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Date: 29-11-2018
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Date: 13-3-2019
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Date: 1-4-2019
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Helium has eight known isotopes but only two are stable: 3He and 4He. 3He is found in only very small quantities compared to 4He. It is produced in trace amounts by the beta decay of tritium. This form is found in abundance in stars, as a product of nuclear fusion. Extraplanetary materials have trace amounts of 3He from solar winds. 4He is produced by the alpha decay of heavier radioactive elements on Earth. It is an unusually stable isotope because its nucleons are arranged in complete shells.
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دخلت غرفة فنسيت ماذا تريد من داخلها.. خبير يفسر الحالة
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ثورة طبية.. ابتكار أصغر جهاز لتنظيم ضربات القلب في العالم
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العتبة العباسية المقدسة تقيم مجلسًا عزائيًّا لإحياء ذكرى هدم قبور أئمة البقيع (عليهم السلام)
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