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Particle physics in everyday life

Pierre Henriquet
Pierre Henriquet
Doctor in Nuclear Physics and Columnist at Polytechnique Insights
Key takeaways
  • The search for the fundamental components of the universe only began in the 19th Century with Compton and de Broglie discovering the quantum nature of X-rays and the wave properties of particles, respectively.
  • One of the techniques of particle physics is based on doping. This involves introducing ‘impurities’ into silicon crystals to modify its electrical properties.
  • Another application is in the food industry, where irradiation is used to extend the shelf life of foodstuffs.
  • In France, for example, in 2014, 370 000 hectares of sunflower crops - i.e. 56% of production - were grown from seedlings obtained by mutagenesis (gamma irradiation).
  • Particle physics is also applied to medicine by making it possible to eliminate cells in the blood in bags used for transfusions but also for medical imaging.

The search for the nature of the fun­da­men­tal com­po­nents of the Uni­verse real­ly began at the start of the 20th Cen­tu­ry. The “atoms” imag­ined by Dem­ocri­tus 300 years before Christ real­ly began to be under­stood when it was realised that con­trary to their ety­mol­o­gy (a‑tomos = unbreak­able, that which can­not be divid­ed into small­er ele­ments), atoms were them­selves com­posed of even small­er elements. 

Par­ti­cles, which, as things stand today, are the most basic ele­ments of mat­ter. But as is often the case in the evo­lu­tion of sci­ence, research that ini­tial­ly served no pur­pose oth­er than to gain a detailed under­stand­ing of the laws of nature and its com­po­nents has led to appli­ca­tions that have pro­found­ly changed our dai­ly lives. How has par­ti­cle physics found its way into our dai­ly lives? 

The gen­er­al prin­ci­ple is often the same: direct a beam of par­ti­cles at a tar­get and study or use its effects. Depend­ing on the type of par­ti­cle used and the tar­get cho­sen, the con­se­quences (and uses) will be very different.

Atoms for electronics

Let’s start with some­thing that this arti­cle could not have been writ­ten with­out: electronics.

The basic prin­ci­ple of all mod­ern elec­tron­ics is the use of sil­i­con, which belongs to the class of “semi­con­duc­tors”. A semi­con­duc­tor is char­ac­terised by the num­ber of charge car­ri­ers it has (elec­trons or elec­tron gaps called “holes”). To increase this num­ber of charge car­ri­ers, « impu­ri­ties » are intro­duced into the sil­i­con crys­tal, atoms that add or remove elec­trons and thus local­ly mod­i­fy the elec­tri­cal prop­er­ties of the medi­um. This is called doping.

Dop­ing must be car­ried out in an extreme­ly pre­cise man­ner: one part of the sil­i­con crys­tal must be doped with an excess of elec­trons while, a few microme­tres deep­er, anoth­er part must be doped with atoms that remove these electrons.

Dia­gram of ion implan­ta­tion in a sil­i­con crys­tal (cred­it Masashi Kato, Nagoya Insti­tute of Tech­nol­o­gy 1

The arti­fi­cial inser­tion of these dop­ing atoms can be done by “ion implan­ta­tion”: they are accel­er­at­ed by an elec­tric field that gives them a greater or less­er ener­gy, which allows them to pen­e­trate more or less deeply into the sub­strate to dope cer­tain lay­ers at pre­cise­ly deter­mined depths.

Irradiation of materials

The irra­di­a­tion of mate­ri­als can be vol­un­tary or invol­un­tary. But in all cas­es, it mod­i­fies their microstruc­ture, and this is why it will be used or stud­ied in order to bet­ter under­stand the prop­er­ties of these mate­ri­als and their evo­lu­tion over time.

Ion implan­ta­tion is a sur­face treat­ment process that can also be applied in many sit­u­a­tions oth­er than elec­tron­ics. It allows the chem­i­cal com­po­si­tion and sur­face struc­ture of a mate­r­i­al to be mod­i­fied. Depend­ing on the nature of the sub­strate and the implant­ed ion, cer­tain mechan­i­cal or chem­i­cal prop­er­ties of the sur­face (hard­ness, wear resis­tance, fatigue, cor­ro­sion resis­tance, etc.) can thus be opti­mised with­out chang­ing its main properties.

The phe­nom­e­non of age­ing under irra­di­a­tion is main­ly stud­ied in the nuclear sec­tor. At the heart of today’s nuclear pow­er plants, steel is sub­ject­ed to intense irra­di­a­tion from the radioac­tive fuel rods used to pow­er the instal­la­tion. The reac­tor ves­sel, for exam­ple, is a non-replace­able com­po­nent. It is vital to know and antic­i­pate the age­ing of its struc­ture over decades of use.

Steel tough­ness of a pres­surised water reac­tor ves­sel before (blue) and after (green) irra­di­a­tion ©CEA 2

But this work is also use­ful for the next gen­er­a­tions of reac­tors, whose tem­per­a­ture and irra­di­a­tion con­di­tions will be even more demand­ing than today, not to men­tion future ther­monu­clear fusion reac­tors, such as ITER, whose mate­ri­als in con­tact with the plas­ma under­go intense neu­tron irradiation.

Particle physics and life

In the food indus­try, food irra­di­a­tion is one of the meth­ods used to extend the shelf life of foods. This tech­nique makes it pos­si­ble to stop the ger­mi­na­tion process (pota­toes, seeds, etc.) and to kill the par­a­sites, moulds, and micro-organ­isms respon­si­ble for the dete­ri­o­ra­tion and/or rot­ting of food.

To do this, three types of radi­a­tion are used: X‑rays or gam­ma (ɣ) rays (which are two types of elec­tro­mag­net­ic radi­a­tion, like light, but whose ener­gy is much high­er than the part vis­i­ble to the eye), or elec­tron accelerators.

How­ev­er, this tech­nique does not com­plete­ly ster­ilise food (which still needs to be pack­aged and cooked prop­er­ly), but it slows down spoilage and allows it to be stored for longer. It also pre­vents insects and oth­er pests from lay­ing eggs in fresh pro­duce and destroy­ing them.

Gam­ma irra­di­a­tion is also used in agri­cul­ture. It is called muta­ge­n­e­sis by gam­ma irra­di­a­tion. The prin­ci­ple is to sim­u­late (and accel­er­ate) the process of genet­ic muta­tion that occurs nat­u­ral­ly in the liv­ing world. This tech­nique, which has been used since the 1950s, makes it pos­si­ble to select new plant strains with favourable muta­tions (taste, colour, growth, fruit size, etc.).

Insti­tute of Radi­a­tion Breed­ing in Kamimu­ra­ta, Japan, where new plant strains are cre­at­ed by gam­ma muta­ge­n­e­sis. Cred­it: Google Maps.

In France, for exam­ple, in 2014, 370 000 hectares of sun­flower crops – i.e. 56% of pro­duc­tion – were grown from seedlings obtained by muta­ge­n­e­sis. In Texas, 75% of the grape­fruits grown are of the Rio Star vari­ety (red­der and sweet­er), also pro­duced by the muta­ge­n­e­sis process.

Particle physics and medicine

The med­ical com­mu­ni­ty also ben­e­fits from the advan­tages of elec­tron accel­er­a­tors in terms of ster­il­is­ing equip­ment. The use of radioac­tive sources of Cae­sium 137 also makes it pos­si­ble to treat blood bags using the gam­ma rays emit­ted, in order to elim­i­nate cer­tain cells that could cause a fatal dis­ease in patients requir­ing a trans­fu­sion. Saline solu­tions used to clean and store con­tact lens­es are also ster­ilised by irradiation.

In nuclear med­i­cine, the use of nuclear reac­tors or par­ti­cle accel­er­a­tors allows the cre­ation of radioac­tive com­pounds that do not exist nat­u­ral­ly on Earth (as they decay in times rang­ing from min­utes to days). How­ev­er, these ele­ments are very impor­tant, both in terms of diag­nos­tic imag­ing (e.g. Positron Emis­sion Tomog­ra­phy which uses a radioac­tive ele­ment: Flu­o­rine-18 or scintig­ra­phy with Tech­netium-99) and also in terms of ther­a­py (Iodine 131 for the treat­ment of thy­roid cancer).

PET (Positron Emis­sion Tomog­ra­phy) scan where the radioac­tive Flu­o­rine-18 atom is bound to glu­cose (left) and dopamine (right) mol­e­cules. Cred­it: Fred­er­ic Compte pour Med​nuc​.net 3

Cur­rent­ly, a new tech­nique for irra­di­at­ing can­cer­ous tumours is being devel­oped: hadron­ther­a­py. This tech­nique uses a par­ti­cle accel­er­a­tor to tar­get tumours inside the patien­t’s body that are dif­fi­cult to treat with oth­er con­ven­tion­al tech­niques (often brain tumours). This is an extreme­ly tar­get­ed radio­ther­a­py tech­nique, the advan­tages of which, in terms of pre­ci­sion and patient radio­pro­tec­tion, give rea­son to hope that, in addi­tion to Ger­many and Italy, a cen­tre may be built in France in the com­ing years.


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