**2. Basic physics of particle activation**

"Particle activation" means "artificial radioactivity" or "man made radioisotopes", far away from "natural radioactivity" which is a basic characteristic of our Universe, that has been present all over the universe history, and it contains only four natural decay series characterized by their numbers of nucleons as is shown in Table 1., artificial radioactivity is a very young phenomena born in 20th century.


Table 1. Natural decay series.

Firstofalll we have to define radioactivity: It is a property of nature in which atoms have such a big amount of energy so they need to discharge it to the surrounding media. The aim of it is to become stable, i.e. have the less amount of energy need to exist, because atom stability is the more cost/efficiency retail in matter. Atom then has design some method to discharge energy and diminish it energy level to become stable. Radioactive atoms can emit some energy packs splitting them in pieces of several dimensions and energy content to reach its stability:

divided into two big groups: Linear accelerators and spiral path accelerators or Cyclotrons. The radioisotopes used in Medicine can be from natural ocurrences like 137Cs (used in the last century in Teletherapy machines and in low dose rate brachytherapy) or 192Ir (used nowadays in high dose rate brachytherapy), or can be produced in Reactors or Cyclotrons.

For diagnostic purposes: 51Cr, 125I, 131I, 59Fe, 42K, 177Lu, 99Mo (fission product), 75Se, 24Na,

For therapeutic purposes: 213Bi, 60Co, 165Dy, 169Er, 125I, 131I, 192Ir, 212Pb, 177Lu, 103Pd, 32P, 188Re,

For diagnostic and therapeutic or other purposes: 60Co, 166Ho, 125I, 99Mo (fission product), 177Yt.

For diagnostic purposes: 11C, 13N, 15O, 18F, (PET studies), 64Cu, 67Ga, 68Ga, 111In, 123I, 124I,

For diagnostic, therapeutic or other purposes: 57Co, 82Sr, 68Ge. All of them have to fulfill the

Knowing all this restrictions radioisotope has to accomplish, to be safely used in human, now we can talk about the characteristics of a cyclotron to produce such an isotope. Later in this chapter we will describe such an installation regarding shielding, environmental safety,

In Venezuela, we start to install the first baby cyclotron for medical purposes on 2001, so our last section of this chapter is to illustrate how this installation works and how its programs

"Particle activation" means "artificial radioactivity" or "man made radioisotopes", far away from "natural radioactivity" which is a basic characteristic of our Universe, that has been present all over the universe history, and it contains only four natural decay series characterized by their numbers of nucleons as is shown in Table 1., artificial radioactivity is

> **Series Parent Nucleons Stable end THORIUM** 232Th90 4n 208Pb82 **NEPTUNIUM** 237Np93 4n+1 209Bi83 **URANIUM** 238U92 4n+2 206Pb82 **ACTINIUM** 235U92 4n+3 207Pb82

Firstofalll we have to define radioactivity: It is a property of nature in which atoms have such a big amount of energy so they need to discharge it to the surrounding media. The aim of it is to become stable, i.e. have the less amount of energy need to exist, because atom stability is the more cost/efficiency retail in matter. Atom then has design some method to discharge energy and diminish it energy level to become stable. Radioactive atoms can emit some energy packs splitting them in pieces of several dimensions and energy content to

Most common radioisotopes produced in Cyclotrons used in Medicine are:

Most common reactor products used in Medicine are:

186Re, 153Sm, 89Sr (fission product), 90Y (fission product).

81mKr, 99Mo (activation product), 82Rb, 201Th.

99mTc, 133Xe (fission product), 159Yt.

For therapeutic purposes: 67Cu.

radiopharmacy lab, etc.

four conditions mentioned above.

has been accomplish to the present date.

**2. Basic physics of particle activation** 

a very young phenomena born in 20th century.

Table 1. Natural decay series.

reach its stability:

Fig. 1. Decay mode of radioactive atoms to reach stability.The action of atoms to split means mass and energy transfer to media. For example, in a 226Ra atom energy excess push it to split out a <sup>4</sup> <sup>2</sup>*He* nucleus (an alpha particle) and 1.4 MeV package of pure energy and another atom of 222Rn, so where there was one atom now there are three different species born out it mass and energy

There are several methods for atoms to transfer energy to the media. Remember Einstein´s principle of ܧ ൌ ݉ܿଶ, which means energy is matter and matter is energy. So in their attempt to become stable emits energy/matter to discharge it excess in several ways as in figure 1.

And scientist began to use this atom fraction to hit different nucleus of known atoms and to observe which was the results of the reverse experiment.

Back in 1929, Ernest Lawrence device a Cyclotron to fulfill his own need to generate high speed ions without needing high voltages he has not access to in Berkeley University. This history began 10 years before when Lord Rutherford used alpha particles coming from Madame Curie´s 226Ra as projectiles to impact a Nitrogen nucleus to transform it into Oxygen.

Fig. 2. Lawrence´s illustration about Rutherford Experiment.

Fig. 5. Percentage of activation products worldwide coming from Reactors or Cyclotrons

In the other hand, cyclotron are electrical machines that generates particle acceleration thru helping them to undergo a circular or elliptical path in which particles gain energy by

Cyclotrons comes from a bigger family of electrical machines called Accelerators, because the make particles to gain energy letting them gain kinetic energy by applying electrical and magnetic fields to the particle trajectory so it can absorb energy from the media where it is travelling. Back to high school physics we can understand easily how cyclotrons accelerate

And also you remember that when you have and electrical and magnetic fields you can

� � �� (1)

�� � ��������) (2)

Fig. 4. Materials for particle absorption in a Reactor.

including medical, industry and research production.

external manipulation of electric an magnetic fields.

write

particles: you must remember that force in an electrical field is:

In the same line of thoughts, Lawrence needs more projectiles to study this new phenomena. That 15th century dream of turning Lead into Gold was now though to be possible. Radioisotopes not always decay to a stable daughter but they continue trying, emitting different kinds of particles until they reach stability. In the sake for such stability they transform themselves into a partner they "believe" is more stable: The fifteen Century "Transmutation of Matter" occurs not for lead to become gold but something alike. Men made transmutation, which arise to be only the modification of the "positive electricity in the atomic nucleus", as Lawrence said.1 He described his method of accelerating particles in Cyclotron as "resonance method" or "method of multiple acceleration:

Fig. 3. Lawrence description of Cyclotron accelerating method.

Few time pass, until man used that newly produce radioactive material to treat and diagnoses different affections. John Lawrence, Ernest brother was the first to use his brother product 32P to treat leukemia starting the medical applications of cyclotron products.

Method of particle activation then, need a Nuclear Reactor or an accelerator (Cyclotron, Syncrothron or Linac) to be produced: Nuclear Reactor is an installation in which big rod of natural occurring radioisotopes are set inside a pile with some stable, neutron absorbent, material. The radioisotopes (Th, U) initiates a chain reaction, the stable rod (such as carbon (graphite)) are used to absorb chain reaction debris, in order to moderate the amount of energy (heat) that is produce by nuclear reactions.

They are considered of two kinds: *Power Nuclear Reactors* which are dedicated to use the energy to produce electricity, for example, boiling water to move turbines with the steam and in this way produce electric power*. Nuclear Research Reactors* are used as a source of neutron of different energies to impact different atoms nuclei to become radioactive. In both cases they need the fission product from the original radioactive atom to undergo the chain reaction. For example, 235U absorb a neutron, it become 236U and this split into 92Kr and 141Ba with several neutron that can impact other 235U and become 236U to repeat the reactions.

<sup>1</sup> E.O.Lawrence:(1939) University of California: "Artificial Radiactivity" speech.

In the same line of thoughts, Lawrence needs more projectiles to study this new phenomena. That 15th century dream of turning Lead into Gold was now though to be possible. Radioisotopes not always decay to a stable daughter but they continue trying, emitting different kinds of particles until they reach stability. In the sake for such stability they transform themselves into a partner they "believe" is more stable: The fifteen Century "Transmutation of Matter" occurs not for lead to become gold but something alike. Men made transmutation, which arise to be only the modification of the "positive electricity in the atomic nucleus", as Lawrence said.1 He described his method of accelerating particles in

Cyclotron as "resonance method" or "method of multiple acceleration:

Fig. 3. Lawrence description of Cyclotron accelerating method.

1 E.O.Lawrence:(1939) University of California: "Artificial Radiactivity" speech.

energy (heat) that is produce by nuclear reactions.

Few time pass, until man used that newly produce radioactive material to treat and diagnoses different affections. John Lawrence, Ernest brother was the first to use his brother product 32P to treat leukemia starting the medical applications of cyclotron products. Method of particle activation then, need a Nuclear Reactor or an accelerator (Cyclotron, Syncrothron or Linac) to be produced: Nuclear Reactor is an installation in which big rod of natural occurring radioisotopes are set inside a pile with some stable, neutron absorbent, material. The radioisotopes (Th, U) initiates a chain reaction, the stable rod (such as carbon (graphite)) are used to absorb chain reaction debris, in order to moderate the amount of

They are considered of two kinds: *Power Nuclear Reactors* which are dedicated to use the energy to produce electricity, for example, boiling water to move turbines with the steam and in this way produce electric power*. Nuclear Research Reactors* are used as a source of neutron of different energies to impact different atoms nuclei to become radioactive. In both cases they need the fission product from the original radioactive atom to undergo the chain reaction. For example, 235U absorb a neutron, it become 236U and this split into 92Kr and 141Ba with several neutron that can impact other 235U and become 236U to repeat the reactions.

Fig. 4. Materials for particle absorption in a Reactor.

Fig. 5. Percentage of activation products worldwide coming from Reactors or Cyclotrons including medical, industry and research production.

In the other hand, cyclotron are electrical machines that generates particle acceleration thru helping them to undergo a circular or elliptical path in which particles gain energy by external manipulation of electric an magnetic fields.

Cyclotrons comes from a bigger family of electrical machines called Accelerators, because the make particles to gain energy letting them gain kinetic energy by applying electrical and magnetic fields to the particle trajectory so it can absorb energy from the media where it is travelling. Back to high school physics we can understand easily how cyclotrons accelerate particles: you must remember that force in an electrical field is:

$$F = qE \tag{1}$$

And also you remember that when you have and electrical and magnetic fields you can write

$$
\vec{F} = q(\vec{v} \times \vec{B})\tag{2}
$$

$$F = q\upsilon B\tag{3}$$

$$F = \frac{mv^2}{r} \tag{4}$$

$$r = \frac{mv}{qB} \tag{5}$$

$$
\omega = \omega r \tag{6}
$$

$$
\omega = 2\pi f \tag{7}
$$

$$\frac{mv^2}{r} = qvB$$

$$qV = \frac{mv^2}{2} \tag{9}$$

$$
v^2 = \frac{2qV}{m}\tag{10}$$

$$
\text{where } V = Er = \upsilon B \tag{11}
$$

$$f = \frac{qB}{2\pi m} \tag{12}$$

$$f = \frac{qB}{2\pi\gamma m\_0} \tag{13}$$

( )(1 ) *act*

λ

<sup>1</sup> = ( )(1 ) *act*

A is the activity at the saturation value that is a function of reactor neutron flue at which

18 1 18 1 8 1 90 *OH Fn* + ⎯⎯→ +

20 18 4 <sup>10</sup>*Ne F He* + ⎯⎯→ + 9 2

14 1 11 4 17 1 *N H C He* + ⎯⎯→ + 6 2

16 1 13 4 81 7 2 *O H N He* + ⎯⎯→ +

14 2 15 1 7 1 80 *NH On* + ⎯⎯→ +

68 2 65 0 30 1 31 1 *Zn H Ga n* + ⎯⎯→ + 2

124 1 123 1 52 1 53 0 *Te H I n* + ⎯⎯→ + 2

<sup>−</sup> Φ −

σ

*<sup>t</sup> Nt e*

λ

λ

*<sup>t</sup> Nt e <sup>N</sup>*

<sup>−</sup> <sup>−</sup> = Φ

σ

*N t*( ) = Number of atoms activated in a time period elapsed t

1

*A N* = λ

Where:

σ

N1 = Atoms of the target Φ = Neutron flux

So, the number of activated atoms is:

And the activity of the sample is:

t is the time of irradiation in seconds

3. Nuclear reaction in cyclotron production

target has been exposed.

( ) *p*,*n* Reaction

) Reaction:

) Reaction

(*d n*, ) Reaction

(*d n* ,2 ) Reaction

,2*n* Reaction

( ) α

(*d*,α

(*p*,α

*act* = Activation cross section

With

$$\chi = \frac{1}{\sqrt{1 - \left(v/c\right)^2}}\tag{14}$$
