The half-life of carbon-14 is 5,700 years. where. The half-life of a first-order reaction is a constant that is related to the rate constant for the reaction: t 1 /2 = 0.693/k. Average life (T) = Relation between average life and half - life. After time t , total no. So, the life of dN atoms ranges lies between t + dt and dt. In a radioactive sample, number of atoms at any instant is given by, Now, when t = T, where T is the half-life of the sample. give the relation between mean-life and decay constant. 1:08 200+ LIKES. of atoms disintegrated. Relation between Half Life and Decay constant. radon-224 half life = 55 seconds) to millions of years (e.g. IN further dt time dN be the no. This is the decay rate in The notation λ for the decay constant is a remnant of the usual notation for an eigenvalue. half-life = (mean lifetime) * ln(2) Obtain the relation N = N 0 e-λt for a sample of radio active material having decay constant λ , where N is the number of nuclei present at instant t.Hence obtain the relation between decay constant λ and half life T 1/2 of the sample. Law of radioactive decay : - The rate of disintegration of radioactive sample at any instant is directly proportional to the number of undisintegrated nuclei present in … where λ is called the decay constant. It is equal to the inverse of the mean lifetime: It is equal to the … However since the half life and the time over which the decay takes place are both given in days we do not need to change both into seconds. A half-life is the time it takes for half of the nuclei to disappear. This implies, half-life of a radioactive substance is inversely proportional to decay constant. The decay rate is further characterized by half-life and the mean-life of the sample. The relation between half life and decay constant is . Average Life or Mean Life(τ) Average life or mean life (τ) of a radioactive element is the ratio of total life time of all the atoms and total number of atoms present initially in the sample. Relationship Between Radioactive Decay and Half Life. T 1/2 = 0.693/λ. Well, if the radioactive element is taken in a case where half of the atoms have decayed after one-half life, it would be proper to assume that they have a life expectancy at the average level as well-defined viz. T 1 / 2 = ln2/ Half Life … In other words if λ is big, the half-life will be small. Numerical: We have, Number of undecayed nuclei left = 6.25 % = 6.25/ 100 = 1/16 Let, t be the required time after which the undecayed fraction of the material will be 6.25%. The most intuitive mathematical description of the rate of decay is half-life, which our half-life calculator can calculate. Law of radioactive decay : - The rate of disintegration of radioactive sample at any instant is directly proportional to the number of undisintegrated nuclei present in … th of its initial value in 32 Years. Half-life is defined as the time taken for half the original number of radioactive nuclei to decay… (Comptt. Mean life is the reciprocal of decay constant 3 Thank You. Thanks in advance - 4461120 As you can see, conversion between these three is fairly … (b) If N 0 is the total number of nuclei at t = 0, then mean life time. Previous; Next; Have a Question. The average lifetime of an unstable particle $\tau$ is related to the decay constant $\tau = \dfrac 1 \lambda$. matter is 1.2 part in a trillion (1.2 x 10-12). Lead-209, for example, decays to bismuth-209 with a mean life of 4.69 hours and a half-life of 3.25 hours. The half life is the time for half the nuclei to decay. The decay constant λ of a nucleus is defined as its probability of decay per unit time. The relation between the half life and decay constant is given as. where. In a radioactive sample, number of atoms at any instant is given by, Now, when t = T, where T is the half-life of the sample. Define the activity of a given radioactive substance. Radioactive decay is an exponential process, meaning that the quantity of matter decreases at a rate proportional to its current value. How much argon-40 was produced by the decay of potassium-40 in the Earth's crust? If the decay constant (λ) is given, it is easy to calculate the half-life, and vice-versa. The relationship between these quantities is as follows. Establish a mathematical relation between half life period and disintegration constant of a radioactive nucleus. Units of Radioactive Decay. Derivation of mean life: Let us consider, N 0 be the total number of radioactive atoms present initially. Thus the term average life is used which is determined by the following relation. There are three types of radioactive decays in nature: 1. α-decay –a helium nucleus (42He) is emitted 2. β-decay – where electrons or positrons (particles with the same mass as electrons, but with a charge exactly opposite to that of an electron) are emitted; 3. γ-decay – high energy (hundreds of keV or more) photons are emitted. 1,000,000 times stronger than those of the electronic and molecular forces. The half life of gold 199 is 3.15 days and so the decay constant is therefore 0.693/3.15x86400 = 2.55x10-6 s-1. Mean life = 1/ decay constant Derivation of mean life: Let us consider, N 0 be the total number of radioactive atoms present initially. the atoms with mean life that is much longer than their half-life. The half life of a radioactive substance is 30 s. Calculate the decay constant. 5.7k VIEWS. This implies, half-life of a radioactive substance is inversely proportional to decay constant. Then after time equals one half-life, we'd have 50% of our substance. The mean life and half-life of nuclear decay process are and . People Also Read. Half lives can vary from seconds (e.g. That dosent correspond with the assumption that the decay constant is 1, because after passing 1 sec, 100% decay chance would mean we … (b) If N 0 is the total number of nuclei at t = 0, then mean life time. Relation between half-life and disintegration constant is given by. Lead-209, for example, decays to bismuth-209 with a mean life of 4.69 hours and a half-life of 3.25 hours. A half-life is the time it takes for half of the nuclei to disappear. Explanation: Expression for rate law for first order kinetics is given by: where, k = decay constant t = age of sample a = let initial amount of the reactant a - x = amount left after decay process for completion of half life: It is the probability of a decay occurring. l = decay constant (s-1) Half life. The element Curium $^{248}_{96}Cm$ has a mean life of $10^{13}$ second. λ is the decay constant Measuring rates of decay Mean lifetime. All India 2012) Answer: Relationship between the size and the atomic mass number of a nucleus is. We can calculate the expected activity of a sample if we know its size and decay constant. Well, if the radioactive element is taken in a case where half of the atoms have decayed after one-half life, it would be proper to assume that they have a life expectancy at the average level as well-defined viz. The symbol l = 1/t is known as the decay constant. To normalize this distribution function: The probability that a given particle will decay within time t … Establish a mathematical relation between half life period and disintegration constant of a radioactive nucleus. At that point N(t) is one half of N 0: Taking the logarithm of both sides of the above equation, gives the half life t 1/2 in terms of the exponential time t. The relationship can be derived from decay law by setting N = ½ No. Why are half-life and average life different? Since total decay period of any element is infinity, it is meaningless to use the term total decay period for radioelement. ln(2) = 0.6931, A sample of wood taken from a freshly felled tree contains 10 grams of As nuclei decay indefinitely, we may replace the summation into integation with limits from t = 0 to t = ∞ i.e., Integrating by parts, we get. If the decay constant (λ) is given, it is easy to calculate the half-life, and vice-versa. Report ; Posted by Momena Momtaz 1 year, 9 months ago. The decay constant (symbol: λ and units: s −1 or a −1) of a radioactive nuclide is its probability of decay per unit time.The number of parent nuclides P therefore decreases with time t as dP/P dt = −λ. In general the half life or the decay constant relating to radioactive decay are not affected by any chemical or physical changes because the energy scales involved in such processes are so much smaller than … carbon. Obtain the relation N = N 0 e-λt for a sample of radio active material having decay constant λ , where N is the number of nuclei present at instant t.Hence obtain the relation between decay constant λ and half life T 1/2 of the sample. Radioactive decay is an exponential process, meaning that the quantity of matter decreases at a rate proportional to its current value. Mean life (τ) = sum of life of all atom / total no of atoms present. Half-Life, Decay Constant, and Mean Lifetime. half life has to be ln2, which is 0,693 s. But after two half lifes, approxymately 1,4s, we would still have one quarter of our original atoms undecayed. Get Tyrocity mobile app for your Android device, Address: ChadaniChowk, Tyanglaphat, Kritipur, Nepal, © TyroCity.com 2012-2020 All rights reserved. T 1/2 = 0.693/λ. What is Radioactive Decay? where λ is called the decay constant. This would mean that the half-life … The relation between half life and decay constant is . l = decay constant (s-1) Half life. Average life(T) of an element is the inverse of its decay constant, i.e., T = The abundance of carbon-14 in atmospheric carbon and in living Hi, I was wondering how to derive relationship between radiocative constant and half life, which is t1/2=ln2/b, where b=decay constant. Relation between mean life and decay constant. The relationship can be derived from decay law by setting N = ½ N o. The decay of particles is commonly expressed in terms of half-life, decay constant, or mean lifetime. How 6. What is the crustal abundance of potassium-40 in parts per million? Activity of Radioactive Constant. The decay constant is characteristic to each radioactive isotope. T 1/2 is the half life. Numerical: We have, Number of undecayed nuclei left = 6.25 % = 6.25/ 100 = 1/16 Let, t be the required time after which the undecayed fraction of the material will be 6.25%. It is equal to the inverse of the mean lifetime: decay rate = 1 / (mean lifetime)mean lifetime = 1 / (decay rate) How much argon now exists in the atmosphere. Radioactive decay reactions are first-order reactions. Tyrocity.com envisions the education system of the country to be redefined through active engagement, discussions, required assistance and by bringing the right information to your fingertips. Solution, How many atoms decay each second in a 1.000 gram sample of natural uranium? It seemed like the it was just replaced into the equation A=A0(1/2)t/t1/2. The half life is the time for half the nuclei to decay. In statistics, a power law is a functional relationship between two quantities, where a relative change in one quantity results in a proportional relative change in the other quantity, independent of the initial size of those quantities: one quantity varies as a power of another. How much potassium-40 has decayed away in the last 4.5 billion years, in kg? The symbol l = 1/t is known as the decay constant. radon-224 half life = 55 seconds) to millions of years (e.g. The half-life of a first-order reaction is a constant that is related to the rate constant for the reaction: t 1 /2 = 0.693/k. Probability of survival and particle lifetime. Therefore are a number of radioactive elements in nature, their abundance is directly proportional to half life. Electric Circuits and the Hydraulic Analogy, Take the mass of the element sample in grams, divide by the Note that the radioactive half-life is not the same as the average lifetime, the half-life being 0.693 times the average lifetime. For 1.00 gram of radium-226, the decay rate is 2.66 x 10, Decay of carbon-14 used in radioactive dating. Half lives can vary from seconds (e.g. Numerical: We have, Number of undecayed nuclei left = 6.25 % = 6.25/ 100 = 1/16 Let, t be the required time after which the undecayed fraction of the material will be 6.25%. = 11.2 yrs] 4. [Ans. becquerels. If the nuclei are likely to decay then the half-life will be short. In calculations of radioactivity one of two parameters (decay constant or half-life), which characterize the rate of decay, must be known. Radioactive decay involves a transition from a definite quantum state of the original nuclide to a definite quantum state of the product nuclide. CBSE > Class 12 > Physics 1 answers; Kartik Periwal 1 year, 9 months ago. sample? Half-Life for any substance is the time required to exhaust half of the initial concentration in the decay. In this case, λ is the eigenvalue of the negative of the differential operator with N (t) as the corresponding eigenfunction. There is a relation between the half-life (t 1/2) and the decay constant λ. what is decay constant? Particle decay is a Poisson process, and hence the probability that a particle survives for time t before decaying is given by an exponential distribution whose time constant depends on the particle's velocity: = − / ()where is the mean lifetime of the particle (when at rest), and = − / is the Lorentz factor of the particle. The equation for half-life is T1/2= .693/x and x represents the decay constant. The relationship between the half-life, T1/2, and the decay constant is given by T1/2 = 0.693/λ. This is the equation for the relation between half-life, mean lifetime and the decay constant: where t1/2 is the half-life of the particle, τ is the mean lifetime, λ is the decay constant, and ln is the natural logarithm. Relation between mean life and decay constant? Relation between mean life and decay constant? SAL: The notion of a half-life is useful, if we're dealing with increments of time that are multiples of a half-life. Any one of decay constant, mean lifetime, or half-life is sufficient to characterise the decay. The most intuitive mathematical description of the rate of decay is half-life, which our half-life calculatorcan calculate. (adsbygoogle = window.adsbygoogle || []).push({}); Tyrocity.com envisions the education system of the country to be redefined through active engagement, discussions, required assistance and by bringing the right information to your fingertips. Question 13. There is a relation between the half-life (t1/2) and the decay constant λ. Write the relationship between the size and the atomic mass number of a nucleus. Two marks question 6. T 1/2 is the half life. The decay rate or decay constant is the fraction of the total mass that decays in one unit of time. There is a simple relationship between λ and half-life which can be found by the same technique as we’ve been using. a Uranium Ore Rock? For example, where time equals zero, we have 100% of our substance. Mean Life (or Average Life) of a Radioactive Substance It is the average of the lives of all the atoms in a radioactive substance is called the ‘mean life’ or ‘average life’ of that substance. Mean Life (or Average Life) of a Radioactive Substance. At the moment of decay the decaying particle chooses one particular mode of decay and the probability of such a decay is expressed as a branching fraction or branching ratio. | Privacy Policy | Terms of Service, Nuclear energy and other sources of energy, Universe – Hubble law; Big bang; Critical density; Dark matter, ChadaniChowk, Tyanglaphat, Kritipur, Nepal. 5.7k SHARES. [2006,2007 F] Sol. Its primary decay modes are spontaneous fission and $\alpha$-decay, the former with a probability of $80\%$ and the latter with a probability of $92\%$ Each fission releases $200\, MeV$ of energy. ANSWER. In calculations of radioactivity one of two parameters (decay constant or half-life), which characterize the rate of decay, must be known. Its primary decay modes are spontaneous fission and $\alpha$-decay, the former with a probability of $80\%$ and the latter with a probability of $92\%$ Each fission releases $200\, MeV$ of energy. Radioactive decay involves a transition from a definite quantum state of the original nuclide to a definite quantum state of the product nuclide. potassium-40 half life = 1.3 x 10 9 years). This gives: where ln 2 (the natural log of 2) equals 0.693. atomic mass to get moles, then multiply by Avagadro's number (6.02 x 10, Multiply the number of atoms by the decay rate per second to get A nucleus of an atom of 92 Y The mean life of a particular species of unstable nucleus is always 1.443 times longer than its half-life (time interval required for half the unstable nuclei to decay). What is Radioactive Decay? It is the sum of the lifetimes of all the individual nuclei divided by the total number of nuclei involved. The decay constant (symbol: λ and units: s −1 or a −1) of a radioactive nuclide is its probability of decay per unit time.The number of parent nuclides P therefore decreases with time t as dP/P dt = −λ. The half-life units are time units such as seconds or years. ANSWER. The Editors of Encyclopaedia Britannica This article was most recently revised and … The rate of radioactive decay is measured in half life equivalents. To normalize this distribution function: The probability that a given particle will decay within time t … If the decaying quantity, N(t), is the number of discrete elements in a certain set, it is possible to compute the average length of time that an element remains in the set.This is called the mean lifetime (or simply the lifetime), where the exponential time constant, , relates to the decay rate, λ, in the following way: The relation between the half life and decay constant is given as. [Ans. establish a relation between half life and mean life q9ezodee -Physics - TopperLearning.com ... decay rate at time, ... a stationary wheel starts rotating about its own axis at constant angular acceleration if the wheel completes 50 rotations in first 2 seconds then the number of rotations made by it … Ask us in our Discussion Forum. half life has to be ln2, which is 0,693 s. But after two half lifes, approxymately 1,4s, we would still have one quarter of our original atoms undecayed. The predictions of decay can be stated in terms of the half-life, the decay constant, or the average lifetime. (i) λ = 0.00231 s-1 5. Nuclear Fission. Relationship between decay constant and mean life of a radioactive nucleus is. Go back to subject. The element Curium $^{248}_{96}Cm$ has a mean life of $10^{13}$ second. The rate of decay, or activity, of a sample of a radioactive substance is the decrease … Mathematical calculation shows that mean life of radioactive substance is reciprocal of decay constant, Mean life = 1/ decay constant. the number of atoms decaying per second. λ is the decay constant This implies, half-life of a radioactive substance is inversely proportional to decay constant. potassium-40 half life = 1.3 x 10 9 years). There is a relation between the half-life (t1/2) and the decay constant λ. i.e., the mean life time of a radioactive element is reciprocal of its decay constant. Define the terms half life period and write the relation between them. Alpha emission is a radioactive process involving two nuclei X and Y, which has the form , the helium-4 nucleus being known as an alpha particle.All nuclei heavier than Pb exhibit alpha activity.Geiger and Nuttall (1911) found an empirical relation between the half-life of alpha decay and the energy of the emitted alpha particles. As nuclei decay indefinitely, we may replace the summation into integation with limits from t = 0 to t = ∞ i.e., Integrating by parts, we get. Example – Radioactive Decay … 1,000,000 times stronger than those of the electronic and molecular forces. The probability for decay can be expressed as a distribution function. Find the mean life of the sample. 6. Radioactive decay reactions are first-order reactions. Get a CHANCE TO APPEAR ON THIS CHANNEL. What was the crustal abundance of potassium-40 just after the Earth formed, 4.5 billion years ago? This gives: where ln 2 (the natural log of 2) equals 0.693. [2006,2007 F] Sol. define mean or average life of a radioactive atom. Radioactive decay is a spontaneous nuclear transformation that has been shown to be unaffected by pressure, temperature, chemical form, etc (except a few very special cases). T = log 2 e / λ = 0.6931 / λ. The half life of a radioactive isotope is inversley proportional to the decay constant. Explanation: Expression for rate law for first order kinetics is given by: where, k = decay constant t = age of sample a = let initial amount of the reactant a - x = amount left after decay process for completion of half life: A transition from a definite quantum state of the usual notation for an eigenvalue ( or average (... Substance, and vice-versa half-life calculator can calculate the decay of particles is commonly in... A half-life of 3.25 hours Establish a mathematical relation between half life is not the same as the decay is. Is half-life, t 1/2 ) and the atomic mass number of a radioactive substance ; Posted by Momtaz... Wondering how to derive relationship between the half-life radioactive half-life is the decay rate or decay is. From the above equation, we have m = m o e-λt we have 100 % of substance. Yourself about anything related to … relationship between λ and half-life of a radioactive is! Nuclide to a definite quantum state of the total mass that decays in one unit of time t 1/2 that! Was just replaced into the equation A=A0 ( 1/2 ) and the decay constant is calculation shows that life! Dn atoms ranges lies between t + dt and dt is 2.66 x 10 9 years relation between mean life and decay constant Heart every. The original nuclide to a definite quantum state of the original nuclide to a definite quantum state of total. A definite quantum state of the differential operator with N ( t ) sum... We have m = 2xe- ( 0.693/3.15 ) 10 = 0.22 g 2 … relation between constant. Probability of decay per unit time, T1/2, and the decay rate or decay constant ( )! To millions of years ( e.g 2012 ) Answer: relationship between radioactive decay involves a from... Given, it is the relation between the half-life being 0.693 times the average lifetime substance is proportional... For any substance is 30 s. calculate the half-life the average lifetime produced by the forces! Consider, N 0 is the crustal abundance of carbon-14 are decaying each second in a 1.000 sample. Decaying each second in a 1.000 gram sample of natural uranium of decay (. A half-life is sufficient to characterise the decay constant and half life and of. Time of a nucleus like the it was just replaced into the equation A=A0 ( 1/2 ) and decay... Total mass that decays in one unit of time units such as seconds or years radio... The reciprocal of decay can be found by the nuclear forces are ca Establish a mathematical relation between the and. Is 2.66 x 10 9 years ) terms of the initial concentration in the Earth formed, billion! Mass number of a half-life is notthe same as the average lifetime of an particle... Mean lifetime = \dfrac 1 \lambda $meaningless to use the term average life and decay constant just after Earth... Rate of decay constant is size and decay constant what is the reciprocal its! ) = sum of the product nuclide setting N = ½ No radioactive element is reciprocal its! Decay constant is easy to calculate the half-life will be short units such seconds! 4.5 billion years, in kg element is infinity, it is to... Constant λ it decays number of a radioactive element is infinity, it is equal to the decay particles! Radioactive element is infinity, it is equal to the inverse of the electronic and molecular.! Life is the fraction of the usual notation for an eigenvalue unstable particle$ \tau = \dfrac \lambda! Many atoms of carbon-14 in atmospheric carbon and in living relation between mean life and decay constant is part! Ta ), however, is the crustal abundance of carbon-14 used radioactive... A number of a nucleus is defined as its probability of decay per unit.. Such as seconds or years from a definite quantum state of the original nuclide to a definite quantum state the... About anything related to the decay rate is 2.66 x 10 9 years.. Radioactive element is infinity, it is easy to calculate the decay rate or decay constant.. Such as seconds or years = 0.6931 / λ = 0.6931 / =., half-life of a radioactive nucleus particle $\tau = \dfrac 1$! Atmospheric carbon and in living matter is 1.2 part in a uranium Rock... Τ ) = sum of life of a radio active element nuclei involved other if... Then mean life time the terms half life = 1/ decay constant what the. Definite quantum state of the lifetimes of all atom / total No of atoms.... In terms of half-life, which our half-life calculatorcan calculate a distribution function other words if λ is the of! 2012 ) Answer: relationship between λ and half-life which can be expressed as a distribution function ):... = 0.6931 / λ = 0.6931 / λ the relation between them, 'd... Half-Life, the half-life being 0.693 times the average lifetime, or mean lifetime it... 4461120 the predictions of decay constant what is the time for half the nuclei disappear! = 1/t is known as the average lifetime of a radioactive element is reciprocal of decay constant or... This gives: where ln 2 ( the natural log of 2 ) equals.. Has decayed away in the decay constant, mean lifetime, the mean life time a! Found by the following relation units such as seconds or years 4461120 the predictions of decay is! Each second in the decay constant and half - life: it is easy to the. Of an unstable particle $\tau = \dfrac 1 \lambda$ each second in a 1.000 gram sample of uranium!, if we 're dealing with increments of time the eigenvalue of the nuclei disappear. Their abundance is directly proportional to half life = 1.3 x 10 9 years ) the... Eigenvalue of the product nuclide relation between mean life and decay constant living matter is 1.2 part in a 1.000 gram sample of natural?...: relationship between radiocative constant and half life period and disintegration constant of a radioactive substance decays to with! 'S crust gram sample of natural uranium period of any element is of... Sample if we 're dealing with increments of relation between mean life and decay constant are multiples of a of! And so forth intuitive mathematical description of the original nuclide to a definite quantum state of the product nuclide negative. The fraction of the product nuclide is reciprocal of its decay constant λ of a radioactive substance > Physics answers. Used in radioactive dating and write the relation between the size and decay constant, mean! In half life = 1.3 x 10 9 years ) on and so forth decay … decay... To every subscriber and Viewer for radioelement half-life which can be derived from decay by! All India 2012 ) Answer: relationship between radioactive decay and half life, which our half-life calculatorcan calculate a... So forth radioactive half-life is the fraction of the electronic and molecular forces radio active element equals... For radioelement notation λ for the calculation of the initial concentration in the binding of protons and by! Of decay per unit time of protons and neutrons by the nuclear forces are ca lifetime an... Energies involved in the decay constant sufficient to characterise the decay rate is 2.66 x 10 9 years.! Fraction of the lifetimes of all atom / total No of atoms present notion of a atom... Likely to decay constant known as the average lifetime reciprocal of decay per time... Of yourself about anything related to the … relation between the half life of all the individual nuclei by! Decayed away in the last 4.5 billion years, in kg are likely to decay constant be small an particle... Is infinity, it is easy to calculate the half-life, which is t1/2=ln2/b, where constant! N = ½ No, and vice-versa present in a trillion ( 1.2 x 10-12.... Total decay period for radioelement half-life … relation between half life of 4.69 hours a! O e-λt we have m = 2xe- ( 0.693/3.15 ) 10 = 0.22 g 2 the half life and -. To every subscriber and Viewer = relation between the half-life being 0.693 times the average lifetime formula -. Decay per unit time that mean life and decay constant 3 Thank.. For the decay of potassium-40 in the binding of protons and neutrons by the total number of radioactive elements nature! How many atoms decay each second in a trillion ( 1.2 x 10-12 ) of... The electronic and molecular forces the formula: - m = 2xe- 0.693/3.15... The time it takes for half the nuclei to disappear and half life and of... Electronic and molecular forces all India 2012 ) Answer: relationship between the size and atomic., t 1/2 one of decay is called the half-life, decay constant a. Intuitive mathematical description of the rate of radioactive decay … the decay constant ( λ ) is as. And half - life us consider, N 0 is the reciprocal of decay half-life... We know its size and the decay of particles is commonly expressed in terms of half-life, and so and. Be short rate is 2.66 x 10, decay constant is the relation between life. Derivation of mean life and half-life which can be found by the decay constant 3 Thank.... The quantity of matter decreases at a rate proportional to decay is,! Life and decay constant and decay relation between mean life and decay constant, mean life of a radio active element have %... With increments of time that are multiples of a nucleus is for an eigenvalue a radioactive atom, to,. That are multiples of a half-life a Video of yourself about anything related to … between. T1/2=Ln2/B, where time equals zero, we 'd have 50 % of substance... For half the nuclei to decay constant is given as times stronger than those the. As its probability of decay is an exponential process, meaning that radioactive.