پلوتونيوم

(تم التحويل من Plutonium)
الپلوتونيوم,  94Pu
Two shiny pellets of plutonium of about 3 cm in diameter
الخصائص العامة
النطق
المظهر أبيض فضي، يفقد لمعانه ويتحول للرمادي الداكن عند التعرض للهواء
عدد الكتلة 244 (most stable isotope)
الپلوتونيوم في الجدول الدوري
Hydrogen (reactive nonmetal)
Helium (noble gas)
Lithium (alkali metal)
Beryllium (alkaline earth metal)
Boron (metalloid)
Carbon (reactive nonmetal)
Nitrogen (reactive nonmetal)
Oxygen (reactive nonmetal)
Fluorine (reactive nonmetal)
Neon (noble gas)
Sodium (alkali metal)
Magnesium (alkaline earth metal)
Aluminium (post-transition metal)
Silicon (metalloid)
Phosphorus (reactive nonmetal)
Sulfur (reactive nonmetal)
Chlorine (reactive nonmetal)
Argon (noble gas)
Potassium (alkali metal)
Calcium (alkaline earth metal)
Scandium (transition metal)
Titanium (transition metal)
Vanadium (transition metal)
Chromium (transition metal)
Manganese (transition metal)
Iron (transition metal)
Cobalt (transition metal)
Nickel (transition metal)
Copper (transition metal)
Zinc (post-transition metal)
Gallium (post-transition metal)
Germanium (metalloid)
Arsenic (metalloid)
Selenium (reactive nonmetal)
Bromine (reactive nonmetal)
Krypton (noble gas)
Rubidium (alkali metal)
Strontium (alkaline earth metal)
Yttrium (transition metal)
Zirconium (transition metal)
Niobium (transition metal)
Molybdenum (transition metal)
Technetium (transition metal)
Ruthenium (transition metal)
Rhodium (transition metal)
Palladium (transition metal)
Silver (transition metal)
Cadmium (post-transition metal)
Indium (post-transition metal)
Tin (post-transition metal)
Antimony (metalloid)
Tellurium (metalloid)
Iodine (reactive nonmetal)
Xenon (noble gas)
Caesium (alkali metal)
Barium (alkaline earth metal)
Lanthanum (lanthanide)
Cerium (lanthanide)
Praseodymium (lanthanide)
Neodymium (lanthanide)
Promethium (lanthanide)
Samarium (lanthanide)
Europium (lanthanide)
Gadolinium (lanthanide)
Terbium (lanthanide)
Dysprosium (lanthanide)
Holmium (lanthanide)
Erbium (lanthanide)
Thulium (lanthanide)
Ytterbium (lanthanide)
Lutetium (lanthanide)
Hafnium (transition metal)
Tantalum (transition metal)
Tungsten (transition metal)
Rhenium (transition metal)
Osmium (transition metal)
Iridium (transition metal)
Platinum (transition metal)
Gold (transition metal)
Mercury (post-transition metal)
Thallium (post-transition metal)
Lead (post-transition metal)
Bismuth (post-transition metal)
Polonium (post-transition metal)
Astatine (metalloid)
Radon (noble gas)
Francium (alkali metal)
Radium (alkaline earth metal)
Actinium (actinide)
Thorium (actinide)
Protactinium (actinide)
Uranium (actinide)
Neptunium (actinide)
Plutonium (actinide)
Americium (actinide)
Curium (actinide)
Berkelium (actinide)
Californium (actinide)
Einsteinium (actinide)
Fermium (actinide)
Mendelevium (actinide)
Nobelium (actinide)
Lawrencium (actinide)
Rutherfordium (transition metal)
Dubnium (transition metal)
Seaborgium (transition metal)
Bohrium (transition metal)
Hassium (transition metal)
Meitnerium (unknown chemical properties)
Darmstadtium (unknown chemical properties)
Roentgenium (unknown chemical properties)
Copernicium (post-transition metal)
Nihonium (unknown chemical properties)
Flerovium (unknown chemical properties)
Moscovium (unknown chemical properties)
Livermorium (unknown chemical properties)
Tennessine (unknown chemical properties)
Oganesson (unknown chemical properties)
Sm

Pu

(Uqh)
نپتونيومالپلوتونيومأمريكيوم
الرقم الذري (Z) 94
المجموعة، الدورة n/a, الفترة 7
المستوى الفرعي المستوى الفرعي f
التوزيع الإلكتروني [Rn] 5f6 7s2
الإلكترونات بالغلاف
2, 8, 18, 32, 24, 8, 2
الخصائص الطبيعية
الطور (عند STP) صلب
نقطة الانصهار 912.5 K ​(639.4 °س، ​1182.9 °F)
نقطة الغليان 3505 K ​(3228 °س، ​5842 °ف)
الكثافة (بالقرب من د.ح.غ.) 19.816 ج/سم³
حين يكون سائلاً (عند ن.إ.) 16.63 ج/سم³
حرارة الانصهار 2.82 kJ/mol
حرارة التبخر 333.5 kJ/mol
السعة الحرارية المولية 35.5 J/(mol·K)
ضغط البخار
P (Pa) 1 10 100 1 k 10 k 100 k
at T (K) 1756 1953 2198 2511 2926 3499
الخصائص الذرية
حالات الأكسدة 8, 7, 6, 5, 4, 3, 2, 1 ​(أكسيد جوي )
الكهرسلبية Pauling scale: 1.28
طاقات التأين
  • 1st: 584.7 kJ/mol
نصف القطر الذري empirical: 159 pm
نصف قطر التكافؤ 187±1 pm
Color lines in a spectral range
متفرقات
البنية البلورية monoclinic
Monoclinic crystal structure for الپلوتونيوم
سرعة الصوت 2260 م/ث
التمدد الحراري 46.7 µm/(m·K) (at 25 °C)
التوصيل الحراري 6.74 W/(m·K)
المقاومة الكهربائية 1.460 µΩ·m (عند 0 °س)
الترتيب المغناطيسي مغناطيس مساير
معامل يونگ 96 GPa
معامل القص 43 GPa
نسبة پواسون 0.21
رقم كاس 7440-07-5
التاريخ
التسمية على اسم الكوكب القزم پلوتو، والذي سمي على اسم إله العالم السفلي الكلاسيكي پلوتو
الاكتشاف گلن ت. سيبورگ، آرثر وال، جوسف و. كندي، إدوين مكميلان (1940–1)
نظائر الپلوتونيوم الرئيسية
نظير التوافر عمر النصف (t1/2) نمط الاضمحلال النواتج
238Pu trace 87.74 y SF 204.66[1]
α 5.5 234U
239Pu trace 2.41×104 y SF 207.06
α 5.157 235U
240Pu trace 6.5×103 y SF 205.66
α 5.256 236U
241Pu syn 14 y β 0.02078 241Am
SF 210.83
242Pu syn 3.73×105 y SF 209.47
α 4.984 238U
244Pu trace 8.08×107 y α 4.666 240U
SF
| المراجع | [[:d:خطأ لوا في وحدة:Wikidata على السطر 890: attempt to index field 'wikibase' (a nil value).|في ويكي‌داتا]]

الپلوتونيوم Plutonium، هو عنصر كيميائي ترابي مشع رمزه الكيميائي وعدده الذري 94. وهو فلز أكتيني ذو لون رمادي-فضي يفقد لمعانه عند التعرض للهواء، ولوناً باهتاً عن تأكسده. يتفاع مع الكربون، الهالوجينات، النيتروجين، السليكون، والهيدروجين. عند تعرضه للهواء الرطب، يشكل أكاسيد وهيدريات تتمدد لأكبر من 70% من حجمها، والتي تتحول بدورها إلى مسحوق تلقائي الاشتعال. وهو مادة مشعة ويمكن أن تتراكم في العظام، مما يجعل التعامل مع الپلوتونيوم خطراً.

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الخصائص المميزة

پلوتونيوم has been called "the most complex metal" and "a physicist's dream but an engineer's nightmare"[2] for its peculiar physical and chemical properties. It has six allotropes normally and a seventh under pressure. The allotropes have very similar energy levels but significantly varying densities, making plutonium very sensitive to changes in temperature, pressure, or chemistry, and allowing for dramatic volume changes following phase transitions (in nuclear applications, it is usually alloyed with a small amount of gallium, which stabilizes it in the delta-phase).[3] Plutonium is silvery in pure form, but has a yellow tarnish when oxidized. It possesses a low-symmetry structure, causing it to become progressively more brittle over time.[4] Because it self-irradiates, it ages both from the outside-in and the inside-out.[3] However, self-irradiation can also lead to annealing which counteracts some of the aging effects. In general, the precise aging properties of plutonium are very complex and poorly understood, greatly complicating efforts to predict future reliability of weapons components.

The heat given off by alpha particle emission makes plutonium warm to the touch in reasonable quantities. It displays five ionic oxidation states in aqueous solution:

  • Pu(III), as Pu3+ (blue lavender)
  • Pu(IV), as Pu4+ (yellow brown)
  • Pu(V), as PuO2+ (thought to be pink; this ion is unstable in solution and will disproportionate into Pu4+ and PuO22+; the Pu4+ will then oxidize the remaining PuO2+ to PuO22+, being reduced in turn to Pu3+. Thus, aqueous solutions of plutonium tend over time towards a mixture of Pu3+ and PuO22+.)[5]
  • Pu(VI), as PuO22+ (pink orange)
  • Pu(VII), as PuO52- (dark red); the heptavalent ion is rare and prepared only under extreme oxidizing conditions.

The actual color shown by Pu solutions depends on both the oxidation state and the nature of the acid anion, which influences the degree of complexing of the Pu species by the acid anion.[6]

البلوتونيوم معدن نشيط كيمياويا،ً مثل عناصر الأكتِينيَّات الأخرى، لذا يمكن استخلاصه بالطرائق المستخدمة في استحضار المعادن النشيطة كطريقة التحليل الكهربائي لصهارة الملح، أو إرجاع الهاليد بمعدنٍ فعال، مثل الليثيوم أو الكلسيوم أو الباريوم. ويُبدي البلوتونيوم حالات تكافؤ مختلفة، مثل عنصري اليورانيوم والنبتونيوم المجاوِريْن، إذ يُعرَف بحالات الأكسدة III، IV، V، VI الثابتة في الوسط الحمضي، ويمكن لهذه العناصر أن يوجد بعضها مع بعض بتراكيز محسوسة، بسبب تقاربها في قيم كمونات الأكسدة. وتعاني حالات الأكسدة لمحاليل المنتجات الوسطية من اللاتناسبية disproportion. ولقد درست هذه التفاعلات اللاتناسبية دراسة مفصلة، وقيست نسب حالات الأكسدة فتبين تناقص ميل تشكل الأيونات المعقدة لحالات الأكسدة المختلفة في البلوتونيوم وفق الترتيب الآتي:


وهكذا لا يبدي البلوتونيوم (III) ميلاً كبيراً إلى تشكيل أيونات معقدة في حين يُعرف للبلوتونيوم (IV) العديد من المعقدات مع الأيونات السالبة العضوية واللاعضوية.


الاستخدامات

النظير 239Pu is a key fissile component in nuclear weapons, due to its ease of fissioning and availability. The critical mass for an unreflected sphere of plutonium is 16 kg, but through the use of a neutron-reflecting tamper the pit of plutonium in a fission bomb is reduced to 10 kg, which is a sphere with a diameter of 10 cm. The Manhattan Project "Fat Man" type plutonium bombs, using explosive compression of Pu to significantly higher densities than normal, were able to function with plutonium cores of only 6.2 kg.[7] Complete detonation may be achieved through the use of an additional neutron source (often from a small amount of fusion fuel). The Fat Man bomb had an explosive yield of 21 kilotons. (See also nuclear weapon design.)

The isotope plutonium-238 (238Pu) has a half-life of 88 years and emits a large amount of thermal energy as it decays. Being an alpha emitter, it combines high energy radiation with low penetration (thereby requiring minimal shielding). These characteristics make it well suited for electrical power generation for devices which must function without direct maintenance for timescales approximating a human lifetime. It is therefore used in radioisotope thermoelectric generators such as those powering the Cassini and New Horizons (Pluto) space probes; earlier versions of the same technology powered the ALSEP and EASEP systems including seismic experiments on the Apollo Moon missions.

238Pu has been used successfully to power artificial heart pacemakers, to reduce the risk of repeated surgery.[بحاجة لمصدر] It has been largely replaced by lithium-based primary cells, but as of 2003 there were somewhere between 50 and 100 plutonium-powered pacemakers still implanted and functioning in living patients.

تاريخ

Glenn Seaborg at the Geiger Counter, 301 Gilman Hall, Berkeley, California, where he discovered plutonium.

The production of plutonium and neptunium by bombarding uranium-238 with neutrons was predicted in 1940 by two teams working independently: Edwin M. McMillan and Philip Abelson at Berkeley Radiation Laboratory at the University of California, Berkeley; and by Egon Bretscher and Norman Feather at the Cavendish Laboratory of the University of Cambridge for the Tube Alloys project.[بحاجة لمصدر] Coincidentally both teams proposed the same names to follow on from uranium, following the sequence of the outer planets.[بحاجة لمصدر]

أول عزل

Plutonium was first produced and isolated on December 14, 1940 by Dr. Glenn T. Seaborg, Edwin M. McMillan, J. W. Kennedy, Z. M. Tatom[بحاجة لمصدر], and A. C. Wahl by deuteron bombardment of uranium in the 60-inch cyclotron at Berkeley. The discovery was kept secret due to the war. It was named after Pluto, having been discovered directly after neptunium (which itself was one higher on the periodic table than uranium), by analogy to solar system planet order as Pluto was considered to be a planet at the time (though technically it should have been "plutium", Seaborg said that he did not think it sounded as good as "plutonium"). Seaborg chose the letters "Pu" as a joke, which passed without notice into the periodic table.[8] Originally, Seaborg and others thought about naming the element "ultinium" or "extremium" because they believed at the time that they had found the last possible element on the periodic table.[9]

Chemists at the University of Chicago began to study the newly manufactured radioactive element. The George Herbert Jones Laboratory at the university was the site where, on 18 August 1942, a trace quantity of this new element was isolated and measured for the first time. This procedure enabled chemists to determine the new element's atomic weight. Room 405 of the building was named a National Historic Landmark in May 1967.[10]

During the Manhattan Project, plutonium was also often referred, simply, to as "49". Number 4 was for the last digit in 94 (atomic number of plutonium) and 9 for the last digit in Pu-239, the weapon-grade fissile isotope used in nuclear bombs. [11] [12]

الانتاج

During the Manhattan Project, the first production reactor, the X-10 Graphite Reactor, was built at the Oak Ridge, تنسي site that became Oak Ridge National Laboratory. Later, large (200MWt) reactors were set up at the Hanford Site (near Richland, Washington), for the production of plutonium, which was used in the first atomic bomb used at the "Trinity" test in July 1945. Plutonium was also used in the "Fat Man" bomb dropped on Nagasaki, Japan in August 1945. The "Little Boy" bomb dropped on Hiroshima utilized uranium-235, not plutonium.

Large stockpiles of "weapons-grade" plutonium were built up by both the الاتحاد السوڤيتي and the الولايات المتحدة during the Cold War. The U.S. reactors at Hanford and the Savannah River Site in South Carolina produced 103,000 kg;[13] It was estimated there are another 170,000 kg of military plutonium in Russia, with 300,000 kg accumulated worldwide. [14] Since the end of the Cold War, these stockpiles have become a focus of nuclear proliferation concerns. In 2002, the United States Department of Energy took possession of 34 metric tons of excess weapons-grade plutonium stockpiles from the United States Department of Defense, and as of early 2003 was considering converting several nuclear power plants in the US from enriched uranium fuel to MOX fuel as a means of disposing of plutonium stocks.

Hanford Site plutonium production reactors along the Columbia River during the Manhattan Project.


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التجارب الطبية

During the initial years after the discovery of plutonium, when its biological and physical properties were very poorly understood, a series of human radiation experiments were performed by the U.S. government and by private organizations acting on its behalf. During and after the end of World War II, scientists working on the Manhattan Project and other nuclear weapons research projects conducted studies of the effects of plutonium on laboratory animals and human subjects. In the case of human subjects, this involved injecting solutions containing (typically) five micrograms of plutonium into hospital patients thought to be either terminally ill, or to have a life expectancy of less than ten years either due to age or chronic disease condition. These eighteen injections were made without the informed consent of those patients and were not done with the belief that the injections would heal their conditions; rather, they were used to develop diagnostic tools for determining the uptake of plutonium in the body for use in developing safety standards for people working with plutonium during the course of developing nuclear weapons.[15]

The episode is now considered to be a serious breach of medical ethics and of the Hippocratic Oath, and has been sharply criticised as failing "both the test of our national values and the test of humanity."[16] More sympathetic commentators have noted that while it was definitely a breach in trust and ethics, "the effects of the plutonium injections were not as damaging to the subjects as the early news stories painted, nor were they so inconsequential as many scientists, then and now, believe."[17]

التواجد

While almost all plutonium is manufactured synthetically, extremely tiny trace amounts are found naturally in uranium ores. These come about by a process of neutron capture by 238U nuclei, initially forming 239U; two subsequent beta decays then form 239Pu (with a 239Np intermediary), which has a half-life of 24,110 years. This is also the process used to manufacture 239Pu in nuclear reactors. Some traces of 244Pu remain[بحاجة لمصدر] from the birth of the solar system from the waste of supernovae, because its half-life of 80 million years is fairly long.

A relatively high concentration of plutonium was discovered at the natural nuclear fission reactor in Oklo, Gabon in 1972. Since 1945, approximately 7700 kg has been released onto Earth through nuclear explosions.

التصنيع

Pu-240, Pu-241 و Pu-242

The activation cross section for 239Pu is 270 barns, while the fission cross section is 747 barns for thermal neutrons. The higher plutonium isotopes are created when the uranium fuel is used for a long time. It is the case that for high burnup used fuel that the concentrations of the higher plutonium isotopes will be higher than the low burnup fuel which is reprocessed to obtain bomb grade plutonium.

تكون 240Pu, 241Pu و 242Pu من 238U
العنصر النظير مقطع عرضي
لنيوترون حراري
decay mode نصف العمر
U 238 2.7 α 4.47 x 109 سنة
U 239 - β 23 دقيقة
Np 239 - β 2.36 يوم
Pu 239 270 (capture) α 24110 سنة
Pu 240 289 (capture) α 6564 سنة
Pu 241 362 (capture) β 14.35 سنة
Pu 242 18.8 α 373300 سنة


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Pu-239

پلوتونيوم-239 is one of the three fissile materials used for the production of nuclear weapons and in some nuclear reactors as a source of energy. The other fissile materials are uranium-235 and uranium-233. Plutonium-239 is virtually nonexistent in nature. It is made by bombarding uranium-238 with neutrons in a nuclear reactor. Uranium-238 is present in quantity in most reactor fuel; hence plutonium-239 is continuously made in these reactors. Since plutonium-239 can itself be split by neutrons to release energy, plutonium-239 provides a portion of the energy generation in a nuclear reactor.

A ring of weapons-grade electrorefined plutonium, with 99.96% purity. This 5.3 kg ring is enough plutonium for use in an efficient nuclear weapon.
تكون 239Pu من 238U
العنصر النظير Thermal neutron
cross section
decay mode نصف العمر
U 238 2.7 α 4.47 x 109 سنة
U 239 - β 23 دقيقة
Np 239 - β 2.36 يوم
Pu 239 - α 24110 سنة

Pu-238

There are small amounts of Pu-238 in the plutonium of usual plutonium-producing reactors. However, isotopic separation would be quite expensive compared to another method: when a U-235 atom captures a neutron, it is converted to an excited state of U-236. Some of the excited U-236 nuclei undergo fission, but some decay to the ground state of U-236 by emitting gamma radiation. Further neutron capture creates U-237 which has a half-life of 7 days and thus quickly decays to Np-237. Since nearly all neptunium is produced in this way or consists of isotopes which decay quickly, one gets nearly pure Np-237 by chemical separation of neptunium. After this chemical separation, Np-237 is again irradiated by reactor neutrons to be converted to Np-238 which decays to Pu-238 with a half-life of 2 days.

تكون 238Pu من 235U
العنصر النظير مقطع عرضي
لنيوترون حراري
decay mode نصف العمر
U 235 99 α 703800000 years
U 236 5.3 α 23420000 years
U 237 - β 6.75 days
Np 237 165 (capture) α 2144000 years
Np 238 - β 2.11 days
Pu 238 - α 87.7 years

المركبات

الصورة تبين حالات الأكسدة المختلفة للـ Pu في محلول إلى اليسار؛ وألوان حالة أكسدة (IV) لذرة Pu واحدة إلى اليمين في محاليل تحتوي على أنيونات مختلفة.

ويتفاعل الپلوتونيوم بسهولة مع الاكسجين، مكوناً PuO وPuO2، وأكاسيد وسيطة. ويتفاعل مع الهالوجينات، منتجاً مركبات مثل PuX3 حيث X يمكن أن تكون F، Cl، Br أو I; PuF4 و PuF6 يُشاهـَدوا. ويُشاهـَد الأكسي‌هاليدات التالية: PuOCl, PuOBr و PuOI. وسيتفاعل مع الكربون ليشكل PuC، والنيتروجين ليشكل PuN والسليكون ليشكل PuSi2.

الپلوتونيوم ومثل الأكتينيدات الأخرى فإنه يشكـِّل بسهولة قلب من ثاني أكسيد الپلوتونيل (PuO2). وفي البيئة، هذا القلب من البلوتونيل يتعقد بتلقائية مع الكربونات وكذلك باقي moieties الأكسجين (OH-, NO2-, NO3-, and SO4-2) ليشكل معقدات مشحونة التي يمكن أن تكون قابلة تلقائياً للحركة with low affinities to soil.

  • PuO2(CO3)1-2
  • PuO2(CO3)2-4
  • PuO2(CO3)3-6

PuO2 formed from neutralizing highly acidic nitric acid solutions tends to form polymeric PuO2 which is resistant to complexation. Plutonium also readily shifts valences between the +3, +4, +5 and +6 states. It is common for some fraction of plutonium in solution to exist in all of these states in equilibrium.

يشكل البلوتونيوم مع الأكسجين ثنائي الأكسيد PuO2 الذي يُعد من أكثر مركبات البلوتونيوم أهمية، وإن درجة انصهاره العالية البالغة نحو 2400ْس، وثباته الكيمياوي والإشعاعي، وتشابهه مع ثنائي أكسيد اليورانيوم UO2 تجعل منه وقوداً ممتازاً للمفاعلات النووية. ويحضر PuO2 بتسخين البلوتونيوم أو أيٍ من مركباته، عدا الفسفات في أكسجين الهواء، في درجة تراوح بين 870ْس و1200ْس. ويشكل مع الهالوجينات عدداً من الهاليدات: ثلاثي الهاليد PuX3، (F=X، Br Cl، I)، ورباعي الفلوريد PuF4 وسداسي الفلوريد PuF6.

ويشكل البلوتونيوم حماضات ثابتة بحالات الأكسدة III وIV وVI. وتُعرف مركبات كثيرة أخرى للبلوتونيوم من بينها: كربيدات البلوتونيوم PuC وPu2C3، سيليسيدات البلوتونيوم α-PuSi2 وß-PuSi2 وكبريتيدات البلوتونيوم PuS، Pu2S3 وPu3S4 ونتريد البلوتونيوم PuN.

التآصلات

A diagram of the allotropes of plutonium at ambient pressure

حتى عند الضغوط العادية، يتواجد الپلوتونيوم في العديد من التآصلات. These allotropes differ widely in crystal structure and density; the α and δ allotropes differ in density by more than 25% at constant pressure.

The presence of these many allotropes makes machining plutonium very difficult, as it changes state very readily. The reasons for the complicated phase diagram are not entirely understood; recent research has focused on constructing accurate computer models of the phase transitions.

In weapons applications, plutonium is often alloyed with another metal (e.g., delta phase with a small percentage of گاليوم) to increase phase stability and thereby enhance workability and ease of handling. Interestingly, in fission weapons, the explosive shock waves used to compress a plutonium core will also cause a transition from the usual delta phase plutonium to the denser alpha phase, significantly helping to achieve supercriticality.

النظائر

Twenty-one plutonium radioisotopes have been characterized. The most stable are Pu-244, with a half-life of 80.8 million years, Pu-242, with a half-life of 373,300 years, and Pu-239, with a half-life of 24,110 years. Because of its comparatively large half-life, minute amounts of Pu-244 can be found in nature[18], All of the remaining radioactive isotopes have half-lives that are less than 7,000 years. This element also has eight meta states, though none are very stable (all have half-lives less than one second).

The isotopes of plutonium range in atomic weight from 228.0387 u (Pu-228) to 247.074 u (Pu-247). The primary decay modes before the most stable isotope, Pu-244, are spontaneous fission and alpha emission; the primary mode after is beta emission. The primary decay products before Pu-244 are uranium and neptunium isotopes (neglecting the wide range of daughter nuclei created by fission processes), and the primary products after are americium isotopes.

A pellet of plutonium-238, glowing due to blackbody radiation, used for radioisotope thermoelectric generators.

Key isotopes for applications are Pu-239, which is suitable for use in nuclear weapons and nuclear reactors, and Pu-238, which is suitable for use in radioisotope thermoelectric generators; see above for more details. The isotope Pu-240 undergoes spontaneous fission very readily, and is produced when Pu-239 is exposed to neutrons. The presence of Pu-240 in a material limits its nuclear bomb potential since it emits neutrons randomly, increasing the difficulty of initiating accurately the chain reaction at the desired instant and thus reducing the bomb's reliability and power. Plutonium consisting of more than about 90% Pu-239 is called weapons-grade plutonium; plutonium obtained from commercial reactors generally contains at least 20% Pu-240 and is called reactor-grade plutonium.

Pu-240, while of little importance by itself, plays a crucial role as a contaminant in plutonium used in nuclear weapons. It spontaneously fissions at a high rate, and a 1% impurity in Pu-239 will lead to unacceptably early initiation of a fission chain reaction in gun-type atomic weapons (e.g. the proposed Thin Man bomb), blowing the weapon apart before much of its material can fission. Pu-240 contamination is the reason plutonium weapons must use an implosion design. A theoretical 100% pure Pu-239 weapon could be constructed as a gun-type device, but achieving this level of purity is prohibitively difficult. Pu-240 contamination has proven a mixed blessing to weapons designers. While it created delays and headaches during the Manhattan Project because of the need to develop implosion technology, those very same difficulties are currently a barrier to nuclear proliferation. Implosion devices are also inherently more efficient and less prone toward accidental detonation than are gun-type weapons.

محاذير

تكمن المخاطر الأساسية للبلوتونيوم في نشاطه الإشعاعي وطاقته النووية وفعاليته الكيماوية كمعدن. وإن التعامل مع البلوتونيوم الذي يشع جسيمات ألفا (α) لا يشكل صعوبة، إذ لا تحتاج الوقاية منها إلى ملابس خاصة، ولكن المشكلة تنشأ عند التعامل مع النظائر الأخرى (غير 239 Pu) التي تصدر أشعة غاما الضعيفة. ويعزى خطر البلوتونيوم الشديد على الصحة إلى توضعه في نقي العظام حيث تتشكل الكريات الدموية. ويستطيع البلوتونيوم دخول الجسم عن طريق الجروح والجلد وجهازي الهضم والتنفس، ويعد دخوله عن طريق التنفس أكثر الطرق احتمالاً، لذا يجري التعامل معه بوساطة تجهيزات خاصة، ضغطها يقل بنحو 0.001 جو عن الضغط الجوي المحيط. إن أفضل التقنيات المستخدمة في إخماد حرائق البلوتونيوم تعتمد على عزل الأكسجين عنه، وذلك إما بجعل الجو المحيط خاملاً وإما بالرش بمسحوق الگرافيت أو أكسيد المغنسيوم.

السمية

قطع ساخنة متوهجة من الپلوتونيوم في صندوق، وقد اشتعلت بسبب طبيعة البلوتونيوم تلقائية الاشتعال.

كل نظائر ومركبات الپلوتونيوم سامة ومشعة. While plutonium is sometimes described in media reports as "the most toxic substance known to man", from the standpoint of actual chemical or radiological toxicity this is incorrect. When taken in by mouth, plutonium is less poisonous than if inhaled, since it is not absorbed into the body efficiently when ingested. The U.S. Department of Energy estimates the increase in lifetime cancer risk for inhaled plutonium as 3×10−8 pCi−1.[19] (this means that inhaling 1 μCi, or about 2.5 μg of reactor-grade plutonium is estimated to increase one's lifetime risk of developing cancer as a result of the exposure to 3%). When plutonium is absorbed into the body, it is excreted very slowly, with a biological half-life of 200 years.[20] From a purely chemical standpoint, it is about as poisonous as lead and other heavy metals. [بحاجة لمصدر] Not surprisingly, it has a metallic taste.[21]

Plutonium may be extremely dangerous when handled incorrectly. The alpha radiation it emits does not penetrate the skin, but can irradiate internal organs when plutonium is inhaled or ingested. Particularly at risk are the skeleton, where it is likely to be absorbed by the bone surface, and the liver, where it will likely collect and become concentrated. Approximately 0.008 microcuries absorbed in bone marrow is the maximum withstandable dose. Anything more is considered toxic. Extremely fine particles of plutonium (on the order of micrograms) can cause lung cancer if inhaled.[بحاجة لمصدر]

Other substances including ricin, tetrodotoxin, botulinum toxin, and tetanus toxin are fatal in doses of (sometimes far) under one milligram, and others (the nerve agents, the amanita toxin) are in the range of a few milligrams. As such, plutonium is not unusual in terms of toxicity, even by inhalation. In addition, those substances are fatal in hours to days, whereas plutonium (and other cancer-causing radioactives) give an increased chance of illness decades in the future. Considerably larger amounts may cause acute radiation poisoning and death if ingested or inhaled; however, so far, no human is known to have immediately died because of inhaling or ingesting plutonium and many people have measurable amounts of plutonium in their bodies.[بحاجة لمصدر]

مشاكل التخلص منه

In contrast to naturally occurring radioisotopes such as radium or C-14, plutonium was manufactured, concentrated, and isolated in large amounts (hundreds of metric tons) during the Cold War for weapons production. These stockpiles, whether or not in weapons form, pose a significant problem because, unlike chemical or biological agents, no chemical process can destroy them. One proposal to dispose of surplus weapons-grade plutonium is to mix it with highly radioactive isotopes (e.g., spent reactor fuel) to deter handling by potential thieves or terrorists. Another is to mix it with uranium and use it to fuel nuclear power reactors (the mixed oxide or MOX approach). This would not only fission (and thereby destroy) much of the Pu-239, but also transmute a significant fraction of the remainder into Pu-240 and heavier isotopes that would make the resulting mixture useless for nuclear weapons.[22]

Criticality potential

Toxicity issues aside, care must be taken to avoid the accumulation of amounts of plutonium which approach critical mass, particularly because plutonium's critical mass is only a third of that of uranium-235's. Despite not being confined by external pressure as is required for a nuclear weapon, it will nevertheless heat itself and break whatever confining environment it is in. Shape is relevant; compact shapes such as spheres are to be avoided. Plutonium in solution is more likely to form a critical mass than the solid form (due to moderation by the hydrogen in water). A weapon-scale nuclear explosion cannot occur accidentally, since it requires a greatly supercritical mass in order to explode rather than simply melt or fragment. However, a marginally critical mass will cause a lethal dose of radiation and has in fact done so in the past on several occasions.

Criticality accidents have occurred in the past, some of them with lethal consequences. Careless handling of tungsten carbide bricks around a 6.2 kg plutonium sphere resulted in a lethal dose of radiation at Los Alamos on August 21, 1945, when scientist Harry K. Daghlian, Jr. received a dose estimated to be 510 rems (5.1 Sv) and died four weeks later. Nine months later, another Los Alamos scientist, Louis Slotin, died from a similar accident involving a beryllium reflector and the same plutonium core (the so-called "demon core") that had previously claimed the life of Daghlian. These incidents were fictionalized in the 1989 film Fat Man and Little Boy. In 1958, during a process of purifying plutonium at Los Alamos, a critical mass was formed in a mixing vessel, which resulted in the death of a crane operator. Other accidents of this sort have occurred in the الاتحاد السوڤيتي, Japan, and many other countries. (See List of nuclear accidents.) The 1986 Chernobyl accident caused a minor release of plutonium.[بحاجة لمصدر]

قابلية الاشتعال

Metallic plutonium is also a fire hazard, especially if the material is finely divided. It reacts chemically with oxygen and water, which may result in an accumulation of plutonium hydride, a pyrophoric substance; that is, a material that will ignite in air at room temperature. Plutonium expands considerably in size as it oxidizes and thus may break its container. The radioactivity of the burning material is an additional hazard. Magnesium-oxide sand is the most effective material for extinguishing a plutonium fire. It cools the burning material, acting as a heat sink, and also blocks off oxygen. There was a major plutonium-initiated fire at the Rocky Flats Plant near Boulder, كولورادو in 1969.[23] To avoid these problems, special precautions are necessary to store or handle plutonium in any form; generally a dry inert atmosphere is required.[24]

انظر أيضاً

المضادر

  1. ^ Magurno & Pearlstein 1981, pp. 835 ff.
  2. ^ Siegfried S. Hecker (2000). "Plutonium: An element at odds with itself" (PDF). Los Alamos Science. 26: 16–23, on 16. 
  3. ^ أ ب Siegfried S. Hecker (2000). "Plutonium and its alloys: from atoms to microstructure" (PDF). Los Alamos Science. 26: 290–335. 
  4. ^ Lawrence Livermore National Laboratory (2006). "Scientists resolve 60-year-old plutonium questions". Retrieved 2006-06-06. 
  5. ^ Crooks, William J. (2002). "Nuclear Criticality Safety Engineering Training Module 10 - Criticality Safety in Material Processing Operations, Part 1" (PDF). Retrieved 2006-02-15. 
  6. ^ Matlack, George: A Plutonium Primer: An Introduction to Plutonium Chemistry and its Radioactivity (LA-UR-02-6594)
  7. ^ Much of the information about the plutonium in the Fat Man bomb comes from reports of the criticality accidents of Harry K. Daghlian, Jr. and Louis Slotin, both of whom died after conducting experiments with plutonium bomb cores. See http://members.tripod.com/~Arnold_Dion/Daghlian/accident.html.
  8. ^ As one article puts it, referring to information Seaborg gave in a talk: "The obvious choice for the symbol would have been Pl, but facetiously, Seaborg suggested Pu, like the words a child would exclaim, 'Pee-yoo!' when smelling something bad. Seaborg thought that he would receive a great deal of flak over that suggestion, but the naming committee accepted the symbol without a word." David L. Clark and David E. Hobart (2000). "Reflections on the Legacy of a Legend: Glenn T. Seaborg, 1912–1999" (PDF). Los Alamos Science. 26: 56–61, on 57. 
  9. ^ Frontline interview with Seaborg
  10. ^ "Room 405, George Herbert Jones Laboratory". National Park Service. 
  11. ^ Hammel, E.F. (2000). "The taming of "49" — Big Science in little time. Recollections of Edward F. Hammel, pp. 2-9. In: Cooper N.G. Ed. (2000). Challenges in Plutonium Science" (PDF). Los Alamos Science. 26 (1): 2–9. 
  12. ^ Hecker, S.S. (2000). "Plutonium: an historical overview. In: Challenges in Plutonium Science". Los Alamos Science. 26 (1): 1–2. 
  13. ^ "Plutonium: The first 50 years: United States plutonium production, acquisition, and utilization from 1944 to 1994". U.S. Department of Energy. September 1994. 
  14. ^ Thomas B. Cochran (Natural Resources Defense Council) (1997-06-12). "Safeguarding nuclear weapons-usable materials in Russia" (PDF). Proceedings of the international forum on illegal nuclear traffic. Retrieved 2007-06-16. 
  15. ^ William Moss and Roger Eckhardt (1995). "The Human Plutonium Injection Experiments" (PDF). Los Alamos Science. 23: 177–233. Retrieved 2006-06-06. 
  16. ^ R.C. Longworth (1999). "Injected! (Review of Eileen Welsome's The Plutonium Files)". Bulletin of the Atomic Scientists. Retrieved 2006-06-06. 
  17. ^ Michael S. Yesley (1995). "'Ethical Harm' and the Plutonium Injection Experiments" (PDF). Los Alamos Science. 23: 280–283, on 283. 
  18. ^ D.C . Hoffman, F. O. Lawrence, J. L. Mewheter, F. M. Rourke: Detection of Plutonium-244 in Nature. In: Nature, Nr. 34, 1971, pp. 132–134
  19. ^ "ANL human health fact sheet--plutonium" (PDF). Argonne National Laboratory. October 2001. Retrieved 2007-06-16. 
  20. ^ "Radiological control technical training DOE-HDBK-1122-99" (PDF). U.S. Department of Energy. 
  21. ^ Welsome, Eileen (2000). The Plutonium Files: America's Secret Medical Experiments in the Cold War. New York: Random House. pp. p. 17. ISBN 0-385-31954-1. 
  22. ^ National Academy of Sciences, Committee on International Security and Arms Control (1994). "Management and Disposition of Excess Weapons Plutonium". 
  23. ^ David Albright and Kevin O'Neill (1999). The Lessons of Nuclear Secrecy at Rocky Flats. ISIS Issue Brief.
  24. ^ Primer on Spontaneous Heating and Pyrophoricity - Pyrophoric Metals - Plutonium, Department of Energy Handbook DOE-HDBK-1081-94, December 1994. U.S. Department of Energy, Washington, D.C.

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