Nuclear Reaction ( Transmutation)
Nuclear reaction: (Nuclear transmutation) The theory is that atoms change from one kind to another wither in nature or lab. by means of bombardment reaction, when this change occur the nucleus of an isotopes emits α or β particles. So the nucleus gain or loss positive charge and its atomic no. is changed.Ex.:- C14 can be produced in lab. By bombarding nitrogen with neutron 10n + 147N 146C + 11HC14 is a good β emitter, it can be placed in biological organism and can be traced in lab. as it travels in living system. 146C 147N + 0-1eBombardment reaction:- A reaction occurs when particles of atomic or subatomic size strike atoms of an element and change them into another:Ex.: α –particle and Beryllium 94Be + 42He 126C + 10n bombardment particle Nuclear transmutation produced in lab. by bombarding nitrogen gas (N2)with 42He nucleus. As 147N+ 42He 189FHighly unstable nucleus is R- a atom and rapidly decay to form 17O 189F 178O + 11H
1- It tells us how long a sample of isotopes will exist: Ex.:- 137N (t1/2) = 10min if we have 1gm of 137N how long will be after 50min. 1gm 10min 0.5gm 10min 0.25gm 10min 0.125gm 10min 0.0625 10min 0.03105 10min - - - - - 137N t1/2 10min 136C + 01e
2- Half life tells us about the stability of the isotopes if t1/2 large (high) isotopes is stability but if t1/2 low (small) isotopes is unstable. 3- Half life of R. a isotopes is independent on the sample size or the amount of material if we have 1kg, 10gm, 1gm it has the same t1/2, so t1/2 are useful in discovery the age of argiological object. Most of the artificially produced radio active isotopes are unstable and have very short t1/2 but natural once have height t1/2 (stable).
Radiation dosage: radiation causes damage to all living system, the degree of damage is related directly to the dose of radiation received.There are different basic units used to describe the activity of radio active material.1. Curie and Becquerel: (symbol ci) This unit is a measure of a no. of nuclei that decay per sec. its independent on the size of radio active material one curic represent a large amount of radio activity so use. Pci = 10-12 ci, μci=10-6, mci=10-3 The SI unit of radio activity is the Becqueral βq 1 curie = 3.7 x 1010 Becquerel
Equal no. of ci of radiation given of by different isotopes do not produce the same biological effect so we use another unit to assess biological damage like (Rad). 2. Rad {Radiation absorbed dose} (D) it’s a unit that express the amount of energy absorbed by irradiated tissue.One rad = 2.4x10-3 cal of energy absorbed by 1kg of tissue. Its very small unit converted to heat, this energy would raise the temp of tissue.
The SI unit of absorbed dose is the gray (Gy) defined as: one joule of energy absorbed per 1 kg of tissue. 100 rad = one gray The energy absorbed by living tissue is not the only factor that contributes to the biological effects (hazards) of radiation. For this reason a dose of 1 rad from one source is not necessary equal to a dose of one rad from another. So we use another unit which takes all these differences like (Rem).
3. Rem= 1 Rad x RBE RBE: factor (relative biological equivalent) no. of Rem= no. of rad x RBE. The factor RBE takes into account the differences in biological damage caused by different kind of ionizing radiation of the same energy. For ex:- RBE of an alpha particle is 10 times that of beta particle. This mean that α-par released in tissue caused damage 10 times that of β-particles of the same energy.The rem is the more accurate measure of biological damage caused by different ionizing radiation.
So its used to describe doses of radio activity.To determine how much radiation is dangerous to human by using LD50 values:-LD50 : Lethal dose valueLD50 value: Ionizing radiation dose at which injury to human begins is unknown. Its better to express the short term exposure to radiation that is fatal to various form life this is expressed as 30 days LD50 value which is defined as the dose in rem that is fatal to 50% of population within 30 days. LD50 value for human is 500 rem LD50 value for mammals is between 250 – 1000 rem