons produced in a particular place, it makes the molecular ionization and scintillation excitation, de-excitation to issue a large number of photons (typically the spectral range from visible to ultraviolet light, and photons shoot out in all directions). In the scintillator material around the package to reflect, to focus the photon direction of the shot to the photomultiplier tube.
The so-called ray spectrum, is the energy of particles of different relative intensity distribution; draw it to the energy e is horizontal, measured per unit time to the number of radiation particles on the vertical axis of the graph is a curve. According to this curve, we can clearly see that such a ray of particles of various energy percentage. There is also a single-channel window width v, so larger than v0 + v pulse was also blocked so that only the range of the signal through a single channel pulse analyzer function is the linear amplifier output pulse by pulse height Category: If the linear pulse amplifier output is 0 ~ 10v, if it is divided into 500 by pulse height, otherwise known as 500, each channel width of 0.02v, which is the height of the output pulse according to the differential to 0.02v classification. Point by point increase in v0, so that you can measure the spectral shape.
γ-ray interaction with matter may have three effects: the photoelectric effect, Compton effect and electron on the effects of these three effects of secondary electrons produced in the nai (tl) crystals in the flickering light; as
Photoelectric effect Compton effect on the effect of electronic
Figure 1 rays nai (tl) scintillator in the basic process of interaction
Table 1γ rays nai (tl) scintillator in the basic process of interaction
Basic process of secondary electrons gain energy t
1) photoelectric effect
→ γ + atom → atom or ion excitation + excited electron (electron binding energy of the layer)
2) Compton effect
γ + e → (scattering) + recoil electron
By,; is the scattering angle, from 0 to maximum continuous energy distribution, the peak energy at the maximum.
3) produce electron
→ γ + atomic atoms + +
Electron energy sharing
Interaction between nuclear radiation and some of the material will make ionization, excitation and fluorescence, scintillation detector is to use this feature to work. The figure is a diagram consisting of scintillation detectors. Scintillation detector with scintillator, photomultiplier tubes and the corresponding
To sum up, scintillation detectors work can be divided into five interrelated processes:
1) ray into the scintillator, interact with them, flashing body to absorb the energy of charged particles leaving the atomic, molecular ionization and excitation;
2) excited atom, molecule, when the de-excitation fluorescence photons;
3) the use of reflectors and flashing light guide will collect as many photons to photomultiplier photocathode, due to the photoelectric effect, photons hit the photocathode on the photoelectron;
4) photomultiplier tube in the photoelectron multiplier, the number from one to 104 ~ 109, the electronic flow of electrical signals generated in the anode load;
5) This signal is recorded and analyzed by the electronics.
Usually nai (tl) single crystal γ scintillation spectrometer energy resolution to 137cs the 0.661mev monoenergetic γ-ray as the standard, its value is generally about 10%, preferably up to 6 to 7%.
Detector linear problem:
Linear refers to the energy output of pulse amplitude and energy of charged particles have a linear relationship, as well as the size of the linear range.
nai (tl) single crystal fluorescent output 150kev <eΥ <6mev ray energy range and is directly proportional. But nai (tl) linear single crystal γ scintillation spectrometer scintillation spectrometer also depends on good or bad working conditions.
Single-channel screening voltage is changed by point counting, measurement is not easy and time-consuming, and therefore the experimental device used in a multi-channel pulse analyzer. The role of multi-channel pulse analyzer is equivalent to hundreds of single-channel analyzer and scaler, which is mainly from the 0 ~ 10v of the a / d converter and storage components, the pulse through the a / d converters after conversion by a high degree of size into high and proportional to the digital pulse output, so you can simultaneously count the pulses of different magnitudes, a measurement of the entire available spectrum curve, convenient and reliable time-saving.
As the single-energy γ-rays produced by three different secondary electron energy, and even Compton effect is continuous, so a single to the corresponding γ-ray, flash output of the probe pulse amplitude spectrum is continuous.
nai (tl) spectrometer measured the spectrum of γ 137cs
Page shown below, the measured γ spectrum has three peaks, and a platform. The peak of a known right round the peak, the pulse amplitude directly reflects the γ-ray energy that 0.661mev; have analyzed above, this peak contains the photoelectric effect and the contribution of several effects, the experimental device flicker detector 0.661mev γ-ray energy resolution of 7.5%.
Platform-shaped curve b is the contribution of the Compton effect, which is characterized by scattered photons escape after leaving a continuous energy from 0 to the electronic spectrum.
Peak c is the anti-scattering peak. Γ-ray through the scintillator by the radiation in the photomultiplier tube photocathode occurred on the anti-Compton scattering or γ-ray source and surrounding material in place anti-Compton scattering, and inverse scattering photons into the scintillator by photoelectric effect and be Record due. This is an anti-scattering peak.
Peak d is the x-ray peak, which is characterized by the 137ba the k-layer x-ray contribution. 137cs decay of the excited state of the body 137ba of 0.661mev emit internal conversion electrons in k space caused by the outer electron transitions resulting from the x photon.
[Content] experiment
1.nai (tl) single crystal γ scintillation spectrometer _set_ of device operation, adjustment and use of debugging a spectrometer to normal operation.
2.137cs, 60co the γ spectrum, calculated energy resolution, peak health ratio, linear and other indicators, and analysis of spectral shape.
3 multi-channel pulse height analyzer in the nai (tl) γ spectrum measured in the single-crystal data collection and its basic functions.
4 treatment (including the smooth shape of the spectrum, peak search, curve fitting, etc.).
5 measuring fast electron momentum.
6 Measuring the electron kinetic energy quickly.
7 Verify that the momentum and kinetic energy of fast electrons relations between the relativistic effects.
[Experimental _set_up]
Shiyan equipment including: ① γ sources 137cs 和 60co (intensity ≈ 1.5 millicuries); ② 200 mal window nai (tl) flashing probe; ③ high voltage power supply, amplifier, multi-channel pulse height analyzer.
Experimental procedures and data processing []
Please see the laboratory manual.
The stability of the spectrometer in this experiment is very important, spectrometer energy resolution, linearity and the normal or the stability of the spectrometer. Therefore, in the measurement process, requiring spectrometer can always work properly, such as high voltage power supply, amplifier magnification, and single-channel pulse analyzer threshold and channel width steamer do. If the optical spectrometer instability is the peak position will change or peak shape distortion. In the measurement process often the peak of 137cs, to verify the reliability of measurement data. To protect electronic equipment with temperature changes, the measuring instrument must warm up before the half hour.
Measurement of kinetic energy β particles
particles interact with matter is a very complex issue, and how its loss of energy is very important to make the necessary amendments.
① al membrane particles in the energy loss correction
particles in the calculation of the kinetic energy of the particles will also be required through the al film (220 m: 200 m for the nai (tl) crystals of the aluminum seal thickness, 20 m thickness for the reflective layer of aluminum) when the kinetic energy to be correction, calculated as follows.
Let al membrane particles in the kinetic energy through the loss of x e, then:
(5-14)
Where () is al particle of energy absorption coefficient, ( is the density al), is a function of e, e case of different values can be calculated. Can be _set_, then e = k (e) x; take x 0, then particles pass through the membrane of the energy loss is al:
(5 ─ 15); that (5 ─ 16)
Where d is the film thickness, e2 is the kinetic energy of a fire-, e1 is the kinetic energy of the incident before. As the experiment was detected after attenuation by the kinetic energy of al membrane, therefore, the formula (4 ─ 9) to calculate the corrected kinetic energy (ie, before the incident kinetic energy). The following table lists the computer program calculated according to the kinetic energy of the incident kinetic energy of e1 and e2 outgoing correspondence between:
e1 (mev) e2 (mev) e1 (mev) e2 (mev) e1 (mev) e2 (mev)
0.317 0.200 0.887 0.800 1.489 1.400
0.360 0.250 0.937 0.850 1.536 1.450
0.404 0.300 0.988 0.900 1.583 1.500
0.451 0.350 1.039 0.950 1.638 1.550
0.497 0.400 1.090 1.000 1.685 1.600
0.545 0.450 1.137 1.050 1.740 1.650
0.595 0.500 1.184 1.100 1.787 1.700
0.640 0.550 1.239 1.150 1.834 1.750
0.690 0.600 1.286 1.200 1.889 1.800
0.740 0.650 1.333 1.250 1.936 1.850
0.790 0.700 1.388 1.300 1.991 1.900
0.840 0.750 1.435 1.350 2.038 1.950
② particles in organic plastic film in the energy loss correction
In addition, experiments show that encapsulation of organic plastic film vacuum chamber there is a certain particle energy absorption, especially for particles smaller than 0.4mev absorption of nearly 0.02mev. As the thickness of plastic film and difficult to measure the material composition, experimental methods can be corrected. Under different experimental incident kinetic energy and the outgoing kinetic energy ek e0 (units are mev) the relationship between the use of sub-interpolation method of calculation. Specific data as follows:
ek (mev) 0.382 0.581 0.777 0.973 1.173 1.367 1.567 1.752
e0 (mev) 0.365 0.571 0.770 0.966 1.166 1.360 1.557 1.747
[Title] thinking
1, a brief description nai (tl) scintillation detector works.
A: The rays enter the scintillator, interact with them, flashing body to absorb the energy of charged particles leaving the atomic, molecular ionization and excitation;
Excited atoms, molecules, when the de-excitation fluorescence photons;
The use of reflector and light guide will blink to collect as many photons photomultiplier photocathode, due to the photoelectric effect, photons hit the photocathode on the photoelectron;
Photoelectron multiplier in the photomultiplier tube, the number increased to 104 from a 109, the electronic flow of electrical signals generated in the anode load;
This signal is recorded and analyzed by the electronics.
Usually nai (tl) single crystal γ scintillation spectrometer energy resolution to 137cs the 0.661mev monoenergetic γ-ray as the standard, its value is generally about 10%, preferably up to 6 to 7%.
Detector linear problem:
Linear refers to the energy output of pulse amplitude and energy of charged particles have a linear relationship, as well as the size of the linear range.
nai (tl) single crystal fluorescent output 150kev <eΥ <6mev ray energy range and is directly proportional. But nai (tl) linear single crystal γ scintillation spectrometer scintillation spectrometer also depends on good or bad working conditions.
2, the scattering peak is formed?
A: The release of radioactive particles into the scintillation detector, depending on the number of particles enter the channel number, can form scattering peak.
3, only 137cs source, can be rough on the scintillation detector energy calibration?
A: Yes, cs can be only two peaks, two points determine a straight line, can also be roughly the energy scale.
4, na (tl) single crystal energy resolution γ scintillation spectrometer What is the definition? How to measure? The amount of energy resolution with which the? What is the significance of energy resolution is good or bad?
A: η = △ e / e × 100%, and by measuring the △ ch ch calculated η = △ ch / ch × 100%, and the incident particle energy and equipment itself, the smaller the instrument energy resolution to distinguish different energy values higher ability.
5, Why measure na (tl) single crystal γ scintillation spectrometer linear? Spectrometer with which the main volume of the linear? Linear indicators mean?
A: Draw energy calibration curve, the road through the unknown number of particles to calculate their energy. Ray energy, the instrument itself. Current as possible, accurate measurement results about the error is smaller.
6, observe the slit positioning and try to focus on β semicircle of imaging magnetic spectrometer to demonstrate the principle of rationality.
A:
7, this experiment in the search for the relationship between p and x using a certain approximation, can use other methods to arrive at a more precise relationship between p and x?
A: do comparative experiments, by varying different x, p produce different losses, make the curve, were compared. But too much trouble, the existing conditions can not be achieved.
8, with γ calibration sources for energy, why does not require γ-rays through the 220 m thick aluminum film when "energy loss of correction"?
A: γ-ray energy loss in air is negligible, so no vacuum, but the β particles need to vacuum, so use aluminum cut off the air, so the need for energy loss correction
9, why does the γ calibration sources for energy scintillation detector can be used to measure the energy of β particles?
A: The calibration is the number of channels and the energy diagram, has nothing to do with what kind of particles, so the measure can be of any particle is
10, discussion of relativistic effects test experimental design.
A: The p = mv = ber calculate the momentum of charged particles through nai (tl) scintillation detector to measure the particle kinetic energy, the use of kinetic energy momentum mapping, and security according to the theory of relativity calculations to compare, the basic agreement, then the relativistic effects to be verification.
11, relativistic effects more significant, the electronic speed?
A: The speed approaching the speed of light.
12, test whether it can be carried out in non-vacuum? How?
A: The vacuum energy will be lost, so if you can fill with the last of these losses are possible.
13, the experimental error analysis.
A: The vacuum is not complete, there is a certain energy loss.
Calculated using some approximation of error.
Have some error to find the summit.
14, energy 1mev particle velocity? Energy 2mev particle velocity? How to calculate?
A: v = c [1-1 / (1 + k/mc2) 2] 1 / 2, 4.19 * 105 m / s, 5.93 * 105m / s
[Discussion, experience]
Theory of relativity for us may be a distant thing, I think it can only have been theoretical studies, ordinary people can not think of a human history of this most important discovery to validation, is really very exciting. Although the sources have some damage to the body, but I trust the scientific precautions, as I also promising scientific spirit of dedication. |
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