In the following sections, the system proposed here will be discussed in depth from a twofold perspective: (i) hardware components used, their connection/integration and (ii) software implemented.
Link to Nuclear & Electronics WiFi Adapter. This component is placed in a USB port, providing access to the Internet thanks to the WiFi hospital infrastructure. It should be noted that our device ensures an Internet connection (and therefore, the dose information for each user in the remote web server) by selecting of one these technologies: WiFi, 3G and Ethernet. 3G dongle. When connecting to the Internet via 3G, it is necessary to put a 3G dongle into the interface USB of the Raspberry Pi. Although there are several models compatible with Raspberry Pi, the selected dongle [ 29 ] together with a prepaid card have allowed the use of the device anywhere in the hospital environment. In addition, in the specific case of not having access to WiFi or Ethernet in the hospital under study, or when the system was verified at CND, the use of the 3G dongle has been essential to dispatch the captured radiation data to the remote web server. To achieve high voltage in the GM tube, an oscillator connected to a voltage multiplier consisting of diodes, transistors, resistors and capacitors is employed. This electronic circuit guarantees a potential difference of 500 V. In the particular case of requiring voltage values above 500 V to feed the tube, they will be obtained from zener diodes connected in series. Geiger Sensor Board [ 18 ]. This board is responsible for measuring radiation values using a Geiger-Müller tube. The radiation board is composed of two parts: the supply side and the signal side. The supply side is responsible for ensuring the high voltage required by the Geiger-Müller tube (400 V–800 V). The signal side adapts the output analog pulses from the GM tube to digital data understandable by the Raspberry Pi. The goal of this bridge board is to facilitate the integration of modules designed for Arduino on Raspberry Pi. This allows us to attach analog and digital sensors using the same pins for Arduino, but with the power and capacity of a Raspberry Pi. So, on the back of this main board, a bridge board will be connected through the GPIO pins. The board including the Geiger counter will be connected to the pins I/O, UART, SPI and I2C, belonging to the bridge board. Raspberry Pi to Arduino Shield Connection Bridge [ 28 ]. Since the connection between the Geiger Sensor Board and Raspberry is not possible, an intermediate board or bridge is required. This board is called Raspberry Pi to Arduino Shield Connection Bridge, but for the sake of brevity, we will denote it a bridge board. A General Purpose Input/Output (GPIO) port consisting of 40 pins allows the Raspberry Pi to communicate with external elements. In particular, GPIO pins are managed and handled directly through code from the intermediate Bridge board. USB ports used to connect the 3G dongle or wireless adapter. In addition, if the Raspberry needs to be programmed, they will be used to connect the mouse and keyboard. Raspberry Pi [ 19 ]. It is a low-cost embedded board developed by the Raspberry Pi Foundation in the UK. Its size is approximately that of a credit card and encapsulates a Broadcom BCM2835 chip with an ARM processor up to 1 GHz speed. In our work, the Raspberry Pi B++ model has been selected for its low cost and ability to carry out all the functions of our system. Note that a MicroSD card including the operating system (Raspbian), is inserted in the back of the Raspberry, which will be explained later. Operating System. The operating system (OS) for Raspberry Pi is denoted as Raspbian. In particular, Raspbian Jessie was the version installed, because it offers multiple functionality and documentation in terms of capturing data and communication issues. Geiger sensor code. This code, implemented in C language, quantifies the counts per minute and equivalent radiation measured by the GM detector on the board. Raspberry Pi executes the programmed code obtaining the dose data from the Geiger detector through its GPIO pins. Since the sensor uses the same connections as Arduino, it is necessary to include the arduPi library codes provided by the manufacturer. shows a flowchart of the way a Geiger operates (and its associated code). Every time the code is initiated, the application remains waiting for a stimulation to occur in the GM tube, increasing the number of counts. Then, the application enters into an infinite loop, in which the radiation values are continuously captured in periods of one second. In reference to the previous figure, each of the blocks is discussed: ● Radiation measurement: display by console terminal As mentioned above, the app shows counts per minute (CPM) and radiation dose (µSv/h). Firstly, it is necessary to calculate the number of counts per minute and to later obtain the equivalent radiation value related to the CPM calculated, multiplying the CPM by the conversion factor provided by the manufacturer. The number of counts corresponding to the GM tube stimulation is stored in a specific variable. The temporal interval lasts one second. In order to obtain equivalent CPMs, it will be necessary to multiply the number of counts per second by 60 (countPerMinute = 60 ∗ count). Finally, before the radiation values are stored in the local and remote databases, the number of counts is reset (variable is set to zero), so when the loop is restarted, a new count value is obtained. ● CPM and radiation value upload to remote web server Once CPM and radiation values have been obtained, the next step is to upload these data to the MySQL remote web server database. To this end, it is necessary to use a method which connects to the server by IP, user name and his/her password. Then, the programmer/developer selects the database which connects to it. Note that each device will have its own database on the web server. Thus, each device is independent of the other ones. On the other hand, to upload the CPM and radiation values, a SQL query is implemented. In this case, programmers dispatch an INSERT type query, including countPerMinute (CPM) and radiationValue (equivalent radiation) values to the remote database. Finally, once these values have been stored, the connection is closed. The results displayed by the smartphone application will be the data (together with their statistics) stored in this database installed in the remote web server. ● CPM and radiation value storage in localhost The dose values are also stored in the localhost database. Any error detected in the remote web server will be mitigated by the localhost. That is, those radiation values which were lost in the period of non-operation of the web server will be recuperated by the localhost. This function is carried out by a method which shares the same code as the previous one, except for the IP address. ● End of loop Finally, once data has been uploaded to the web server and stored in the localhost, there is a one second delay in the following set of measurements. This delay implies an appropriate time interval, from the time the radiation level is measured by the Geiger detector, to the time the Android application displays this value on the screen. If the delay decreases to values inferior to one second, the GM detector would be able to measure more accurately. However, there would not be enough time to upload the data to the web server and download it onto the app. It is notable that other systems are capable of showing radiation levels, but taking more time, demonstrating that this system is more accurate in adjusting the intervals to radiation samples. Finally, an automatic code startup has been implemented. To avoid the manual execution of the code in Raspberry Pi (resulting in inefficient application in hospital environments), a script has been programmed to automatically start the code every time the Raspberry Pi is connected to a power supply or is booted. To this end, as Raspberry Pi is a Unix system, the script will be created within the /etc./init.d directory, in which the start and stop commands are specified. Additionally, the different interfaces to access Internet (WiFi, 3G and Ethernet) will also connect automatically, without requiring support from specialist personnel or developers.
3. Servers. A server is required to store the dose data collected by the device. The one selected for both the remote web server and the localhost is Apache [ 30 ], which is a free-service and open-source HTTP server with the same features as other high-cost competitors. The Apache web server is responsible for storing the GM-captured radiation data and managing them in an Android application. In this case, the Android application accesses this server, both to log in or register a new user, and to display the radiation measurements/statistics. The remote web server requires Internet access, so, it must have a domain and therefore, a public IP address. In a certain way, both the device and the Android application connect to the server through this public IP. Under this premise, note that a web server allows us to access data anywhere. Using the Android application or a PC, we check the radiation values at any time and place, even if the detector fails or turns off. This also allows us to control the login and registration of users, avoiding, for instance, that two different users employ the same user name. The Apache localhost is configured as a backup service, lacks an Internet connection, and data are recovered via USB. 4. Database. They are responsible for storing both radiation data from the GM detector and information from user registers. PhpMyAdmin [ 31 ] has been selected as the tool to generate database, both in the local server and the remote web server. PhpMyAdmin written in PHP ensures the database management and handles the MySQL facilitates. For instance, the user can create/delete databases, generate/delete/modify tables, delete/edit/add fields, execute any SQL statement, handle keys in fields, manage privileges, and export data in various formats. Keeping in mind that the devices are independent from each other, labeling each device with its own unique identification number means that each device has its own database. The result is a more intuitive and appropriate management of different devices deployed in a hospital, thus facilitating the data recovery and the data security. The fields composing the databases are, as well as the CPM and radiation value, the following: (i) an identifier for each measurement uploaded; (ii) a timestamp of the captured dose, both coming from the device; and (iii) registered users, including user name, password and email data, dispatched by the smartphone application. Regarding the latter, the goal is for each hospital to have its own databases of users, which would be independent of the others.
5. Android application. The application developed for smartphones is in charge of displaying all the radiation results captured by devices. This application has been implemented in Android because, among other factors, it is an open source. Furthermore, Android makes the simulation and testing of different versions of our application on different devices easier, without the requirement of them having been previously developed in emulators. The development of the app is divided into two main parts: The appearance, focused on the graphic interfaces and the specific functions of each of them. presents a flowchart including the overall functionality of the app. The application links the database through SQL queries. These communications are asynchronous due to the fact that the server runs diverse processes, so this issue will stop the main application if it is coded in a synchronous way. To implement asynchronous tasks, the AsyncTask class [32] is employed. This communicates with the process of the main thread, only performing operations and showing the results in the main thread. An advantage of our implementation is the reduction of the number of database accesses. So, the application is more efficient and dynamic, decreasing the probability of connection errors. To this end, the Intent class [33] is in charge of sending the user name and device number, among different activities, without requiring remote connection to the database. Therefore, SQL queries are only demanded when users want to obtain some type of results, such as radiation statistics. Finally, in the following subsections, the appearance and function of each of the parts in which the app has been divided will be detailed, according to the general diagram shown in . Each time the app is started, an image, like in , presenting a login form, appears. As shown, this form inputs the user name, password and device number. First of all, the user name linked with the password is required. Those values are stored in the database. The device number is the identifier assigned to each device. Each hospital has a specific number of catalogued devices, allowing the user to select the device which they want to receive radiation information from. This selection is manually accomplished when logging in, and depends on the area where the staff is working. Therefore, by filling in the device number field, the app connects to the database corresponding to that device. This is possible because, as discussed above, each healthcare worker is exposed to radiation in an enclosed hospital area, and it will not be necessary to modify the device number every time. On the other hand, if the user doesn’t input data in the form fields or a device number is not one of those assigned to the hospital, an error message will be shown, alerting the user. The Inputvalidation class is in charge of these functions. However, if the proccess is correct, the Login button is enabled and the user name and password are checked against the database through the CheckUser class. In the affirmative case, the main view of the application is depicted in . All views and styles have been programmed in XML. To achieve this, the official Android API has been used. The code corresponding to Start session is denoted as “LogicActivity”. The flowchart of this activity is presented in . For more radiation detection and measurement solutionsinformation, please contact us. We will provide professional answers. Each time the user clicks on the screen “No account yet? Create one”, located in “LoginActivity”, the activity called “RegisterActivity” will start. This activity shows a registration form, as shown in . As we can see, this form asks for the user name, e-mail address, password and password confirmation of the user. As in “LoginActivity”, the login form is accessed again by clicking on the sentence “Already a member? Login”, shown in the following . “RegisterActivity” contains the same features as “LoginActivity”. The InputValidation class executes a function in charge of ensuring that if the user introduces empty fields in the form or if the password field does not match the confirm password field, an error message will alert the user. The class CheckUserRegis, extended to the class AsyncTask, checks if the application has a user name which already exists, thus comparing the one introduced in the application with the user’s database. Finally, if a user name doesn’t match a previous one introduced in the database, it means that this name is available and the new user’s data is stored in the database. The class responsible for this function is called AddUser. The following flowchart summarizes how this activity works ( ). The appearance of the main menu corresponds to the Technical University of Cartagena (UPCT) logo as well as a dropdown menu which lets us select the action we want the device to furnish is shown in . Each menu item is associated with a different activity. A particular case is the “Sensor” action, which shows GM detector (sensor) results in real time. The MainActivity allows a user who requires any stadistical action, for example, to download the monthly average radiation, to finish this action, and again access real time dose values in their smartphone. The goal is to provide an extra function to the main menu, which goes beyond an intermediary between activities. Finally, the function corresponding to the main activity is “MainActivity”, and is reflected in the following flowchart ( ). As shown in , depending on the item of the dropdown menu which the user clicks, one action or another starts, and then a different activity begins. As previously illustrated in the “Intent” description, before starting a new activity, the user name and device number are obtained from “LoginActivity”. This activity is implemented in the “MainActivity”, sharing appearance and functionality with the dropdown main menu. The appearance depends on its state. If the “Sensor” icon has not been clicked by the user to start collecting and displaying values in real time, the following depicts the graphic user interface which appears. However, if the user clicks the “Sensor” icon, the window is . Values belong to counts per minute (CPM) and their corresponding radiation value, together with the user who has downloaded them, as shown in this view ( ). These values are updated each second, collected by the GM detector. If the device turns off, the last value captured by the sensor is displayed. Note that the appearance changes (each second) once the first SQL query arrives to the database. The Query class directs this issue. This activity addresses the last counts per minute (and thus, radiation values) and the timestamp registered by the user device as well. The activity in charge of this function is Main2Activity. However, the class which leads to the connection to the database is Last class. This furnishes the required operations to obtain last dose values by means of SQL queries as shown in . The appearance and functionality for the daily, weekly, monthly and annual average is the same. Only the SQL queries vary, taking into consideration the time period to compute. The statistic view shows the user name, the device number and the average value that is required to download from the remote database. The function is similar to the previous Last Values view. However, they are very different in the SQL query message. In detail, the activity addressed to the daily average is Main4Activity and the attachment to the database is carried out by the diarilyaverage class. Regarding the weekly average, it is accomplished by Main5Activity and the weeklyaverage class. The monthly average is run by Main3Activity and the Middle class. Finally, for the annual average, Main6Activity, together with the MediaAnnual class exhibit the annual statistics. These codes, together with the complete software here proposed, are available in [3].3.3.2. Software Description
App Initialization
User Register
Main Menu
Sensor (GM Detector)
Showing Last Values
Statistics
17.3 SCINTILLATION DETECTORS
17.3.1 Basic Principles
Scintillators
are materials that emit visible light or UV radiation after the interaction of ionizing radiation with the material. Scintillators are the oldest type of radiation detectors; Roentgen discovered x-radiation and the fact that x-rays induce scintillation in barium platinocyanide in the same fortuitous experiment. Scintillators are used in conventional film-screen radiography, many direct digital radiographic image receptors, fluoroscopy, scintillation cameras, CT scanners, and positron emission tomography (PET) scanners.Although the light emitted from a single interaction can be seen if the viewer’s eyes are dark adapted, most scintillation detectors incorporate a means of signal amplification. In conventional film-screen radiography, photographic film is used to amplify and record the signal. In other applications, electronic devices such as photomultiplier tubes (PMTs), photodiodes, or image-intensifier tubes convert the light into electrical signals. PMTs and image-intensifier tubes amplify the signal as well. However, most photodiodes do not provide amplification; if amplification of the signal is required, it must be provided by an electronic amplifier. A
scintillation detector
consists of a scintillator and a device, such as a PMT, that converts the light into an electrical signal.Luminescence
is the emission of light after excitation.Fluorescence
is the prompt emission of light, whereasphosphorescence
(also calledafterglow
)When ionizing radiation interacts with a scintillator, electrons are raised to an excited energy level. Ultimately, these electrons fall back to a lower energy state, with the emission of visible light or UV radiation. Most scintillators have more than one mode for the emission of visible light or UV radiation, and each mode has its characteristic decay constant.is the emission of light after excitation.is the prompt emission of light, whereas(also calledis the delayed emission of light. When scintillation detectors are operated in current mode, the prompt signal from an interaction cannot be separated from the phosphorescence caused by previous interactions. When a scintillation detector is operated in pulse mode, afterglow is less important because electronic circuits can separate the rapidly rising and falling components of the prompt signal from the slowly decaying delayed signal resulting from previous interactions.
It is useful, before discussing actual scintillation materials, to consider properties that are desirable in a scintillator.
The
conversion efficiency
, the fraction of deposited energy that is converted into light or UV radiation, should be high. (Conversion efficiency should not be confused with detection efficiency.)For many applications, the decay times of excited states should be short. (Light or UV radiation is emitted promptly after an interaction.)
The material should be transparent to its own emissions. (Most emitted light or UV radiation escapes reabsorption.)
The frequency spectrum (color) of emitted light or UV radiation should match the spectral sensitivity of the light receptor (PMT, photodiode, or film).
If used for x-ray and
γ
-ray detection, the attenuation coefficient (µ
) should be large, so that detectors made of the scintillator have high detection efficiencies. Materials with large atomic numbers and high densities have large attenuation coefficients.The material should be rugged, unaffected by moisture, and inexpensive to manufacture.
In all scintillators, the amount of light emitted after an interaction increases with the energy deposited by the interaction. Therefore, scintillators may be operated in pulse mode as spectrometers. When a scintillator is used for spectroscopy, its energy resolution (ability to distinguish between interactions depositing different energies) is primarily determined by its conversion efficiency. A high conversion efficiency is required for superior energy resolution.
There are several categories of materials that scintillate. Many organic compounds exhibit scintillation. In these materials, the scintillation is a property of the molecular structure. Solid organic scintillators are used for timing experiments in particle physics because of their extremely prompt light emission. Organic scintillators include the liquid scintillation fluids that are used extensively in biomedical research. Samples containing radioactive tracers such as 3H, 14C, and 32P are mixed in vials with liquid scintillators, and the light flashes are detected and counted by PMTs and associated electronic circuits. Organic scintillators are not used for medical imaging because the low atomic numbers of their constituent elements and their low densities make them poor x-ray and
γ
-ray detectors. When photons in the diagnostic energy range do interact with organic scintillators, it is primarily by Compton scattering.There are also many inorganic crystalline materials that exhibit scintillation. In these materials, the scintillation is a property of the crystalline structure: if the crystal is dissolved, the scintillation ceases. Many of these materials have much larger average atomic numbers and higher densities than organic scintillators and therefore are excellent photon detectors. They are widely used for radiation measurements and imaging in radiology.
Most inorganic scintillation crystals are deliberately grown with trace amounts of impurity elements called
activators.
The atoms of these activators form preferred sites in the crystals for the excited electrons to return to the ground state. The activators modify the frequency (color) of the emitted light, the promptness of the light emission, and the proportion of the emitted light that escapes reabsorption in the crystal.For more information, please visit radiation protection solutions.