"ব্যবহারকারী:Sammay Sarkar/খসড়া/২" পাতাটির দুইটি সংশোধিত সংস্করণের মধ্যে পার্থক্য

(→‎আলোচনা: অনুবাদ)
 
== নিউট্রন, প্রোটন ও বন্ধন শক্তি ==
{{See also|অর্ধ-পরীক্ষালদ্ধ ভর সুত্র}}
{{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>
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|স্থায়িত্ব উপত্যকার তলদেশে অবস্থিত স্থায়ী নিউক্লাইডগুলোর নিউক্লিয়ন-প্রতি ঋণাত্বক বন্ধন শক্তির গ্রাফ। [[লোহা]]-৫৬ সবচেয়ে স্থায়ী নিউক্লাইডসমূহের মধ্যে একটি, এবং এটি স্থায়িত্ব উপত্যকার সবচেয়ে নিম্নতর অবস্থানে উপস্থিত।]]
[[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.
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|১২৫ এর বেশি পারমাণবিক সংখ্যা বিশিষ্ট নিউক্লাইডের নিউক্লিয়ন-প্রতি ঋণাত্বক বন্ধন শক্তি, পারমাণবিক সংখ্যার ফাংশন হিসেবে গ্রাফে স্থাপিত। স্থায়িত্ব উপত্যকা জুড়ে বন্ধন শক্তির ধারা একটি অধিবৃত্তের আকারের পথ গঠন করে। [[টেলুরিয়াম]]-৫২ (<sub>52</sub>Te) স্থায়ী, অন্যদিকে [[এন্টিমনি]]-৫১ (<sub>51</sub>Sb) অস্থায়ী (β− ক্ষয়ের কারণে)।]]
[[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.
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