SteemSTEM Science Fair Entry: Radioactive Detection: from homemade to smartphone app -- SteemSTEM科學節參賽作品: 動手自製亞原子粒子顯示器

SteemSTEM Science Fair Entry: Radioactive Detection: from homemade to smartphone app -- SteemSTEM科學節參賽作品: 動手自製亞原子粒子顯示器

Hi Steemian,
各位Steemian，大家好！

This post is for the entry of the First #sciencefair organized by @steemSTEM, hope you guys enjoy my little project.
這是第一屆 由 @steemSTEM 舉辦的 #sciencefair 參賽貼文，希望大家會喜歡我的小小研究

Precaution and Disclaimer:

• The performed experiments in the following project involve the use of radioactive source.
• Radioactive substance should only be handled by professionals or under supervision of the professionals.
• Please check with the local law regulations regarding the handling of radioactive substance.
• Proper protective measure should be use during the use of radioactive substance, and disposal of radioactive substance must be performed according to regulations.
• Alpha particle are dangerous if swallow or enter biological system
• The use of the "Radioactivity Counter" app may potentially cause damage to the sensor of your camera
• Radioactive substance determined from this experiments does not reflect the actual readings, and should not be use to infer any potential threats of those daily items.

注意事項及免責聲明:

• 本項目進行的實驗會使用放射性物質
• 放射性物質應該只能由專業人士使用或者在他們的監督下使用
• 請查閱使用有關放射性物質在你身處的國家之法律規定
• 使用放射性物質的時候請配備相關保護裝備。請在棄置放射性物質之前查閲並遵從相關法律規定
• 吞食 α粒子或讓其進入生物體係會有機會構成危險
• 使用智能電話"Radioactivity Counter"之應用程式去測量放射性物質有機會會破壞電話的感光元件
• 以此應用程式去測量放射性物質不一定能正確反映實際數字，由此不應只以此程式推斷物品放射性物質的潛在威脅

Abstract of radioactive detection studies

放射性物質檢測之研究摘要

In this project, I demonstrated how we can obtain radioactive substance, in particular, an alpha particle emitter, from a household source. The radiations emitted from the radioactive sources were tested to see if they could be detected with a web camera Charge-Coupled Device (CCD).
With the help of a 3^rd party smartphone app, I have extended the same principle to monitor the detection of higher energy subatomic particles from some daily household item using an old smartphone.

在這個研究中， 我展示了如何以家用物品去取得放射性物質，更準確來説，α粒子發射體。及后，我嘗試以網絡攝像器的感光耦合元件去觀測這些放射性物質。
在第三方智能電話的應用程式協助下，我以同樣原理延伸了感光元件的應用，去檢測一些家用並會釋放高能量放射性物質的物品。

Introduction -- 簡介

I have been doing chemistry research for a while and I am really a science lover. As usual, I will do my best to share interesting science to everyone on Steemit.

When I was young, almost every electronics in my house were eventually disassembled by me, and it had great fun playing with them. As I grow up, I started to get fascinated with chemistry, so I will try all sorts of way to get as many crazy chemicals as possible and try to do experiments at home.

A little while ago, I received an old smoke detector from a friend of mine. Which reminded me of my high school time when I had physics class. The classical smoke detectors contain radioactive materials! The details of the principle for these smoke detectors could be found here in case you are interested in knowing it. Being a graduate student doing chemistry and now with the SteemSTEM Science Fair, I think it is the right time for me to disassemble it. I now have my very first radioactive material, and it is probably one of my favorite in my personal chemicals collections.

我已經在化學研究的領域中做了好一段時間，而我都算是一個熱愛科學的人。一如以往，我會盡力去把我認爲有趣的科學東西分享到Steemit 之中。

在小時候，幾乎每一樣電子物品都會被我拆散，而我都挺享受這個過程。在長大以後，我對化學的着迷讓我絞盡腦汁去取得各式各樣的化學樣品，然後在家裏動手做做實驗。

早前友人把一個舊的煙霧探測器轉贈於我。還記得在高中物理課的時候，曾經說過煙霧探測器有放射性元素！如果你有興趣知道有關放射性元素如何在煙霧探測器中運作，可以到這裡看看。既然到了這個科學節，我認爲這是一個很好的機會去讓我拆散這個煙霧器。現在我擁有第一隻放射性物質，亦是我各樣化學收藏品最愛之一。

What is radioactive substance -- 什麽是放射性物質

Radioactive substance or more specific radioactive elements are elements that are physically unstable and will decay to give out radiations. I have talked a little about what elements are, how they formed and what affected their stability Here. This instability is largely related to the unbalanced force within the nucleus and so it tends to decay into the more stable ones. The instability is often a result of excessive amount of energy stored within one’s nucleus and therefore when decayed, radiations are emitted as a form of energy release.

3 types of radiations are can be emitted by radioactive substance decay: alpha particles, beta particles and gamma rays. The Alpha particles are actually the nucleus of the helium, the beta particles are electrons and the gamma rays are purely electromagnetic waves.

放射性物質或是放射性元素是一些不穩定的原子核自發地放出射線。早前我講過 元素是如何生成，以及什麽會影響他們的穩定性。這個不穩定的特性源自於原子核中不平衡的結合能量，並有過量的能量儲存在核中，由此會籍著衰變去釋放射綫並變成更穩定的元素。

放射性物質通常會釋放三種射綫，包括 α粒子(射線)、β粒子(射線)、γ射線。α粒子其實就是氦的原子核，β粒子就是電子，而 γ射線是電磁波。

Challenge -- 解決難題

All of the three types of radiations are invisible to our nake eyes, so in order to visualize or detect them, we would need some tools. Tools can be photographic films / x-ray films to the more frequently used GM counter in labs, or the more sophisticated nuclear spinthariscope.

In my project, I will use the Charge-Coupled Device(CCD) to capture the radiations. Furthermore, there is a smartphone application that makes use of the similar principle to allow the detection of radiation with the use of the camera on a smartphone. The radioactive source for my experiments will be the one extracted from the smoke alarm.

我們肉眼都是看不見這三種放射性射綫的。由此，要讓我們去觀測或檢測這些射綫，我們需要一些工具。這些工具包括攝影底片/X-光片，以至實驗室常用的蓋革計數器，或閃爍盒。

在這項研究中，我會展示如何用電荷耦合元件去展現這些射綫。同時市面上有一款智能電話應用程式能以類似原理去以電話鏡頭檢測高能量放射性射綫。在這研究中，我會使用在煙霧探測器中取出來的放射性物質做不同的實驗。

Part 1: Acquire the radioactive source: Disassemble of smoke detector

第一部分：取得放射性物質：拆解煙霧探測器

Once the smoke detector cage is removed, this is the only thing in it. The left hand side plastic drum is the alarm, where the right hand side is the key to a smoke detector.
一旦把煙霧探測器的外殼取走之後，你就會看見以下的配件。左邊的塑膠殼是警報器，而右邊是探測器之靈魂。

The casing on the right hand side holds the radioactive source; there are a few words on the top "Caution, Radioactive material Am-241 1.0 uCi 37 kBq"
右邊的圓筒内放著放射性物料；上面的金屬寫著“（翻譯）危險，放射性物料，鋂-241，0.1 微居里，37千貝克”

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Eventually, I remove everything except the little metal ring holding the radioactive material. As the ring is too small for me to hold, so I decided to carry it with a plastic straw.
最後，我把所有東西都移除，剩下放著放射性元素的小小的金屬器皿。由於那金屬器皿實在細得讓我難以拿著它，所以我決定用一個飲筒去連接它

Something about Am-241 and the concept of radioactive decay

關於 Am-241 的背景以及衰變的基本概念

Americum is a synthetic radioactive element which all of its isotopes are radioactive. In particular, in smoke detector, the isotope americium-241 is being used. It will emit alpha particles, which is a helium atom with no electrons. So alpha particles is a 2+ charged ion. At the same time, weak gamma ray will be emitted as well.

鋂是一隻人工合成的放射性元素，其所有同位素都是由放射性的特徵。在煙霧探測器中使用的是它的同位素鋂-214。它主要會釋放出 α粒子，亦即氦的原子核，並沒有任何電子，由此 α粒子是帶2+電荷的；而弱 γ射線亦會同時釋放。

As time progress, the radioactivity will decrease. For Am²⁴¹ has a half-life of 432.2 years, meaning that the radioactivity decrease by half after 432.2 years.
(ie: If it emit 100 alpha particles every second at this moment, it will only emit 50 alpha particles every second after 432.2 years.)
隨著時間流逝，放射頻率會減少。就著Am²⁴¹來説，它有一個 432.2 年的半衰期，即代表放射頻率會在432.2年后減少一半。假若現在樣品每秒會釋放100粒α粒子，在 432.2 年后每秒只會釋放 50粒α粒子

Alpha particles are high energy ions which have many interesting properties. To visualize and play with the particles, we need something which can interact with alpha particles and give out signals.
α粒子是一些有著很多有趣特性的高電離性粒子。去讓我們觀測者種粒子，我們需要一些會能與α粒子相互作用的物質來給我們適當的資訊。

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Part 2: Acquiring the detector: Disassemble a web-cam

第二部分：取得檢測器：拆解網路錄像器

In a camera, there is a charge-coupled device, also known as CCD. It is an image sensor and is the heart of a camera. It is made up of metal-oxide-semiconductors (MOS) capacitors, when there is light/ photons striking onto the CCD surface, an electric signal will be transferred, and those signals eventually give out the images. This process also takes place when a highly ionizing ion like the alpha particles hit the surface of the CCD.

Noted that the alpha particles are highly charged, so once they come in with contact air, the charges will be neutralized by the surrounding air molecules and their flight-path will get blocked easily. So alpha particles is known to have a low penetration power.

As a result, alpha particles cannot directly get in to the CCD of the web camera without removing the barriers between the CCD and the radioactive source. I have to disassemble all the glass and plastic cover in order to allow the particles to reach the sensor.

Disassembling a web cam a lot easier: just remove all the screw and can reach the circuit board.

在鏡頭内都有一個感光耦合元件。它是一個影像感光元件，亦是相機的核心。這元件是由半導體電容器做成的。當光射到感光元件的表面后，就會產生電子訊號去傳送到電腦中，而最後生成影像。當α粒子等放射物質射到感光元件的表面亦能達到同樣效果。

由於α粒子是高電離性的，所以當它一遇到空氣的時候，粒子的電荷會快速被周邊的空氣中和，最後它的飛行很快就停下來。由此，α粒子亦是一種低穿透性的粒子。

基於這些原因，在拆散鏡頭之前，α粒子不能直接進入感光元件，因爲鏡頭的玻璃等物料已經足以阻擋α粒子。所以接著，我就要把所有玻璃及塑料外殼拆除，好讓我們去觀測α粒子！

拆解網絡錄像器相對來説就是容易得多啦：只要把螺絲鬆掉然後就能取得電子板

You may see that the CCD is actually quite small as the web-cam have only ~ 1 Mega pixel.
你可以看到這個感光元件其實是挺細的，因爲這個錄像器只有大概一百萬像素。

Part 3: Qualitative test on the radioactivity

第三部分：放射性物質的定性檢測

As the Am-241 source approaching the CCD, the sparkling effect get much more intense. Each spark corresponding to a sub-atomic particle hitting the sensor, with a larger spot corresponding to a higher energy particle.
當Am-241 靠近感光元件的時候，你就會在屏幕上看到更多閃爍。每一格閃爍至少代表一粒射綫打到感光元件上。同時，越大點側代表越高的粒子能量。

Part 4: Quantitative test on the radioactivity with smartphone

第四部分：以智能電話為放射性物質作定量檢測

Radioactivity could be expressed in different ways, including the energy of the particles per unit of matter, as well as number of particles emitted over a certain period of time.

The radioactive source was measured by a GM-counter, and found to have an average of about 200 count per second; where GM-counter is a standard detecting instruments for these ionizing particles.

With the CCD from the web cam, there is no easy way to quantify the number of particles emitted unless you count all the bright dots in every frame of the video. Thanks to a Germany scientist who had developed a smartphone app, using the same principle as the experiment demonstrated above, the application can record and quantify the number of bright dots.

放射頻率可以以不同的方式表達出來，包括物質吸收到的粒子能量，又或者是以粒子射出的頻率來表示。

放射性粒子的頻率通常以蓋革計數器 來量度，而我從煙霧器拿出來的樣品平均每秒大概有200粒粒子射出來。

雖然網絡錄像器的感光元件能測量放射性物質，但就很難去量化究竟有多少粒子打到它的表面，除非你人手把視頻的每一個影像的每一個點光點都數一次。幸好有位德國科學家研發了一個智能電話應用程式 ；這個應用程式就用上了感光元件檢測放射性的原理，並會自動記錄亮了的光點的數目。

The absorption dose: Gray

能量吸收劑量: 戈雷

Aside from radiation count per unit of time, radioactivity can also be interpreted in terms of energy. Gray is one of the International System of Units, which is defined as the absorption of one joule of radiation energy per kilogram of matter. The energy absorbed by the CCD could be reflected by the size of the dot, while different mobile phone have different response. The developer had do calibration for a list of smartphones, if you got one match from their list, you can also obtain a the corresponding energy received by the CCD. Unfortunately, they did not test with the phone which I am using, as a result, you may see that not set µGy/h in the screen cap and gif.
除了以頻率表示以外，放射性亦可以以能量去表達。戈雷就是其中一個國際通用的單位，一戈雷(1 Gy)就代表一公斤物質吸收了一焦耳的輻射能量。放射性物質打到CCD 的屏幕上會以亮點顯示，同時點的大小亦反映了粒子的能量。由於不同電話的牌子和型號會有不同的效果，所以如果要真正量度粒子的能量就需要校正。官方網頁列出了一堆已校正好的電話，可惜我電話的型號沒有在列表内，由此在我的測試中可以看到我的截圖表示 µGy/h 還沒有校正。

Previously, they had published a free beta version, which I am currently using. The software is currently available in appstore: android & IOS.
Before I start, background radiation was measured over five minutes. It was found to have a mean of 0.2 count per minute (cpm).
早前這個軟件官方出了個免費版好讓用家看看有沒有什麽缺憾，而我剛好在那個時候下載，亦是在這裡展示給大家看到版本。這個軟件現在能在應用程式的網上商店購買：android & IOS.
在我開始之前，我先花了五分鐘用程式量度了室内背景的放射性，並錄得平均每分鐘 0.2 粒放射性粒子(cpm)。

Radiation count with Am-241 was then again measured for 5 minutes. The mean count was found to be 35.6 cpm, showing that there are high energy ionizing radiations (like beta and gamma radiation) reaching the camera sensor.
然後我再在把Am-241 放到鏡頭前面再量度一次。五分鐘錄得的平均數為35.6 cpm，表示有高能量放射性物質(β粒子和γ射線)進入鏡頭的感光元件。

The radiation count observed by this app is much lower than that detected from the GM counter. One possible explanation is that only a small amount of high energy low-ionization particles, like beta and gamma radiation, emitted by the Am-241 reach the smartphone camera sensor. Majority of the alpha particles were blocked by the glass cover of the smartphone camera.
你會發現由這個程式量度出來的例子數目遠比蓋革計的少。其中一個原因就是因爲Am-241只有小量高能量低電離性的粒子(β粒子和γ射線)到達電話鏡頭。大部分的α粒子都會被電話鏡頭前面的玻璃面阻隔。

Part 5: Radioactivity of low sodium salt

第五部分: 低鈉鹽的放射性

In atmosphere, the top 3 abundance atmospheric gases are

• Nitrogen (78.09 %)
• Oxygen (20.95 %)
• Argon (0.93 %)
  Had you ever thought about why ARGON is relatively abundance on Earth?

On Earth, there are a lot of minerals which contain potassium ion. Potassium have 3 isotopes:

• ³⁹K : Abudance = 93.26% (stable nuclei)
• ⁴⁰K : Abudance = 0.012% (radioactive isotope with half-life of 1.25×10⁹ years)
• ⁴¹K : Abudance = 6.730% (stable nuclei)

在大氣層中最主要的三種氣體就是:

• 氮氣 (78.09 %)
• 氧氣 (20.95 %)
• 氬氣 (0.93 %)
  你有想過爲何氬氣爲何會相對地那麽高濃度呢?

地球上，有很多礦物都含有鉀離子，而鉀離子有三個同位素：

• ³⁹K : 豐度 = 93.26% (穩定原子核)
• ⁴⁰K : 豐度 = 0.012% (半衰期為 1.25×10⁹ 年的放射性同位素)
• ⁴¹K : 豐度 = 6.730% (穩定原子核)
  
  

The ⁴⁰K may undergo electron capture and decay to ⁴⁰Ar with emission of gamma ray and neutrino; or undergo decay to give ⁴⁰Ca and emit beta particles and antineutrino.

This radioactive decay is the main contribution of argon in the atmosphere.

Potassium chloride would be one of the readily available potassium source, which is sold as low sodium table salt substitute for patient with high blood pressure.
A pack of potassium chloride was bought in the grocery store, which contain ~ 1/3 potassium chloride by weight. It is well known that potassium chloride is radioactive. Therefore the radioactivity of the salt was tested with the app.

As shown below, with the potassium salt, the average radioactive count was found to be 0.8 cpm, which is slightly higher then then the background. Yet, the result is still better then expected: As potassium emit beta-particles, which have only relatively low penetration power. At the same time, the low abundance of ⁴⁰K give rise to minimal amount of beta-particles, resulting the low radioactive count number.

⁴⁰K 會以吸收電子的方式然後衰變成⁴⁰Ar 以及釋放出γ射線以及中微子；又或者衰變到⁴⁰Ca 同時釋放β粒子以及反中微子。

由此可知，大氣中的氬氣其實是主要由放射性衰變產生出來的。

氯化鉀其實就是一種日常會遇上鉀離子的原料，它通常會以低鈉鹽的形式售賣，以作爲高血壓病人取代餐桌鹽的代替品。
我在超市買了一包低鈉鹽，大概含有~1/3重量的氯化鉀。氯化鉀是已知會有微量放射性特質的東西，由此我又嘗試一下用電話去量度這低鈉鹽的放射性。

從下圖可看到，平均的放射性大概為每分鐘0.8粒粒子，只是略高於背景的放射性。這少量的差別其實都可以說是預料之内：鉀釋放出的β粒子其實只有不太高的穿透性，同時，⁴⁰K 的豐量其實是非常低，所以導致只錄得低放射性的數字

Conclusion -- 總結

In this project, I had isolated the radioactive alpha particle source Am-241 from an old smoke detector and use it as a radioactive source for the experiment. The real life monitoring of the alpha particles can be detected with the CCD of a web cam. High energy radiation emitted by Am-241 was further quantified by the use of a smartphone application, and was estimated to have a mean value of 35.6 count per minute, compared to the background of 0.2 count per minute.
I have also explained the origin of high abundance of argon in the atmosphere, which is the result of radioactive decay of a potassium isotope. The radioactivity of potassium chloride, which is a readily available house hold radioactive source, was tested with the smartphone app, it was shown that there is a slightly higher count rate (0.8 cpm) than the background (0.2 cpm).
My experiments confirmed the CCD from web cams and that of smart phone, along with the application developed by Rolf-Dieter Klein can be readily available tools for the general public to roughly determine the radioactivity of some daily household items, such as the Am-241 in ionization-type smoke detectors or K-40 in low sodium salt.

在這個研究裏，我在煙霧探測器中取出放射性物質 Am-241 作爲實驗的主要物資。我以網路錄像器的感光元件去實時監測α粒子的活性。由Am-241發射出的高能量的粒子再以智能電話程式去量化，相對背景平均0.2粒粒子，煙霧探測器的放射性物質錄得平均每分鐘35.6粒粒子。我亦解釋了大氣中的高含量氬氣源自於鉀同位素的衰變，並以日常用品氯化鉀作爲另一放射性樣品作量度，錄得略高於背景的平均每分鐘0.8粒粒子。
這個實驗證實了網絡錄像器以及電話相機的感光元件，以配合由Rolf-Dieter Klein研發的應用程式，能作爲平民化的放射性測量工具。由此能為一些好像煙霧探測器以及低鈉鹽等日常用品為放射性作出估算。

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Supporting information 附加資料

The camera lens was covered with black wire tape to avoid any entry of light as suggested by the official web page.
Mobile App: Radioactive Counter version: Year 2011
Mobile brand: Sony Xperia T2 Ultra dual
App setting: Noise: 9 ; border: -2

鏡頭根據官方網頁建議，以黑色電線膠布包裹
電話應用程式: Radioactive Counter, 版本 2011年
電話牌子: Sony Xperia T2 Ultra dual
程式設置: Noise: 9 ; border: -2

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