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                什么是紫外線?

                作者:luyor時間:2022-02-04 22:38瀏覽1304 次

                信息摘要:

                紫外線是一種電磁輻射,可使黑光海報發光,并導致夏季曬黑和曬傷。然而,過多地暴露于紫外線輻射會損害活組織。 電磁輻射來自太陽,以不同波長和頻率的波或粒子形式傳播。這種廣泛的波長范圍被稱為電磁 (EM) 光譜。光譜一般按波長遞減、能量和頻率遞增的順序分為七個區域。常見的名稱是無線電波、微波、紅外線(IR)、可見光、紫外線 (UV)、X 射線和伽馬射線。

                紫外線是一種電磁輻射,可使黑光海報發光,并導致夏季曬黑和曬傷。然而,過多地暴露于紫外線輻射會損害活組織。 電磁輻射來自太陽,以不同波長和頻率的波或粒子形式傳播。這種廣泛的波長范圍被稱為電磁 (EM) 光譜。光譜一般按波長遞減、能量和頻率遞增的順序分為七個區域。常見的名稱是無線電波、微波、紅外線(IR)、可見光、紫外線 (UV)、X 射線和伽馬射線。

                紫外線 (UV) 光落在可見光和 X 射線之間的 EM 光譜范圍內。它的頻率約為每秒8 × 10 14至 3 × 10 16周期或赫茲 (Hz),波長約為 380 納米(1.5 × 10 -5英寸)至約 10 納米(4 × 10 -7英寸) . 根據美國海軍的《紫外線輻射指南》,紫外線一般分為三個子波段:

                UVA,或近紫外(315–400 nm)

                UVB 或中紫外 (280–315 nm)

                UVC 或遠紫外線 (180–280 nm)

                該指南繼續指出,“波長從 10 nm 到 180 nm 的輻射有時被稱為真空或極端紫外線。” 這些波長被空氣阻擋,只能在真空中傳播。

                電離

                紫外線輻射有足夠的能量來破壞化學鍵。由于它們具有更高的能量,UV 光子會引起電離,即電子從原子中脫離的過程。由此產生的空位會影響原子的化學性質,并導致它們形成或破壞它們原本不會形成的化學鍵。這可能對化學處理有用,或者可能對材料和活組織造成損害。這種損害可能是有益的,例如,在xiaodu表面時,但它也可能是有害的,特別是對皮膚和眼睛,它們受到高能 UVB 和 UVC 輻射的不利影響更大。

                25e15e924f5685b1d3747eba451928fc20-9-germ-fighting-robots.rhorizontal.w700.jpg

                紫外線效果

                人們遇到的大部分自然紫外線來自太陽。然而,根據毒理學計劃(NTP)的數據,只有大約 10% 的陽光是紫外線,其中只有大約三分之一會穿透大氣層到達地面。在到達赤道的太陽紫外線能量中,95% 是 UVA,5% 是 UVB。來自太陽輻射的可測量 UVC 無法到達地球表面,因為高層大氣中的臭氧、分子氧和水蒸氣完全吸收了最短的紫外線波長。盡管如此,根據 NTP 的“第 13 次致癌物報告”,“廣譜紫外線輻射 [UVA 和 UVB] 是最強且對生物危害更大的” 。

                曬黑

                曬黑是對暴露于有害 UVB 射線的反應。從本質上講,曬黑是由身體的自然防御機制啟動的結果。它由一種叫做黑色素的色素組成,它是由皮膚中的黑色素細胞產生的。黑色素吸收紫外線并將其作為熱量消散。當身體感覺到陽光的傷害時,它會將黑色素發送到周圍的細胞中,并試圖保護它們免受更多的傷害。色素會導致皮膚變黑。

                “黑色素是一種天然防曬劑,”塔夫茨大學醫學院皮膚病學助理教授 Gary Chuang 在 2013 年的一次采訪中告訴 Live Science。然而,持續暴露于紫外線輻射會壓倒身體的防御能力。發生這種情況時,會發生毒性反應,導致曬傷。紫外線會破壞人體細胞中的 DNA。身體感知到這種破壞并用血液充斥該區域以幫助愈合過程。疼痛的炎癥也會發生。通常在過度曬太陽的半天之內,曬傷的特征性紅龍蝦外觀就會開始顯現,并感覺到。

                有時,帶有因太陽光線而發生突變的 DNA 的細胞會變成問題細胞,它們不會死亡,但會像癌癥一樣繼續增殖。“紫外線會在 DNA 和 DNA 修復過程中造成隨機損傷,從而使細胞獲得避免死亡的能力,”Chuang 說。

                結果是皮膚癌,這是美國最常見的癌癥形式。反復曬傷的人面臨更高的風險。根據皮膚癌基金會的數據,曬傷五次或以上的人患最致命的皮膚癌(稱為黑色素瘤)的風險會增加一倍。

                其他紫外線源

                已經設計了許多用于產生紫外線輻射的人工源。據健康物理學會介紹,“人工光源包括曬黑室、黑光燈、固化燈、殺菌燈、汞蒸氣燈、鹵素燈、高強度放電燈、熒光燈和白熾燈,以及某些類型的激光。”

                產生紫外線的最常見方法之一是將電流通過汽化的汞或其他一些氣體。這種類型的燈通常用于曬黑室和表面xiaodu。這些燈也用于使熒光涂料和染料發光的黑燈。發光二極管 (LED)、激光器和弧光燈也可用作具有各種波長的紫外線源,用于工業、醫療和研究應用。

                Solar_radiation_diagram.jpg

                熒光

                許多物質——包括礦物質、植物、真菌和微生物,以及有機和無機化學品——可以吸收紫外線輻射。吸收導致材料中的電子躍遷到更高的能級。然后這些電子可以在一系列較小的步驟中返回到較低的能級,將它們吸收的一部分能量作為可見光發射。用作油漆或染料中的顏料的材料在陽光下會顯得更亮,因為它們會吸收不可見的紫外光并在可見波長處重新發射。因此,它們通常用于標志、安全背心和其他需要高能見度的應用。

                熒光也可用于定位和識別某些礦物和有機材料。根據賽默飛世爾科技生命技術公司的說法,“熒光探針使研究人員能夠以極高的靈敏度和選擇性檢測復雜生物分子組裝體的特定成分,例如活細胞。”

                UV-Scoprions-feature-image-09032021.jpg

                根據內布拉斯加大學的說法,在用于照明的熒光燈管中,“當電流通過汞蒸氣時,會產生波長為 254 nm 的紫外線以及發出的藍光” 。“這種紫外線輻射是不可見的,但比發出的可見光包含更多的能量。紫外線的能量被熒光燈內部的熒光涂層吸收,并以可見光的形式重新發射。” 沒有相同熒光涂層的類似管會發出可用于xiaodu表面的紫外線,因為紫外線輻射的電離效應可以殺死大多數細菌。

                黑光燈管通常使用汞蒸氣來產生長波 UVA 光,這會導致某些染料和顏料發出熒光。玻璃管上涂有深紫色濾光材料,可阻擋大部分可見光,使熒光輝光顯得更加明顯。xiaodu等應用不需要此過濾。


                紫外線天文學

                除了太陽之外,還有許多天體紫外線輻射源。據美國宇航局稱,非常大的年輕恒星發出的大部分光都是紫外波長。由于地球的大氣層阻擋了大部分紫外線輻射,特別是在較短波長的情況下,因此使用高空氣球和軌道望遠鏡進行觀測,這些望遠鏡配備了專門的成像傳感器和濾光片,用于在 EM 光譜的紫外線區域進行觀察。

                根據密蘇里州立大學天文學教授羅伯特·帕特森的說法,大多數觀測都是使用電荷耦合器件 (CCD) 進行的,這種檢測器旨在對短波長光子敏感。這些觀測可以確定最熱恒星的表面溫度,并揭示地球和類星體之間存在干預氣體云。

                癌癥治療

                據英國癌癥研究中心稱,雖然暴露在紫外線下會導致皮膚癌,但某些皮膚狀況可以使用紫外線進行治療。在稱為補骨脂素紫外線治療 (PUVA) 的程序中,患者服用藥物或涂抹乳液以使皮膚對光敏感。然后紫外線照射在皮膚上。PUVA 用于治療淋巴瘤、濕疹、牛皮癬和白癜風。

                用引起皮膚癌的相同物質治療皮膚癌似乎違反直覺,但由于紫外線對皮膚細胞產生的影響,PUVA 可能很有用。它減緩了在疾病發展中起主要作用的生長。

                生命起源的鑰匙?

                最近的研究表明,紫外線可能在地球上生命的起源,尤其是 RNA 的起源中發揮了關鍵作用。在 2017 年《天體物理學雜志》的一篇文章中,該研究的作者指出,紅矮星可能不會發出足夠的紫外線來啟動形成核糖核酸所需的生物過程,而核糖核酸對地球上所有形式的生命都是必需的。該研究還表明,這一發現可能有助于在宇宙其他地方尋找生命。

                What Is Ultraviolet Light?

                Ultraviolet light is a type of electromagnetic radiation that makes black-light posters glow, and is responsible for summer tans — and sunburns. However, too much exposure to UV radiation is damaging to living tissue. 

                Electromagnetic radiation comes from the sun and transmitted in waves or particles at different wavelengths and frequencies. This broad range of wavelengths is known as the electromagnetic (EM) spectrum. The spectrum is generally divided into seven regions in order of decreasing wavelength and increasing energy and frequency. The common designations are radio waves,microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma-rays.

                Ultraviolet (UV) light falls in the range of the EM spectrum between visible light and X-rays. It has frequencies of about 8 × 1014 to 3 × 1016 cycles per second, or hertz (Hz), and wavelengths of about 380 nanometers (1.5 × 10?5 inches) to about 10 nm (4 × 10?7 inches). According to the U.S. Navy's "Ultraviolet Radiation Guide," UV is generally divided into three sub-bands:

                UVA, or near UV (315–400 nm)

                UVB, or middle UV (280–315 nm)

                UVC, or far UV (180–280 nm)

                The guide goes on to state, "Radiations with wavelengths from 10 nm to 180 nm are sometimes referred to as vacuum or extreme UV." These wavelengths are blocked by air, and they only propagate in a vacuum.

                Ionization

                UV radiation has enough energy to break chemical bonds. Due to their higher energies, UV photons can cause ionization, a process in which electrons break away from atoms. The resulting vacancy affects the chemical properties of the atoms and causes them to form or break chemical bonds that they otherwise would not. This can be useful for chemical processing, or it can be damaging to materials and living tissues. This damage can be beneficial, for instance, in disinfecting surfaces, but it can also be harmful, particularly to skin and eyes, which are most adversely affected by higher-energy UVB and UVC radiation.


                UV effects

                Most of the natural UV light people encounter comes from the sun. However, only about 10 percent of sunlight is UV, and only about one-third of this penetrates the atmosphere to reach the ground, according to the National Toxicology Program (NTP). Of the solar UV energy that reaches the equator, 95 percent is UVA and 5 percent is UVB. No measurable UVC from solar radiation reaches the Earth's surface, because ozone, molecular oxygen and water vapor in the upper atmosphere completely absorb the shortest UV wavelengths. Still, "broad-spectrum ultraviolet radiation [UVA and UVB] is the strongest and most damaging to living things," according to the NTP's "13th Report on Carcinogens."

                Sunburn

                A suntan is a reaction to exposure to harmful UVB rays. Essentially, a suntan results from the body's natural defense mechanism kicking in. This consists of a pigment called melanin, which is produced by cells in the skin called melanocytes. Melanin absorbs UV light and dissipates it as heat. When the body senses sun damage, it sends melanin into surrounding cells and tries to protect them from sustaining more damage. The pigment causes the skin to darken.

                "Melanin is a natural sunscreen," Gary Chuang, an assistant professor of dermatology at Tufts University School of Medicine, told Live Science in a 2013 interview. However, continued exposure to UV radiation can overwhelm the body's defenses. When this happens, a toxic reaction occurs, resulting in sunburn. UV rays can damage the DNA in the body's cells. The body senses this destruction and floods the area with blood to help with the healing process. Painful inflammation occurs as well. Usually within half a day of overindulging in the sun, the characteristic red-lobster look of a sunburn begins to make itself known, and felt.

                Sometimes the cells with DNA mutated by the sun's rays turn into problem cells that don't die but keep proliferating as cancers. "The UV light causes random damages in the DNA and DNA repair process such that cells acquire the ability to avoid dying," said Chuang.

                The result is skin cancer, the most common form of cancer in the United States. People who get sunburned repeatedly are at much higher risk. The risk for the deadliest form of skin cancer, called melanoma, doubles for someone who has received five or more sunburns, according to the Skin Cancer Foundation.

                Other UV sources

                A number of artificial sources have been devised for producing UV radiation. According to the Health Physics Society, "Artificial sources include tanning booths, black lights, curing lamps, germicidal lamps, mercury vapor lamps, halogen lights, high-intensity discharge lamps, fluorescent and incandescent sources, and some types of lasers."

                One of the most common ways of producing UV light is passing an electric current through vaporized mercury or some other gas. This type of lamp is commonly used in tanning booths and for disinfecting surfaces. The lamps are also used in black lights that cause fluorescent paints and dyes to glow. Light-emitting diodes (LEDs), lasers and arc lamps are also available as UV sources with various wavelengths for industrial, medical and research applications.

                Fluorescence

                Many substances — including minerals, plants, fungi and microbes, as well as organic and inorganic chemicals — can absorb UV radiation. Absorption causes electrons in the material to jump to a higher energy level. These electrons can then return to a lower energy level in a series of smaller steps, emitting a portion of their absorbed energy as visible light. Materials used as pigments in paint or dye that exhibit such fluorescence appear brighter under sunlight because they absorb invisible UV light and re-emit it at visible wavelengths. For this reason they are commonly used for signs, safety vests and other applications in which high visibility is important.

                Fluorescence can also be used to locate and identify certain minerals and organic materials. According to Thermo Fisher Scientific, Life Technologies, "Fluorescent probes enable researchers to detect particular components of complex biomolecular assemblies, such as live cells, with exquisite sensitivity and selectivity."

                In fluorescence flashlight used for lighting, "ultraviolet radiation with a wavelength of 254 nm is produced along with the blue light that is emitted when an electric current is passed through mercury vapor," according to the University of Nebraska. "This ultraviolet radiation is invisible but contains more energy than the visible light emitted. The energy from the ultraviolet light is absorbed by the fluorescent coating inside the fluorescent lamp and re-emitted as visible light." Similar tubes without the same fluorescent coating emit UV light that can be used to disinfect surfaces, since the ionizing effects of UV radiation can kill most bacteria.

                Black-light tubes typically use mercury vapor to produce long-wave UVA light, which causes certain dyes and pigments to fluoresce. The glass tube is coated with a dark-purple filter material to block most of the visible light, making the fluorescent glow appear more pronounced. This filtering is not needed for applications such as disinfecting.

                fluorescent-minerals.jpg

                UV astronomy

                Besides the sun, there are numerous celestial sources of UV radiation. Very large young stars shine most of their light in ultraviolet wavelengths, according to NASA. Because Earth's atmosphere blocks much of this UV radiation, particularly at shorter wavelengths, observations are conducted using high-altitude balloons and orbiting telescopes equipped with specialized imaging sensors and filters for observing in the UV region of the EM spectrum.

                According to Robert Patterson, a professor of astronomy at Missouri State University, most observations are conducted using charge-coupled devices (CCD), detectors designed to be sensitive to short-wavelength photons. These observations can determine the surface temperatures of the hottest stars and reveal the presence of intervening gas clouds between the Earth and quasars.

                Cancer treatment

                While exposure to UV light can lead to skin cancer, some skin conditions can be treated using UV light, according to Cancer Research UK. In a procedure called psoralen ultraviolet light treatment (PUVA), patients take a drug or apply a lotion to make their skin sensitive to light. Then a UV light is shone on the skin. PUVA is used to treat lymphoma, eczema, psoriasis and vitiligo.

                It may seem counterintuitive to treat skin cancer with the same thing that caused it, but PUVA can be useful due to UV light’s effect on the production of skin cells. It slows down the growth that plays a major role in the disease’s development.

                Key to the origin of life?

                Recent research suggests that UV light may have played a key role in the origin of life on Earth, especially the origin of RNA. In a 2017 article in the Astrophysics Journal, the authors of the study note that red dwarf stars may not emit enough UV light to start the biological processes needed for the formation of ribonucleic acid, which is necessary for all forms of life on Earth. The study also suggests this finding could help in the search for life elsewhere in the universe.



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