Alpha譜儀系列產品，可以滿足您各式各樣的應用需求，不管是大樣品還是小樣品的測量，大樣品量測量還是小樣品測量，或者是原有系統升級還是全新購置。本設計采用模塊化結構，不管是在機械性能方面還是在測量性能上都擁有了極大的提升，同時也具備了靈活性。完全支持在原有系統上的升級。
伽太科技提供ORTEC公司全系列Alpha譜儀系列產品，可以滿足您各式各樣的應用需求，不管是大樣品還是小樣品的測量，大樣品量測量還是小樣品測量，或者是原有系統升級還是全新購置。總有一款可以滿足您的需求。最新設計采用模塊化結構，不管是在機械性能方面還是在測量性能上都擁有了極大的提升，同時也具備了原有產品所不具備的靈活性。完全支持在原有系統上的升級。 產品聯系：sales@gamtic.com，021-5197 0121.
Alpha Aria：
單通道Alpha譜儀系統，占用NIM機箱的兩個標準寬度。可直接插入NIM機箱，通過機箱供電，與計算機通過USB進行連接。前面板設置機械旋鈕，可以極為方便的實現抽氣/保持/放氣操作。用戶只需將插件插入NIM機箱。
Alpha Duo：
桌面式雙路Alpha譜儀擁有兩個Alpha譜測量通道。每個測量通道包含100%的全電腦控制真空系統，內置可程控高壓系統，前置放大器，可變幅度脈沖發生器，以及漏電流監測系統。Alpha Duo模塊每一個通道均擁有獨立的數字MCA，每個測量通道可進行完全獨立的操作。
Alpha Mega：
桌面式單通道Alpha譜儀，擁有目前最大的測量艙室，可測量直徑106mm的樣品。外形尺寸與Alpha Duo一致。同時該型號的的Alpha譜儀可以配置更大的探測器，最大可到3000mm2。具有與Alpha Duo同樣的特性，并且完全計算機程序控制。可作為單獨的設備采購，也可作為Alpha Ensemble的部件采購。
Alpha Ensemble：
一套Alpha譜儀系統可以隨意配置多達4個模塊（Alpha Duo和Alpha Mega），每個Alpha模塊中均包含獨立的真空電磁閥，探測器偏壓，前置放大器，可調節脈沖發生器，反沖抑制模塊和漏電流監測器等。
內置的USB集線器，可以將不同模塊之間的連接通過一根USB電纜直接連接到計算機。每個探測通道可以在計算機中單獨設置轉換增益等參數。提供了極大的靈活性。
Alpha Spectrometry is a fascinating technique because it allows you to have accurate information about the radioactive decay of heavy nuclei and about the physics of the interaction of charged particles with matter. But this is a rather difficult technique, even more difficult than gamma spectrometry. The difficulties of this technique lie in the type of detector, usually a solid state silicon detector (rather expensive) that produces a very weak signal which requires, to be analyzed, very low noise amplifiers.
The measurement has to be made in vacuum conditions (however not high vacuum) so that the alpha particles are not shielded from the air. The sources that are measured have to be carefully prepared so as to have a layer as thin and uniform as possible so that alpha particles are not diffused and absorbed within the source itself.
Despite these difficulties it is possible, with a fair amount of work and patience, prepare a DIY instrument that can give a lot of satisfaction.
The alpha radioactive nuclei (typically heavy nuclei) can decay by emitting alpha particles (helium nuclei) with energies of the order of a few MeV, with spectra with lines, corresponding to the energy levels of involved nuclei .
In the figure aside it is an example of energy spectrum of alpha emissions of U-238.
The alpha-active nuclei are heavy nuclei with atomic number greater than 82 (lead). Examples are Polonium, Radium, Thorium, Uranium, etc …
The alpha decay has been explained theoretically by G. Gamow in the first half of the previous century
making use of the tunnel effect in quantum mechanics. In the figure is a graph which shows the wave function of the alpha particle inside the nucleus and outside, beyond the Coulomb barrier. Although the alpha particle does not have enough energy to overcome the barrier it is seen as outside the nucleus the wave function is not zero and thus there is a non-zero probability that the alpha particle is ejected from the nucleus. Using this model it is possible to explain with good accuracy the characteristics of alpha decay.
In a semiconductor, the equivalent of the ionization energy is the band-gap energy to promote an electron from the valence to the conduction band. In Si at room temperature, Eg = 1.1 eV, compared to ~15 eV to ionize a gas. A charged particle moving through Si therefore creates more ionization and a larger signal.
When n-type and p-type silicon are put in contact, creating a p-n junction, the flow of the two different free charges across the boundary creates a depletion zone, an electrically neutral area near the junction where an internal electric field sweeps out any free charge. By reverse biasing the junction, the depletion zone can be made large, ~hundreds of microns. If an energetic charged particle ranges out in the depletion zone, an amount of ionization proportional to the particle’s initial energy will be created there, and swept out. By plating metallic ohmic contacts on the outer surfaces of the crystal, it is possible to both apply the bias and collect the free charge from the depletion zone, so that the whole assembly is a high gain, solid state version of the capacitive ionization chamber.
In our project we have used the detector shown in the image aside (thanks to Professor John Bland).
It features the following technical data :
– Canberra PIPS SPD-100-12 (partially depleted)
– Active area = 100mm2
– FWHM 12KeV at 5MeV
– Bias Voltage = 40V
– Thickness = 100μm
The signal produced by the detector has very low amplitude and therefore it requires an appropriate amplification. Given the very low level of the signal you must use very low noise amplifiers, also the bias voltage must be free of ripple, which is why we have adopted a power-based batteries. The preamplifier of the signal is based on a charge sensitive preamplifier type (CSP): the current pulse generated by the detector is converted into a voltage pulse by means of the charge of a capacitor. In the scheme below it is presented ta basic diagram of a charge preamplifier :
At time domains lasting up to a few microseconds, the CSP output is the time integral of the current pulse from the PIPS/Surface barrier detector. The output rise time is approximately equal to the duration of the current pulse, although the speed of the CSP sets a lower limit to this rise time.
Because the CSP Produces an output voltage step that is proportional to the time integral of the current input and remembering that :
the CSP output is proportional to the total charge (Q) from the PIPS detector. At much longer time domains the response of a CSP to a fast current pulse from a PIPS detectors is in the form of a tail pulse. A tail pulse has a fast initial rise time followed by a very long exponential decay back to the baseline. A tail pulse response from a CSP module is shown below.