Particle physics in everyday life

The search for the nature of the fun­da­men­tal com­po­nents of the Uni­verse real­ly began at the start of the 20^th 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.

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.

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.

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.

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.

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.).

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.

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).

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.