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Tritium - what is it? mass of tritium. Mass defect of atomic nuclei. Bond energy

Since the nucleons in the nucleus are bound by nuclear forces, it takes a lot of energy to split the nucleus into its component protons and neutrons. The same energy is released when free protons and neutrons combine to form a nucleus. This energy is called the binding energy of the nucleus. According to Einstein's theory of relativity, energy corresponds to mass. Therefore, the mass of the nucleus must be less than the sum of the masses of its constituent free protons and neutrons. The difference between the sum of the rest masses of free protons and neutrons from which the nucleus is formed and the mass of the nucleus is called nuclear mass defect. The bond energy is: E sv = FROM 2×D m

D m is the nuclear mass defect.

The binding energy is expressed in mega-electronvolts (MeV) (MeV=10 6 EV). Since the atomic mass unit (a.m.u.) is equal to 1.66 × 10 -27 kg, we can determine the energy corresponding to it:

Using a mass spectrograph, the masses of all isotopes were measured and the values ​​of the mass defect and binding energy were calculated for all nuclei that are used to calculate nuclear reactions. If in some reaction nuclei and particles are obtained, the total mass of which is less than that of the original nuclei and particles, then energy is released in such reactions; if more, then it is absorbed and such a reaction will not occur spontaneously.

Let's carry out an energy calculation of the nuclear reaction of the transformation of radium into radon: . The binding energy of the original nucleus is 1731.6 MeV, and the total binding energy of the formed nuclei is 1708.2+28.3=176.5 MeV and is greater than the binding energy of the original nucleus by 4.9 MeV. Therefore, this reaction releases an energy of 4.9 MeV, which is basically kinetic energy g-particles.

Great importance has a binding energy per nucleon. The larger it is, the stronger the core. The most durable medium cores. Light nuclei underutilize their binding energies. Heavy nuclei are weakened by the Coulomb repulsive forces, which, unlike nuclear ones, act between all the nucleons of the nucleus. An important conclusion follows from this: energy is released when middle nuclei are formed. This can be when dividing a heavy nucleus into two medium ones in nuclear reactors or in the synthesis of the middle nucleus from two lighter ones. These are thermonuclear fusion reactions occurring in the sun and stars.

OBJECTIVES FOR UNIT 25

1. What does a thorium isotope turn into, the nucleus of which undergoes three successive a decays.

Solution:

When an a-particle is emitted, the nuclear charge decreases by 2 units, and the mass number by 4 units, which means that when 3 a-particles are emitted, the nuclear charge decreases by 2 × 3 = 6 units, and the mass number by 4 × 3 = 12 units and then you get an isotope according to the table, we find that it is polonium or

2. When nitrogen is bombarded with neutrons, two isotopes are formed, one of which is an isotope of hydrogen. The isotope of which element is formed in this nuclear reaction.

IN this case a nuclear reaction occurs to produce an unknown isotope X.

In nuclear reactions, the number of nucleons and charge are conserved, so the sum of subscripts and superscripts is constant.

According to the periodic table, we find that carbon is obtained:

In this way:

3. Add nuclear reaction:

We determine that the unknown particle has a charge number of 1 and a mass of 1, which means that the hydrogen isotope , i.e. proton, i.e. we have:

4. Find the energy corresponding to 1 a.m.u. Express it in MeV.

Solution:

E \u003d m c 2

m\u003d 1 amu \u003d 1.66 × 10 -27 kg

FROM= 3 × 10 8 m/s

E\u003d 1.66 × 10 -27 × (3 × 10 8) 2 \u003d 14.94 × 10 -11 J

1 EV = 1.6 × 10 -19 J

So: 1 a.m.u. corresponds to 931 MEV.

5. Calculate the energy of the tritium nucleus if the mass of the proton m p= 1.00814 amu, neutron mass m n= 1.00898 and the mass of the tritium atom BUT= 3.01700 amu


Given:

m p= 1.00814 amu

m n = 1,00898

A = 3.01700 amu

__________________

E St – ?


Solution:

Tritium nucleus: consists of one proton and two neutrons, the total mass of which is: m p + 2m n = 1.00814 + 2 × 1.00898 = = 3.02610

So the mass defect is:

D m= 3.02610 - 3.01700 amu = 0.00910 amu

because 1 amu - 931 MEV; then E St= 931×D m or

E St= 931 × 0.00910 (MEV) = 8.5 MeV

Answer: 8.5 MeV


6. Energy is released or absorbed in a reaction:

It was possible to calculate the binding energy of each nucleus, but you can also use a special table:

The total mass of nuclei and particles before the reaction: 39.2 + 28.3 = 67.5 MEV

after reaction: 64.7 + 0 = 64.7 MeV

This means that energy is absorbed in such a reaction: 67.5 - 64.7 = 2.8 MeV

7. Determine the energy in the reaction:

before reaction: 2.2 + 2.2 = 4.4 MEV

after reaction: 8.5 MeV

energy released: 8.5 - 4.4 = 4.1 MeV

8. There are 4 g of radioactive cobalt. How many grams of cobalt decays in 216 days if its half-life is 72 days?


Given:

m 0 = 4 g

t= 216 days

T= 72 days

D m – ?


Solution:

Since the mass of a substance is directly proportional to the number of atoms, then: DN=N 0 - N;

Means:

This means: and

Answer: 3.5 g


9. There are 8 kg of radioactive cesium. Determine the mass of undecayed cesium after 135 years of radioactive decay if its half-life is 27 years.

More recently, people believed that the atom is an integral indivisible particle. Later it became clear that it consists of a nucleus and electrons revolving around it. At the same time, the central part was again considered indivisible and integral. Today we know that it is made up of protons and neutrons. Moreover, depending on the number of the latter, the same substance can have several isotopes. So, tritium is for the substance, how to get and use it?

Tritium - what is it?

Hydrogen is the simplest substance in nature. If we talk about its most common form, which will be discussed in more detail below, then its atom consists of only one proton and one electron. However, it can also accept "extra" particles, which somewhat change its properties. Thus, the nucleus of tritium consists of a proton and two neutrons. And if protium, then there is the most simple form hydrogen - this is something you cannot say about its "improved" version - in nature it is found in small amounts.

The hydrogen isotope tritium (the name comes from the Greek word for "third") was discovered in 1934 by Rutherford, Oliphant and Harteck. And in fact, they tried to find him for a very long time and hard. Immediately after the discovery of deuterium and heavy water in 1932, scientists began to search for this isotope by increasing the sensitivity of conventional hydrogen. However, in spite of everything, their attempts were in vain - even in the most concentrated samples it was not possible to get even a hint of the presence of a substance that was simply obliged to exist. But in the end, the search was nevertheless crowned with success - Oliphant synthesized the element with the help of Rutherford's laboratory.

In short, the definition of tritium is as follows: a radioactive isotope of hydrogen, the nucleus of which consists of a proton and two neutrons. So what is known about him?

About hydrogen isotopes

The first element on the periodic table is also the most common element in the universe. At the same time, it occurs in nature in the form of one of its three isotopes: protium, deuterium or tritium. The nucleus of the former consists of a single proton, which gave it its name. By the way, this is the only stable element that does not have neutrons. The next in the series of hydrogen isotopes is deuterium. The nucleus of its atom consists of a proton and a neutron, and the name goes back to the Greek word for "second".

Even heavier hydrogen isotopes with mass numbers from 4 to 7 were also obtained in the laboratory. Their half-life is limited to fractions of seconds.

Properties

The atomic mass of tritium is approximately 3.02 amu. e. m. According to their own physical properties this substance is almost no different from ordinary hydrogen, that is, in normal conditions It is a light, colorless, tasteless and odorless gas with high thermal conductivity. At a temperature of about -250 degrees Celsius, it becomes a light and flowing colorless liquid. The range within which it is in this state of aggregation is rather narrow. The melting point is about 259 degrees Celsius, below which hydrogen becomes a snow-like mass. In addition, this element is quite soluble in some metals.

However, there are some differences in properties. Firstly, the third isotope is less reactive, and secondly, tritium is radioactive and therefore unstable. is just over 12 years old. In the process of radiolysis, it turns into a third isotope of helium with the emission of an electron and an antineutrino.

Receipt

In nature, tritium is found in small amounts and is most often formed in upper layers atmosphere in the collision of cosmic particles and, for example, nitrogen atoms. However, there is also industrial method obtaining this element by irradiating lithium-6 with neutrons in

Synthesis of tritium in volume, the mass of which is about 1 kilogram, costs about 30 million dollars.

Usage

So, we learned a little more about tritium - what it is and its properties. But why is it needed? Let's find out a little lower. According to some reports, the global commercial need for tritium is about 500 grams per year, and another 7 kilograms goes to military needs.

According to the American Institute for Energy Research and environment, from 1955 to 1996, 2.2 centners of superheavy hydrogen were produced in the USA. And in 2003, the total reserves of this element were about 18 kilograms. What are they used for?

First, tritium is needed to maintain the combat capability of nuclear weapons, which some countries are known to still possess. Secondly, thermonuclear energy is indispensable without it. Tritium is also used in some scientific research, for example, in geology, it is used to date natural waters. Another purpose is the backlight power supply in the watch. In addition, experiments are currently underway to create ultra-low power radioisotope generators, for example, to power autonomous sensors. It is expected that in this case their service life will be about 20 years. The cost of such a generator will be about one thousand dollars.

As original souvenirs there are also key chains with a small amount tritium inside. They emit a glow and look quite exotic, especially if you know about the internal content.

Danger

Tritium is radioactive, which explains some of its properties and uses. Its half-life is about 12 years, producing helium-3 with the emission of an antineutrino and an electron. During this reaction, 18.59 kW of energy is released and beta particles propagate in the air. It may seem strange to the average person that a radioactive isotope is used, say, for lighting in watches, because it can be dangerous, right? In fact, tritium is hardly a threat to human health, since beta particles in the process of its decay spread a maximum of 6 millimeters and cannot overcome the simplest obstacles. However, this does not mean that working with it is absolutely safe - any ingestion with food, air or absorption through the skin can lead to problems. Although in most cases it is easily and quickly removed, this is not always the case. So, tritium - what is it in terms of radiation hazard?

Protective Measures

Though low energy The decay of tritium does not allow radiation to spread seriously, so that beta particles cannot even penetrate the skin, do not neglect your health. When working with this isotope, you can, of course, not use a radiation protection suit, but elementary rules such as closed clothing and surgical gloves must be observed. Since tritium poses the main danger through ingestion, it is important to stop activities in which this becomes possible. Otherwise, there is nothing to worry about.

However, if he in large numbers entered the tissues of the body, acute or chronic radiation sickness may develop, depending on the duration, dose and regularity of exposure. In some cases, this disease is successfully cured, but with extensive lesions, a fatal outcome is possible.

In any normal body there are traces of tritium, although they are absolutely insignificant and hardly affect Well, for lovers of watches with luminous hands, its level is several times higher, although it is still considered safe.

Super heavy water

Tritium, like ordinary hydrogen, can form new substances. In particular, it enters the molecule of the so-called superheavy (superheavy) water. The properties of this substance are not too different from the usual H 2 O for every person. Despite the fact that tritium water can also participate in metabolism, it is quite toxic and is excreted within a ten-day period, during which tissues can get quite a high degree irradiation. And although this substance is less dangerous in itself, it is more dangerous due to the period during which it is in the body.

Absolutely any chemical consists of a certain set of protons and neutrons. They are held together due to the fact that there is a binding energy inside the particle. atomic nucleus.

A characteristic feature of the nuclear forces of attraction is their very high power at relatively small distances (from about 10 -13 cm). As the distance between particles increases, the forces of attraction inside the atom also weaken.

Reasoning about the binding energy inside the nucleus

If you imagine that there is a way to separate protons and neutrons in turn from the nucleus of an atom and arrange them at such a distance that the binding energy of the atomic nucleus ceases to act, then this must be very hard work. In order to extract its components from the nucleus of an atom, one must try to overcome intra-atomic forces. These efforts will go towards dividing the atom into the nucleons it contains. Therefore, it can be judged that the energy of the atomic nucleus is less than the energy of the particles of which it consists.

Is the mass of subatomic particles equal to the mass of an atom?

Already in 1919, researchers learned how to measure the mass of an atomic nucleus. Most often, it is “weighed” using special technical devices, which are called mass spectrometers. The principle of operation of such devices is that the characteristics of the movement of particles with different masses are compared. Moreover, such particles have the same electric charges. Calculations show that those particles that have different indicators masses move along different trajectories.

Modern scientists have found out with great accuracy the masses of all nuclei, as well as the protons and neutrons that make up them. If we compare the mass of a certain nucleus with the sum of the masses of the particles contained in it, then it turns out that in each case the mass of the nucleus will be greater than the mass of individual protons and neutrons. This difference will be approximately 1% for any chemical. Therefore, we can conclude that the binding energy of an atomic nucleus is 1% of its rest energy.

Properties of intranuclear forces

Neutrons that are inside the nucleus are repelled from each other by Coulomb forces. However, the atom does not fall apart. This is facilitated by the presence of an attractive force between particles in an atom. Such forces, which are of a nature other than electrical, are called nuclear. And the interaction of neutrons and protons is called the strong interaction.

Briefly, the properties of nuclear forces are as follows:

  • this is charge independence;
  • action only at short distances;
  • as well as saturation, which refers to the retention of only a certain number of nucleons near each other.

According to the law of conservation of energy, at the moment when nuclear particles are combined, energy is released in the form of radiation.

Binding energy of atomic nuclei: formula

For the above calculations, the generally accepted formula is used:

E St=(Z m p +(A-Z) m n -MI) s²

Here under E St refers to the binding energy of the nucleus; from- the speed of light; Z-number of protons; (A-Z) is the number of neutrons; m p denotes the mass of the proton; but m n is the mass of the neutron. M i denotes the mass of the nucleus of an atom.

Internal energy of nuclei of various substances

To determine the binding energy of the nucleus, the same formula is used. The binding energy calculated by the formula, as previously indicated, is no more than 1% of total energy atom or rest energy. However, on closer examination, it turns out that this number fluctuates quite strongly from substance to substance. If you try to determine its exact values, then they will differ especially for the so-called light nuclei.

For example, the binding energy inside a hydrogen atom is zero because there is only one proton in it. The binding energy of a helium nucleus would be 0.74%. For nuclei of a substance called tritium, this number will be 0.27%. Oxygen has 0.85%. In nuclei, where there are about sixty nucleons, the intra-atomic bond energy will be about 0.92%. For atomic nuclei with a larger mass, this number will gradually decrease to 0.78%.

To determine the binding energy of the nucleus of helium, tritium, oxygen, or any other substance, the same formula is used.

Types of protons and neutrons

The main reasons for such differences can be explained. Scientists have found that all the nucleons that are contained inside the nucleus are divided into two categories: surface and internal. Internal nucleons are those that are surrounded by other protons and neutrons from all sides. Surface ones are surrounded by them only from the inside.

The binding energy of an atomic nucleus is a force that is more pronounced for internal nucleons. Something similar, by the way, occurs with the surface tension of various liquids.

How many nucleons fit in a nucleus

It has been found that the number of internal nucleons is especially small in the so-called light nuclei. And in those that belong to the category of the lightest, almost all nucleons are regarded as surface. It is believed that the binding energy of the atomic nucleus is a quantity that should increase with the number of protons and neutrons. But even this growth cannot continue indefinitely. At a certain amount nucleons - and this is from 50 to 60 - another force comes into play - their electrical repulsion. It occurs even independently of the presence of binding energy within the nucleus.

The binding energy of the atomic nucleus in various substances used by scientists to release nuclear energy.

Many scientists have always been interested in the question: where does the energy come from when lighter nuclei merge into heavy ones? Actually, this situation similar to atomic fission. In the process of fusion of light nuclei, just as occurs during the splitting of heavy ones, nuclei of a stronger type are always formed. In order to “get” all the nucleons in them from light nuclei, it is required to spend less quantity energy than what is released when they are combined. The converse is also true. In fact, the energy of fusion, which falls on a certain unit of mass, may be greater than the specific energy of fission.

Scientists who studied the processes of nuclear fission

The process was discovered by the scientists Hahn and Strassmann in 1938. Within the walls of the Berlin University of Chemistry, researchers discovered that when uranium is bombarded with other neutrons, it turns into lighter elements, standing in the middle of the periodic table.

A significant contribution to the development of this field of knowledge was also made by Lise Meitner, whom Hahn once proposed to study radioactivity together. Hahn allowed Meitner to work only on the condition that she conduct her research in the basement and never climb upper floors which was a fact of discrimination. However, this did not prevent her from achieving significant success in the study of the atomic nucleus.