PRESENTED BY

1. PRESENTED BY • NAME - SOUMYA.V • CLASS - IX – C • SUBJECT – CHEMISTRY • TOPIC – DISCOVERY OF NEUTRON

2. CLASSIFICATION OF ATOMS

3. NUETRON • Composition – one up, two down. • Family - fermions. • Interaction- gravity , electromagnetic , weak, strong. • Antiparticle – antineutron. • Discovered – James Chadwick. • Symbol – n. • Mass – 1.67492729(28) kg and 939.56560(81)mebv/c². • Electric charge – 0c. • Spin -½

4. INTRODUCTION (NEUTRON) • In physics neutron is a subatomic particle with no net electric charge and a mass of 939.573 Mev/c² [1.008 664 915 (78)u kg less than a proton]. • Its spin is½ . Its antiparticle is called ANTINUERON . The neutron along with the proton is a NUCLEON. • The nuclei of all atoms (except the lightest isotope of hydrogen , which has only single proton) consists of protons and neutrons. • The number of neutrons determines the isotope of an element. For example-: carbon12 isotope has 6 protons and 6 neutrons, while the carbon14 isotope has 6 protons and 8 neutrons • Isotopes are atoms of the same element that have same atomic number but different mass number due to the number of neutrons . • A neutron consists of two down quark one up quark it is called aBARYON.

5. DISCOVERY • In 1930 ,WALTHER BOTHE and H.BECKER in Germany found that if the very energetic alpha particles emitted from polonium fell on certain light elements , specifically beryllium ,boron (or) lithium , an unusually penetrating ray was produced. • At first this radiation was thought as gamma radiation although it was more penetrating than any gamma rays known and the details of experimental results were very difficult to interpret on this basis. • The next important contribution was reported in 1932 by IRENE JOLIOT CURIE and FREDERIC JOLIOT in Paris • They showed that if this unknown radiation fell on paraffin or some other hydrogen containing compounds it ejected protons of very high energy. • Finally (later in 1932) the physicist named JAMES CHADWICK in England performed a series of experiments showing that gamma ray hypothesis was untenable.

6. CONTINUATION OF DISCOVERY • He suggested that in fact the new radiation consisted of uncharged particles approximately having the mass of the proton , and he performed a series of experiments verifying this suggestion. • Such uncharged particles were eventually called the neutrons from the Latin root of NEUTRAL and from the Greek word on. (by imitation of proton and neutron)

7. NEUTRON STABILITY AND BETADECAY • Outside the nucleus , free neutrons are unstable and have a mean lifetime of about 15 minutes , decaying by emission of a negative electron and antineutrino to become a proton. • n= p+e¯ +v¯ • This decay mode known as beta decay can also transform the character of neutrons within unstable nuclei . • Beta decay and electron capture are types of radioactive decay and are both governed by the weak interaction.

8. DETECTION • The common means of detecting a charged particle by looking for a track of ionization (such as in a cloud chamber) does not work for neutrons directly. • Neutrons that elastically scatter off atoms can create an ionization track that is detectable , but the experiments are not as simple to carry out other ; other means for detecting neutrons ,consisting of allowing them to interact with atomic nuclei are commonly used. • A common method for detecting neutrons involves converting the energy released from such reactions into electrical signals. • The nuclides 3He , 6Li , 10B , 233U , 235U,237Np and 239Pu are useful for this purpose.

9. SOURCES • Due to the fact that free neutrons are unstable , they can be obtained only from nuclear disintegrations , nuclear reactions , and high- energy reactions (such as in cosmic radiation showers or accelerator collisions). • Free neutron beams are obtained from neutron sources by neutron transport. • For access to intense neutron sources , researchers must go to specialist facilities , such as the ISIS facility in the U.K , which is currently the world’s most intense pulsed neutron and muon source • Neutrons lack of total electric charge prevents from being able to steer or accelerate them. • Charged particles can be accelerated , decelerated or deflected by electric or magnetic fields. • However these methods have no effect on neutrons except for a small effect of a magnetic field because of the neutrons magnetic moment.

10. USES • The neutron plays an important role in many nuclear reactions. For example-:neutron capture often results in neutron activation , inducing radioactivity. • In particular , knowledge of neutrons and their behaviour has been important in the development of nuclear reactors and nuclear weapons. • Cold , thermal and hot neutron radiation is commonly employed in neutron scattering facilities , where the radiation is used in a similar way one uses x-rays for the analysis of condensed matter. • Neutrons are complementary to the later in terms of atomic contrasts by different scattering cross – sections ; sensitivity to magnetism ; energy range for inelastic neutron spectroscopy ; and deep penetration into matter.

11. QUARKS MODEL • In physics , the quark model is a classification scheme for hadrons in terms of their valence quarks i.e. the quarks which give rise to quantum numbers. • These quantum numbers are labels identifying the hadrons and are of two types. • There are generalization to number of flavors.

12. THANKS GIVINGTO My sincere thanks to- • My mom • My dad • The children’s encyclopedia (book) • Wikipedia the free encyclopedia (internet)

13. THANKING YOU