ব্যবহারকারী:Sammay Sarkar/খসড়া/২: সংশোধিত সংস্করণের মধ্যে পার্থক্য

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{{পারমাণবিক পদার্থবিদ্যা}}
 
'''স্থায়িত্ব উপত্যকা''' বা '''valley of stability''' (অথবা '''পারমাণবিক উপত্যকা''', '''শক্তি উপত্যকা''', বা '''বিটা স্থায়িত্ব উপত্যকা''') হল [[তেজস্ক্রিয়তা]]র সাপেক্ষে [[নিউক্লিয় বন্ধন শক্তি|বন্ধন শক্তির]] ভিত্তিতে [[নিউক্লাইড]]ের স্থায়িত্বের বৈশিষ্ট্য।<ref name="Mackintosh">{{Cite book| title=Nucleus: A trip into the heart of matter | first1=R.|last1=Mackintosh | first2=J.|last2=Ai-Khalili | first3=B.| last3=Jonson | first4=T.|last4=Pena | location=Baltimore, MD | publisher=The Johns Hopkins University Press|pages=Chapter 6| year=2001 | isbn=0-801 8-6860-2 | url=http://www.nupecc.org/pans/Data/CHAPT_6.PDF}}</ref> উপত্যকাটির গড়পড়তা আকৃতি দীর্ঘায়িত উপবৃত্তাকার, যা নিউট্রন ও প্রোটন সংখ্যার ফাংশন হিসেবে বন্ধন শক্তির একটি চিত্র গঠন করে।<ref name="Mackintosh"/> উপত্যকার গভীরতর এলাকায় স্থিতিশীল নিউক্লাইডের অবস্থান।<ref>[https://www.youtube.com/watch?v=UTOp_2ZVZmM&t=192 The Valley of Stability (video) - a virtual "flight" through 3D representation of the nuclide chart, by [[French Alternative Energies and Atomic Energy Commission|CEA]] (France)]</ref> উপত্যকার মধ্যভাগ বরাবর অবস্থিত স্থিতিশীল নিউক্লাইডের সারিকে [[বেটা-ক্ষয় স্থিতিশীল আইসোবার|বিটা স্থায়িত্ব রেখা]] বলা হয়। উপত্যকার দুই প্রান্তের দিকে বিটা ক্ষয় (β<sup>−</sup> or β<sup>+</sup>) জনিত ক্রমাগত উচ্চতর অস্থিতিশীলতা পাওয়া যায়। স্থায়িত্ব উপত্যকায় কোন নিউক্লাইড বিটা স্থায়িত্ব রেখা থেকে যত দূরে অবস্থিত, তার অস্থায়িত্বের সম্ভাবনা তত বেশি। উপত্যকার সীমানা অঞ্চল [[পারমাণবিক ক্ষরণ রেখা]]র সাথে সম্পর্কিত, যেখানে নিউক্লাইডগুলো এতটা অস্থায়ী যে [[প্রোটন বিকিরণ|একক প্রোটন]] এবং [[নিউট্রন বিকিরণ|একক নিউট্রন]] বিকিরণ করতে থাকে। উপত্যকার অভ্যন্তরে উচ্চ [[পারমাণবিক সংখ্যা]] এলাকায় [[আলফা ক্ষয়]] বা [[স্বত:স্ফূর্ত ফিশন]] জনিত অস্থায়িত্ব দেখা যায়।
 
স্থায়িত্ব উপত্যকা [[নিউক্লাইড সারণী]]র সকল সদস্যকে ধারণ করে। এই তালিকাটি পদার্থবিজ্ঞানি [[এমিলিও জিনো সেগরে|এমিলিও সেগরের]] নামানুসারে সেগরে তালিকা নামে পরিচিত।<ref name="Byrne">{{ cite book |title=Neutrons, Nuclei and Matter: An Exploration of the Physics of Slow Neutrons |author=J. Byrne | isbn= 978-0486482385 | year=2011 |location=Mineola, New York | publisher=Dover Publications}}</ref> সেগরে তালিকাটিকে স্থায়িত্ব উপত্যকার মানচিত্র হিসেবে গণ্য করা যায়। স্থায়িত্ব উপত্যকার বহি:স্থ অঞ্চলটি ''অস্থায়িত্বের সমুদ্র'' নামে পরিচিত।<ref name="LLNL">{{ cite web |title=Discovery of Elements 113 and 115 |author=D. Shaughnessy |url=https://pls.llnl.gov/research-and-development/nuclear-science/project-highlights/livermorium/elements-113-and-115 | access-date=July 31, 2016 | publisher=Lawrence Livermore National Laboratory}}</ref><ref name="Seaborg1">{{Cite journal | journal = Science | volume = 203 | issue = 4382 | pages = 711–717| year = 1979 | title = Superheavy elements: a crossroads | author1 = G. T. Seaborg | author2 = W. Loveland | author3 = D. J. Morrissey | doi = 10.1126/science.203.4382.711 | pmid=17832968| bibcode = 1979Sci...203..711S }}</ref>
 
বিজ্ঞানীরা বহুদিন ধরে স্থায়িত্ব উপত্যকার বাইরে অবস্থিত দীর্ঘস্থায়ী ভারী আইসোটোপের অনুসন্ধান করেছেন,<ref name="longlived">{{Cite journal|journal=Phys. Rev. C|volume=77|issue=4|page=044603|year=2008|title=Search for long lived heaviest nuclei beyond the valley of stability|author1=P. Roy Chowdhury |author2=C. Samanta |author3=D. N. Basu |doi=10.1103/PhysRevC.77.044603 |url=http://prc.aps.org/abstract/PRC/v77/i4/e044603|bibcode = 2008PhRvC..77d4603C |arxiv = 0802.3837 }}</ref><ref name="rare-isotope">{{Cite book | author1= Rare Isotope Science Assessment| author2= Committee Board on Physics and Astronomy | author3= Division on Engineering and Physical Sciences| author4=National Research Council|title=Scientific Opportunities with a Rare-Isotope Facility in the United States| publisher=National Academies Press|url=https://books.google.com/books?id=y8uaAgAAQBAJ|year=2007| isbn= 9780309104081 }}</ref><ref name="Boutin">{{Cite journal|journal=CERN Courier|year=2002|title=Climbing out of the nuclear valley|first1=C. | last1=Boutin |url=http://cerncourier.com/cws/article/cern/28587 |access-date=13 July 2016}}</ref> যাদের উপস্থিতি প্রস্তাব করেছিলেন [[গ্লেন থিওডোর সিবোর্গ]], ১৯৬০ দশকের শেষাংশে।<ref name="Seaborg2">{{Cite journal | doi = 10.1080/00107518708211038| title = Superheavy elements| journal = Contemporary Physics| volume = 28| pages = 33–48| year = 1987| last1 = Seaborg | first1 = G. T.|bibcode = 1987ConPh..28...33S }}</ref><ref name=OS-NYT>{{Cite news |url=https://www.nytimes.com/2004/02/08/opinion/greetings-from-the-island-of-stability.html |title=Greetings From the Island of Stability |year=2004 |author=Sacks |journal=The New York Times }}</ref> এই আপাত স্থায়ী নিউক্লাইডসমূহের কণা গঠনে "[[ম্যাজিক সংখ্যা (পদার্থবিদ্যা)|ম্যাজিক]]" পারমাণবিক এবং [[নিউট্রন সংখ্যা]]র উপস্থিতি অনুমিত, এবং এরা স্থায়িত্ব উপত্যকার বাইরে একটি তথাকথিত স্থায়িত্ব দ্বীপ (''island of stability'') গঠন করে।
 
== বর্ণনা ==
সকল পরমাণুর নিউক্লিয়াস গঠিত হয় [[পারমাণবিক বল]] দ্বারা আবদ্ধ [[নিউট্রন]] এবং [[প্রোটন]]ের সমন্বয়ে। পৃথিবীতে প্রাকৃতিকবাবে ২৮৬ রকমের নিউক্লিয়াস পাওয়া যায়, যাদের প্রত্যেকের ভিন্ন ভিন্ন প্রোটন সংখ্যা বা [[পারমাণবিক সংখ্যা]] ''Z'', অনন্য [[নিউট্রন সংখ্যা]] ''N'', এবং [[ভর সংখ্যা]] ''A'' = ''Z'' + ''N''। তবে সকল নিউক্লাইড স্থিতিশীল নয়। বায়ার্নের মতে,<ref name="Byrne"/> কোন নিউক্লাইডকে স্থায়িত্বপূর্ণ বলে সংজ্ঞায়িত করার জন্য তার [[অর্ধায়ু]] ১০<sup>১৮</sup> বছরের বেশি হতে হবে। তবে প্রোটন-নিউট্রনের প্রচুর সংখ্যক সন্নিবেশ অস্থায়ী। একটি সাধারণ উদাহরণ হল [[কার্বন-১৪]] যা [[বিটা ক্ষয়]] দ্বারা [[নাইট্রোজেন-১৪]] তে পরিণত হয় (অর্ধায়ু ~৫,৭৩০ বছর)
:{{nuclide|carbon|14}} → {{nuclide|nitrogen|14}} + {{subatomic particle|electron}} + {{subatomic particle|electron antineutrino}}
এধরণের ক্ষয়ের মাধ্যমে একটি পদার্থের পরমাণু অন্য পদার্থের পরমাণুতে [[পারমাণবিক রূপান্তর|রুপান্তরিত]] হয় এবং একটি বিটা কণা ও একটি ইলেক্ট্রন [[অ্যান্টিনিউট্রিনো]] বিকিরিত হয়। সকল নিউক্লাইড ক্ষয়ের সাধারণ বৈশিষ্ট্য হচ্ছে, ক্ষয় থেকে উৎপন্ন কণাগুলোর মোট ভর, মূল নিউক্লাইডের ভরের চেয়ে কম হয়। প্রাথমিক এবং সর্বশেষ বন্ধন শক্তির পার্থক্যটুকু ক্ষয়লদ্ধ কণাসমূহের গতিশক্তি দ্বারা ব্যায়িত হয়।<ref name="Byrne"/>
 
''স্থায়িত্ব উপত্যকা'' ধারণাটির একটি ফল হচ্ছে নিউট্রন ও প্রোটন সংখ্যার ফাংশন হিসেবে বন্ধন শক্তি অনুসারে সকল নিউক্লাইডকে সজ্জিত করার সুবিধা।<ref name="Mackintosh"/> অধিকাংশ স্থিতিশীল নিউক্লাইডের প্রোটন ও নিউট্রন সংখ্যা অনেকটাই একে-অপরের কাছাকাছি, ফলে ''Z'' = ''N'' নির্দেশক রেখাটি স্থায়ী নিউক্লাইডসমূহকপর চিহ্নিত করার একটি প্রাথমিক উপায়। তবে প্রোটনের সংখ্যা বৃদ্ধি পেলে নিউক্লাইডকে স্থায়িত্ব দানের জন্য দরকারী নিুট্রনের সংখ্যাও বৃদ্ধি পায়, তাই বৃহঞ ''Z'' সংখ্যা সম্পন্ন নিউক্লাইডের স্থায়িত্বের জন্য আরও বৃহত্তর নিউট্রন সংখ্যা, ''N'' > ''Z'', প্রয়োজন হয়। স্থায়িত্ব উপত্যকা গঠিত হয় বন্ধন শক্তির ঋণাত্বক মান দ্বারা, যেখানে বন্ধন শক্তি হল নিউক্লাইডকে এর উপাদান কণায় বিভক্ত করতে প্রয়োজনীয় শক্তি। স্থিতিশীল নিউক্লাইডের বন্ধন শক্তি উচ্চ, এবং এরা স্থায়িত্ব উপত্যকার গভীরতর এলাকায় অবস্থিত। অন্যদিকে দুর্বল বন্ধন শক্তিসম্পন্ন নিউক্লাইডে ''N'' এবং ''Z'' এর সন্নিবেশ স্থায়িত্ব রেখার বাইরে এবং স্থায়িত্ব উপত্যকার উপরিভাগে অবস্থিত। অস্থিতিশীল নিউক্লাইড গঠিত হতে পারে [[পারমাণবিক রিঅ্যাক্টর]] বা [[সুপারনোভা]] প্রভৃতি উৎস হতে। এধরণের নিউক্লাইড সাধারণত [[ক্ষয় শৃঙ্খল]] নামক কতগুলো ক্রমানুসারী [[পারমাণবিক বিক্রিয়া]]র মাধ্যমে ধাপে ধাপে স্থায়িত্ব উপত্যকার ঢাল বেয়ে নামে। এই ক্ষয় ধারার প্রতিটি ধাপে উৎপন্ন নিউক্লাইড পূর্ববর্তী ধাপের চেয়ে বেশি বন্ধন শক্তি সম্পন্ন এবং ধারার সর্বশেষ নিউক্লাইডটি স্থিতিশীল।<ref name="Mackintosh"/> স্থায়িত্ব উপত্যকা ধারণার মাধ্যমে স্থায়ী এবং অস্থায়ী প্রচুর সংখ্যক নিউক্লাইডগুলোকে সামঞ্জস্যপূর্ণভাবে সাজানোর একটি পদ্ধতি পাওয়া যায়, এবং কখন, কেন ও কী ধারায় তেজষ্ক্রিয় ক্ষয় ঘটে তার একটি সহায়ক চিত্র গঠিত হয়।<ref name="Mackintosh"/>
 
<gallery mode="packed" widths="200px" heights="200px">
File:BindingNuDat2.png|Chart of nuclides (isotopes) by binding energy, depicting the valley of stability. The diagonal line corresponds to equal numbers of neutrons and protons. Dark blue squares represent nuclides with the greatest binding energy, hence they correspond to the most stable nuclides. The binding energy is greatest along the floor of the valley of stability.
File:HalflifeNuDat2.png|Chart of nuclides by half life. Black squares represent nuclides with the longest half lives hence they correspond to the most stable nuclides. The most stable, long-lived nuclides lie along the floor of the valley of stability. Nuclides with more than 20 protons must have more neutrons than protons to be stable.
File:DecayModeNuDat2.png|Chart of nuclides by type of decay. Black squares are stable nuclides. Nuclides with excessive neutrons or protons are unstable to β<sup>−</sup> (light blue) or β<sup>+</sup> (green) decay, respectively. At high atomic number, alpha emission (orange) or spontaneous fission (dark blue) become common decay modes.
</gallery>
 
== নিউট্রনের ভূমিকা ==
The protons and neutrons that comprise an atomic nucleus behave almost identically within the nucleus. The approximate symmetry of [[isospin]] treats these particles as identical, but in a different quantum state. This symmetry is only approximate, however, and the [[nuclear force]] that binds nucleons together is a complicated function depending on nucleon type, spin state, electric charge, momentum, etc. and with contributions from non-[[central forces]]. The nuclear force is not a fundamental force of nature, but a consequence of the residual effects of the [[strong force]] that surround the nucleons. One consequence of these complications is that although [[deuterium]], a bound state of a proton (p) and a neutron (n) is stable, exotic nuclides such as [[diproton]] or [[Neutronium|dineutron]] have no stability.<ref name="Schirber">{{Cite journal|journal=Physics|volume=5|page=30|year=2012|title=Focus: Nuclei Emit Paired-up Neutrons|author1=M. Schirber |url=http://physics.aps.org/articles/v5/30 |accessdate=July 24, 2016|doi=10.1103/physics.5.30|bibcode=2012PhyOJ...5...30S}}</ref> The nuclear force is not sufficiently strong to form either p-p or n-n bound states, or equivalently, the nuclear force does not form a [[potential well]] deep enough to bind these identical nucleons.
 
Stable nuclides require approximately equal numbers of protons and neutrons. The stable nuclide [[carbon-12]] (<sup>12</sup>C) is composed of six neutrons and six protons, for example. Protons have a positive charge, hence within a nuclide with many protons there are large repulsive forces between protons arising from the [[Coulomb's law|Coulomb force]]. By acting to separate protons from one another, the neutrons within a nuclide play an essential role in stabilizing nuclides. With increasing atomic number, even greater numbers of neutrons are required to obtain stability. The heaviest stable element, [[Isotopes of lead|lead]] (Pb), has many more neutrons than protons. The stable nuclide <sup>206</sup>Pb has ''Z'' = 82 and ''N'' = 124, for example. For this reason, the valley of stability does not follow the line ''Z'' = ''N'' for A larger than 40 (''Z'' = 20 is the element [[Isotopes of calcium|calcium]]).<ref name="Byrne" /> Neutron number increases along the line of beta stability at a faster rate than atomic number.
 
The line of beta stability follows a particular curve of [[neutron–proton ratio]], corresponding to the most stable nuclides. On one side of the valley of stability, this ratio
is small, corresponding to an excess of protons over neutrons in the nuclides. These nuclides tend to be unstable to β<sup>+</sup> decay or electron capture, since such decay converts a proton to a neutron. The decay serves to move the nuclides toward a more stable neutron-proton ratio. On the other side of the valley of stability, this ratio is large, corresponding to an excess of neutrons over protons in the nuclides. These nuclides tend to be unstable to β<sup>−</sup> decay, since such decay converts neutrons to protons. On this side of the valley of stability, β<sup>−</sup> decay also serves to move nuclides toward a more stable neutron-proton ratio.
 
== নিউট্রন, প্রোটন ও বন্ধন শক্তি ==
{{See also|Semi-empirical mass formula}}
The mass of an atomic nucleus is given by
:<math>m = Z m_{p} + N m_{n} - \frac{E_{B}}{c^{2}}</math>
where <math>m_{p}</math> and <math>m_{n}</math> are the rest mass of a proton and a neutron, respectively, and <math>E_{B}</math> is the total [[binding energy]] of the nucleus. The [[mass–energy equivalence]] is used here. The binding energy is subtracted from the sum of the proton and neutron masses because the mass of the nucleus is ''less'' than that sum. This property, called the [[mass defect]], is necessary for a stable nucleus; within a nucleus, the nuclides are trapped by a [[potential well]]. A semi-empirical mass formula states that the binding energy will take the form
:<math>E_{B} = a_{V} A - a_{S} A^{2/3} - a_{C} \frac{Z^2}{A^{1/3}} - a_{A} \frac{(A - 2Z)^{2}}{A} \pm \delta(A,Z)</math><ref name=OSUFormula>{{cite web|author1=Oregon State University|title=Nuclear Masses and Binding Energy Lesson 3|url=http://oregonstate.edu/instruct/ch374/ch418518/lecture3-1.pdf|accessdate=30 September 2015|archiveurl=https://web.archive.org/web/20150930014054/http://oregonstate.edu/instruct/ch374/ch418518/lecture3-1.pdf|archivedate=30 September 2015}}</ref>
The difference between the mass of a nucleus and the sum of the masses of the neutrons and protons that comprise it is known as the [[mass defect]]. E<sub>B</sub> is often divided by the mass number to obtain binding energy per nucleon for comparisons of binding energies between nuclides. Each of the terms in this formula has a theoretical basis. The coefficients <math>a_{V}</math>, <math>a_{S}</math>, <math>a_{C}</math>, <math>a_{A}</math> and a coefficient that appears in the formula for <math>\delta(A,Z)</math> are determined empirically.
 
The binding energy expression gives a quantitative estimate for the neutron-proton ratio. The energy is a quadratic expression in {{mvar|Z}} that is minimized when the neutron-proton ratio is <math>N/Z \approx 1 + \frac{a_C}{2a_A} A^{2/3} </math>. This equation for the neutron-proton ratio shows that in stable nuclides the number of neutrons is greater than the number of protons by a factor that scales as <math>A^{2/3}</math>.
 
[[File:Binding energy curve - common isotopes2.jpg|thumb|right|300 px|The negative of binding energy per nucleon for the stable nuclides located along the bottom of the valley of stability. [[Iron-56]] is about the most stable nuclide, and it is about the lowest point within the valley of stability.]]
 
The figure at right shows the average binding energy per nucleon as a function of atomic mass number along the line of beta stability, that is, along the bottom of the valley of stability. For very small atomic mass number (H, He, Li), binding energy per nucleon is small, and this energy increases rapidly with atomic mass number. [[Nickel-62]] (28 protons, 34 neutrons) has the highest mean binding energy of all nuclides, while [[iron-58]] (26 protons, 32 neutrons) and [[iron-56]] (26 protons, 30 neutrons) are a close second and third.<ref>{{cite journal | last1 = Fewell | first1 = M. P. | year = 1995 | title = The atomic nuclide with the highest mean binding energy | journal = American Journal of Physics | volume = 63 | issue = 7| pages = 653–58 | bibcode=1995AmJPh..63..653F | doi=10.1119/1.17828}}</ref> These nuclides lie at the very bottom of the valley of stability. From this bottom, the average binding energy per nucleon slowly decreases with increasing atomic mass number. The heavy nuclide [[uranium-238|<sup>238</sup>U]] is not stable, but is slow to decay with a half-life of 4.5 billion years.<ref name="Mackintosh"/> It has relatively small binding energy per nucleon.
 
For β<sup>−</sup> decay, nuclear reactions have the generic form
: {{Physics particle|TL={{mvar|A}}|BL={{mvar|Z}}|X}} → {{Physics particle|TL={{mvar|A}}|BL={{math|''Z''+1}}|X&prime;}} + {{SubatomicParticle|Electron}} + {{SubatomicParticle|Electron Antineutrino}}<ref name="konya74">{{cite book
|last1=Konya |first1=J.
|last2=Nagy |first2=N. M.
|year=2012
|title=Nuclear and Radio-chemistry
|pages=74–75
|publisher=[[Elsevier]]
|isbn=978-0-12-391487-3
}}</ref>
where {{mvar|A}} and {{mvar|Z}} are the [[mass number]] and [[atomic number]] of the decaying nucleus, and X and X&prime; are the initial and final nuclides, respectively. For β<sup>+</sup> decay, the generic form is
: {{Physics particle|TL={{mvar|A}}|BL={{mvar|Z}}|X}} → {{Physics particle|TL={{mvar|A}}|BL={{math|''Z''−1}}|X&prime;}} + {{SubatomicParticle|Positron}} + {{SubatomicParticle|Electron Neutrino}}<ref name="konya74"/>
These reactions correspond to the decay of a neutron to a proton, or the decay of a proton to a neutron, within the nucleus, respectively. These reactions begin on one side or the other of the valley of stability, and the directions of the reactions are to move the initial nuclides down the valley walls towards a region of greater stability, that is, toward greater binding energy.
 
[[File:Valley of Stability Parabola 2.jpg|thumb|right|300 px|The negative of binding energy per nucleon for nuclides with atomic mass number 125 plotted as a function of atomic number. The profile of binding energy across the valley of stability is roughly a parabola. [[Isotopes of tellurium|Tellurium]]-52 (<sub>52</sub>Te) is stable, while [[Isotopes of antimony|antimony]]-51 (<sub>51</sub>Sb) is unstable to β− decay.]]
 
The figure at right shows the average binding energy per nucleon across the valley of stability for nuclides with atomic mass number A=125.<ref name="Krane">{{cite book |title=Introductory Nuclear Physics |author=K. S. Krane | year=1988 |location= New York | publisher=John Wiley and Sons}}</ref> At the bottom of this curve is [[Isotopes of tellurium|tellurium]] (<sub>52</sub>Te), which is stable. Nuclides to the left of <sub>52</sub>Te are unstable with an excess of neutrons, while those on the right are unstable with an excess of protons. A nuclide on the left therefore undergoes β<sup>−</sup> decay, which converts a neutron to a proton, hence shifts the nuclide to the right and toward greater stability. A nuclide on the right similarly undergoes β<sup>+</sup> decay, which shifts the nuclide to the left and toward greater stability.
 
Heavy nuclides are susceptible to α decay, and these nuclear reactions have the generic form,
: {{Physics particle|TL={{mvar|A}}|BL={{mvar|Z}}|X}} → {{Physics particle|TL={{math|''A''-4}}|BL={{math|''Z''-2}}|X&prime;}} + {{Physics particle|TL=4|BL=2|He}}
As in β decay, the decay product X&prime; has greater binding energy and it is closer to the middle of the valley of stability. The [[Alpha particle|α particle]] carries away two neutrons and two protons, leaving a lighter nuclide. Since heavy nuclides have many more neutrons than protons, α decay increases a nuclide's neutron-proton ratio.
 
== প্রোটন ও নিউট্রন ক্ষরণ রেখা ==
{{Main|Nuclear drip line|proton emission|neutron emission}}
 
The boundaries of the valley of stability, that is, the upper limits of the valley walls, are the neutron drip line on the neutron-rich side, and the proton drip line on the proton-rich side. The nucleon drip lines are at the extremes of the neutron-proton ratio. At neutron–proton ratios beyond the drip lines, no nuclei can exist. The location of the neutron drip line is not well known for most of the Segrè chart, whereas the proton and alpha drip lines have been measured for a wide range of elements. Drip lines are defined for protons, neutrons, and alpha particles, and these all play important roles in nuclear physics.
 
The difference in binding energy between neighboring nuclides increases as the sides of the valley of stability are ascended, and correspondingly the nuclide half-lives decrease, as indicated in the figure above. If one were to add nucleons one at a time to a given nuclide, the process will eventually lead to a newly formed nuclide that is so unstable that it promptly decays by emitting a proton (or neutron). Colloquially speaking, the nucleon has 'leaked' or 'dripped' out of the nucleus, hence giving rise to the term "drip line".
 
Proton emission is not seen in naturally occurring nuclides. Proton emitters can be produced via [[nuclear reaction]]s, usually utilizing [[linear particle accelerator]]s (linac). Although prompt (i.e. not beta-delayed) proton emission was observed from an isomer in [[cobalt-53]] as early as 1969, no other proton-emitting states were found until 1981, when the proton radioactive ground states of [[lutetium-151]] and [[thulium-147]] were observed at experiments at the [[Gesellschaft für Schwerionenforschung|GSI]] in West Germany.<ref>{{cite book | author = S. Hofmann | title= Proton radioactivity, Ch. 3 of Nuclear Decay Modes, Ed. Dorin N. Poenaru| publisher = Institute of Physics Publishing, Bristol | year = 1996 | pages = 143–203 | isbn = 978-0-7503-0338-5| title-link= Dorin N. Poenaru}}</ref> Research in the field flourished after this breakthrough, and to date more than 25 nuclides have been found to exhibit proton emission. The study of proton emission has aided the understanding of nuclear deformation, masses and structure, and it is an example of [[quantum tunneling]].
 
Two examples of nuclides that emit neutrons are [[beryllium-13]] (mean life {{val|2.7|e=-21|ul=s}}) and [[helium-5]] ({{val|7|e=-22|u=s}}). Since only a neutron is lost in this process, the atom does not gain or lose any protons, and so it does not become an atom of a different element. Instead, the atom will become a new [[isotope]] of the original element, such as [[beryllium-13]] becoming [[beryllium-12]] after emitting one of its neutrons.<ref>{{cite web|url=http://education.jlab.org/glossary/neutron_emission.html |title=Neutron Emission|format=webpage |date= |accessdate=2014-10-30}}</ref>
 
In [[nuclear engineering]], a [[prompt neutron]] is a [[neutron]] immediately emitted by a [[nuclear fission]] event. Prompt neutrons emerge from the fission of an unstable [[fissionable]] or [[fissile]] heavy nucleus almost instantaneously. [[delayed neutron|Delayed neutron decay]] can occur within the same context, emitted after [[beta decay]] of one of the [[fission product]]s. Delayed neutron decay can occur at times from a few milliseconds to a few minutes.<ref>{{Citation | title = DOE Fundamentals Handbook - Nuclear Physics and Reactor Theory | url = http://energy.gov/sites/prod/files/2013/06/f2/h1019v1.pdf | page = 29 (p. 133 of .pdf format) | series = DOE-HDBK-1019/1-93 | date = January 1993 | publisher = U.S. Department of Energy | access-date = 2010-06-03 | archive-url = https://web.archive.org/web/20140319145623/http://energy.gov/sites/prod/files/2013/06/f2/h1019v1.pdf | archive-date = 2014-03-19 | dead-url = yes | df = }}</ref> The U.S. [[Nuclear Regulatory Commission]] defines a prompt neutron as a neutron emerging from fission within 10<sup>−14</sup> seconds.
<ref>{{Citation
| first = John T. | last = Mihalczo
| title = Radiation Detection From Fission
| url = http://www.ornl.gov/~webworks/cppr/y2004/rpt/121589.pdf?origin=publication_detail
| page = 1 (p. 11 of .pdf format)
| series = ORNL/TM-2004/234
| date = November 19, 2004
| publisher = Oak Ridge National Laboratory
}}</ref>
 
== স্থায়িত্ব দ্বীপ ==
{{Main|Island of stability}}
The island of stability is a region outside the valley of stability where it is predicted that a set of heavy [[isotopes]] with near [[Magic number (physics)|magic numbers]] of protons and neutrons will locally reverse the trend of decreasing stability in [[transuranium element|elements heavier than uranium]].
The hypothesis for the island of stability is based upon the [[nuclear shell model]], which implies that the [[atomic nucleus]] is built up in "shells" in a manner similar to the structure of the much larger electron shells in atoms. In both cases, shells are just groups of quantum [[energy level]]s that are relatively close to each other. Energy levels from quantum states in two different shells will be separated by a relatively large energy gap. So when the number of [[neutron]]s and [[proton]]s completely fills the [[energy level]]s of a given shell in the nucleus, the [[binding energy]] per nucleon will reach a local maximum and thus that particular configuration will have a longer lifetime than nearby isotopes that do not possess filled shells.<ref>{{cite web| title = Shell Model of Nucleus | work = HyperPhysics | publisher = Department of Physics and Astronomy, Georgia State University | url = http://hyperphysics.phy-astr.gsu.edu/hbase/nuclear/shell.html | accessdate = 22 January 2007 }}</ref>
 
A filled shell would have "[[Magic number (physics)|magic numbers]]" of neutrons and protons. One possible magic number of neutrons for spherical nuclei is 184, and some possible matching proton numbers are 114, 120 and 126. These configurations imply that the most stable spherical isotopes would be [[flerovium]]-298, [[unbinilium]]-304 and [[unbihexium]]-310. Of particular note is <sup>298</sup>Fl, which would be "[[Double magic|doubly magic]]" (both its [[proton number]] of 114 and [[neutron number]] of 184 are thought to be magic). This doubly magic configuration is the most likely to have a very long half-life. The next lighter doubly magic spherical nucleus is [[lead]]-208, the heaviest known stable nucleus and most stable heavy metal.
 
== আলোচনা ==
The valley of stability can be helpful in interpreting and understanding properties of nuclear decay processes such as [[decay chains]] and [[nuclear fission]].
 
[[File:Valley of Stability U-238 Series.png|400px|thumb|The uranium-238 series is a series of alpha (N and Z less 2) and beta- decays (N less 1, Z plus 1) to nuclides that are successively deeper into the valley of stability. The series terminates at lead-206, a stable nuclide at the bottom of the valley of stability.]]
 
Radioactive decay often proceeds via a sequence of steps known as a decay chain. For example, [[Uranium-238|<sup>238</sup>U]] decays to <sup>234</sup>Th which decays to <sup>234m</sup>Pa and so on, eventually reaching [[Lead-206|<sup>206</sup>Pb]]:
:<math chem>\begin{array}{l}{}\\
\ce{^{238}_{92}U->[\alpha][4.5 \times 10^9 \ \ce y] {^{234}_{90}Th} ->[\beta^-][24 \ \ce d] {^{234\!m}_{91}Pa}}
\ce{->[\beta^-][1 \ \ce{min}]}
\ce{^{234}_{92}U ->[\alpha][2.4 \times 10^5 \ \ce y] {^{230}_{90}Th} ->[\alpha][7.7 \times 10^4 \ \ce y] }
\\
\ce{^{226}_{88}Ra ->[\alpha][1600 \ y] {^{222}_{86}Rn} ->[\alpha][3.8 \ \ce d] {^{218}_{84}Po} ->[\alpha][3 \ \ce{min}] {^{214}_{82}Pb} ->[\beta^-][27 \ \ce{min}] {^{214}_{83}Bi} ->[\beta^-][20 \ \ce{min}]}
\\
\ce{^{214}_{84}Po ->[\alpha][164 \ \mu\ce{s}] {^{210}_{82}Pb} ->[\beta^-][22 \ \ce y] {^{210}_{83}Bi} ->[\beta^-][5 \ \ce d] {^{210}_{84}Po} ->[\alpha][138 \ \ce d] {^{206}_{82}Pb}}\\{}
\end{array}
</math>
With each step of this sequence of reactions, energy is released and the [[decay product]]s move further down the valley of stability towards the line of beta stability. <sup>206</sup>Pb is stable and lies on the line of beta stability.
 
[[File:Nuclear fission.svg|thumb|150px|right|Nuclear fission seen with a uranium-235 nucleus]]
The [[Nuclear fission|fission]] processes that occur within [[nuclear reactors]] are accompanied by the release of neutrons that sustain the [[chain reaction]]. Fission occurs when a heavy nuclide such as [[uranium-235]] absorbs a neutron and breaks into lighter components such as [[barium]] or [[krypton]], usually with the release of additional neutrons. Like all nuclides with a high atomic number, these uranium nuclei require many neutrons to bolster their stability, so they have a large neutron-proton ratio (''N''/''Z''). The nuclei resulting from a fission ([[Nuclear fission product|fission products]]) inherit a similar ''N''/''Z'', but have atomic numbers that are approximately half that of uranium.<ref name="Mackintosh"/> Isotopes with the atomic number of the fission products and an ''N''/''Z'' near that of uranium or other fissionable nuclei have too many neutrons to be stable; this neutron excess is why multiple free neutrons but no free protons are usually emitted in the fission process, and it is also why many fission product nuclei undergo a long chain of β<sup>−</sup> decays, each of which converts a nucleus ''N''/''Z'' to (''N'' − 1)/(''Z'' + 1), where ''N'' and ''Z'' are, respectively, the numbers of neutrons and protons contained in the nucleus.
 
When fission reactions are sustained at a given rate, such as in a liquid-cooled or solid fuel nuclear reactor, the nuclear fuel in the system produces many [[neutrino|antineutrinos]] for each fission that has occurred. These antineutrinos come from the decay of fission products that, as their nuclei progress down a β<sup>−</sup> decay chain toward the valley of stability, emit an antineutrino along with each β<sup>−</sup> particle. In 1956, [[Frederick Reines|Reines]] and [[Clyde Cowan|Cowan]] exploited the (anticipated) intense flux of antineutrinos from a nuclear reactor in the design of [[Cowan–Reines neutrino experiment|an experiment]] to detect and confirm the existence of these elusive particles.<ref name="Nobel lecture">{{cite web |url=http://nobelprize.org/nobel_prizes/physics/laureates/1995/reines-lecture.pdf |title=The Neutrino: From Poltergeist to Particle |quote=Nobel Prize lecture |first=Frederick |last=Reines |date=December 8, 1995 |publisher=Nobel Foundation |accessdate=February 20, 2015 }}</ref>
 
== আরও দেখুন ==
* [[আলফা ক্ষয়]]
* [[গামা ক্ষয়]]
* [[নিউট্রন বিকিরণ]]
* [[প্রোটন বিকিরণ]]
* [[গুচ্ছ ক্ষয়]]
* [[স্থিতিশীল নিউক্লাইড]]
* [[পরমাণুর শেল কাঠামো]]
* [[পারমাণবিক ক্ষরণ রেখা]]
 
== তথ্যসূত্র ==
{{Reflist}}
 
== বহি:সংযোগ ==
* [[File:Ndslivechart.png]] '''[https://www-nds.iaea.org/livechart The Live Chart of Nuclides - IAEA ]''' with filter on decay type
* [https://www.youtube.com/watch?v=UTOp_2ZVZmM&t=192 The Valley of Stability (video)] - a virtual "flight" through 3D representation of the nuclide chart, by [[French Alternative Energies and Atomic Energy Commission|CEA]] (France)
* [http://www.nupecc.org/pans/Data/CHAPT_6.PDF The nuclear landscape: The variety and abundance of nuclei] - Chapter 6 of the book ''Nucleus: A trip into the heart of matter'' by Mackintosh, Ai-Khalili, Jonson, and Pena describes the valley of stability and its implications (Baltimore, MD:The Johns Hopkins University Press), 2001. {{ISBN|0-801 8-6860-2}}
 
[[Category:পারমাণবিক পদার্থবিদ্যা]]
[[Category:তেজষ্ক্রিয়তা]]
[[Category:আইসোটোপ]]