**5. Differences and similarities between reactors and cyclotrons**

Cyclotron is not the only way of activating matter. Going through history, side by side cyclotron development in America, Europe was devoted to the natural radioactive material discovered by many scientists, from Madame Curie (1898), Pierre, Irene and also Joliot till Enrico Fermi, Otto Hahn, Lise Meitner and Fritz Strassman (1939). Neils Bohr and Jhon A. Wheeler published their explanation of the method for moderating, "modulating", chain reactions in a paper published only 2 days after WWII starts in 1939. The first reactor was then brought into criticality in Fermi´s Lab on December 2nd, 1942 in very controlled experiment including radiation safety and protection considerations. Proving that chain reaction can be controlled, it was matter of time to find uses for the products obtain from a nuclear reactor. The neutron from reactors are projectiles for many (n,p), (n,β), reactions to produce many radioisotopes. So time has come to begin talking about which of all this radioactive products can be used in medicine. The first radioactive material used in humans with medical purposes was 226Ra, (1898) used by Madame and Mousier Curie to treat skin lesion they called "benign". Their daughter Irene used 214Bi to measure blood flow, this two products come directly from the 238U natural decay series. By the artificial radioisotopes side, the first one was that 32P John Lawrence (1929) used to treat leukemia. After of it, a lot of radioisotopes and a lot of uses have been developed for diagnostic and therapy uses, so for this time, we can say that the radioisotopes used in Medicine distributions is as it is shown in Table 2:


Table 2. Distribution of the radioisotope production for medical applications.

Like the Curie's began using their newly discovered natural radioisotopes to treat cancer lesion in the skin, very short time after the construction of the cyclotron and the production of its radioisotopes, makes the medical applications to be easily spread.

But there is another mechanism for particle activation and it comes from the nuclear reactor where a bunch of natural radioisotopes "bars" are used to produced spontaneous fission products to aim the nucleus of stable atom or its electronic crown.

Nowadays reactors are the core of the nuclear power plants, but in their beginnings they were developed for research proposes to military applications only. Due to the natural "nuclear fuel" reactors were better in cost/efficiency fashion and in the late 30's and early 40's many budgets and efforts were driven to their construction to regulated nuclear chain reaction and its control, until the atomic bomb development to win WWII.

65 4 67 1 29 2 31 0 *Cu He Ga n* + ⎯⎯→ + 2

Cyclotron is not the only way of activating matter. Going through history, side by side cyclotron development in America, Europe was devoted to the natural radioactive material discovered by many scientists, from Madame Curie (1898), Pierre, Irene and also Joliot till Enrico Fermi, Otto Hahn, Lise Meitner and Fritz Strassman (1939). Neils Bohr and Jhon A. Wheeler published their explanation of the method for moderating, "modulating", chain reactions in a paper published only 2 days after WWII starts in 1939. The first reactor was then brought into criticality in Fermi´s Lab on December 2nd, 1942 in very controlled experiment including radiation safety and protection considerations. Proving that chain reaction can be controlled, it was matter of time to find uses for the products obtain from a nuclear reactor. The neutron from reactors are projectiles for many (n,p), (n,β), reactions to produce many radioisotopes. So time has come to begin talking about which of all this radioactive products can be used in medicine. The first radioactive material used in humans with medical purposes was 226Ra, (1898) used by Madame and Mousier Curie to treat skin lesion they called "benign". Their daughter Irene used 214Bi to measure blood flow, this two products come directly from the 238U natural decay series. By the artificial radioisotopes side, the first one was that 32P John Lawrence (1929) used to treat leukemia. After of it, a lot of radioisotopes and a lot of uses have been developed for diagnostic and therapy uses, so for this time, we can say that the radioisotopes used in Medicine distributions is as it is

Neutron activation

Like the Curie's began using their newly discovered natural radioisotopes to treat cancer lesion in the skin, very short time after the construction of the cyclotron and the production

But there is another mechanism for particle activation and it comes from the nuclear reactor where a bunch of natural radioisotopes "bars" are used to produced spontaneous fission

Nowadays reactors are the core of the nuclear power plants, but in their beginnings they were developed for research proposes to military applications only. Due to the natural "nuclear fuel" reactors were better in cost/efficiency fashion and in the late 30's and early 40's many budgets and efforts were driven to their construction to regulated nuclear chain

59Fe, 177Lu, 42K, 75Se, 24Na,

131I, 192Ir, 212Pb, 177Lu, 103Pd, 32P, 186Re, 188Re, 153Sm

133Xe, 99Mo 51Cr, 125I, 131I, 89Sr, 153Sm,

99mTc, 159Yt

89Sr, 90Y 213Bi, 60Co, 165Dy, 169Er, 125I,

Table 2. Distribution of the radioisotope production for medical applications.

of its radioisotopes, makes the medical applications to be easily spread.

reaction and its control, until the atomic bomb development to win WWII.

products to aim the nucleus of stable atom or its electronic crown.

**Reactors Produced Cyclotrons Produced** 

11C, 13N, 15O, 18F, 57Co, 82Sr, 68Ge 64Cu,67Ga, 68Ga, 111In, 123I, 124I, 81mKr, 82Rb, 201Tl

67Cu, 57Co, 82Sr, 68Ge

**5. Differences and similarities between reactors and cyclotrons** 

shown in Table 2:

**Diagnostic Purposes** 

**Therapeutic Application** 

Fission Products But passing thru that dark hour, all the money spend in its development seems to be not that important.

And cyclotron has to compete (and win) against reactors that were redeeming themselves by producing "atoms for the peace" trying to justify the large budget assign to them during WWII.

And for a long period of time the guilt drop the balance to reactors side until middle 70's when positron emission tomography arised based in a component containing 18F: 18FDG (Fluorodexoxy glucose).

This isotope was only produced in cyclotron and the compound could be synthetized in a straight forward relative easy way.

This made cyclotrons an Hospital equipment because, due to the short half-life of 18F, it was necessary to stablish the supplier so near to the costumer as it can be, and being a hospital a places were pureness and asepsie is well know, and treat with reverential respect, which other place would be better to activated pure 18F and synthetize the 18FDG in a sterile form to be safe to apply in human.

And between 1929 and 1974 lot of things happened to cyclotron to develop its actual characteristic. From Lawrence Cyclotron to Hospital one, until CERN´s a lot of energy has pass through.

Fig. 7. Different cyclotron size: a) Lawrence´s first one, b) Venezuela First one (courtesy of Dorly Coehlo), c) Fermi National Laboratory at CERN.

And size matters, and Cyclotrons win as best hospital candidates due to Reactors are bigger, harder and difficult to be set in a hospital installation. Can you imagine a nuclear reactor inside a health installation? Radiation Protection Program will consume all the budget available. Size, controlled reactions, electrical control, made cyclotrons easy to install, and baby cyclotrons come selfshielded so hospital don´t need to spend money in a extremely large bunker. Now on, we are going to talk about our first experience with the set up of a baby cyclotron for medical uses inside the first PET installation in Latin America. "Baby" means its acceleration "D" diameters are suitable to be set inside a standard hospital room dimensions, with all its needs to be safetly shielded for production transmision and synthetized for human uses for imaging in Nuclear Medicine PET routine. When we ask why Cyclotrons are better than reactors for radioisotopes production to be used in Medicine, we also have to have in mind that they has:


Medical Cyclotrons generally often comes with 4 targets to activated: Fluor 18, Oxigen 15, Nitrogen 13 and Carbon 11. In Venezuela we have one with only one target to activated

Remembering what we want for a radioisotopes to be safely used in medicine, Natural decay series has had a very bad performance. For example, 226Ra was used in Medicine until users realized that its daughter was 222Rn, a gas. Since 226Ra was encapsulated in stainless steel tubes the accumulation of Radon from Radium decay inside the tube, cause the gaseous pressure to increase in a non controlled way, so more than 10 years after its encapsulation, the gas pressure was so high as to break the capsule and escape. So as 222Rn is a radioactive gas and it half life is not short (almost 4 days), contamination was hard to

Activation products from Cyclotrons are in general of short half life, so the control can be focus in the energy users can handle. In such a way, we can say activation products can be tailored to our needs. But medical uses are little complicated. Nuclear Medicine consist in mix the radioisotope with a pharmaceutical product which is characterized by the organ they are going to address the isotope. What Nuclear Medicine really needs is to send the radioisotope to get inside the organ we want to study, and as the radioisotope is inside a molecule that can be metabolized by this organ, this metabolization function can be easily watch and measure with the appropriate radiation detectors. The name "radiopharmaceuticals" refers to the metabolically stable combination of a biochemical molecule to which radioisotope in bind that act as the vehicle through which, organ of interest can be reach. There are several mechanism

1. Ionic compound: In which the radioisotopes determine the metabolic route to be follow as in 131I to thyroid uses, because thyroid likes iodine and do not distinguish between

fluor 18 to sintethized 18FDG, for PET studies.

**6. Activation products medical uses** 

contain, so Radium use was declined.

Fig. 10. Radium Tubes.

for the radioisotope to join the address molecule such as:

different isotopes of the same element iodine.


Compare with a reactor.

Fig. 8. Artificial radioisotopes.

Fig. 9. Difference in size between a) Venezuelan medical cyclotron (courtesy of Indira Lugo) and b)Venezuelan research reactor (in desuse).

Fig. 9. Difference in size between a) Venezuelan medical cyclotron (courtesy of Indira Lugo)

a) b)

and b)Venezuelan research reactor (in desuse).

3. They can be installed inside hospital decentralizing radioisotope production. 4. Almost zero risk of nuclear accidents (Because there is no chain reaction to control)

5. There is no risk of nuclear proliferation

Compare with a reactor.

Fig. 8. Artificial radioisotopes.

Medical Cyclotrons generally often comes with 4 targets to activated: Fluor 18, Oxigen 15, Nitrogen 13 and Carbon 11. In Venezuela we have one with only one target to activated fluor 18 to sintethized 18FDG, for PET studies.
